- Email: [email protected]
Techno-economic evaluation of small-hydro power plants: Modelling and characterisation of the Abruzzo region in Italy
Renewable Energy 75 (2015) 395e406
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Techno-economic evaluation of small-hydro power plants: Modelling and characterisation of the Abruzzo region in Italy Roberto Carapellucci*, Lorena Giordano, Fabio Pierguidi Dipartimento di Ingegneria Industriale e dell'Informazione e di Economia, University of L'Aquila, Via Giovanni Gronchi 18, 67100 L'Aquila, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 January 2014 Accepted 2 October 2014 Available online
The potential of “small hydro” power generation in Europe is still largely unexploited because of strict environmental requirements and legal rights for water use. Among the EU-27 member states, Italy is recognised as one of the most promising countries for the further exploitation of small hydro power. This paper presents a methodology for assessing the technical and economic potential of small hydro on a regional scale. The methodology is applied to the Abruzzo region in Italy. The investigation covers approximately 90 river branches belonging to the major regional basins. The methodology characterises the flow duration curves of suitable stretches of river using a regional analysis based on a graphical approach. An energy model evaluates the rated power and the annual electricity production of installable smallhydro power plants based on the flow duration curve and the type of hydraulic turbine. The economic analysis estimates the unit cost of electricity produced and the profitability of the initial investment assuming two scenarios based on different fixed- and variable-cost models. The net potential obtained from the energy analysis is adjusted to give the economically feasible potential at different levels of economic competitiveness for the regional basins investigated. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Small-hydro Duration curves Regionalisation procedure Graphical approach Residual potential
1. Introduction In Europe, exploiting the potential of small hydroelectric power plants, or small hydro, is attracting growing interest because of the concerns over the lack of suitable sites for large installations and the environmental effects of related civil structures [1]. According to the definition proposed by the ESHA (European Small Hydropower Association) [2], small-hydro power plants are those installations with a rated capacity of less than 10 MW. The small-hydro power capacity in the EU-27 reached approximately 13.7 GW in 2010, resulting in an annual electricity production of 50 TWh that prevented the release of 29 Mt of CO2 emissions into atmosphere. According to the roadmap outlined by the HYDI (Hydro Data Initiative) [2], over the next 10 years the installed capacity will increase by nearly 30%, reaching 17.3 GW in 2020. Among the individual countries, Germany has the largest number of installations (over 7500), followed by Austria (2590), Italy (2430) and France (1900). Moreover, Italy has the largest installed capacity (2.73 GW) and electricity production (10.9 TWh). According to HYDI projections,
* Corresponding author. Tel.: þ39 0862 434320; fax: þ39 0862 434403. E-mail address: [email protected] (R. Carapellucci). http://dx.doi.org/10.1016/j.renene.2014.10.008 0960-1481/© 2014 Elsevier Ltd. All rights reserved.
this leadership position will continue in 2020, when the installed capacity will reach nearly 4 GW [2]. Among the regions of southern Italy, the Abruzzo region has the largest number of hydroelectric plants (57) and a total installed capacity of 1002 MW, with approximately 10% contributed by small-hydro installations [3]. However, because of the morphological characteristics of this territory, the Abruzzo region has a number of suitable sites for the construction of small hydro power plants. In fact, the Abruzzo region includes 25 river basins, with 8 having catchment areas greater than 200 km2. The Regional Water Protection Plan [4] evaluated the availability of the water resources of these basins, focussing on river branches regarded as “significant” according to the definition of Legislative Decree 152/06 [5]. As part of that investigation, a water balance model was implemented in the commercial software MIKE BASIN [6] to evaluate the main hydrological variables of each river branch, including the natural water flow rate (Qn), the minimum vital flow (MVF) and the actual water flow rate (Qm), considering derivations for drinking water or irrigation [7]. Then, the gross heads of the watercourses were characterised in the water resource planning study [8], which allowed the identification of river branches suitable for hydro power production.
396
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Starting from the results of the previously cited studies, the goal of this paper is the development of a methodology for assessing the technical and economic potential of small hydro power plants on a regional scale. The study focused on 87 river branches within the Aterno-Pescara, Sangro, Vomano, Saline, Foro, Tordino, LiriGarigliano and Sinello river basins. The methodology is based on the definition of a specific flow duration curve [9] for each suitable river branch to characterise the river flow regime on an annual basis. The flow duration curve is evaluated through a regionalisation procedure based on a graphical approach [10,11]. For the Aterno-Pescara, Sangro, Vomano, Saline, Foro and Tordino basins, the starting point for implementing the graphical method is the regionalisation study of the CESI Research Institute [12] involving the main river basins between the Marche and Abruzzo regions. In this paper, the regionalisation procedure has also been extended to the Sinello and Liri-Garigliano basins. Thus, two homogeneous regions have been identified (Liri-Garigliano and Trigno-Sinello), and the corresponding regional flow duration curves were evaluated by processing the daily flow rate data of gauging stations in these regions. The homogeneity of these areas with respect to the flow duration curve is verified by implementing the Hosking and Wallis test [13] in the software R, a free tool for computing statistics [14]. The rated capacity of each installable small-hydro power plant is defined on the basis of the net head, the design flow rate (Qd) and the hydraulic turbine efficiency. The annual electricity production is then evaluated by integrating the instantaneous power over the entire period of plant operation, given the flow duration curve and the technological constraints of the hydraulic turbine. For the economic analysis, two different scenarios are investigated. In the first one, capital costs and operating and maintenance expenses are evaluated through cost functions presented in a study by the Polytechnic of Milan [15]. In the second scenario, the cost items are estimated using statistical data provided by the HYDI [16]. The economic analysis of a small-hydro power project attempts to evaluate the unit cost of electricity (COE) and the profitability of the initial investment, taking into account the Italian incentive scheme that was recently reformed by the Ministerial Decree of 6 July 2012 [17]. Given the net potential from the energy analysis, the economically feasible potential is evaluated at various levels of economic competitiveness on the basis of the cost of electricity and the profitability of the initial investment [18]. 2. Characterisation of regional water resources availability The actual availability of regional water resources was evaluated in a study conducted by the Abruzzo region with the purpose of defining the Water Protection Plan [4], a document designed to ensure the water environmental quality and the sustainability of the water supply in compliance with the European Directive 2000/ 60/EC [19]. As part of this investigation, the surface and ground water resources of each regional river basin were characterised qualitatively and quantitatively. In particular, the study focused on the watercourses identified as significant according to Legislative Decree 152/06 [5], namely: - watercourses of the first order (discharging into the sea), having a catchment area of at least 200 km2; - watercourses of the second (discharging into first-order watercourses) or higher order, having a catchment area of at least 400 km2. The methodology adopted for estimating water resources includes the following main phases [20]:
- the delimitation of the Abruzzo region in the river basins; - the acquisition of hydro-meteorological data; - a hydrogeological characterisation of the area and the identification of ground water bodies; - a quantitative assessment of surface and ground water resources. The river basins were delimitated through a digital elevation model of the soil [21] using a horizontal resolution of 250 m and a vertical resolution of 1 m. Thus, the basins were identified by an automatic procedure known as the eight-direction four-point algorithm, or method D8. This method is based on subdividing the land into cells (250 m 250 m), thus allowing the flow direction to be defined with the maximum slope among the eight directions connecting a given cell with the adjacent ones. Having identified the drainage network, the boundaries of the regional basins were traced, allowing the evaluation of the corresponding surface area. Unlike the definition of boundaries based on the knowledge of regional topographical features, the results of this procedure do not depend on user choices, only on the model resolution. The regional river basins were characterised from the hydrological, hydrogeological and climatic conditions on the basis of information provided by local administrations or gathered from previous studies [20]. The hydrological and hydrogeological balances were defined for each river basin using the simulation software MIKE BASIN (DHI Water and Environment) [6]. MIKE BASIN is an integrated tool for the simulation of drainage basins that operates in a GIS environment. This software is an efficient tool for lowflow and data-scarce hydrological simulations that allows the rivers and the main tributaries to be described by a network consisting of branches and nodes. The subdivisions are defined in such a way that the branches correspond to river stretches with constant flow rates and the nodes are located at the confluence points between different branches or at important locations where model results are required. Thus, the river branches are identified on the basis of the numbers of upstream and downstream nodes. The implementation of river basin models in MIKE BASIN requires the time series of the rainfall, the temperature and the aquifer flow rates, which were obtained from the Hydrographic Service of Pescara [22], that provides data updated until the year 2000. With regard to weather and climate data, the mean monthly rainfall and temperature data recorded at 172 stations between 1920 and 2000 were used. The aquifer flow rate data were obtained from field measurements taken between 1898 and 2000 (more frequently from 1954 to 1963 and from 1980 to 1986). Based on these data and using a rainfall-runoff model, the MIKE BASIN software allowed the evaluation of the natural flow rate (Qn) and the actual flow rate (Qm), taking into account deductions for human consumption, irrigation, industrial and hydroelectric purposes. Moreover, the model allowed the minimum vital flow (MVF) to be defined, representing the minimum flow to be restored to safeguard aquatic wildlife and to guarantee that underground water is replenished [7]. Finally, the available flow (Qav) was evaluated, which is the difference between the actual flow rate and the minimum vital flow. 3. Identification of suitable river branches for installing hydroelectric power plants The river stretches that are suitable for the exploitation of water resources for hydroelectric purposes were identified as a part of a study of water resources planning for hydro power production [8]. This investigation involved the main regional river basins, except for the interregional-basins of Tronto and Trigno. Preliminary data
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
were acquired to characterise the flow regimes of the various river basins. Using data from the Water Protection Plan [4], the branches of the river network were characterised in terms of the actual flow, the minimum vital flow and the value of criticality, that is the number of months in which the actual flow rate is less than the hydrological component of the MVF [7]. After excluding the river branches falling within protected areas (parks and nature reserves), a database of suitable stretches for the exploitation of water resources for hydroelectric purposes was defined. Moreover, the gross head of each river branch was evaluated through the digital elevation model based on the 1:10,000 orthophoto of the Abruzzo region [23]. The results of this investigation were the starting point for the evaluation of the residual hydroelectric potential on a regional scale. In the present study, attention is focused on 87 branches belonging to 8 regional river basins: Aterno-Pescara, Sangro, Vomano, Saline, Liri-Garigliano, Tordino, Sinello and Foro. Fig. 1 summarises for each investigated basin the extension, the number of exploitable river branches and their main hydrological variables, i.e., the actual flow rate and the gross head. The figure shows that the actual flow rates of the river branches in the Sangro and Aterno-Pescara basins vary over a rather wide range, from 0.4 to 47 m3/s and from 2.1 to 17 m3/s, respectively. In the remaining basins, the actual flow rates of the river branches are nearly always less than 10 m3/s. Moreover, all the branches with the exception of a branch belonging to the Sangro basin have a gross head less than 250 m, and the majority have a gross head of less than 50 m. Linear curves plotted on logarithmic scales highlight the gross or natural potential, the maximum theoretical potential for a hydro power plant, which depends on the gross head (Hg) and the actual flow rate (Qm). The river branches have gross potentials generally between 1 MW and 5 MW in the Aterno-Pescara, Sangro, Vomano and Liri-Garigliano basins and less than 1 MW in the remaining basins. It is noteworthy to observe that the actual flow rate could be changed over the years, due to climate change related to global warming effects. According to the projections of IPCC, the mean annual flow rate of rivers in Southern Europe should decrease in the period of 2016e2035 compared to 1986e2005; as regard to Italy, such reduction is expected to be moderated, varying in the range of 10÷0% [24].
397
4. Characterisation of the methodology for the technoeconomic evaluation of small-hydro power potential at regional scale The identification and characterisation of the suitable river branches for the exploitation of water resources for electricity production are the starting point for the modelling of the technical and economical small-hydro power potential at regional scale. The methodology outlined in the present study consists of the following main steps: - Definition of a specific flow duration curve for the suitable river branches, by multiplying the mean actual flow rate by the dimensionless regional flow duration curve, arising from a regionalisation procedure based on graphical approach (Section 5.1); - Correction of the flow duration curve to account for the value of the criticality, that identifies the number of months with actual flow rate less than the hydrological component of the minimum vital flow (Section 5.1.2); - Evaluation of the rated power and the annual electricity production, based on the corrected flow duration curve and the small-hydro turbine technology (Section 5.2); - Estimation of unit cost of electricity and the profitability of the investment with reference to different scenarios for estimating capital and operating and maintenance costs (Section 6); - Evaluation of the net potential at regional scale by summing contributions of the different river branches (Section 7.1); - Definition of the economically feasible potential, assumed as the fraction of net potential that meets different level of economic competitiveness, defined with respect to the unit cost of electricity (COE) and the profitability index (PI) (Section 7.2).
5. Energy model for evaluating the potential for small hydro on a regional scale To evaluate the residual potential for small hydro, the methodology requires that the suitable river branches are defined in terms of the net head and the flow duration curve to reveal the
Fig. 1. Characterisation of the regional river basins in terms of actual flow rate (Qm), gross head (Hg) and natural potential.
398
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
variability of the flow regime throughout the year [25]. The net head is evaluated assuming reasonable values for the concentrated and distributed head losses due to friction and turbulence in the penstock. Flow duration curves are defined through a regional approach if historical flow rate time series are lacking for the river branches under investigation.
5.1. Flow duration curve The definition of a flow duration curve is based on knowledge of the historical time series of stream-flow data, whose availability is generally limited to only a small number of rivers. If there is a lack of observed stream-flow data, a flow duration curve can be obtained by spatially transferring the flow information from nearby gauged sites through a regionalisation of the flow characteristics [26]. Various procedures for regionalisation have been proposed in the literature; they can be grouped into three main categories: statistical, parametric and graphical approaches [11]. In statistical methods, the flow duration curve is defined as the complement of the flow rate cumulative distribution function. Parametric methods represent flow duration curves through an analytic function (polynomial, exponential, logarithmic or power function) whose parameters are determined by a multiple-regression analysis that includes morphological characteristics and climatic conditions. Unlike other methods, the graphical approaches do not rely on specific assumptions for the distribution or the shape of the regional flow duration curve but use standardised graphical representations of FDCs with a regional validity. In this paper, the graphical approach proposed by Smakhtin [25] will be used for evaluating the flow duration curves of the river
branches under investigation. The methodology includes the following main steps: - a preliminary division of the territory into homogeneous zones that are characterised by a significant hydrological affinity; - the identification of gauging stations in each homogeneous zone with measured daily stream-flow time series extended over a period longer than five years; - the normalisation of the experimental duration curves by dividing the empirical FDCs by an index of flow such as the mean daily stream flow evaluated in the available record period; - the determination of the regional flow duration curves for the homogeneous zones by averaging the normalised flow duration curves. The flow duration curve for an ungauged river branch in a given homogeneous region is therefore obtained by multiplying the dimensionless regional flow duration curve by the mean daily stream flow [12]:
Q ðDÞ ¼ Q ðDÞadim Qm
(1)
In this study, the average flow (Qm) is assumed to be the actual flow rate of the river branch under consideration, as identified by the Regional Water Protection Plan [4]. The regional dimensionless flow duration curves coincide with those resulting from the regionalisation study by the CESI Research Centre [12], which involved the major river basins of the Abruzzo region including the Aterno-Pescara, Sangro, Vomano and Tordino, and smaller basins near the coast (Saline, Tavo-Fino, Alento, Foro, Moro and Feltrino). In particular, to apply the graphical method, this portion of regional territory is subdivided into 8 homogeneous areas shown in Fig. 2.
Fig. 2. Subdivision of the study area into homogeneous regions for the application of the graphical method.
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
2.5
2.5
Vomano-Aterno Castellano-Tordino Coastal basins of type I Coastal basins of type II Sangro and Tasso Upper Sangro basins Lower Aterno and SagiƩario Lower Pescara
2.0 1.8 1.5 1.3
2.3
Qadim (D)
2.3
Q adim (D)
399
2.0
Liri-Giovenco
1.8
Trigno-Sinello
1.5 1.3 1.0
1.0
0.8 0.8
0.5
0.5
0.3
0.3
0.0 10
0.0
10
20
30
40
50
60
DuraƟon (%)
70
80
90
20
30
40
100
Fig. 3. Regional dimensionless flow duration curves based on the graphical approach.
The regional FDCs in those areas were evaluated using the daily stream flow data collected between 1921 and 2000 in 35 hydrographic stations located in the Abruzzo region. Fig. 3 shows the regional flow duration curves obtained by applying the graphical approach. 5.1.1. Regionalisation to characterise the Liri-Garigliano and Sinello basins The regionalisation procedure for the flow duration curves was extended in this study to the Sinello and Liri-Garigliano basins, thus leading to the identification of two other homogeneous zones, namely, the LirieGiovenco and Trigno-Sinello zones (Fig. 2). Initially, the daily stream flow time series were collected for the gauging stations of Liri-Garigliano and Sinello from the National Hydrographic Service of Italy [22]. For the Liri-Garigliano basin, attention focused on the Liri and Giovenco rivers, where the river stretches suitable for small hydro are located. The daily stream flow time series were collected for the gauging stations of Liri at Sora and Giovenco at Pescina, where hydrological data have been recorded for 46 and 29 years, respectively. Regarding the Sinello basin, there is only one gauging station (Sinello at Casalbordino), where stream flow data were recorded for only one year. In this case, the regionalisation procedure was applied using the gauging stations of the Trigno basin, which had the greatest similarity to the Sinello basin hydrologically because of the geographic proximity [27]. The data from the two gauging stations located on the river Trigno (at Pescolanciano and at Chiauci) were considered, being the only ones with recording periods exceeding 5 years. The regional flow duration curves for the two homogeneous zones were derived by applying the graphical method described. Fig. 4 shows the trends of the regional flow duration curves for the homogeneous zones LirieGiovenco and Trigno-Sinello. The homogeneity of these regions was checked with the Hosking and Wallis method [13], which is based on the L-moment ratios LCV (coefficient of L-variation) and LCS (coefficient of L-skewness). This test compares the regional variance of the L-moment ratios in a pooling group to the variation that would be expected in a homogeneous group. The expected mean value (mV) and the standard deviation (sV) of the L-moment ratios for a homogeneous group are evaluated through repeated simulations, thereby generating
50
60
70
80
90
100
DuraƟon (%) Fig. 4. Regional dimensionless flow duration curves for homogeneous zones LirieGiovenco and Trigno-Sinello.
homogeneous groups of basins having the same record lengths as those of the observed data. According to Hosking and Wallis, the region should be regarded as acceptably homogeneous if the test metric Hk satisfies Hk < 1, possibly heterogeneous if 1 < Hk < 2, and definitely heterogeneous if Hk > 2. The heterogeneity measures are evaluated as follows:
Hk ¼
Vk mk sk
for k ¼ 1; 2
(2)
where
V1 ¼
R X
2 ni t2; i t 2
,
i¼1
R X
ni
(3)
i¼1
and
V2 ¼
R X
ni
h
t2; i t 2
i¼1
2
2 i1=2 þ t3; i t 3
,
R X
ni
(4)
i¼1
give measures of dispersion, V1 for LCV and V2 for both LCV and LCS. In Equations (3) and (4), t2,i, t3,i and ni are the values of LCV and LCS and the sample size of the site i, respectively, t 2 , t 3 and R are the mean values of LCV and LCS and the number of sites, respectively. The Hosking and Wallis homogeneity test [13] was applied to the three parameters, i.e., the stream flow variability index (Q20/ Q90), the low-flow variability index (Q50/Q90) [25] and the concavity index (CI), based on the flow duration curve. The last index establishes the shape of the dimensionless flow duration curve, providing a measure of the contrast between the low-flow and high-flow regimes [28]:
CI ¼
Q10 Q99 Q1 Q99
(5)
The results of the test, listed in Table 1, show that the LirieGiovenco region can be considered homogeneous because the heterogeneity measures H1 and H2 are always less than unity for all three parameters investigated. In the Trigno-Sinello region, a substantial degree of homogeneity is detected because only the value
400
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Table 1 Results of the Hosking and Wallis homogeneity tests for CI, Q20/Q90 and Q50/Q90. LirieGiovenco
Trigno-Sinello
Index
H1
H2
H1
H2
CI Q20/Q90 Q50/Q90
0.13 1.1 0.57
0.83 0.55 0.66
1.1 0.32 0.77
0.4 0.36 0.65
of H1 related to the concavity index has a value slightly greater than unity (1.1).
5.2. Rated power and annual electricity production The rated capacity of a small hydroelectric power plant in each suitable river branch can be calculated as:
Pn ¼ rgQd Hn hturb ðQd Þ
where Qd and hturb(Qd) are the flow rate and the efficiency at the design condition, respectively, and Hn is the net head. The design flow rate is the difference between the available flow rate and the minimum vital flow [29]:
Qd ¼ Qm MVF 5.1.2. Correction of flow duration curve to account for criticality The regional flow duration curves do not account for differences among the river branches in the criticality, the number of months in which the actual flow rate is less than the hydrological component of the MVF [23]. The values of the criticality in the basins investigated in this study ranged from 1 to 6. The criticality is 0 for 64 river branches and greater than 3 (which is considered significant) in 24 stretches, mainly those belonging to the Vomano (7), Liri-Garigliano (5) and Sangro (5) basins. To avoid overestimating the annual electricity production for river branches with significant values of criticality, the flow duration curves produced by the regionalisation procedure were corrected by holding constant the mean annual flow rate. Therefore, the regional flow duration curves of certain river branches are rotated about Qm in such a way that the flow rate is less than or equal to the hydrological component of the minimum vital flow for a period corresponding to the value of the criticality. Fig. 5 compares the flow duration curves for a river branch in the Saline basin resulting from the regionalisation procedure with and without the correction, taking into account the effective value of the criticality, which is 3 for the case examined. As shown, by rotating about the mean value (Qm ¼ 1.62 m3/s), the corrected FDC shows a flow rate coincident with the hydrological component of the MVF (Q* ¼ 0.2 m3/s) for a duration of 75%, corresponding to a criticality of 3.
(6)
(7)
As is well known, friction losses strongly depend on the material, the length and the diameter of the penstock [30]. For the sake of simplicity, in this paper the net head is evaluated assuming that the concentrated and distributed head losses amount to 6% of the gross head [31]. The efficiency of the hydraulic turbine at the design condition is calculated as a function of the design flow rate, the net head and the hydraulic turbine type through Gordon's empirical relationships [32]. The annual electricity production is evaluated by integrating the instantaneous power during the operational period of the plant:
Z1 Ep ¼ he hop
rgQt ðDÞHn hturb ðQt ðDÞÞdD
(8)
0
where hop is the plant operating time in hours and he is the system electrical efficiency, which takes into account the gearbox, electric generator and transformer losses. The hydro-turbine flow rate, that is, the amount of water flowing through the hydro turbine, Qt(D), is defined on the basis of flow duration curve [33]:
Qt ðDÞ ¼
8 < :
0; Q ðDÞ; Qd ;
Q ðDÞ < Qmin Qmin Q ðDÞ Qd Q ðDÞ > Qd
(9)
The definition includes the constraints related to the design flow rate and the minimum allowable flow rate passing through the hydraulic turbine. The latter is selected to minimise the unit cost of electricity production of the small-hydro power plant while taking into account the domain of application of the various technologies with regard to the design flow rate and the net head. 6. Economic model
Fig. 5. Comparison between regional FDC and corrected regional FDC for a river branch in the Saline basin.
The estimation of the unit cost of electricity of a small-hydro power plant involves a preliminary evaluation of the initial investment and the annual operating and maintenance costs. The initial investment cost can be divided into three main components: electro-mechanical equipment costs, civil works costs and engineering and administration costs [34]. As well known, investment costs of hydro power systems are highly sitedependent. However, cost data for small hydro power plants operating in the Abruzzo region are not readily available from technical literature or power companies. Hence, based on cost data at a national level, two different models for estimating capital and O&M costs of SHPs have been implemented, thus reflecting a pessimistic and an optimistic scenario. In the first one (the pessimistic scenario), cost functions have been derived by interpolating data arising from the study conducted by the Polytechnic of Milan [15]:
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
( CI ¼
4929Pn0:26 Hn < 80m 4257Pn0:2 Hn > 80m
CO&M ¼ 180:4Pn0:47
(10)
(11)
where CI and CO&M are capital cost and the annual operating and maintenance cost, respectively. In the second one (optimistic scenario), costs functions of the pessimistic scenario have been modified to take into account economic statistics provided by HYDI (Hydro Data Initiative) [16]. For the EU-27 Member States, it defines an average capital cost per unit of installed capacity and a range of variability of operating and maintenance costs, expressed as a percentage of capital costs:
8 0:26 > Hn < 30m < 4500Pn CI ¼ 4150Pn0:23 30 < Hn < 100m > : Hn > 100m 3800Pn0:2
CO&M
8 0:51 > Hn < 30m < 84:1Pn 0:47 ¼ 30 < Hn < 100m 70Pn > : Hn > 100m 55:8Pn0:45
CI CRF þ CO&M Ep
7. Evaluation of net and economically feasible potential of small-hydro power plants
(13)
(14)
where CRF is the capital recovery factor, assuming a discount rate of 5% and a power plant lifetime of 30 years. In addition to the unit cost of electricity, the profitability of the investment was assessed by means of two common indices [18], the discounted payback period (DPP) and the profitability index (PI):
PI ¼
NPV þ CI CI
an all-inclusive tariff, comprising both the incentive and the remuneration of the energy production. Furthermore, in the present study it is assumed that for these small-hydro power plants, where the effective lifetime is greater than the conventional one, the energy production at the end of the incentive period benefits from the simplified purchase/resale arrangements. The simplified purchase/resale arrangements provide that the energy supplied to the grid is sold at a guaranteed minimum price, depending on the type of renewable energy source and the amount of energy supplied to the grid. For small-hydro power plants with a rated capacity exceeding 1 MW, the incentive is the difference between the “base tariff” and the hourly zone price. In this case, the energy production, which is at the producer's disposal, cannot be sold through the simplified purchase-resale arrangements but only through bilateral contracts in the energy market.
(12)
Thus, the unit cost of electricity is given by:
COE ¼
401
(15)
These parameters were evaluated assuming that small-hydro power plants will benefit from the Italian incentives program, which was radically redefined by the Ministerial Decree of 6 July 2012 [17]. According to this decree, the incentive for small hydro power plants with a rated capacity of less than 1 MW is a “base tariff” defined according to the size and guaranteed for the conventional plant lifetime. In this case, the incentive is configured as
The implementation of the methodology previously described allows the evaluation of the net potential and the economically feasible potential of small-hydro power plants for the river basins investigated. As depicted in Fig. 6, more than 70% (63) of the potential smallhydro power plants are low-flow installations (Qd < 10 m3/s), and the remainder (24) are medium-flow installations (10 < Qd < 100 m3/s). Focussing on the individual river basins, it is noted that medium-flow small-hydro power plants are located only in the Aterno-Pescara (10), Vomano (10), Sangro (3) and LiriGarigliano (1) basins. Regarding the net head, 48 of the potential installations are lowhead (Hn < 30 m), 25 are medium-head (30 < Hn < 100 m) and 14 are high-head (100 < Hn < 1000 m). The prevalence of low-head installations directly affects the choice of the type of hydraulic turbine to be installed. Fig. 7 shows that a Kaplan turbine is the best choice in more than 70% of the potential installations, followed by Pelton (15%) and Francis (9%) turbines; a cross-flow turbine is the best choice in only one installation, located in the Aterno-Pescara basin. 7.1. Rated power classes and electricity production Table 2 summarises the main results of the energy analysis for the river basins investigated, including the total rated power, the
Fig. 6. Classification of small hydro power potential installations with respect to design flow rate and net head.
402
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Fig. 7. Distribution of types of potential installable small hydro power plants. Fig. 8. Distribution of potential installations with respect to rated power classes.
average power of the potential installations and the annual electricity production. Thus, the net residual potential of small-scale hydro power in the Abruzzo region amounts to 146.1 MW. The Aterno-Pescara basin, with an installed capacity of 52 MW, has the highest potential, accounting for more than 35% of the total rated power. The Sangro basin is the second most important basin with 46.1 MW (31.5%), followed by the Vomano basin with 16.3 MW (11.2%) and the Liri-Garigliano basin with 13.8 MW (9.4%). Indeed, the aforementioned basins are characterised by the greater number of suitable river branches and by the highest average rated power, ranging between 1.4 MW in the Vomano basin to approximately 3 MW in the Sangro basin. The rated capacities are significantly lower in the other river basins, which overall account for approximately 12% of the total net potential, with rated capacities ranging between 2.5 MW (Foro) and 7.1 MW (Tordino). Fig. 8 shows that 44 of the 87 potential small-hydro power plants have a rated capacity less than 1 MW, 36 have a rated capacity between 1 MW and 5 MW and the remainder have a rated capacity greater than 5 MW. As regards the individual river basins, the rated capacity is less than 1 MW for all the potential installations in the Saline basin; small-hydro power plants with a rated power greater than 5 MW are possible only in the AternoPescara (3), Sangro (3) and Liri-Garigliano (1) basins. In this
Table 2 Net residual potential of small hydro power for regional basins investigated. River basin
River Pn Pn,mean Pn (%) branches (MW) (MW)
Aterno-Pescara Foro Liri-Garigliano Saline Sangro Sinello Tordino Vomano
20 3 9 12 15 6 10 12
Total
87
52.1 2.5 13.8 5.2 46.1 2.9 7.1 16.3
2.6 0.8 1.5 0.4 3.1 0.5 0.7 1.4
146.1 1.7
Ep Ep (%) (GWh)
35.7% 313 1.7% 10 9.4% 64 3.6% 19 31.5% 185 2.0% 10 4.9% 27 11.2% 62 100%
690
45.4% 1.5% 9.3% 2.8% 26.9% 1.4% 3.9% 8.9%
Ep/Pn (GWh/MW) 6.0 3.9 4.6 3.7 4.0 3.3 3.7 3.8
100.0% 4.7
regard, it should be noted that the design flow rates for two river branches, one in the Aterno-Pescara basin and one in the Sangro basin, were not the difference between the actual mean flow rate and the minimum vital flow but were set to the limit value so that the rated power did not exceed 10 MW. With regard to the capacity factor, more than 40% (37) of the total potential installations have values between 0.4 and 0.6, whereas only 20% (18) have values greater than 0.6. The differences in the behaviour of the river basins are depicted in Fig. 9, representing the capacity factor as a function of the rated power of the potential installations. It is noted that the capacity factor ranges between 0.3 and 0.5 for the Vomano, Tordino, Saline and Foro basins; the same is true for the Sangro basin, except for two installations having a capacity factor close to 0.6. As regards the Aterno-Pescara basin, 15 of the 20 potential installations have a capacity factor greater than 0.6. Conversely, the capacity factor is less than 0.4 for each investigated river branch in the Sinello basin. This is primarily due to the differences in the flow duration curves, which are generally more flat for river stretches in the Aterno-Pescara basin than for those in the Sinello basin, as revealed by the dimensionless regional flow duration curves presented in Figs. 3 and 4. Therefore, the total electricity production amounts to 690 GWh, with the most important contributions coming from the AternoPescara (45.4%) and Sangro (26.9%) basins, followed by the LiriGarigliano (9.3%) and Vomano (8.9%) basins. Fig. 10 shows the distribution of annual electricity production with respect to the rated capacity class of the small-hydro power plants. It is noted that approximately 90% of the overall electricity production is from installations with a rated capacity greater than 1 MW, and the contributions of those plants with up to 5 MW of capacity are greater than 50%. This is because of the predominant contributions of the Aterno-Pescara, Sangro and Liri-Garigliano basins, where the incidence of installations with a rated power of greater than 1 MW is greater than 90%. Moreover, it is interesting to observe that there are significant contributions from installations with a rated power ranging from
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
403
Fig. 9. Capacity factor as a function of rated capacity of small-hydro power plants.
1 MW to 5 MW, not only for the Vomano basin but also for the Tordino and Foro basins, despite the greater number of plants with smaller capacities. The share of small-hydro power plants with capacities between 1 MW and 5 MW decreases significantly in the Sinello basin (38%) and down to zero in the Saline basin, where the electricity production is totally attributable to installations of less than 1 MW, with approximately 60% of those greater than 500 kW. Thus, the annual electricity production potential of small-hydro power plants would increase by approximately 40% the current
hydroelectric production of the Abruzzo region (1756.4 GWh). This contribution is even more significant considering that approximately 90% of hydro power is currently produced by large plants with a rated power exceeding 10 MW. 7.2. Cost of electricity and economically feasible potential The semi-logarithmic plots of Fig. 11 show the trend of the unit cost of electricity production as a function of the small-hydro
Fig. 10. Distribution of electricity production with respect to rated power classes.
404
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Fig. 11. Unit cost of electricity production as a function of rated capacity of small-hydro power plants.
power plant rated capacity and the river basin investigated. The COE was evaluated in two different economic scenarios: - the pessimistic scenario, shown in blue (in the web version), which is based on cost models obtained from the Polytechnic of Milan investigation [15]; - the optimistic scenario, shown in red (in the web version), which is based on cost models derived from HYDI statistics [16]. It is noted that the COE for the river basins investigated decreases with increasing rated capacity according to a specific power law. In the case of the Aterno-Pescara basin, the unit cost of electricity varies over a rather wide range, between 3 and 27 cV/kWh.
In the pessimistic scenario, the COE is less than 10 cV/kWh for more than 70% of the potential installations, with a clear prevalence of those with a COE greater than 5 cV/kWh. Conversely, assuming the optimistic scenario, more than 50% of the small-hydro power plants have a COE lower than 5 cV/kWh. As regards the Sangro basin, the unit cost of electricity is between 4 and 34 cV/kWh. However, except for the installations with a rated power of less than 1 MW, the COE is always less than 15 cV/ kWh. Moreover, switching from the pessimistic to the optimistic scenario, the number of installations with a COE greater than 10 cV/ kWh markedly declines because of an increase in the number of plants with a COE less than 5 cV/kWh. In the Liri-Garigliano basin, the unit cost of electricity shows a pronounced variability
Fig. 12. Comparison between net and economically feasible potential for pessimistic (a) and optimistic (b) economic scenarios.
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
(4e43 cV/kWh), but with a clear prevalence of installations with a COE of approximately 10 cV/kWh. In the Vomano basin, the COE varies over a more restricted range, from 5 to 21 cV/kWh. Finally, in the Saline, Sinello, Tordino and Foro basins, the unit cost of electricity is greater than 10 cV/kWh in nearly all cases because of the moderate rated capacities of the potential installations. It is important to recognise that the differences in terms of the cost of electricity are not only related to the rated capacity of a potential installation but also to the capacity factor, which influences the annual electricity production. For instance, for a fixed rated power in the Sangro basin, the cost of electricity is greater than in the Aterno-Pescara basin because of the lower capacity factors (Fig. 9). This aspect is even more noticeable in the Saline and Sinello basins, where the capacity factor is always less than 0.5. At the global level, the COE in the pessimistic scenario is less than 5 cV/kWh for approximately 3% of the total installations, between 5 and 15 cV/kWh for approximately 55%, and greater than 15 cV/kWh for the remainder. However, in the optimistic scenario the percentage of installations with a COE less than 5 cV/kWh increases to approximately 18%, with a corresponding reduction in those with a COE greater than 15 cV/kWh (22%). The net potential of the regional basins investigated was compared with the economically feasible potential. In this paper, the latter is the fraction of the net potential that meets the prescribed economic requirements defined in terms of the cost of electricity (COE) and the profitability index (PI). Considering the variability in the COE for small hydro in Italy (8e15 cV/kWh), a limit value of 15 cV/kWh was used to evaluate the economically feasible potential. As shown in Fig. 12, to obtain a COE <15 cV/kWh and a PI > 1, the economically feasible potential ranges from 121.8 MW (pessimistic scenario) to 142.6 MW (optimistic scenario), whereas the corresponding annual electricity production ranges from 605 to 678 GWh. In the pessimistic scenario, the economically feasible potential is more than 80% of the net potential, despite the reduction in the number of potential installations from 87 to 40. This is because of the small contribution of non-viable power plants in terms of rated capacity, as highlighted by the increase in the average capacity of installable power plants from 1.7 MW to approximately 3 MW. In this case, the Aterno-Pescara basin accounts for approximately 41% (50.2 MW) of the total economically feasible potential, whereas the Sangro and Vomano basins account for 35% (42.9 MW) and 9% (10.9 MW), respectively. In the optimistic scenario, the economically feasible potential is approximately 98% of the net potential, and the number of
405
installations is 68. In this case, the contributions from the AternoPescara (36%) and Sangro (32%) basins decrease and that from the Vomano basin (11%) significantly increases. Fig. 13 shows the distribution of small-hydro power plants with respect to the length of the discounted payback period (DPP). In both scenarios, nearly all viable installations in the Aterno-Pescara basin have a DPP less than 10 years, with a clear prevalence of those with a DPP greater than 5 years. This trend is basically true for the Sangro basin, whereas the remainder, particularly those in the Vomano basin, are dominated by small-hydro power plants with a DPP greater than 10 years. To obtain a COE <15 cV/kWh and a PI > 1.5, the number of viable installations varies from 28 (pessimistic scenario) to 48 (optimistic scenario), whereas the economically feasible potential varies from 102.6 MW to 124.8 MW (Fig. 12), thus allowing an electricity production per year in the range of 533e616 GWh. The contribution of the Vomano basin decreases (4e6%) and that of the Aterno-Pescara basin markedly increases, reaching a peak of approximately 50% in the first scenario. Finally, the economically feasible potential resulting in a COE less than 15 cV/kWh and a PI greater than 2 remains approximately 54% (78.6 MW) and 72% (105 MW) of the net capacity in the first and second scenarios, respectively. In both cases, nearly all the viable installations are located in the Aterno-Pescara basin, accounting for approximately either 60% (pessimistic scenario) or 50% (optimistic scenario) of total feasible potential. 8. Conclusions The goal of this paper was to define a methodology for evaluating the technical and economic residual potential of small-hydro power plants having a rated capacity less than 10 MW. The methodology was applied to the case of the Abruzzo region of Italy, which has a considerable number of suitable sites for the construction of small hydro power installations. Specifically, the investigation involved 87 river stretches belonging to the main regional basins, namely, the Aterno-Pescara, Sangro, Vomano, Saline, Foro, Tordino, LiriGarigliano and Sinello basins. The energy model proposed evaluates the design flow rate, the net head, the rated power and the annual electricity production of potential installations based on the flow duration curve and the hydraulic turbine type. The flow duration curves were defined through a regionalisation procedure based on a graphical approach, and the type of hydraulic turbine was selected to minimise the unit cost of
Fig. 13. Discounted payback period of economically feasible installations with COE <15 cV/kWh and PI > 1.
406
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
electricity produced. The cost of electricity was evaluated assuming two economic scenarios based on different capital, operating and maintenance cost functions. Moreover, the economic model allowed the assessment of the profitability of the initial investment by evaluating the profitability index and the discounted payback period. The residual potential of small hydro in the investigated basins was 146.1 MW. The most important contribution is provided by the Aterno-Pescara basin (52.1 MW), followed by the Sangro (46.1 MW), Vomano (16.3 MW) and Liri Garigliano (13.8 MW) basins. More than 50% of the total potential installations had a rated capacity less than 1 MW (44), approximately 40% had a rated capacity between 1 and 5 MW, and the remaining 8% (7) had a rated capacity exceeding 5 MW (these seven were located in the AternoPescara (3), Sangro (3) and Liri-Garigliano (1) basins). The annual electricity production amounted to 690 GWh, with the Aterno-Pescara and Sangro basins accounting for more than 70% (498 GWh). Regarding the distribution of the energy production with respect to the rated capacity of small-hydro power plants, it is noted that over 90% of the electricity is produced by installations exceeding 1 MW, despite the greater number of plants of smaller size. The electricity generated by these new potential installations could increase the current hydroelectric energy production of the Abruzzo region (1756.4 GWh) by approximately 40%. In the case of a pessimistic economic scenario, the unit cost of electricity production was less than 15 cV/kWh for approximately 60% (51) of potential installations. Assuming as economic constraints that the COE <15 cV/kWh and the PI > 1, the economically feasible potential amounted to 121.8 MW, or approximately 80% of the net capacity for an annual electricity production of 605 GWh. The number of viable installations was 40, which were mainly located in the Aterno-Pescara (16), Sangro (10) and Vomano (5) basins, with rated capacities of 50.2 MW, 42.9 MW and 10.9 MW, respectively. In the case of the optimistic economic scenario, the number of installations with a COE <15 cV/kWh reached approximately 80% (68); the economically feasible potential (COE <15 cV/kWh, PI > 1) was approximately 97% (142.6 MW) of the net rated capacity, thus enabling an electricity production per year of 678 GWh. Assuming more stringent economic constraints (COE <15 cV/ kWh, PI > 2), the economically feasible potential ranges from 78.6 MW (pessimistic scenario) to 104.9 MW (optimistic scenario), thus representing over 50% of the net potential, mainly because of the viable installations in the Aterno-Pescara basin. Nomenclature
Symbols CI CI CO&M Ep Hg Hn LCV LCS Pn Qd Qm Qmin
investment cost, MV/MW concavity index operating and maintenance cost, MV/(MW year) annual electricity production, GWh gross head, m net head, m coefficient of L-variation coefficient of L-skewness net hydro power potential, MW design flow rate, m3/s mean actual flow rate, m3/s hydraulic turbine minimum flow rate, m3/s
Acronyms COE cost of electricity, cV/kWh CRF capital recovery factor, % DPP discounted payback period, years FDC flow duration curve
MVF NPV PI
minimum vital flow, m3/s net present value, MV profitability index
Greek letters electrical efficiency hydraulic turbine efficiency
he hturb
References [1] Dursun B, Gokcol C. The role of hydroelectric power and contribution of small hydropower plants for sustainable development in Turkey. Renew Energy 2011;36:1227e35. [2] European Small Hydropower Association. Small hydropower roadmap e condensed research for EU-27. 2012. [3] Gestore Servizi Energetici. Statistical report 2011 e renewable energy power plants in Italy. [4] Abruzzo Region. Abruzzo water protection plan: general report. 2008. [5] Legislative decree of 3 April 2006, n. 152 e Environmental Regulations. [6] DHI Water & Environment. MIKE BASIN e a versatile decision support tool for integrated water resources management planning. 2003. [7] Abruzzo water protection plan: evaluation of minimum vital flow. 2008. [8] Abruzzo Region. A water resource planning study for hydropower production. 2008. [9] Davie T. Fundamental of hydrology. 2nd ed. Taylor & Francis; 2012. [10] Booker DJ, Snelder TH. Comparing methods for estimating flow duration curves at ungauged sites. J Hydrol 2012;434e435:78e94. [11] Masih I, Uhlenbrook S, Maskey S, Ahmad MD. Regionalization of a conceptual rainfall-runoff model based on similarity of the flow duration curve: a case study from the semi-arid Karkheh basin, Iran. J Hydrol 2010;391:188e201. [12] Galeati G. Analysis of water resources supporting power system e evaluation of surfacewater resource at regional scale, Italy. 2002. [13] Hosking JRM, Wallis JR. Regional frequency analysis e an approach based on L-moments. New York: Cambridge University Press; 1997. [14] R Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2013. [15] Department of Energy of Polytechnic of Milan. Cost of electricity production from renewable energy sources. December 2010. [16] HYDI (Hydro Data Initiative) of European small hydropower association. http://streammap.esha.be. [17] Ministry of Economic Development, Ministerial Decree of 6 July 2012. Incentives for the electricity production from renewable energy sources other than photovoltaic power plants e implementation of Article 24 of Decree No. 28/2011. [18] Pasqual J, Padilla E, Jadotte E. Technical note: equivalence of different profitability criteria with the net present value. Int J Prod Econ 2013;142:205e10. [19] Commission of European Communities. Council directive 2000/60/EC of 23 October 2000 establishing a framework for community action in the field of water policy. [20] Abruzzo Region. Abruzzo water protection plan: methodology. 2008. [21] Turcotte R, Fortin JP, Rousseau AN, Massicotte S, Villeneuve JP. Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network. J Hydrol 2001;240:225e42. [22] IHS. Annali Idrologici, edited by Italian Hydrografic Service. www.acq. isprambiente.it/annalipdf/. [23] Abruzzo Region. A water resource planning study for hydropower production: annex 1. 2008. [24] Kirtman B, Power SB, Adedoyin JA, Boer GJ, Bojariu R, Camilloni I, et al. Nearterm climate change: projections and predictability. In: Climate change 2013: the physical science basis; 2013. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [25] Smakhtin VU. Low flow hydrology: a review. J Hydrol 2001;240:147e86. [26] Niadas IA. Regional flow duration curve estimation in small ungauged catchments using instantaneous flow measurements and a censored data approach. J Hydrol 2005;314:48e66. [27] Abruzzo Region. Abruzzo water protection plan: hydrologic and hydrogeologic balances. 2008. [28] Sauquet E, Catalogne C. Comparison of catchment grouping methods for flow duration curve estimation at ungauged sites in France. Hydrol Earth Syst Sci 2011;15:2421e35. [29] European Small Hydropower Association. On how to develop a small hydro site. 2nd ed. 1998. [30] Alexander KV, Giddens EP. Optimum penstocks for low head microhydro schemes. Renew Energy 2008;33:507e19. [31] Natural Resources Canada. Micro-hydropower systems: a buyer's guide. 2004. [32] Gordon JL. Hydraulic turbine efficiency. Can J Civ Eng 2001;28:238e53. [33] Kaldellis JK, Vlachou DS, Korbakis G. Techno-economic evaluation of small hydro power plants in Greece: a complete sensitivity analysis. Energy Policy 2005;33:1969e85. [34] Aggidis GA, Luchinskaya E, Rothschild R, Howard DC. The costs of small-scale hydro power production: impact on the development of existing potential. Renew Energy 2010;35:2632e8.
Contents lists available at ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Techno-economic evaluation of small-hydro power plants: Modelling and characterisation of the Abruzzo region in Italy Roberto Carapellucci*, Lorena Giordano, Fabio Pierguidi Dipartimento di Ingegneria Industriale e dell'Informazione e di Economia, University of L'Aquila, Via Giovanni Gronchi 18, 67100 L'Aquila, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 January 2014 Accepted 2 October 2014 Available online
The potential of “small hydro” power generation in Europe is still largely unexploited because of strict environmental requirements and legal rights for water use. Among the EU-27 member states, Italy is recognised as one of the most promising countries for the further exploitation of small hydro power. This paper presents a methodology for assessing the technical and economic potential of small hydro on a regional scale. The methodology is applied to the Abruzzo region in Italy. The investigation covers approximately 90 river branches belonging to the major regional basins. The methodology characterises the flow duration curves of suitable stretches of river using a regional analysis based on a graphical approach. An energy model evaluates the rated power and the annual electricity production of installable smallhydro power plants based on the flow duration curve and the type of hydraulic turbine. The economic analysis estimates the unit cost of electricity produced and the profitability of the initial investment assuming two scenarios based on different fixed- and variable-cost models. The net potential obtained from the energy analysis is adjusted to give the economically feasible potential at different levels of economic competitiveness for the regional basins investigated. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Small-hydro Duration curves Regionalisation procedure Graphical approach Residual potential
1. Introduction In Europe, exploiting the potential of small hydroelectric power plants, or small hydro, is attracting growing interest because of the concerns over the lack of suitable sites for large installations and the environmental effects of related civil structures [1]. According to the definition proposed by the ESHA (European Small Hydropower Association) [2], small-hydro power plants are those installations with a rated capacity of less than 10 MW. The small-hydro power capacity in the EU-27 reached approximately 13.7 GW in 2010, resulting in an annual electricity production of 50 TWh that prevented the release of 29 Mt of CO2 emissions into atmosphere. According to the roadmap outlined by the HYDI (Hydro Data Initiative) [2], over the next 10 years the installed capacity will increase by nearly 30%, reaching 17.3 GW in 2020. Among the individual countries, Germany has the largest number of installations (over 7500), followed by Austria (2590), Italy (2430) and France (1900). Moreover, Italy has the largest installed capacity (2.73 GW) and electricity production (10.9 TWh). According to HYDI projections,
* Corresponding author. Tel.: þ39 0862 434320; fax: þ39 0862 434403. E-mail address: [email protected] (R. Carapellucci). http://dx.doi.org/10.1016/j.renene.2014.10.008 0960-1481/© 2014 Elsevier Ltd. All rights reserved.
this leadership position will continue in 2020, when the installed capacity will reach nearly 4 GW [2]. Among the regions of southern Italy, the Abruzzo region has the largest number of hydroelectric plants (57) and a total installed capacity of 1002 MW, with approximately 10% contributed by small-hydro installations [3]. However, because of the morphological characteristics of this territory, the Abruzzo region has a number of suitable sites for the construction of small hydro power plants. In fact, the Abruzzo region includes 25 river basins, with 8 having catchment areas greater than 200 km2. The Regional Water Protection Plan [4] evaluated the availability of the water resources of these basins, focussing on river branches regarded as “significant” according to the definition of Legislative Decree 152/06 [5]. As part of that investigation, a water balance model was implemented in the commercial software MIKE BASIN [6] to evaluate the main hydrological variables of each river branch, including the natural water flow rate (Qn), the minimum vital flow (MVF) and the actual water flow rate (Qm), considering derivations for drinking water or irrigation [7]. Then, the gross heads of the watercourses were characterised in the water resource planning study [8], which allowed the identification of river branches suitable for hydro power production.
396
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Starting from the results of the previously cited studies, the goal of this paper is the development of a methodology for assessing the technical and economic potential of small hydro power plants on a regional scale. The study focused on 87 river branches within the Aterno-Pescara, Sangro, Vomano, Saline, Foro, Tordino, LiriGarigliano and Sinello river basins. The methodology is based on the definition of a specific flow duration curve [9] for each suitable river branch to characterise the river flow regime on an annual basis. The flow duration curve is evaluated through a regionalisation procedure based on a graphical approach [10,11]. For the Aterno-Pescara, Sangro, Vomano, Saline, Foro and Tordino basins, the starting point for implementing the graphical method is the regionalisation study of the CESI Research Institute [12] involving the main river basins between the Marche and Abruzzo regions. In this paper, the regionalisation procedure has also been extended to the Sinello and Liri-Garigliano basins. Thus, two homogeneous regions have been identified (Liri-Garigliano and Trigno-Sinello), and the corresponding regional flow duration curves were evaluated by processing the daily flow rate data of gauging stations in these regions. The homogeneity of these areas with respect to the flow duration curve is verified by implementing the Hosking and Wallis test [13] in the software R, a free tool for computing statistics [14]. The rated capacity of each installable small-hydro power plant is defined on the basis of the net head, the design flow rate (Qd) and the hydraulic turbine efficiency. The annual electricity production is then evaluated by integrating the instantaneous power over the entire period of plant operation, given the flow duration curve and the technological constraints of the hydraulic turbine. For the economic analysis, two different scenarios are investigated. In the first one, capital costs and operating and maintenance expenses are evaluated through cost functions presented in a study by the Polytechnic of Milan [15]. In the second scenario, the cost items are estimated using statistical data provided by the HYDI [16]. The economic analysis of a small-hydro power project attempts to evaluate the unit cost of electricity (COE) and the profitability of the initial investment, taking into account the Italian incentive scheme that was recently reformed by the Ministerial Decree of 6 July 2012 [17]. Given the net potential from the energy analysis, the economically feasible potential is evaluated at various levels of economic competitiveness on the basis of the cost of electricity and the profitability of the initial investment [18]. 2. Characterisation of regional water resources availability The actual availability of regional water resources was evaluated in a study conducted by the Abruzzo region with the purpose of defining the Water Protection Plan [4], a document designed to ensure the water environmental quality and the sustainability of the water supply in compliance with the European Directive 2000/ 60/EC [19]. As part of this investigation, the surface and ground water resources of each regional river basin were characterised qualitatively and quantitatively. In particular, the study focused on the watercourses identified as significant according to Legislative Decree 152/06 [5], namely: - watercourses of the first order (discharging into the sea), having a catchment area of at least 200 km2; - watercourses of the second (discharging into first-order watercourses) or higher order, having a catchment area of at least 400 km2. The methodology adopted for estimating water resources includes the following main phases [20]:
- the delimitation of the Abruzzo region in the river basins; - the acquisition of hydro-meteorological data; - a hydrogeological characterisation of the area and the identification of ground water bodies; - a quantitative assessment of surface and ground water resources. The river basins were delimitated through a digital elevation model of the soil [21] using a horizontal resolution of 250 m and a vertical resolution of 1 m. Thus, the basins were identified by an automatic procedure known as the eight-direction four-point algorithm, or method D8. This method is based on subdividing the land into cells (250 m 250 m), thus allowing the flow direction to be defined with the maximum slope among the eight directions connecting a given cell with the adjacent ones. Having identified the drainage network, the boundaries of the regional basins were traced, allowing the evaluation of the corresponding surface area. Unlike the definition of boundaries based on the knowledge of regional topographical features, the results of this procedure do not depend on user choices, only on the model resolution. The regional river basins were characterised from the hydrological, hydrogeological and climatic conditions on the basis of information provided by local administrations or gathered from previous studies [20]. The hydrological and hydrogeological balances were defined for each river basin using the simulation software MIKE BASIN (DHI Water and Environment) [6]. MIKE BASIN is an integrated tool for the simulation of drainage basins that operates in a GIS environment. This software is an efficient tool for lowflow and data-scarce hydrological simulations that allows the rivers and the main tributaries to be described by a network consisting of branches and nodes. The subdivisions are defined in such a way that the branches correspond to river stretches with constant flow rates and the nodes are located at the confluence points between different branches or at important locations where model results are required. Thus, the river branches are identified on the basis of the numbers of upstream and downstream nodes. The implementation of river basin models in MIKE BASIN requires the time series of the rainfall, the temperature and the aquifer flow rates, which were obtained from the Hydrographic Service of Pescara [22], that provides data updated until the year 2000. With regard to weather and climate data, the mean monthly rainfall and temperature data recorded at 172 stations between 1920 and 2000 were used. The aquifer flow rate data were obtained from field measurements taken between 1898 and 2000 (more frequently from 1954 to 1963 and from 1980 to 1986). Based on these data and using a rainfall-runoff model, the MIKE BASIN software allowed the evaluation of the natural flow rate (Qn) and the actual flow rate (Qm), taking into account deductions for human consumption, irrigation, industrial and hydroelectric purposes. Moreover, the model allowed the minimum vital flow (MVF) to be defined, representing the minimum flow to be restored to safeguard aquatic wildlife and to guarantee that underground water is replenished [7]. Finally, the available flow (Qav) was evaluated, which is the difference between the actual flow rate and the minimum vital flow. 3. Identification of suitable river branches for installing hydroelectric power plants The river stretches that are suitable for the exploitation of water resources for hydroelectric purposes were identified as a part of a study of water resources planning for hydro power production [8]. This investigation involved the main regional river basins, except for the interregional-basins of Tronto and Trigno. Preliminary data
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
were acquired to characterise the flow regimes of the various river basins. Using data from the Water Protection Plan [4], the branches of the river network were characterised in terms of the actual flow, the minimum vital flow and the value of criticality, that is the number of months in which the actual flow rate is less than the hydrological component of the MVF [7]. After excluding the river branches falling within protected areas (parks and nature reserves), a database of suitable stretches for the exploitation of water resources for hydroelectric purposes was defined. Moreover, the gross head of each river branch was evaluated through the digital elevation model based on the 1:10,000 orthophoto of the Abruzzo region [23]. The results of this investigation were the starting point for the evaluation of the residual hydroelectric potential on a regional scale. In the present study, attention is focused on 87 branches belonging to 8 regional river basins: Aterno-Pescara, Sangro, Vomano, Saline, Liri-Garigliano, Tordino, Sinello and Foro. Fig. 1 summarises for each investigated basin the extension, the number of exploitable river branches and their main hydrological variables, i.e., the actual flow rate and the gross head. The figure shows that the actual flow rates of the river branches in the Sangro and Aterno-Pescara basins vary over a rather wide range, from 0.4 to 47 m3/s and from 2.1 to 17 m3/s, respectively. In the remaining basins, the actual flow rates of the river branches are nearly always less than 10 m3/s. Moreover, all the branches with the exception of a branch belonging to the Sangro basin have a gross head less than 250 m, and the majority have a gross head of less than 50 m. Linear curves plotted on logarithmic scales highlight the gross or natural potential, the maximum theoretical potential for a hydro power plant, which depends on the gross head (Hg) and the actual flow rate (Qm). The river branches have gross potentials generally between 1 MW and 5 MW in the Aterno-Pescara, Sangro, Vomano and Liri-Garigliano basins and less than 1 MW in the remaining basins. It is noteworthy to observe that the actual flow rate could be changed over the years, due to climate change related to global warming effects. According to the projections of IPCC, the mean annual flow rate of rivers in Southern Europe should decrease in the period of 2016e2035 compared to 1986e2005; as regard to Italy, such reduction is expected to be moderated, varying in the range of 10÷0% [24].
397
4. Characterisation of the methodology for the technoeconomic evaluation of small-hydro power potential at regional scale The identification and characterisation of the suitable river branches for the exploitation of water resources for electricity production are the starting point for the modelling of the technical and economical small-hydro power potential at regional scale. The methodology outlined in the present study consists of the following main steps: - Definition of a specific flow duration curve for the suitable river branches, by multiplying the mean actual flow rate by the dimensionless regional flow duration curve, arising from a regionalisation procedure based on graphical approach (Section 5.1); - Correction of the flow duration curve to account for the value of the criticality, that identifies the number of months with actual flow rate less than the hydrological component of the minimum vital flow (Section 5.1.2); - Evaluation of the rated power and the annual electricity production, based on the corrected flow duration curve and the small-hydro turbine technology (Section 5.2); - Estimation of unit cost of electricity and the profitability of the investment with reference to different scenarios for estimating capital and operating and maintenance costs (Section 6); - Evaluation of the net potential at regional scale by summing contributions of the different river branches (Section 7.1); - Definition of the economically feasible potential, assumed as the fraction of net potential that meets different level of economic competitiveness, defined with respect to the unit cost of electricity (COE) and the profitability index (PI) (Section 7.2).
5. Energy model for evaluating the potential for small hydro on a regional scale To evaluate the residual potential for small hydro, the methodology requires that the suitable river branches are defined in terms of the net head and the flow duration curve to reveal the
Fig. 1. Characterisation of the regional river basins in terms of actual flow rate (Qm), gross head (Hg) and natural potential.
398
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
variability of the flow regime throughout the year [25]. The net head is evaluated assuming reasonable values for the concentrated and distributed head losses due to friction and turbulence in the penstock. Flow duration curves are defined through a regional approach if historical flow rate time series are lacking for the river branches under investigation.
5.1. Flow duration curve The definition of a flow duration curve is based on knowledge of the historical time series of stream-flow data, whose availability is generally limited to only a small number of rivers. If there is a lack of observed stream-flow data, a flow duration curve can be obtained by spatially transferring the flow information from nearby gauged sites through a regionalisation of the flow characteristics [26]. Various procedures for regionalisation have been proposed in the literature; they can be grouped into three main categories: statistical, parametric and graphical approaches [11]. In statistical methods, the flow duration curve is defined as the complement of the flow rate cumulative distribution function. Parametric methods represent flow duration curves through an analytic function (polynomial, exponential, logarithmic or power function) whose parameters are determined by a multiple-regression analysis that includes morphological characteristics and climatic conditions. Unlike other methods, the graphical approaches do not rely on specific assumptions for the distribution or the shape of the regional flow duration curve but use standardised graphical representations of FDCs with a regional validity. In this paper, the graphical approach proposed by Smakhtin [25] will be used for evaluating the flow duration curves of the river
branches under investigation. The methodology includes the following main steps: - a preliminary division of the territory into homogeneous zones that are characterised by a significant hydrological affinity; - the identification of gauging stations in each homogeneous zone with measured daily stream-flow time series extended over a period longer than five years; - the normalisation of the experimental duration curves by dividing the empirical FDCs by an index of flow such as the mean daily stream flow evaluated in the available record period; - the determination of the regional flow duration curves for the homogeneous zones by averaging the normalised flow duration curves. The flow duration curve for an ungauged river branch in a given homogeneous region is therefore obtained by multiplying the dimensionless regional flow duration curve by the mean daily stream flow [12]:
Q ðDÞ ¼ Q ðDÞadim Qm
(1)
In this study, the average flow (Qm) is assumed to be the actual flow rate of the river branch under consideration, as identified by the Regional Water Protection Plan [4]. The regional dimensionless flow duration curves coincide with those resulting from the regionalisation study by the CESI Research Centre [12], which involved the major river basins of the Abruzzo region including the Aterno-Pescara, Sangro, Vomano and Tordino, and smaller basins near the coast (Saline, Tavo-Fino, Alento, Foro, Moro and Feltrino). In particular, to apply the graphical method, this portion of regional territory is subdivided into 8 homogeneous areas shown in Fig. 2.
Fig. 2. Subdivision of the study area into homogeneous regions for the application of the graphical method.
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
2.5
2.5
Vomano-Aterno Castellano-Tordino Coastal basins of type I Coastal basins of type II Sangro and Tasso Upper Sangro basins Lower Aterno and SagiƩario Lower Pescara
2.0 1.8 1.5 1.3
2.3
Qadim (D)
2.3
Q adim (D)
399
2.0
Liri-Giovenco
1.8
Trigno-Sinello
1.5 1.3 1.0
1.0
0.8 0.8
0.5
0.5
0.3
0.3
0.0 10
0.0
10
20
30
40
50
60
DuraƟon (%)
70
80
90
20
30
40
100
Fig. 3. Regional dimensionless flow duration curves based on the graphical approach.
The regional FDCs in those areas were evaluated using the daily stream flow data collected between 1921 and 2000 in 35 hydrographic stations located in the Abruzzo region. Fig. 3 shows the regional flow duration curves obtained by applying the graphical approach. 5.1.1. Regionalisation to characterise the Liri-Garigliano and Sinello basins The regionalisation procedure for the flow duration curves was extended in this study to the Sinello and Liri-Garigliano basins, thus leading to the identification of two other homogeneous zones, namely, the LirieGiovenco and Trigno-Sinello zones (Fig. 2). Initially, the daily stream flow time series were collected for the gauging stations of Liri-Garigliano and Sinello from the National Hydrographic Service of Italy [22]. For the Liri-Garigliano basin, attention focused on the Liri and Giovenco rivers, where the river stretches suitable for small hydro are located. The daily stream flow time series were collected for the gauging stations of Liri at Sora and Giovenco at Pescina, where hydrological data have been recorded for 46 and 29 years, respectively. Regarding the Sinello basin, there is only one gauging station (Sinello at Casalbordino), where stream flow data were recorded for only one year. In this case, the regionalisation procedure was applied using the gauging stations of the Trigno basin, which had the greatest similarity to the Sinello basin hydrologically because of the geographic proximity [27]. The data from the two gauging stations located on the river Trigno (at Pescolanciano and at Chiauci) were considered, being the only ones with recording periods exceeding 5 years. The regional flow duration curves for the two homogeneous zones were derived by applying the graphical method described. Fig. 4 shows the trends of the regional flow duration curves for the homogeneous zones LirieGiovenco and Trigno-Sinello. The homogeneity of these regions was checked with the Hosking and Wallis method [13], which is based on the L-moment ratios LCV (coefficient of L-variation) and LCS (coefficient of L-skewness). This test compares the regional variance of the L-moment ratios in a pooling group to the variation that would be expected in a homogeneous group. The expected mean value (mV) and the standard deviation (sV) of the L-moment ratios for a homogeneous group are evaluated through repeated simulations, thereby generating
50
60
70
80
90
100
DuraƟon (%) Fig. 4. Regional dimensionless flow duration curves for homogeneous zones LirieGiovenco and Trigno-Sinello.
homogeneous groups of basins having the same record lengths as those of the observed data. According to Hosking and Wallis, the region should be regarded as acceptably homogeneous if the test metric Hk satisfies Hk < 1, possibly heterogeneous if 1 < Hk < 2, and definitely heterogeneous if Hk > 2. The heterogeneity measures are evaluated as follows:
Hk ¼
Vk mk sk
for k ¼ 1; 2
(2)
where
V1 ¼
R X
2 ni t2; i t 2
,
i¼1
R X
ni
(3)
i¼1
and
V2 ¼
R X
ni
h
t2; i t 2
i¼1
2
2 i1=2 þ t3; i t 3
,
R X
ni
(4)
i¼1
give measures of dispersion, V1 for LCV and V2 for both LCV and LCS. In Equations (3) and (4), t2,i, t3,i and ni are the values of LCV and LCS and the sample size of the site i, respectively, t 2 , t 3 and R are the mean values of LCV and LCS and the number of sites, respectively. The Hosking and Wallis homogeneity test [13] was applied to the three parameters, i.e., the stream flow variability index (Q20/ Q90), the low-flow variability index (Q50/Q90) [25] and the concavity index (CI), based on the flow duration curve. The last index establishes the shape of the dimensionless flow duration curve, providing a measure of the contrast between the low-flow and high-flow regimes [28]:
CI ¼
Q10 Q99 Q1 Q99
(5)
The results of the test, listed in Table 1, show that the LirieGiovenco region can be considered homogeneous because the heterogeneity measures H1 and H2 are always less than unity for all three parameters investigated. In the Trigno-Sinello region, a substantial degree of homogeneity is detected because only the value
400
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Table 1 Results of the Hosking and Wallis homogeneity tests for CI, Q20/Q90 and Q50/Q90. LirieGiovenco
Trigno-Sinello
Index
H1
H2
H1
H2
CI Q20/Q90 Q50/Q90
0.13 1.1 0.57
0.83 0.55 0.66
1.1 0.32 0.77
0.4 0.36 0.65
of H1 related to the concavity index has a value slightly greater than unity (1.1).
5.2. Rated power and annual electricity production The rated capacity of a small hydroelectric power plant in each suitable river branch can be calculated as:
Pn ¼ rgQd Hn hturb ðQd Þ
where Qd and hturb(Qd) are the flow rate and the efficiency at the design condition, respectively, and Hn is the net head. The design flow rate is the difference between the available flow rate and the minimum vital flow [29]:
Qd ¼ Qm MVF 5.1.2. Correction of flow duration curve to account for criticality The regional flow duration curves do not account for differences among the river branches in the criticality, the number of months in which the actual flow rate is less than the hydrological component of the MVF [23]. The values of the criticality in the basins investigated in this study ranged from 1 to 6. The criticality is 0 for 64 river branches and greater than 3 (which is considered significant) in 24 stretches, mainly those belonging to the Vomano (7), Liri-Garigliano (5) and Sangro (5) basins. To avoid overestimating the annual electricity production for river branches with significant values of criticality, the flow duration curves produced by the regionalisation procedure were corrected by holding constant the mean annual flow rate. Therefore, the regional flow duration curves of certain river branches are rotated about Qm in such a way that the flow rate is less than or equal to the hydrological component of the minimum vital flow for a period corresponding to the value of the criticality. Fig. 5 compares the flow duration curves for a river branch in the Saline basin resulting from the regionalisation procedure with and without the correction, taking into account the effective value of the criticality, which is 3 for the case examined. As shown, by rotating about the mean value (Qm ¼ 1.62 m3/s), the corrected FDC shows a flow rate coincident with the hydrological component of the MVF (Q* ¼ 0.2 m3/s) for a duration of 75%, corresponding to a criticality of 3.
(6)
(7)
As is well known, friction losses strongly depend on the material, the length and the diameter of the penstock [30]. For the sake of simplicity, in this paper the net head is evaluated assuming that the concentrated and distributed head losses amount to 6% of the gross head [31]. The efficiency of the hydraulic turbine at the design condition is calculated as a function of the design flow rate, the net head and the hydraulic turbine type through Gordon's empirical relationships [32]. The annual electricity production is evaluated by integrating the instantaneous power during the operational period of the plant:
Z1 Ep ¼ he hop
rgQt ðDÞHn hturb ðQt ðDÞÞdD
(8)
0
where hop is the plant operating time in hours and he is the system electrical efficiency, which takes into account the gearbox, electric generator and transformer losses. The hydro-turbine flow rate, that is, the amount of water flowing through the hydro turbine, Qt(D), is defined on the basis of flow duration curve [33]:
Qt ðDÞ ¼
8 < :
0; Q ðDÞ; Qd ;
Q ðDÞ < Qmin Qmin Q ðDÞ Qd Q ðDÞ > Qd
(9)
The definition includes the constraints related to the design flow rate and the minimum allowable flow rate passing through the hydraulic turbine. The latter is selected to minimise the unit cost of electricity production of the small-hydro power plant while taking into account the domain of application of the various technologies with regard to the design flow rate and the net head. 6. Economic model
Fig. 5. Comparison between regional FDC and corrected regional FDC for a river branch in the Saline basin.
The estimation of the unit cost of electricity of a small-hydro power plant involves a preliminary evaluation of the initial investment and the annual operating and maintenance costs. The initial investment cost can be divided into three main components: electro-mechanical equipment costs, civil works costs and engineering and administration costs [34]. As well known, investment costs of hydro power systems are highly sitedependent. However, cost data for small hydro power plants operating in the Abruzzo region are not readily available from technical literature or power companies. Hence, based on cost data at a national level, two different models for estimating capital and O&M costs of SHPs have been implemented, thus reflecting a pessimistic and an optimistic scenario. In the first one (the pessimistic scenario), cost functions have been derived by interpolating data arising from the study conducted by the Polytechnic of Milan [15]:
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
( CI ¼
4929Pn0:26 Hn < 80m 4257Pn0:2 Hn > 80m
CO&M ¼ 180:4Pn0:47
(10)
(11)
where CI and CO&M are capital cost and the annual operating and maintenance cost, respectively. In the second one (optimistic scenario), costs functions of the pessimistic scenario have been modified to take into account economic statistics provided by HYDI (Hydro Data Initiative) [16]. For the EU-27 Member States, it defines an average capital cost per unit of installed capacity and a range of variability of operating and maintenance costs, expressed as a percentage of capital costs:
8 0:26 > Hn < 30m < 4500Pn CI ¼ 4150Pn0:23 30 < Hn < 100m > : Hn > 100m 3800Pn0:2
CO&M
8 0:51 > Hn < 30m < 84:1Pn 0:47 ¼ 30 < Hn < 100m 70Pn > : Hn > 100m 55:8Pn0:45
CI CRF þ CO&M Ep
7. Evaluation of net and economically feasible potential of small-hydro power plants
(13)
(14)
where CRF is the capital recovery factor, assuming a discount rate of 5% and a power plant lifetime of 30 years. In addition to the unit cost of electricity, the profitability of the investment was assessed by means of two common indices [18], the discounted payback period (DPP) and the profitability index (PI):
PI ¼
NPV þ CI CI
an all-inclusive tariff, comprising both the incentive and the remuneration of the energy production. Furthermore, in the present study it is assumed that for these small-hydro power plants, where the effective lifetime is greater than the conventional one, the energy production at the end of the incentive period benefits from the simplified purchase/resale arrangements. The simplified purchase/resale arrangements provide that the energy supplied to the grid is sold at a guaranteed minimum price, depending on the type of renewable energy source and the amount of energy supplied to the grid. For small-hydro power plants with a rated capacity exceeding 1 MW, the incentive is the difference between the “base tariff” and the hourly zone price. In this case, the energy production, which is at the producer's disposal, cannot be sold through the simplified purchase-resale arrangements but only through bilateral contracts in the energy market.
(12)
Thus, the unit cost of electricity is given by:
COE ¼
401
(15)
These parameters were evaluated assuming that small-hydro power plants will benefit from the Italian incentives program, which was radically redefined by the Ministerial Decree of 6 July 2012 [17]. According to this decree, the incentive for small hydro power plants with a rated capacity of less than 1 MW is a “base tariff” defined according to the size and guaranteed for the conventional plant lifetime. In this case, the incentive is configured as
The implementation of the methodology previously described allows the evaluation of the net potential and the economically feasible potential of small-hydro power plants for the river basins investigated. As depicted in Fig. 6, more than 70% (63) of the potential smallhydro power plants are low-flow installations (Qd < 10 m3/s), and the remainder (24) are medium-flow installations (10 < Qd < 100 m3/s). Focussing on the individual river basins, it is noted that medium-flow small-hydro power plants are located only in the Aterno-Pescara (10), Vomano (10), Sangro (3) and LiriGarigliano (1) basins. Regarding the net head, 48 of the potential installations are lowhead (Hn < 30 m), 25 are medium-head (30 < Hn < 100 m) and 14 are high-head (100 < Hn < 1000 m). The prevalence of low-head installations directly affects the choice of the type of hydraulic turbine to be installed. Fig. 7 shows that a Kaplan turbine is the best choice in more than 70% of the potential installations, followed by Pelton (15%) and Francis (9%) turbines; a cross-flow turbine is the best choice in only one installation, located in the Aterno-Pescara basin. 7.1. Rated power classes and electricity production Table 2 summarises the main results of the energy analysis for the river basins investigated, including the total rated power, the
Fig. 6. Classification of small hydro power potential installations with respect to design flow rate and net head.
402
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Fig. 7. Distribution of types of potential installable small hydro power plants. Fig. 8. Distribution of potential installations with respect to rated power classes.
average power of the potential installations and the annual electricity production. Thus, the net residual potential of small-scale hydro power in the Abruzzo region amounts to 146.1 MW. The Aterno-Pescara basin, with an installed capacity of 52 MW, has the highest potential, accounting for more than 35% of the total rated power. The Sangro basin is the second most important basin with 46.1 MW (31.5%), followed by the Vomano basin with 16.3 MW (11.2%) and the Liri-Garigliano basin with 13.8 MW (9.4%). Indeed, the aforementioned basins are characterised by the greater number of suitable river branches and by the highest average rated power, ranging between 1.4 MW in the Vomano basin to approximately 3 MW in the Sangro basin. The rated capacities are significantly lower in the other river basins, which overall account for approximately 12% of the total net potential, with rated capacities ranging between 2.5 MW (Foro) and 7.1 MW (Tordino). Fig. 8 shows that 44 of the 87 potential small-hydro power plants have a rated capacity less than 1 MW, 36 have a rated capacity between 1 MW and 5 MW and the remainder have a rated capacity greater than 5 MW. As regards the individual river basins, the rated capacity is less than 1 MW for all the potential installations in the Saline basin; small-hydro power plants with a rated power greater than 5 MW are possible only in the AternoPescara (3), Sangro (3) and Liri-Garigliano (1) basins. In this
Table 2 Net residual potential of small hydro power for regional basins investigated. River basin
River Pn Pn,mean Pn (%) branches (MW) (MW)
Aterno-Pescara Foro Liri-Garigliano Saline Sangro Sinello Tordino Vomano
20 3 9 12 15 6 10 12
Total
87
52.1 2.5 13.8 5.2 46.1 2.9 7.1 16.3
2.6 0.8 1.5 0.4 3.1 0.5 0.7 1.4
146.1 1.7
Ep Ep (%) (GWh)
35.7% 313 1.7% 10 9.4% 64 3.6% 19 31.5% 185 2.0% 10 4.9% 27 11.2% 62 100%
690
45.4% 1.5% 9.3% 2.8% 26.9% 1.4% 3.9% 8.9%
Ep/Pn (GWh/MW) 6.0 3.9 4.6 3.7 4.0 3.3 3.7 3.8
100.0% 4.7
regard, it should be noted that the design flow rates for two river branches, one in the Aterno-Pescara basin and one in the Sangro basin, were not the difference between the actual mean flow rate and the minimum vital flow but were set to the limit value so that the rated power did not exceed 10 MW. With regard to the capacity factor, more than 40% (37) of the total potential installations have values between 0.4 and 0.6, whereas only 20% (18) have values greater than 0.6. The differences in the behaviour of the river basins are depicted in Fig. 9, representing the capacity factor as a function of the rated power of the potential installations. It is noted that the capacity factor ranges between 0.3 and 0.5 for the Vomano, Tordino, Saline and Foro basins; the same is true for the Sangro basin, except for two installations having a capacity factor close to 0.6. As regards the Aterno-Pescara basin, 15 of the 20 potential installations have a capacity factor greater than 0.6. Conversely, the capacity factor is less than 0.4 for each investigated river branch in the Sinello basin. This is primarily due to the differences in the flow duration curves, which are generally more flat for river stretches in the Aterno-Pescara basin than for those in the Sinello basin, as revealed by the dimensionless regional flow duration curves presented in Figs. 3 and 4. Therefore, the total electricity production amounts to 690 GWh, with the most important contributions coming from the AternoPescara (45.4%) and Sangro (26.9%) basins, followed by the LiriGarigliano (9.3%) and Vomano (8.9%) basins. Fig. 10 shows the distribution of annual electricity production with respect to the rated capacity class of the small-hydro power plants. It is noted that approximately 90% of the overall electricity production is from installations with a rated capacity greater than 1 MW, and the contributions of those plants with up to 5 MW of capacity are greater than 50%. This is because of the predominant contributions of the Aterno-Pescara, Sangro and Liri-Garigliano basins, where the incidence of installations with a rated power of greater than 1 MW is greater than 90%. Moreover, it is interesting to observe that there are significant contributions from installations with a rated power ranging from
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
403
Fig. 9. Capacity factor as a function of rated capacity of small-hydro power plants.
1 MW to 5 MW, not only for the Vomano basin but also for the Tordino and Foro basins, despite the greater number of plants with smaller capacities. The share of small-hydro power plants with capacities between 1 MW and 5 MW decreases significantly in the Sinello basin (38%) and down to zero in the Saline basin, where the electricity production is totally attributable to installations of less than 1 MW, with approximately 60% of those greater than 500 kW. Thus, the annual electricity production potential of small-hydro power plants would increase by approximately 40% the current
hydroelectric production of the Abruzzo region (1756.4 GWh). This contribution is even more significant considering that approximately 90% of hydro power is currently produced by large plants with a rated power exceeding 10 MW. 7.2. Cost of electricity and economically feasible potential The semi-logarithmic plots of Fig. 11 show the trend of the unit cost of electricity production as a function of the small-hydro
Fig. 10. Distribution of electricity production with respect to rated power classes.
404
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
Fig. 11. Unit cost of electricity production as a function of rated capacity of small-hydro power plants.
power plant rated capacity and the river basin investigated. The COE was evaluated in two different economic scenarios: - the pessimistic scenario, shown in blue (in the web version), which is based on cost models obtained from the Polytechnic of Milan investigation [15]; - the optimistic scenario, shown in red (in the web version), which is based on cost models derived from HYDI statistics [16]. It is noted that the COE for the river basins investigated decreases with increasing rated capacity according to a specific power law. In the case of the Aterno-Pescara basin, the unit cost of electricity varies over a rather wide range, between 3 and 27 cV/kWh.
In the pessimistic scenario, the COE is less than 10 cV/kWh for more than 70% of the potential installations, with a clear prevalence of those with a COE greater than 5 cV/kWh. Conversely, assuming the optimistic scenario, more than 50% of the small-hydro power plants have a COE lower than 5 cV/kWh. As regards the Sangro basin, the unit cost of electricity is between 4 and 34 cV/kWh. However, except for the installations with a rated power of less than 1 MW, the COE is always less than 15 cV/ kWh. Moreover, switching from the pessimistic to the optimistic scenario, the number of installations with a COE greater than 10 cV/ kWh markedly declines because of an increase in the number of plants with a COE less than 5 cV/kWh. In the Liri-Garigliano basin, the unit cost of electricity shows a pronounced variability
Fig. 12. Comparison between net and economically feasible potential for pessimistic (a) and optimistic (b) economic scenarios.
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
(4e43 cV/kWh), but with a clear prevalence of installations with a COE of approximately 10 cV/kWh. In the Vomano basin, the COE varies over a more restricted range, from 5 to 21 cV/kWh. Finally, in the Saline, Sinello, Tordino and Foro basins, the unit cost of electricity is greater than 10 cV/kWh in nearly all cases because of the moderate rated capacities of the potential installations. It is important to recognise that the differences in terms of the cost of electricity are not only related to the rated capacity of a potential installation but also to the capacity factor, which influences the annual electricity production. For instance, for a fixed rated power in the Sangro basin, the cost of electricity is greater than in the Aterno-Pescara basin because of the lower capacity factors (Fig. 9). This aspect is even more noticeable in the Saline and Sinello basins, where the capacity factor is always less than 0.5. At the global level, the COE in the pessimistic scenario is less than 5 cV/kWh for approximately 3% of the total installations, between 5 and 15 cV/kWh for approximately 55%, and greater than 15 cV/kWh for the remainder. However, in the optimistic scenario the percentage of installations with a COE less than 5 cV/kWh increases to approximately 18%, with a corresponding reduction in those with a COE greater than 15 cV/kWh (22%). The net potential of the regional basins investigated was compared with the economically feasible potential. In this paper, the latter is the fraction of the net potential that meets the prescribed economic requirements defined in terms of the cost of electricity (COE) and the profitability index (PI). Considering the variability in the COE for small hydro in Italy (8e15 cV/kWh), a limit value of 15 cV/kWh was used to evaluate the economically feasible potential. As shown in Fig. 12, to obtain a COE <15 cV/kWh and a PI > 1, the economically feasible potential ranges from 121.8 MW (pessimistic scenario) to 142.6 MW (optimistic scenario), whereas the corresponding annual electricity production ranges from 605 to 678 GWh. In the pessimistic scenario, the economically feasible potential is more than 80% of the net potential, despite the reduction in the number of potential installations from 87 to 40. This is because of the small contribution of non-viable power plants in terms of rated capacity, as highlighted by the increase in the average capacity of installable power plants from 1.7 MW to approximately 3 MW. In this case, the Aterno-Pescara basin accounts for approximately 41% (50.2 MW) of the total economically feasible potential, whereas the Sangro and Vomano basins account for 35% (42.9 MW) and 9% (10.9 MW), respectively. In the optimistic scenario, the economically feasible potential is approximately 98% of the net potential, and the number of
405
installations is 68. In this case, the contributions from the AternoPescara (36%) and Sangro (32%) basins decrease and that from the Vomano basin (11%) significantly increases. Fig. 13 shows the distribution of small-hydro power plants with respect to the length of the discounted payback period (DPP). In both scenarios, nearly all viable installations in the Aterno-Pescara basin have a DPP less than 10 years, with a clear prevalence of those with a DPP greater than 5 years. This trend is basically true for the Sangro basin, whereas the remainder, particularly those in the Vomano basin, are dominated by small-hydro power plants with a DPP greater than 10 years. To obtain a COE <15 cV/kWh and a PI > 1.5, the number of viable installations varies from 28 (pessimistic scenario) to 48 (optimistic scenario), whereas the economically feasible potential varies from 102.6 MW to 124.8 MW (Fig. 12), thus allowing an electricity production per year in the range of 533e616 GWh. The contribution of the Vomano basin decreases (4e6%) and that of the Aterno-Pescara basin markedly increases, reaching a peak of approximately 50% in the first scenario. Finally, the economically feasible potential resulting in a COE less than 15 cV/kWh and a PI greater than 2 remains approximately 54% (78.6 MW) and 72% (105 MW) of the net capacity in the first and second scenarios, respectively. In both cases, nearly all the viable installations are located in the Aterno-Pescara basin, accounting for approximately either 60% (pessimistic scenario) or 50% (optimistic scenario) of total feasible potential. 8. Conclusions The goal of this paper was to define a methodology for evaluating the technical and economic residual potential of small-hydro power plants having a rated capacity less than 10 MW. The methodology was applied to the case of the Abruzzo region of Italy, which has a considerable number of suitable sites for the construction of small hydro power installations. Specifically, the investigation involved 87 river stretches belonging to the main regional basins, namely, the Aterno-Pescara, Sangro, Vomano, Saline, Foro, Tordino, LiriGarigliano and Sinello basins. The energy model proposed evaluates the design flow rate, the net head, the rated power and the annual electricity production of potential installations based on the flow duration curve and the hydraulic turbine type. The flow duration curves were defined through a regionalisation procedure based on a graphical approach, and the type of hydraulic turbine was selected to minimise the unit cost of
Fig. 13. Discounted payback period of economically feasible installations with COE <15 cV/kWh and PI > 1.
406
R. Carapellucci et al. / Renewable Energy 75 (2015) 395e406
electricity produced. The cost of electricity was evaluated assuming two economic scenarios based on different capital, operating and maintenance cost functions. Moreover, the economic model allowed the assessment of the profitability of the initial investment by evaluating the profitability index and the discounted payback period. The residual potential of small hydro in the investigated basins was 146.1 MW. The most important contribution is provided by the Aterno-Pescara basin (52.1 MW), followed by the Sangro (46.1 MW), Vomano (16.3 MW) and Liri Garigliano (13.8 MW) basins. More than 50% of the total potential installations had a rated capacity less than 1 MW (44), approximately 40% had a rated capacity between 1 and 5 MW, and the remaining 8% (7) had a rated capacity exceeding 5 MW (these seven were located in the AternoPescara (3), Sangro (3) and Liri-Garigliano (1) basins). The annual electricity production amounted to 690 GWh, with the Aterno-Pescara and Sangro basins accounting for more than 70% (498 GWh). Regarding the distribution of the energy production with respect to the rated capacity of small-hydro power plants, it is noted that over 90% of the electricity is produced by installations exceeding 1 MW, despite the greater number of plants of smaller size. The electricity generated by these new potential installations could increase the current hydroelectric energy production of the Abruzzo region (1756.4 GWh) by approximately 40%. In the case of a pessimistic economic scenario, the unit cost of electricity production was less than 15 cV/kWh for approximately 60% (51) of potential installations. Assuming as economic constraints that the COE <15 cV/kWh and the PI > 1, the economically feasible potential amounted to 121.8 MW, or approximately 80% of the net capacity for an annual electricity production of 605 GWh. The number of viable installations was 40, which were mainly located in the Aterno-Pescara (16), Sangro (10) and Vomano (5) basins, with rated capacities of 50.2 MW, 42.9 MW and 10.9 MW, respectively. In the case of the optimistic economic scenario, the number of installations with a COE <15 cV/kWh reached approximately 80% (68); the economically feasible potential (COE <15 cV/kWh, PI > 1) was approximately 97% (142.6 MW) of the net rated capacity, thus enabling an electricity production per year of 678 GWh. Assuming more stringent economic constraints (COE <15 cV/ kWh, PI > 2), the economically feasible potential ranges from 78.6 MW (pessimistic scenario) to 104.9 MW (optimistic scenario), thus representing over 50% of the net potential, mainly because of the viable installations in the Aterno-Pescara basin. Nomenclature
Symbols CI CI CO&M Ep Hg Hn LCV LCS Pn Qd Qm Qmin
investment cost, MV/MW concavity index operating and maintenance cost, MV/(MW year) annual electricity production, GWh gross head, m net head, m coefficient of L-variation coefficient of L-skewness net hydro power potential, MW design flow rate, m3/s mean actual flow rate, m3/s hydraulic turbine minimum flow rate, m3/s
Acronyms COE cost of electricity, cV/kWh CRF capital recovery factor, % DPP discounted payback period, years FDC flow duration curve
MVF NPV PI
minimum vital flow, m3/s net present value, MV profitability index
Greek letters electrical efficiency hydraulic turbine efficiency
he hturb
References [1] Dursun B, Gokcol C. The role of hydroelectric power and contribution of small hydropower plants for sustainable development in Turkey. Renew Energy 2011;36:1227e35. [2] European Small Hydropower Association. Small hydropower roadmap e condensed research for EU-27. 2012. [3] Gestore Servizi Energetici. Statistical report 2011 e renewable energy power plants in Italy. [4] Abruzzo Region. Abruzzo water protection plan: general report. 2008. [5] Legislative decree of 3 April 2006, n. 152 e Environmental Regulations. [6] DHI Water & Environment. MIKE BASIN e a versatile decision support tool for integrated water resources management planning. 2003. [7] Abruzzo water protection plan: evaluation of minimum vital flow. 2008. [8] Abruzzo Region. A water resource planning study for hydropower production. 2008. [9] Davie T. Fundamental of hydrology. 2nd ed. Taylor & Francis; 2012. [10] Booker DJ, Snelder TH. Comparing methods for estimating flow duration curves at ungauged sites. J Hydrol 2012;434e435:78e94. [11] Masih I, Uhlenbrook S, Maskey S, Ahmad MD. Regionalization of a conceptual rainfall-runoff model based on similarity of the flow duration curve: a case study from the semi-arid Karkheh basin, Iran. J Hydrol 2010;391:188e201. [12] Galeati G. Analysis of water resources supporting power system e evaluation of surfacewater resource at regional scale, Italy. 2002. [13] Hosking JRM, Wallis JR. Regional frequency analysis e an approach based on L-moments. New York: Cambridge University Press; 1997. [14] R Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2013. [15] Department of Energy of Polytechnic of Milan. Cost of electricity production from renewable energy sources. December 2010. [16] HYDI (Hydro Data Initiative) of European small hydropower association. http://streammap.esha.be. [17] Ministry of Economic Development, Ministerial Decree of 6 July 2012. Incentives for the electricity production from renewable energy sources other than photovoltaic power plants e implementation of Article 24 of Decree No. 28/2011. [18] Pasqual J, Padilla E, Jadotte E. Technical note: equivalence of different profitability criteria with the net present value. Int J Prod Econ 2013;142:205e10. [19] Commission of European Communities. Council directive 2000/60/EC of 23 October 2000 establishing a framework for community action in the field of water policy. [20] Abruzzo Region. Abruzzo water protection plan: methodology. 2008. [21] Turcotte R, Fortin JP, Rousseau AN, Massicotte S, Villeneuve JP. Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network. J Hydrol 2001;240:225e42. [22] IHS. Annali Idrologici, edited by Italian Hydrografic Service. www.acq. isprambiente.it/annalipdf/. [23] Abruzzo Region. A water resource planning study for hydropower production: annex 1. 2008. [24] Kirtman B, Power SB, Adedoyin JA, Boer GJ, Bojariu R, Camilloni I, et al. Nearterm climate change: projections and predictability. In: Climate change 2013: the physical science basis; 2013. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [25] Smakhtin VU. Low flow hydrology: a review. J Hydrol 2001;240:147e86. [26] Niadas IA. Regional flow duration curve estimation in small ungauged catchments using instantaneous flow measurements and a censored data approach. J Hydrol 2005;314:48e66. [27] Abruzzo Region. Abruzzo water protection plan: hydrologic and hydrogeologic balances. 2008. [28] Sauquet E, Catalogne C. Comparison of catchment grouping methods for flow duration curve estimation at ungauged sites in France. Hydrol Earth Syst Sci 2011;15:2421e35. [29] European Small Hydropower Association. On how to develop a small hydro site. 2nd ed. 1998. [30] Alexander KV, Giddens EP. Optimum penstocks for low head microhydro schemes. Renew Energy 2008;33:507e19. [31] Natural Resources Canada. Micro-hydropower systems: a buyer's guide. 2004. [32] Gordon JL. Hydraulic turbine efficiency. Can J Civ Eng 2001;28:238e53. [33] Kaldellis JK, Vlachou DS, Korbakis G. Techno-economic evaluation of small hydro power plants in Greece: a complete sensitivity analysis. Energy Policy 2005;33:1969e85. [34] Aggidis GA, Luchinskaya E, Rothschild R, Howard DC. The costs of small-scale hydro power production: impact on the development of existing potential. Renew Energy 2010;35:2632e8.