- Email: [email protected]
Hot water production improves the energy return on investment of geothermal power plants
Energy 51 (2013) 273e280
Contents lists available at SciVerse ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Hot water production improves the energy return on investment of geothermal power plants R.S. Atlason*, R. Unnthorsson University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, Hjardarhagi 6, 107 Reykjavik, Iceland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 August 2012 Received in revised form 29 November 2012 Accepted 2 January 2013 Available online 10 February 2013
Our aim was to examine the energy efficiency at Nesjavellir geothermal power plant by calculating its EROI (energy return on investment). For calculations, real data was acquired from stakeholders on materials used in the construction, maintenance and operation of the plant. A previously proposed standard for EROI calculations is tested in this study. Also calculated is the EPT (energy payback time). The paper presents a new EROI metric which is given the name EROI ideal which looks at the maximum theoretical EROI, which shows the potential room for improvement in efficiency. Findings show that the infrastructure to deliver energy to Reykjavik is the largest contributor when looking at the embodied energy of used material. The power plant itself uses 12 MW of the produced 120 MW of electricity and 300 MW of hot water, which makes the plant itself the single largest energy consumer. EROI3,i was found to be 32.4 over a 40-year lifetime, EROIstnd 33 and EROIide 80.9. However, excluding hot water, the EROI dropped to 9.5. This indicates that the efficiency has not improved in electricity production using geothermal technology since the 1970’s. Hot water production for domestic heating was therefore found to increase the EROI significantly. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: EROI Geothermal Power plant
1. Introduction Energy Return on Investment or EROI is an approach to calculate the ratio between the energy needed to get energy and the energy delivered to society. The notion relates to ecology [1], where food gathering must leave more energy behind than was used in the gathering process. This is the same for power plants, where society wants the plants to leave more energy behind than was used in the power generation process. The concept has in recent times mostly been used to study energy sources such as oil and natural gas [2]. The methodology has gained much interest in recent years, especially in discussions around peak oil. Less interest has been in the EROI of renewable sources such as geothermal and hydroelectric and there have been very few studies done since the 1980’s. The EROI concept is often credited to Charles A. S. Hall, where he used the concept in his PhD dissertation and resulting publications [3e5]. Similar concept was put forward by Herendeen & Plant [6], which described the term “Energy cost of Energy” which in essence is the same as EROI. Net energy analysis is related to EROI and has been thoroughly investigated in recent times to study various energy sources [7], including geothermal [8]. The methodology has
* Corresponding author. Tel.: þ354 6605725. E-mail addresses: [email protected] (R.S. Atlason), [email protected] (R. Unnthorsson). 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2013.01.003
been criticized for its lack of standardization since different studies of the same energy source might produce different results. This is due to the fact that different boundaries can be set, and therefore different parameters can be included between studies. Different timeframes also give different results. Murphy and Hall claimed in 2010 that no data exists on geothermal EROI [9], this is supported by Mansure [10], who states that no studies have been done on the subject of geothermal EROI in recent times. Further review showed that Gilliland [11] calculated the EROI to be 12.6 for a dry steam reservoir and 10.7 for a wet steam reservoir. Herendeen & Plant [6] claim that an EROI of 3 might be a reasonable guess for geothermal energy production, which seems a very low estimate. Mansure concludes that up to date analysis on the EROI of geothermal has yet to be made [10] and at least this field lacks recent and reliable analysis. This is a gap, which this study attempts to fulfill using real data. Efficiency at Nesjavellir geothermal power plant is therefore studied using methods proposed by Murphy et al. [12].
2. Methodology and study area When conducting an EROI analysis, the scope must be well defined. One of the biggest discussions around EROI is the lack of standardization, that each study can have different parameters. These parameters include factors such as transportation of goods,
274
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
refinery of the product etc. In the beginning of the study, a clear set of boundaries regarding the data collection is set. When all boundaries have been set and data gathered, values are converted to energy. The total energy needed to create, operate and maintain a given power plant will form a baseline for the different EROI calculations. The original concept of EROI, the ratio between energy delivered against the energy required in the process can be described as follows [13]:
EROI ¼
Quantity of energy supplied Quantity of energy used in supply process
(1)
This equation, which seems straightforward at first, becomes more complex when deciding what is to be included in the numerator and denominator. For example: is the energy required to transport all the material to a given location included? What about the energy that was used to create that material? What about the energy needed to create the machines, which were used to create the material? And so forth. Since various factors can be included within an EROI study, and no standard exists on what should be included or where the boundaries should be set, an attempt has been put forward by at least two parties to standardize the method. Mulder & Hagens [14] claim that since no consistent framework exists around the EROI concept, it can be manipulated to give the desired results. An effort to prevent this was done by supplying a standard which calculations should be derived from. Non-energy inputs are often not considered in EROI equations. However, Mulder & Hagens [14] recommend that they should be, therefore they provided the following equation (2)
EROI ¼
EDout P EDin þ gk Ik
(2)
where EDout is the direct energy output, EDin is the direct energy input, gk is a set of well defined input co-efficient and Ik is the energy per unit of the given co-efficient. This equation does not take into account parameters such as indirect energy outputs, non-energy outputs, land, ground water or time. Some of these parameters can be difficult to convert to energy equivalents (or perhaps impossible). However, most of the time, co-products do have energy content (such as co-products from farming to produce oil seeds, or hot water from a geothermal plant) and can therefore be accounted for. Mulder & Hagens [14] therefore provided another EROI equation that does so:
EROI ¼
P EDout þ nj Oj P EDin þ gk Ik
(3)
where EDout is the direct energy output, nj is a set of well defined coefficient output, Oj is the energy per unit of the given output coefficient, EDin is the direct energy input, gk is a set of well defined input co-efficient and Ik is the energy per unit of the given coefficient. Factors such as soil erosion, ground water pollution and loss of food production are not included within these equations, neither are any fixed set of boundaries. Mulder & Hagens [14] proposed a method for calculating the loss of such factors, but they are irrelevant to the goal of this study, so they will not be discussed any further. Mulder & Hagens [14] suggest three versions (levels) of EROI calculations, depending on the boundaries they include. 1) First order EROI includes only direct inputs and outputs. This is the most superficial of the three levels but the most precise. It does not include any co-products 2) 2nd order EROI includes indirect energy, as well as non-energy inputs. It also includes co-products. This is the methodology used currently in the LCA (Life Cycle Assessment) literature. When using the 2nd order EROI,
two assumptions must be defined: i) how co-products are allocated (heat content, mass etc.) and ii) what boundaries are to be drawn. Mulder & Hagens suggest that the boundaries are to be drawn where the input is less than 1% of the total energy used (invested). 3) The 3rd level EROI incorporates all additional costs and benefits for the process. This is the most accurate method, but the most imprecise. Mulder & Hagens [14] do not provide any standardization in regards to the boundaries of EROI. They merely mention that boundaries should be drawn and well defined, except on the 2nd level EROI where they mention that boundaries can be drawn where the energy input is less than 1% of the energy invested. This is however discussed in detail by Murphy et al. [12] who introduced more detailed definition of boundaries, which are listed in Table 1. The further the boundaries are stretched, the smaller the EROI becomes. Murphy [9] states that the larger the boundary gets, the smaller the EROI will be. This is evident by the fact that the larger the boundary is, the more inputs will go into the process, at the same time energy is lost in every step after its extraction (when refined, transported etc.). Murphy [9] states that all EROI studies should include at least EROIstnd so different studies can be compared. EROIstnd includes indirect energy and material inputs and the energy retrieved in the extraction before processing. This makes the EROI calculations more transparent. The approach by Murphy et al. [12] is used in this study, where the EROIstnd for Nesjavellir power plant as well as the EROI3,i are calculated. The EROIstnd has never been calculated for geothermal power plants and this study should allow for future comparison. Soon after the plant begins its operation, the EROI will most likely be much lower than 1, but with time the EROI is expected to rise. When the EROI reaches 1 with regards to the total output over the lifetime of the plant, the EPT (energy payback time) can be seen. With the information on how much energy a given plant produces, and how much energy it takes to operate and maintain that given plant, the EROI for the given plant over its expected lifetime can be calculated. 2.1. Nesjavellir geothermal power plant Owned by Reykjavik Energy, Nesjavellir power plant is one of Iceland’s greatest technological achievements [15]. Located on the south-western part of Iceland, its construction began in 1987 and operations started on 29th of September 1990. The plant currently produces 120 MW of electricity and 300 MW of heat power delivered as district heating. At site, 25 holes have been drilled to harness the geothermal power. The depth varies between 1000 and 2200 m with temperatures up to 380 C. The average hole produces over 60 MW of power, which, according to Reykjavik Energy is enough to heat the homes and provide electricity for 7500 people [15]. This study investigated the plant using real data collected from respective firms on quantities of material used in the construction, amount of oil and energy used. A map of the area, provided by Icelandic Energy Grid hf. [16] which includes Gramelur pump station, the power plant, and Nesjavallalina 1 & 2 power lines can be found as a Supplementary Material to this article.
Table 1 System boundaries provided by Murphy et al. [12]. Boundary for energy inputs
1. Extraction 2. Processing 3. End use
1. 2. 3. 4. 5.
EROI1,d EROIstnd EROI1,lab EROI1,aux EROI1,env
Direct energy and material inputs Indirect energy and material inputs Indirect labor consumption Auxiliary services consumption Environmental
EROI2,d EROI2,i EROI2,lab EROI2,aux EROI2,env
EROI3,d EROI3,i EROI3,lab EROI3,aux EROI3,env
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
2.2. EROIide In some scenarios, it can prove helpful to know the maximum EROI a given source can provide. Ideal EROI or EROIide is therefore introduced to the literature. This will, due to its nature, require the decision maker to speculate on the future of technological advancements and how fast the EROI of the source will grow (if it on the other hand will) and how much energy has to be invested in the growth. It will further give the decision maker knowledge about the limits of the particular source. The following equation is therefore proposed:
EROIide ¼
P b P EDin þ gk Ik
(4)
where b is the total energy at wellhead, omitting energy losses. This is after construction to access, e.g. borehole for geothermal. EDin is the energy required for building, operating and maintaining the power plant, gk is a set of well-defined co-efficient input and Ik is the energy per unit of the given input co-efficient. To be able to retrieve b, one must calculate the total geothermal energy at wellhead. In the case of Nesjavellir power plant, a steam table was used to calculate the total energy blowing out of the associated holes. This involves both steam and water. 2.3. Parts calculated This study includes different parts, which were calculated as an input to Equation (3). These are 1) The energy the plant uses directly at site. 2) The energy used to maintain the plant. 3) The energy used to transport the materials to Iceland from mainland Europe. 4) All groundwork done in the construction. 5) Embodied energy involved in producing the parts to transfer the electricity from the plant. This also includes the embodied energy in the hot water pipe and its foundations transporting the hot water produced at the plant to Reykjavik over approximately 25 km. 6) Gramelur pump station. 7) All embodied energy relating to the production of the general plant itself. This accounts for all the major relevant parts of the plant and the embodied energy that went into producing these parts. 2.3.1. Power usage at site According to Reykjavik Energy, the energy usage at the plant is 12 MW for the 120 MW electric and 300 MW hot water output [17]. A majority of this energy is used to pump water to and from the plant over mountainous terrain. This equals to 105,120 MWh every year, or 378,432 GJ per year. This makes the own usage of the plant the biggest energy-consuming factor of the plant over its proposed 40-year lifetime. This usage can for example be associated to the on-site water pumps delivering water to the plant. To cool down steam, the water is then pumped to Reykjavik for district heating. 2.3.2. Maintenance According to the LCA (Life Cycle Assessment) report on the Nesjavellir geothermal plant done by the Technological Institute of Iceland, where the environmental impact from the plant was studied, maintenance is considered to be 2% of the original material usage per year [18]. Since no other data was available on maintenance on the plant, this parameter was used. 2.3.3. Transportation Iceland is an island, and most materials for construction must be imported. This study assumes that relevant parts are transported from mainland Europe through the normal route of the Icelandic shipping company Eimskip [19], which is Rotterdam e Immingham e Reykjavik. For the allocation of energy usage in the
275
transportation, it is assumed that the ship fully loads in Rotterdam. Only the energy used for transportation of the fully loaded ship was accounted for, from Rotterdam to Immingham and from there to Reykjavik where the sea route was estimated to be ca. 3000 km. Information about the Dettifoss, one of the company ships was provided by the Eimskip shipping company. Given the parameters, one can calculate that the ships travel [20] approximately 97 h between Rotterdam and Reykjavik. One can therefore see that the ship uses 161 tonnes of oil on this route, transporting 17,034 tonnes. The total weight of material transported for the power plant amounts to approximately 21,000 tonnes. This accounts for 1.37 trips to Iceland from Rotterdam and 220 tonnes of oil. This is a rough estimate though, since many materials have not been counted due to the minimal weight they account for. Within the calculations, it has been estimated that oil has the average energy value of 41.87 GJ/tonne [21]. To transport the materials from mainland Europe to Iceland, approximately 9211 GJ were needed. These results show that the transportation amounts for a small proportion of the whole input, it therefore does not need to be clarified in greater detail. 2.3.4. Groundwork When all the energy consumed by removing and replacing soil, transporting materials from the harbor and transporting concrete from Reykjavik to various sites is put together the result is 21,725 GJ. Table 2 sums up the energy used in various phases for soil handling and transport of materials. The distribution can further be seen in Fig. 1. This shows that most energy went into the plant construction, or 35%, followed by the groundwork to form the water pipe, which amounted to 26%. Electricity transport amounted to 33% in total as is shown by Nesjavallalina power line 1 and 2. 2.3.5. Embodied energy of the energy transfer system At Nesjavellir power plant, energy in form of hot water and electricity is produced. The hot water is delivered through an approximately 25 km long pipe, which stretches from the plant to Reykjavik. Electricity is delivered through two power lines that are in three sections. Nesjavallalina power line 1 consists of 15.64 km of overhead power line running through masts and 15.65 km of underground cable. Nesjavallalina power line 2 consists solely of an underground cable and is 24.6 km long [22]. The total energy used to produce Nesjavallalina power line 1 is 16,274 GJ, Nesjavallalina power line 2 amounts to 7180 GJ and Nesjavellir hot water pipe 267,511. In total, this amounts to 290,965 GJ. This shows that the largest embodied energy is in the equipment for transporting hot water. This is mostly due to the large amount of steel needed in the pipe or 5980 metric tonnes. 2.3.6. Gramelur pump station Gramelur pump station pumps up cold water from 6 boreholes, the water is used to cool down steam at Nesjavellir power plant, subsequently some water is pumped to Reykjavik for heating [23]. The total energy used in material production of Gramelur pump Table 2 Energy used for groundwork. Phases and parts
Energy (GJ)
Transport from harbor Nesjavallalina power line 1 Nesjavallalina power line 2 Water pipe Plant Gramelur pump station Total
1117 4296 2783 5759 7526 244 21,725
276
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
demonstrates the relative distribution between the parts. The general plant was found to include the largest amount of embodied energy. It was however also observed that energy transfer in the form of hot water and electricity expressed a major proportion of the total embodied energy. 3. Results The EROIstnd, EROI3,i, EROIide and the energy payback time for the power plant were calculated using different lifetime scenarios. Scenario excluding hot water was also calculated, to show the EROI of the plant if it produced solely electricity. 3.1. EROIstnd
Fig. 1. Relative distribution of energy use by machinery in construction of various parts.
station amounts to 62,697 GJ. This shows that Gramelur is a minor part of the construction. The water pipe, and the steel within, which transfers cold water from 6 wells to Nesjavellir power plant amounts to the largest portion of embodied energy related to Gramelur pump station. 2.3.7. Embodied energy in the general plant This part was calculated to be the largest energy-consuming part. The energy used in the drilling and construction of the geothermal holes was the biggest factor in this part, using, when put together, a total of 134,648 GJ. No other part of this part amounted for such vast amount of energy. The construction of the station house followed, with the total amount of 36,044 GJ used. 2.4. Sum of embodied energy When the previously discussed parts have been added together, the total energy embodied (used in the production of the parts) in the construction materials amounts to 692,465 GJ. Fig. 2 further
As stated, the EROIstnd is the indirect and direct inputs to the plant, but only the energy output without delivery to the consumer. This is a good factor for comparison of energy sources since the plants may need more or less distances for transport of the energy. The distance might disadvantage some energy sources even though the source might have a relatively good EROI. In the case of Nesjavellir power plant, this will include the same inputs as before, but will exclude the mechanisms for delivering the energy. That is the pipe, which delivers the hot water, as well as the mechanisms for delivering the electricity, namely Nesjavallalina power lines 1 and 2. The input will be 779,931 GJ for the first year, which are the entire input factors summed up, plus the operational power usage. Table 3 shows the EROIstnd scenario over the lifetime of the plant. This scenario shows that the EROIstnd is around 33 over the lifetime of the plant. Fig. 3 explains the development of the EROIstnd over the lifetime. 3.2. EROI3,i With the knowledge compiled, the following calculation can be made from Equation (3). This includes the direct energy for the operation of the plant, as well as the indirect energy used for construction of materials and groundwork. EROI3,i also includes the direct energy output from the plant as well as the co-efficient energy output, which in this case is hot water. Summing all these Table 3 EROI results using various boundaries. Year
Output (GJ)
EROIstnd calculations 1 13,245,000 10 132,451,200 20 264,900,000 30 397,353,600 40 529,804,800 EROI3,i calculations 1 13,245,000 10 132,451,200 20 264,900,000 30 397,353,600 40 529,804,800 EROI3,i no hot water 1 3,784,000 10 37,840,000 20 75,680,000 30 113,520,000 40 151,360,000 EROIide calculations 1 33,112,000 10 331,120,000 20 662,240,000 30 993,360,000 40 1,324,480,000 Fig. 2. Relative distribution of embodied energy.
Input (GJ)
EROI
779,931 4,310,463 8,233,276 12,156,089 16,078,902
17.0 30.7 32.2 32.7 33.0
1,070,896 4,601,428 8,524,241 12,447,054 16,369,867
12.3 28.8 31.1 31.9 32.4
803,385 4,285,765 8,155,076 12,024,386 15,893,697
4.7 8.8 9.3 9.4 9.5
1,070,896 4,601,428 8,524,241 12,447,054 16,369,867
30.9 72.0 77.7 79.8 80.9
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
277
Fig. 3. Different EROI scenarios calculated for Nesjavellir power plant. The x-axis shows lifetime [years], the y-axis shows EROI values.
factors up, the plant reaches an EROI of 12.3. This however only describes the first year of energy production, where the annual energy output is 13,245,000 GJ. After the first year, 2% maintenance of original embodied energy will occur annually and operational usage is 12 MW of every 120 MW of electricity produced. This will therefore be calculated in the EROI of the plant. Table 3 shows the EROI for every 10 years, for 40 years, which is approximately the expected lifetime of the plant. One can therefore see that over the lifetime of the plant, the EROI will be just a little more than 32. It increases rapidly in the beginning but as times goes by and operational and maintenance costs increase, it levels off. This can be seen in Fig. 3 where the development of different EROIs as a function of lifetime is visualized. 3.3. EROI3,i scenario without hot water A vast amount of hot water is delivered from the plant, and the part, which has the largest embodied energy associated to it is the pipe, which delivers the hot water to the nearby city. It is therefore interesting to see how the plant would perform without the hot water production. The plant produces 300 MW equivalent of hot water of the 420 MW produced at the plant [15]. In this scenario, the plant only produces 120 MW of electricity since the hot water production is excluded but still uses the same amount of operation energy, the amount of energy embodied in Nesjavellir hot water pipe is however removed, as well as all other related activities such as groundwork in its construction. Table 3 shows the results from this scenario. This shows that the EROI levels off and stagnates at around 9. Hot water production therefore increases the efficiency at the plant more than threefold, where the EROI with the hot water production and associated energy costs and benefits is around 33. The development of the EROI is similar in this scenario as compared to the previous one, this can be observed in Fig. 3. 3.4. EROIide With the knowledge of the total input required to construct, maintain and operate Nesjavellir power plant over its lifetime, it is possible to estimate the EROIide as was described in Equation (4). The EROIide was found to be 30.9 for the first year. Table 3 shows the EROIide for the same intervals as the EROI3,i calculations show. The output was calculated using a steam table and data from Reykjavik Energy. The numbers provided in Table 3 show the EROI of the power plant if it was 100% efficient, which according to modern physics can never be achieved. It is illustrated that as before, the
EROIide increases rapidly the first decade, but then the increase slows down and stabilizes around 80, this can be seen in Fig. 3. This version of EROI assumes that the output power from the holes remains at the same level throughout the lifetime of the plant. 3.5. Energy payback time The energy payback time is the time it takes the power plant to produce the same amount of energy it originally took to construct the plant in the first place, factoring in maintenance and operational energy used over its lifetime. With all the knowledge needed to calculate the EROI scenarios calculated above, calculating the energy payback time is relatively straightforward. This was calculated using the same scenarios as were used in the previous EROI calculations. Table 4 shows the energy payback time of the plant, which is the time it takes the plant to reach the EROI of 1 in different scenarios. This shows that the EROIide has the shortest payback time, or approximately half a year when all energy expenditures over the lifetime where included. The scenario with no hot water production was found to have the longest energy payback. However, the EROIstnd and EROI3,i were found to have almost the same amount of energy payback time, or around 1 year and 3 months (1.21 and 1.23 years). Another method was also used to calculate the EPT, where consumption was put in real time sequence instead of counting total energy consumption over its lifetime. This method shows that under normal circumstances the EPT in the EROIstnd scenario is only a little less than 2 weeks and EROI3,i a little less than 3 weeks. Fig. 4 shows the different EPT if energy consumption is put in logical order. 3.6. Sensitivity analysis A sensitivity analysis was conducted, to see the effects if the uncertainty factors (own usage and maintenance) would change over time. Maintenance was increased up to 10% and own usage was increased by 10% as well as lowered by the same amount. The scenario used in the sensitivity analyses was the EROI3,i over 40 Table 4 Energy payback times depending on different EROI scenarios. Scenario
Output per year (GJ)
Input over 40 years (GJ)
EPT (years)
EROIstnd EROI3,i EROI3,i (no water) EROIide
13,245,000 13,245,000 3,784,000 33,112,000
16,078,902 16,369,867 15,902,196 16,369,867
1.21 1.23 4.2 0.49
278
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
Fig. 4. Energy payback time when energy consumption is put in logical order. The xaxis shows weeks, y-axis shows EROI values.
years time. The analysis shows that if maintenance remains at 2%, but the operational cost decreases by 10%, the EROI increases from 32.4 to 35.7. It also shows that if the operational cost increases by 10% from the current status the EROI decreases to 29.6. It was shown that if the operational cost remains as predicted (12 MW) but the maintenance cost increases up to 10% per year of the original energy cost, the EROI declines down to 28.6. However, in the worst-case scenario where the maintenance cost was 10% per year and the operational cost had increased by 10%, the EROI dropped down to 26.4. The sensitivity analysis is further depicted in Table 5. The equation used to modify these parameters is as follows:
EROI3;i ¼
EDout ðOpyÞ þ E þ ðEx39Þ
(5)
where EDout is the total output energy delivered to consumer over the lifetime of the plant, Op is the total operational energy usage, y is the percentage of the original embodied energy to be used as maintenance. E is the total embodied energy of the plant, x is the fraction of the embodied energy used for maintenance. 39 accounts for the years of maintenance over the 40 years lifetime of the plant. 4. Discussions This study calculated four EROI scenarios and the energy payback time of the Nesjavellir power plant. All the major parts of the power plant have been canvassed, and the embodied energy of these given parts calculated. A comparison of the results after the plants lifetime can be seen in Table 3. The energy required to operate the machinery in the general construction of the major parts was also calculated. However, it was found that the largest energy-consuming factor on a yearly basis was the plant itself, which consumed 12 MW. The EROIstnd was found to be 32 over a 40-year lifetime of the plant. The EROI3,i was found to be slightly lower, or 32.4 since it included the energy needed to transfer the electricity and hot water to Reykjavik. To see how much difference the hot water made, the EROI3,i was also calculated excluding the hot water production. This resulted in a much lower EROI of 9.5 over the lifetime of the plant. This clearly illustrates how the efficiency increases at the plant when hot water production is included. The EROI more than tripled. Table 5 The EROI results if energy consumption changes in the maintenance and operational phase. Own power usage
2%
5%
10%
10% Normal þ10%
35.7 32.4 29.6
33.8 30.8 28.3
31.1 28.6 26.4
A new concept was introduced to the literature in this study, EROIide, which calculates the EROI at the plant if the efficiency at site was 100%, as was explained in Chapter 2.1. The EROIide was calculated to be 80.9 over the 40-year lifetime of the plant. Fig. 3 further illustrates the differences between the EROI scenarios, clearly illustrating that the efficiency can be improved at the plant significantly, but only up to the limit that the EROIide indicates. The energy payback time was calculated to be 1.21 years in the EROIstnd scenario and 1.23 in the EROI3,i scenario, which is around 1 year and 3 months it would take the plant to produce the amount of energy it consumed to be constructed and used during its operational lifetime. The energy payback time was however only 6 months (0.49 year) for the EROIide scenario. The increase in efficiency when hot water is produced at the plant as well as electricity was demonstrated, where the energy payback time went from 4.2 years down to 1.23 years. The overall impact of the maintenance and operational factor can be observed in Fig. 5 where the operational cost in energy terms increases from year to year, as well as the maintenance cost. This can be observed by looking at the thickness of the bars, the fixed costs get narrower the further time passes, but the increasing costs get thicker (operation and maintenance). In the discussion around renewable energy, many of the options available are often considered to be energy sinks rather than energy sources [24]. EROI results, like presented in this paper show that the source studied provides more energy to society than it consumed over its lifetime [25]. The results from Nesjavellir geothermal power plant show that over the estimated 40-year lifetime, the Energy Return on Investment is around 33. The EROIstnd boundaries were used which allows this study to be compared to similar studies. It was demonstrated that production of hot water at the plant increased its efficiency dramatically, where the EROI would otherwise be around 9. This indicates that producers of such plants and policy makers should promote production of hot water at site if possible (and feasible). Interestingly it was found that the plant consumed a huge proportion of its own production, if this could be reduced the EROI would improve significantly. This paper further presented EROI ideal, a new concept which shows the upper limits an EROI of a given energy source, which is bound never to reach. EROIide can show decision makers, whether in the private or public sector, how much potential is for improvement at the source studied with regards to its efficiency. This knowledge can therefore encourage stakeholders to seek technological advancements since that would most likely result in economic profits. With the knowledge of the EROIide it is possible to see that the EROI can be improved by an EROI of approximately 50, up to an EROI of 80 at Nesjavellir. Transportation of materials to Iceland was, interestingly, shown to have a minimal effect on the results. Therefore, the isolation of the country should not be a barrier in constructions of this kind. By comparing this study to the one conducted by Gilliland in 1975 [11], one can see that the results are strikingly similar. The plant studied in the 70’s had only electricity as an energy output, and therefore the EROI scenario at Nesjavellir, which excluded hot water production, is suited for comparison to that study. The EROI’s provided by Gilliland were between 10 and 12, where Nesjavellir was around 9. Both studies might have some uncertainty in the calculations but the results show that the efficiency is around the same, or even less at Nesjavellir. This comes across as odd, since Gilliland’s study was conducted more than 40 years ago [11] and technological advancements in electricity production from geothermal power were expected to have increased the efficiency. These results show that they have however not. However, compared to Herendeen & Plant [6], who showed the EROI to be around 4, the EROI has improved, but only slightly with regards to electricity production. The EROI of
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
279
Fig. 5. Proportion of energy consumption from different parts of Nesjavellir geothermal power plant. The x-axis shows years.
33 when hot water is included at Nesjavellir proves to be relatively low compared to energy sources such as coal and hydro (with the EROI of approximately 80 and >100 respectively) [2,26]. Nesjavellir however scores a better EROI than oil (With a declining EROI from approximately 100 in the 30’s to approximately 11 in the mid 2000) [2,27,28], and Nuclear of around 10 [25,29]. If however hot water would not be produced at Nesjavellir, the EROI would be so low that it would score even less than oil and nuclear. This might be an indicator that geothermal power plants which do not produce other forms of energy (such as hot water for heating) have a relatively low EROI compared to most other energy sources. EROI does not consider parameters such as economical, social or environmental factors. It does however relate to all these parameters and can provide an insight to the efficiency of various energy sources. It has even been claimed that, “Energy Return on Investment is a powerful metric for weighing which energy systems are worth pursuing” [25]. A single number score, like the EROI provides, should however not be taken as the whole truth since there are, like mentioned, other factors to be included. A proposed standard was followed throughout the study. Instead of monetary data, real data was acquired directly from stakeholders, which allowed for a very precise analysis, except for the case of shipping. Shipping was however was shown to be almost irrelevant, even though the energy used in shipping doubled, it would not have reached 1% of the total energy consumption. As was the case with Gilliland’s research [11], the methodology put forward and used in this study should not be considered as a completed framework for conducting an EROI analysis. Since the field is relatively new, the methodology is under constant change. However, the attempt for a standard suggested by Murphy et al. [9] is relatively good and should allow for comparison between studies at present time. EROI research in the field of other renewable energy sources seems to have been left out to some extent. Oil and gas have been thoroughly studied, which results in a timeline of EROI’s where the efficiency or availability of the energy sources can be examined. It would therefore give a valuable insight to research other renewable sources like hydro, or even other geothermal plants so they can be compared and analyzed. Acknowledgments This research was supported by the Icelandic Energy Fund (Orkusjodur). Acknowledgments go to Reykjavik Energy hf, Landsnet hf and Efla Engineering hf for providing data.
Appendix A. Supplementary material Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.energy.2013.01.003. References [1] Hall CA. Introduction to special issue on new studies in EROI (energy return on investment). Sustainability 2011;3(10):1773e7. [2] Cleveland C. Net energy from the extraction of oil and gas in the United States. Energy 2005;30(5):769e82. [3] Hall CAS. Migration and metabolism in a temperate stram ecosystem. Ecology 1972;53:585e604. [4] Hall CAS. The biosphere, the industriosphere and their interactions. Bulletin of Atomic Scientists 1975;31:11e21. [5] Hall CAS. Petroleum drilling and production in the U.S.: yield per effort and net energy analysis. Science 1981;211:576e9. [6] Herendeen RA, Plant RL. Energy analysis of four geothermal technologies. Energy 1981;6(1):73e82. [7] Tyner Sr G, Costanza R, Fowler RG. The net-energy yield of nuclear power. Energy 1988;13(1):73e81. [8] Icerman L. Net energy production history of the geysers geothermal project. Energy 1980;5(1):29e33. [9] Murphy DJ, Hall CAS. Year in reviewdEROI or energy return on (energy) invested. Annals of the New York Academy of Sciences 2010;1185(1):102e18. [10] Mansure A. Are geothermal energy returns on investment high enough. In: Proceedings, Thirty-Sixth Workshop on Geothermal Reservoir Engineering; 2011. [11] Gilliland MW. Energy analysis and public policy. Science 1975;189(4208): 1051e6. [12] Murphy DJ, Hall CA, Dale M, Cleveland C. Order from chaos: a preliminary protocol for determining the EROI of fuels. Sustainability 2011;3(10):1888e907. [13] Cleveland C. Energy return on investment (EROI) [cited 17.05.2011]. URL, http://www.eoearth.org/article/Energy_return_on_investment_(EROI); 2008. [14] Mulder K, Hagens NJ. Energy return on investment: toward a consistent framework. Ambio 2008;37(2):74e9. [15] Nesjavallavirkjun (n.d.) [cited 02.02.2012]. URL http://www.or.is/UmOR/ Veiturogveitusvaedi/Virkjanir/Nesjavallavirkjun/. [16] Grid IE. Map of Nesjavellir and relevant power lines. Landsnet. [17] Rafnsson K. E-mail communication; 2012. [18] T K, Jonsdottir H. Life cycle analysis of Nesjavellir geothermal power plant. Tech. Rep.. Technological Institute of Iceland; 2008 [19] Eimskip, Siglingaaaetlun (n.d.) [cited 07.03.2012]. URL http://eimskip.is/IS/ Um-Eimskip/siglingar/default.html. [20] EHO/MAO, M/v Dettifoss datasheet. Tech. Rep., Eimskip (n.d.). [21] Energy units (n.d.) [cited 15.02.2012]. URL http://www.aps.org/policy/reports/ popa-reports/energy/units.cfm. [22] Linuhonnun. 132 kv nesjavallalina 1, bygging og rekstur. Tech. Rep.. Orkuveita Reykjavikur; 2002 [23] VGK. Nesjavallavirkjun afangi 4b stækkun rafstodvar ur 76 í 90 mw. Tech. Rep.. Orkuveita Reykjavíkur; 2000 [24] Gonçalves da Silva C. The fossil energy/climate change crunch: can we pin our hopes on new energy technologies? Energy 2010;35(3):1312e6. [25] Kreith F. Bang for the buck e energy return on investment is a powerful metric for weighing which energy systems are worth pursuing. Journal of Mechanical Engineering May 2012:26e31.
280
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
[26] Gagnon L, Belanger C, Uchiyama Y. Life-cycle assessment of electricity generation options: the status of research in year 2001. Energy Policy 2002; 30(14):1267. [27] Cleveland CJ. Energy quality and energy surplus in the extraction of fossil fuels in the U.S. Ecological Economics 1992;6(2):139e62.
[28] Guilford MC, Hall CA, O’Connor P, Cleveland CJ. A new long term assessment of energy return on investment (EROI) for U.S. oil and gas discovery and production. Sustainability 2011;3(10):1866e87. [29] Manfred L. Life cycle energy and greenhouse gas emissions of nuclear energy: a review. Energy Conversion and Management 2008;49(8):2178e99.
Contents lists available at SciVerse ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Hot water production improves the energy return on investment of geothermal power plants R.S. Atlason*, R. Unnthorsson University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, Hjardarhagi 6, 107 Reykjavik, Iceland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 August 2012 Received in revised form 29 November 2012 Accepted 2 January 2013 Available online 10 February 2013
Our aim was to examine the energy efficiency at Nesjavellir geothermal power plant by calculating its EROI (energy return on investment). For calculations, real data was acquired from stakeholders on materials used in the construction, maintenance and operation of the plant. A previously proposed standard for EROI calculations is tested in this study. Also calculated is the EPT (energy payback time). The paper presents a new EROI metric which is given the name EROI ideal which looks at the maximum theoretical EROI, which shows the potential room for improvement in efficiency. Findings show that the infrastructure to deliver energy to Reykjavik is the largest contributor when looking at the embodied energy of used material. The power plant itself uses 12 MW of the produced 120 MW of electricity and 300 MW of hot water, which makes the plant itself the single largest energy consumer. EROI3,i was found to be 32.4 over a 40-year lifetime, EROIstnd 33 and EROIide 80.9. However, excluding hot water, the EROI dropped to 9.5. This indicates that the efficiency has not improved in electricity production using geothermal technology since the 1970’s. Hot water production for domestic heating was therefore found to increase the EROI significantly. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: EROI Geothermal Power plant
1. Introduction Energy Return on Investment or EROI is an approach to calculate the ratio between the energy needed to get energy and the energy delivered to society. The notion relates to ecology [1], where food gathering must leave more energy behind than was used in the gathering process. This is the same for power plants, where society wants the plants to leave more energy behind than was used in the power generation process. The concept has in recent times mostly been used to study energy sources such as oil and natural gas [2]. The methodology has gained much interest in recent years, especially in discussions around peak oil. Less interest has been in the EROI of renewable sources such as geothermal and hydroelectric and there have been very few studies done since the 1980’s. The EROI concept is often credited to Charles A. S. Hall, where he used the concept in his PhD dissertation and resulting publications [3e5]. Similar concept was put forward by Herendeen & Plant [6], which described the term “Energy cost of Energy” which in essence is the same as EROI. Net energy analysis is related to EROI and has been thoroughly investigated in recent times to study various energy sources [7], including geothermal [8]. The methodology has
* Corresponding author. Tel.: þ354 6605725. E-mail addresses: [email protected] (R.S. Atlason), [email protected] (R. Unnthorsson). 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2013.01.003
been criticized for its lack of standardization since different studies of the same energy source might produce different results. This is due to the fact that different boundaries can be set, and therefore different parameters can be included between studies. Different timeframes also give different results. Murphy and Hall claimed in 2010 that no data exists on geothermal EROI [9], this is supported by Mansure [10], who states that no studies have been done on the subject of geothermal EROI in recent times. Further review showed that Gilliland [11] calculated the EROI to be 12.6 for a dry steam reservoir and 10.7 for a wet steam reservoir. Herendeen & Plant [6] claim that an EROI of 3 might be a reasonable guess for geothermal energy production, which seems a very low estimate. Mansure concludes that up to date analysis on the EROI of geothermal has yet to be made [10] and at least this field lacks recent and reliable analysis. This is a gap, which this study attempts to fulfill using real data. Efficiency at Nesjavellir geothermal power plant is therefore studied using methods proposed by Murphy et al. [12].
2. Methodology and study area When conducting an EROI analysis, the scope must be well defined. One of the biggest discussions around EROI is the lack of standardization, that each study can have different parameters. These parameters include factors such as transportation of goods,
274
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
refinery of the product etc. In the beginning of the study, a clear set of boundaries regarding the data collection is set. When all boundaries have been set and data gathered, values are converted to energy. The total energy needed to create, operate and maintain a given power plant will form a baseline for the different EROI calculations. The original concept of EROI, the ratio between energy delivered against the energy required in the process can be described as follows [13]:
EROI ¼
Quantity of energy supplied Quantity of energy used in supply process
(1)
This equation, which seems straightforward at first, becomes more complex when deciding what is to be included in the numerator and denominator. For example: is the energy required to transport all the material to a given location included? What about the energy that was used to create that material? What about the energy needed to create the machines, which were used to create the material? And so forth. Since various factors can be included within an EROI study, and no standard exists on what should be included or where the boundaries should be set, an attempt has been put forward by at least two parties to standardize the method. Mulder & Hagens [14] claim that since no consistent framework exists around the EROI concept, it can be manipulated to give the desired results. An effort to prevent this was done by supplying a standard which calculations should be derived from. Non-energy inputs are often not considered in EROI equations. However, Mulder & Hagens [14] recommend that they should be, therefore they provided the following equation (2)
EROI ¼
EDout P EDin þ gk Ik
(2)
where EDout is the direct energy output, EDin is the direct energy input, gk is a set of well defined input co-efficient and Ik is the energy per unit of the given co-efficient. This equation does not take into account parameters such as indirect energy outputs, non-energy outputs, land, ground water or time. Some of these parameters can be difficult to convert to energy equivalents (or perhaps impossible). However, most of the time, co-products do have energy content (such as co-products from farming to produce oil seeds, or hot water from a geothermal plant) and can therefore be accounted for. Mulder & Hagens [14] therefore provided another EROI equation that does so:
EROI ¼
P EDout þ nj Oj P EDin þ gk Ik
(3)
where EDout is the direct energy output, nj is a set of well defined coefficient output, Oj is the energy per unit of the given output coefficient, EDin is the direct energy input, gk is a set of well defined input co-efficient and Ik is the energy per unit of the given coefficient. Factors such as soil erosion, ground water pollution and loss of food production are not included within these equations, neither are any fixed set of boundaries. Mulder & Hagens [14] proposed a method for calculating the loss of such factors, but they are irrelevant to the goal of this study, so they will not be discussed any further. Mulder & Hagens [14] suggest three versions (levels) of EROI calculations, depending on the boundaries they include. 1) First order EROI includes only direct inputs and outputs. This is the most superficial of the three levels but the most precise. It does not include any co-products 2) 2nd order EROI includes indirect energy, as well as non-energy inputs. It also includes co-products. This is the methodology used currently in the LCA (Life Cycle Assessment) literature. When using the 2nd order EROI,
two assumptions must be defined: i) how co-products are allocated (heat content, mass etc.) and ii) what boundaries are to be drawn. Mulder & Hagens suggest that the boundaries are to be drawn where the input is less than 1% of the total energy used (invested). 3) The 3rd level EROI incorporates all additional costs and benefits for the process. This is the most accurate method, but the most imprecise. Mulder & Hagens [14] do not provide any standardization in regards to the boundaries of EROI. They merely mention that boundaries should be drawn and well defined, except on the 2nd level EROI where they mention that boundaries can be drawn where the energy input is less than 1% of the energy invested. This is however discussed in detail by Murphy et al. [12] who introduced more detailed definition of boundaries, which are listed in Table 1. The further the boundaries are stretched, the smaller the EROI becomes. Murphy [9] states that the larger the boundary gets, the smaller the EROI will be. This is evident by the fact that the larger the boundary is, the more inputs will go into the process, at the same time energy is lost in every step after its extraction (when refined, transported etc.). Murphy [9] states that all EROI studies should include at least EROIstnd so different studies can be compared. EROIstnd includes indirect energy and material inputs and the energy retrieved in the extraction before processing. This makes the EROI calculations more transparent. The approach by Murphy et al. [12] is used in this study, where the EROIstnd for Nesjavellir power plant as well as the EROI3,i are calculated. The EROIstnd has never been calculated for geothermal power plants and this study should allow for future comparison. Soon after the plant begins its operation, the EROI will most likely be much lower than 1, but with time the EROI is expected to rise. When the EROI reaches 1 with regards to the total output over the lifetime of the plant, the EPT (energy payback time) can be seen. With the information on how much energy a given plant produces, and how much energy it takes to operate and maintain that given plant, the EROI for the given plant over its expected lifetime can be calculated. 2.1. Nesjavellir geothermal power plant Owned by Reykjavik Energy, Nesjavellir power plant is one of Iceland’s greatest technological achievements [15]. Located on the south-western part of Iceland, its construction began in 1987 and operations started on 29th of September 1990. The plant currently produces 120 MW of electricity and 300 MW of heat power delivered as district heating. At site, 25 holes have been drilled to harness the geothermal power. The depth varies between 1000 and 2200 m with temperatures up to 380 C. The average hole produces over 60 MW of power, which, according to Reykjavik Energy is enough to heat the homes and provide electricity for 7500 people [15]. This study investigated the plant using real data collected from respective firms on quantities of material used in the construction, amount of oil and energy used. A map of the area, provided by Icelandic Energy Grid hf. [16] which includes Gramelur pump station, the power plant, and Nesjavallalina 1 & 2 power lines can be found as a Supplementary Material to this article.
Table 1 System boundaries provided by Murphy et al. [12]. Boundary for energy inputs
1. Extraction 2. Processing 3. End use
1. 2. 3. 4. 5.
EROI1,d EROIstnd EROI1,lab EROI1,aux EROI1,env
Direct energy and material inputs Indirect energy and material inputs Indirect labor consumption Auxiliary services consumption Environmental
EROI2,d EROI2,i EROI2,lab EROI2,aux EROI2,env
EROI3,d EROI3,i EROI3,lab EROI3,aux EROI3,env
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
2.2. EROIide In some scenarios, it can prove helpful to know the maximum EROI a given source can provide. Ideal EROI or EROIide is therefore introduced to the literature. This will, due to its nature, require the decision maker to speculate on the future of technological advancements and how fast the EROI of the source will grow (if it on the other hand will) and how much energy has to be invested in the growth. It will further give the decision maker knowledge about the limits of the particular source. The following equation is therefore proposed:
EROIide ¼
P b P EDin þ gk Ik
(4)
where b is the total energy at wellhead, omitting energy losses. This is after construction to access, e.g. borehole for geothermal. EDin is the energy required for building, operating and maintaining the power plant, gk is a set of well-defined co-efficient input and Ik is the energy per unit of the given input co-efficient. To be able to retrieve b, one must calculate the total geothermal energy at wellhead. In the case of Nesjavellir power plant, a steam table was used to calculate the total energy blowing out of the associated holes. This involves both steam and water. 2.3. Parts calculated This study includes different parts, which were calculated as an input to Equation (3). These are 1) The energy the plant uses directly at site. 2) The energy used to maintain the plant. 3) The energy used to transport the materials to Iceland from mainland Europe. 4) All groundwork done in the construction. 5) Embodied energy involved in producing the parts to transfer the electricity from the plant. This also includes the embodied energy in the hot water pipe and its foundations transporting the hot water produced at the plant to Reykjavik over approximately 25 km. 6) Gramelur pump station. 7) All embodied energy relating to the production of the general plant itself. This accounts for all the major relevant parts of the plant and the embodied energy that went into producing these parts. 2.3.1. Power usage at site According to Reykjavik Energy, the energy usage at the plant is 12 MW for the 120 MW electric and 300 MW hot water output [17]. A majority of this energy is used to pump water to and from the plant over mountainous terrain. This equals to 105,120 MWh every year, or 378,432 GJ per year. This makes the own usage of the plant the biggest energy-consuming factor of the plant over its proposed 40-year lifetime. This usage can for example be associated to the on-site water pumps delivering water to the plant. To cool down steam, the water is then pumped to Reykjavik for district heating. 2.3.2. Maintenance According to the LCA (Life Cycle Assessment) report on the Nesjavellir geothermal plant done by the Technological Institute of Iceland, where the environmental impact from the plant was studied, maintenance is considered to be 2% of the original material usage per year [18]. Since no other data was available on maintenance on the plant, this parameter was used. 2.3.3. Transportation Iceland is an island, and most materials for construction must be imported. This study assumes that relevant parts are transported from mainland Europe through the normal route of the Icelandic shipping company Eimskip [19], which is Rotterdam e Immingham e Reykjavik. For the allocation of energy usage in the
275
transportation, it is assumed that the ship fully loads in Rotterdam. Only the energy used for transportation of the fully loaded ship was accounted for, from Rotterdam to Immingham and from there to Reykjavik where the sea route was estimated to be ca. 3000 km. Information about the Dettifoss, one of the company ships was provided by the Eimskip shipping company. Given the parameters, one can calculate that the ships travel [20] approximately 97 h between Rotterdam and Reykjavik. One can therefore see that the ship uses 161 tonnes of oil on this route, transporting 17,034 tonnes. The total weight of material transported for the power plant amounts to approximately 21,000 tonnes. This accounts for 1.37 trips to Iceland from Rotterdam and 220 tonnes of oil. This is a rough estimate though, since many materials have not been counted due to the minimal weight they account for. Within the calculations, it has been estimated that oil has the average energy value of 41.87 GJ/tonne [21]. To transport the materials from mainland Europe to Iceland, approximately 9211 GJ were needed. These results show that the transportation amounts for a small proportion of the whole input, it therefore does not need to be clarified in greater detail. 2.3.4. Groundwork When all the energy consumed by removing and replacing soil, transporting materials from the harbor and transporting concrete from Reykjavik to various sites is put together the result is 21,725 GJ. Table 2 sums up the energy used in various phases for soil handling and transport of materials. The distribution can further be seen in Fig. 1. This shows that most energy went into the plant construction, or 35%, followed by the groundwork to form the water pipe, which amounted to 26%. Electricity transport amounted to 33% in total as is shown by Nesjavallalina power line 1 and 2. 2.3.5. Embodied energy of the energy transfer system At Nesjavellir power plant, energy in form of hot water and electricity is produced. The hot water is delivered through an approximately 25 km long pipe, which stretches from the plant to Reykjavik. Electricity is delivered through two power lines that are in three sections. Nesjavallalina power line 1 consists of 15.64 km of overhead power line running through masts and 15.65 km of underground cable. Nesjavallalina power line 2 consists solely of an underground cable and is 24.6 km long [22]. The total energy used to produce Nesjavallalina power line 1 is 16,274 GJ, Nesjavallalina power line 2 amounts to 7180 GJ and Nesjavellir hot water pipe 267,511. In total, this amounts to 290,965 GJ. This shows that the largest embodied energy is in the equipment for transporting hot water. This is mostly due to the large amount of steel needed in the pipe or 5980 metric tonnes. 2.3.6. Gramelur pump station Gramelur pump station pumps up cold water from 6 boreholes, the water is used to cool down steam at Nesjavellir power plant, subsequently some water is pumped to Reykjavik for heating [23]. The total energy used in material production of Gramelur pump Table 2 Energy used for groundwork. Phases and parts
Energy (GJ)
Transport from harbor Nesjavallalina power line 1 Nesjavallalina power line 2 Water pipe Plant Gramelur pump station Total
1117 4296 2783 5759 7526 244 21,725
276
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
demonstrates the relative distribution between the parts. The general plant was found to include the largest amount of embodied energy. It was however also observed that energy transfer in the form of hot water and electricity expressed a major proportion of the total embodied energy. 3. Results The EROIstnd, EROI3,i, EROIide and the energy payback time for the power plant were calculated using different lifetime scenarios. Scenario excluding hot water was also calculated, to show the EROI of the plant if it produced solely electricity. 3.1. EROIstnd
Fig. 1. Relative distribution of energy use by machinery in construction of various parts.
station amounts to 62,697 GJ. This shows that Gramelur is a minor part of the construction. The water pipe, and the steel within, which transfers cold water from 6 wells to Nesjavellir power plant amounts to the largest portion of embodied energy related to Gramelur pump station. 2.3.7. Embodied energy in the general plant This part was calculated to be the largest energy-consuming part. The energy used in the drilling and construction of the geothermal holes was the biggest factor in this part, using, when put together, a total of 134,648 GJ. No other part of this part amounted for such vast amount of energy. The construction of the station house followed, with the total amount of 36,044 GJ used. 2.4. Sum of embodied energy When the previously discussed parts have been added together, the total energy embodied (used in the production of the parts) in the construction materials amounts to 692,465 GJ. Fig. 2 further
As stated, the EROIstnd is the indirect and direct inputs to the plant, but only the energy output without delivery to the consumer. This is a good factor for comparison of energy sources since the plants may need more or less distances for transport of the energy. The distance might disadvantage some energy sources even though the source might have a relatively good EROI. In the case of Nesjavellir power plant, this will include the same inputs as before, but will exclude the mechanisms for delivering the energy. That is the pipe, which delivers the hot water, as well as the mechanisms for delivering the electricity, namely Nesjavallalina power lines 1 and 2. The input will be 779,931 GJ for the first year, which are the entire input factors summed up, plus the operational power usage. Table 3 shows the EROIstnd scenario over the lifetime of the plant. This scenario shows that the EROIstnd is around 33 over the lifetime of the plant. Fig. 3 explains the development of the EROIstnd over the lifetime. 3.2. EROI3,i With the knowledge compiled, the following calculation can be made from Equation (3). This includes the direct energy for the operation of the plant, as well as the indirect energy used for construction of materials and groundwork. EROI3,i also includes the direct energy output from the plant as well as the co-efficient energy output, which in this case is hot water. Summing all these Table 3 EROI results using various boundaries. Year
Output (GJ)
EROIstnd calculations 1 13,245,000 10 132,451,200 20 264,900,000 30 397,353,600 40 529,804,800 EROI3,i calculations 1 13,245,000 10 132,451,200 20 264,900,000 30 397,353,600 40 529,804,800 EROI3,i no hot water 1 3,784,000 10 37,840,000 20 75,680,000 30 113,520,000 40 151,360,000 EROIide calculations 1 33,112,000 10 331,120,000 20 662,240,000 30 993,360,000 40 1,324,480,000 Fig. 2. Relative distribution of embodied energy.
Input (GJ)
EROI
779,931 4,310,463 8,233,276 12,156,089 16,078,902
17.0 30.7 32.2 32.7 33.0
1,070,896 4,601,428 8,524,241 12,447,054 16,369,867
12.3 28.8 31.1 31.9 32.4
803,385 4,285,765 8,155,076 12,024,386 15,893,697
4.7 8.8 9.3 9.4 9.5
1,070,896 4,601,428 8,524,241 12,447,054 16,369,867
30.9 72.0 77.7 79.8 80.9
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
277
Fig. 3. Different EROI scenarios calculated for Nesjavellir power plant. The x-axis shows lifetime [years], the y-axis shows EROI values.
factors up, the plant reaches an EROI of 12.3. This however only describes the first year of energy production, where the annual energy output is 13,245,000 GJ. After the first year, 2% maintenance of original embodied energy will occur annually and operational usage is 12 MW of every 120 MW of electricity produced. This will therefore be calculated in the EROI of the plant. Table 3 shows the EROI for every 10 years, for 40 years, which is approximately the expected lifetime of the plant. One can therefore see that over the lifetime of the plant, the EROI will be just a little more than 32. It increases rapidly in the beginning but as times goes by and operational and maintenance costs increase, it levels off. This can be seen in Fig. 3 where the development of different EROIs as a function of lifetime is visualized. 3.3. EROI3,i scenario without hot water A vast amount of hot water is delivered from the plant, and the part, which has the largest embodied energy associated to it is the pipe, which delivers the hot water to the nearby city. It is therefore interesting to see how the plant would perform without the hot water production. The plant produces 300 MW equivalent of hot water of the 420 MW produced at the plant [15]. In this scenario, the plant only produces 120 MW of electricity since the hot water production is excluded but still uses the same amount of operation energy, the amount of energy embodied in Nesjavellir hot water pipe is however removed, as well as all other related activities such as groundwork in its construction. Table 3 shows the results from this scenario. This shows that the EROI levels off and stagnates at around 9. Hot water production therefore increases the efficiency at the plant more than threefold, where the EROI with the hot water production and associated energy costs and benefits is around 33. The development of the EROI is similar in this scenario as compared to the previous one, this can be observed in Fig. 3. 3.4. EROIide With the knowledge of the total input required to construct, maintain and operate Nesjavellir power plant over its lifetime, it is possible to estimate the EROIide as was described in Equation (4). The EROIide was found to be 30.9 for the first year. Table 3 shows the EROIide for the same intervals as the EROI3,i calculations show. The output was calculated using a steam table and data from Reykjavik Energy. The numbers provided in Table 3 show the EROI of the power plant if it was 100% efficient, which according to modern physics can never be achieved. It is illustrated that as before, the
EROIide increases rapidly the first decade, but then the increase slows down and stabilizes around 80, this can be seen in Fig. 3. This version of EROI assumes that the output power from the holes remains at the same level throughout the lifetime of the plant. 3.5. Energy payback time The energy payback time is the time it takes the power plant to produce the same amount of energy it originally took to construct the plant in the first place, factoring in maintenance and operational energy used over its lifetime. With all the knowledge needed to calculate the EROI scenarios calculated above, calculating the energy payback time is relatively straightforward. This was calculated using the same scenarios as were used in the previous EROI calculations. Table 4 shows the energy payback time of the plant, which is the time it takes the plant to reach the EROI of 1 in different scenarios. This shows that the EROIide has the shortest payback time, or approximately half a year when all energy expenditures over the lifetime where included. The scenario with no hot water production was found to have the longest energy payback. However, the EROIstnd and EROI3,i were found to have almost the same amount of energy payback time, or around 1 year and 3 months (1.21 and 1.23 years). Another method was also used to calculate the EPT, where consumption was put in real time sequence instead of counting total energy consumption over its lifetime. This method shows that under normal circumstances the EPT in the EROIstnd scenario is only a little less than 2 weeks and EROI3,i a little less than 3 weeks. Fig. 4 shows the different EPT if energy consumption is put in logical order. 3.6. Sensitivity analysis A sensitivity analysis was conducted, to see the effects if the uncertainty factors (own usage and maintenance) would change over time. Maintenance was increased up to 10% and own usage was increased by 10% as well as lowered by the same amount. The scenario used in the sensitivity analyses was the EROI3,i over 40 Table 4 Energy payback times depending on different EROI scenarios. Scenario
Output per year (GJ)
Input over 40 years (GJ)
EPT (years)
EROIstnd EROI3,i EROI3,i (no water) EROIide
13,245,000 13,245,000 3,784,000 33,112,000
16,078,902 16,369,867 15,902,196 16,369,867
1.21 1.23 4.2 0.49
278
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
Fig. 4. Energy payback time when energy consumption is put in logical order. The xaxis shows weeks, y-axis shows EROI values.
years time. The analysis shows that if maintenance remains at 2%, but the operational cost decreases by 10%, the EROI increases from 32.4 to 35.7. It also shows that if the operational cost increases by 10% from the current status the EROI decreases to 29.6. It was shown that if the operational cost remains as predicted (12 MW) but the maintenance cost increases up to 10% per year of the original energy cost, the EROI declines down to 28.6. However, in the worst-case scenario where the maintenance cost was 10% per year and the operational cost had increased by 10%, the EROI dropped down to 26.4. The sensitivity analysis is further depicted in Table 5. The equation used to modify these parameters is as follows:
EROI3;i ¼
EDout ðOpyÞ þ E þ ðEx39Þ
(5)
where EDout is the total output energy delivered to consumer over the lifetime of the plant, Op is the total operational energy usage, y is the percentage of the original embodied energy to be used as maintenance. E is the total embodied energy of the plant, x is the fraction of the embodied energy used for maintenance. 39 accounts for the years of maintenance over the 40 years lifetime of the plant. 4. Discussions This study calculated four EROI scenarios and the energy payback time of the Nesjavellir power plant. All the major parts of the power plant have been canvassed, and the embodied energy of these given parts calculated. A comparison of the results after the plants lifetime can be seen in Table 3. The energy required to operate the machinery in the general construction of the major parts was also calculated. However, it was found that the largest energy-consuming factor on a yearly basis was the plant itself, which consumed 12 MW. The EROIstnd was found to be 32 over a 40-year lifetime of the plant. The EROI3,i was found to be slightly lower, or 32.4 since it included the energy needed to transfer the electricity and hot water to Reykjavik. To see how much difference the hot water made, the EROI3,i was also calculated excluding the hot water production. This resulted in a much lower EROI of 9.5 over the lifetime of the plant. This clearly illustrates how the efficiency increases at the plant when hot water production is included. The EROI more than tripled. Table 5 The EROI results if energy consumption changes in the maintenance and operational phase. Own power usage
2%
5%
10%
10% Normal þ10%
35.7 32.4 29.6
33.8 30.8 28.3
31.1 28.6 26.4
A new concept was introduced to the literature in this study, EROIide, which calculates the EROI at the plant if the efficiency at site was 100%, as was explained in Chapter 2.1. The EROIide was calculated to be 80.9 over the 40-year lifetime of the plant. Fig. 3 further illustrates the differences between the EROI scenarios, clearly illustrating that the efficiency can be improved at the plant significantly, but only up to the limit that the EROIide indicates. The energy payback time was calculated to be 1.21 years in the EROIstnd scenario and 1.23 in the EROI3,i scenario, which is around 1 year and 3 months it would take the plant to produce the amount of energy it consumed to be constructed and used during its operational lifetime. The energy payback time was however only 6 months (0.49 year) for the EROIide scenario. The increase in efficiency when hot water is produced at the plant as well as electricity was demonstrated, where the energy payback time went from 4.2 years down to 1.23 years. The overall impact of the maintenance and operational factor can be observed in Fig. 5 where the operational cost in energy terms increases from year to year, as well as the maintenance cost. This can be observed by looking at the thickness of the bars, the fixed costs get narrower the further time passes, but the increasing costs get thicker (operation and maintenance). In the discussion around renewable energy, many of the options available are often considered to be energy sinks rather than energy sources [24]. EROI results, like presented in this paper show that the source studied provides more energy to society than it consumed over its lifetime [25]. The results from Nesjavellir geothermal power plant show that over the estimated 40-year lifetime, the Energy Return on Investment is around 33. The EROIstnd boundaries were used which allows this study to be compared to similar studies. It was demonstrated that production of hot water at the plant increased its efficiency dramatically, where the EROI would otherwise be around 9. This indicates that producers of such plants and policy makers should promote production of hot water at site if possible (and feasible). Interestingly it was found that the plant consumed a huge proportion of its own production, if this could be reduced the EROI would improve significantly. This paper further presented EROI ideal, a new concept which shows the upper limits an EROI of a given energy source, which is bound never to reach. EROIide can show decision makers, whether in the private or public sector, how much potential is for improvement at the source studied with regards to its efficiency. This knowledge can therefore encourage stakeholders to seek technological advancements since that would most likely result in economic profits. With the knowledge of the EROIide it is possible to see that the EROI can be improved by an EROI of approximately 50, up to an EROI of 80 at Nesjavellir. Transportation of materials to Iceland was, interestingly, shown to have a minimal effect on the results. Therefore, the isolation of the country should not be a barrier in constructions of this kind. By comparing this study to the one conducted by Gilliland in 1975 [11], one can see that the results are strikingly similar. The plant studied in the 70’s had only electricity as an energy output, and therefore the EROI scenario at Nesjavellir, which excluded hot water production, is suited for comparison to that study. The EROI’s provided by Gilliland were between 10 and 12, where Nesjavellir was around 9. Both studies might have some uncertainty in the calculations but the results show that the efficiency is around the same, or even less at Nesjavellir. This comes across as odd, since Gilliland’s study was conducted more than 40 years ago [11] and technological advancements in electricity production from geothermal power were expected to have increased the efficiency. These results show that they have however not. However, compared to Herendeen & Plant [6], who showed the EROI to be around 4, the EROI has improved, but only slightly with regards to electricity production. The EROI of
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
279
Fig. 5. Proportion of energy consumption from different parts of Nesjavellir geothermal power plant. The x-axis shows years.
33 when hot water is included at Nesjavellir proves to be relatively low compared to energy sources such as coal and hydro (with the EROI of approximately 80 and >100 respectively) [2,26]. Nesjavellir however scores a better EROI than oil (With a declining EROI from approximately 100 in the 30’s to approximately 11 in the mid 2000) [2,27,28], and Nuclear of around 10 [25,29]. If however hot water would not be produced at Nesjavellir, the EROI would be so low that it would score even less than oil and nuclear. This might be an indicator that geothermal power plants which do not produce other forms of energy (such as hot water for heating) have a relatively low EROI compared to most other energy sources. EROI does not consider parameters such as economical, social or environmental factors. It does however relate to all these parameters and can provide an insight to the efficiency of various energy sources. It has even been claimed that, “Energy Return on Investment is a powerful metric for weighing which energy systems are worth pursuing” [25]. A single number score, like the EROI provides, should however not be taken as the whole truth since there are, like mentioned, other factors to be included. A proposed standard was followed throughout the study. Instead of monetary data, real data was acquired directly from stakeholders, which allowed for a very precise analysis, except for the case of shipping. Shipping was however was shown to be almost irrelevant, even though the energy used in shipping doubled, it would not have reached 1% of the total energy consumption. As was the case with Gilliland’s research [11], the methodology put forward and used in this study should not be considered as a completed framework for conducting an EROI analysis. Since the field is relatively new, the methodology is under constant change. However, the attempt for a standard suggested by Murphy et al. [9] is relatively good and should allow for comparison between studies at present time. EROI research in the field of other renewable energy sources seems to have been left out to some extent. Oil and gas have been thoroughly studied, which results in a timeline of EROI’s where the efficiency or availability of the energy sources can be examined. It would therefore give a valuable insight to research other renewable sources like hydro, or even other geothermal plants so they can be compared and analyzed. Acknowledgments This research was supported by the Icelandic Energy Fund (Orkusjodur). Acknowledgments go to Reykjavik Energy hf, Landsnet hf and Efla Engineering hf for providing data.
Appendix A. Supplementary material Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.energy.2013.01.003. References [1] Hall CA. Introduction to special issue on new studies in EROI (energy return on investment). Sustainability 2011;3(10):1773e7. [2] Cleveland C. Net energy from the extraction of oil and gas in the United States. Energy 2005;30(5):769e82. [3] Hall CAS. Migration and metabolism in a temperate stram ecosystem. Ecology 1972;53:585e604. [4] Hall CAS. The biosphere, the industriosphere and their interactions. Bulletin of Atomic Scientists 1975;31:11e21. [5] Hall CAS. Petroleum drilling and production in the U.S.: yield per effort and net energy analysis. Science 1981;211:576e9. [6] Herendeen RA, Plant RL. Energy analysis of four geothermal technologies. Energy 1981;6(1):73e82. [7] Tyner Sr G, Costanza R, Fowler RG. The net-energy yield of nuclear power. Energy 1988;13(1):73e81. [8] Icerman L. Net energy production history of the geysers geothermal project. Energy 1980;5(1):29e33. [9] Murphy DJ, Hall CAS. Year in reviewdEROI or energy return on (energy) invested. Annals of the New York Academy of Sciences 2010;1185(1):102e18. [10] Mansure A. Are geothermal energy returns on investment high enough. In: Proceedings, Thirty-Sixth Workshop on Geothermal Reservoir Engineering; 2011. [11] Gilliland MW. Energy analysis and public policy. Science 1975;189(4208): 1051e6. [12] Murphy DJ, Hall CA, Dale M, Cleveland C. Order from chaos: a preliminary protocol for determining the EROI of fuels. Sustainability 2011;3(10):1888e907. [13] Cleveland C. Energy return on investment (EROI) [cited 17.05.2011]. URL, http://www.eoearth.org/article/Energy_return_on_investment_(EROI); 2008. [14] Mulder K, Hagens NJ. Energy return on investment: toward a consistent framework. Ambio 2008;37(2):74e9. [15] Nesjavallavirkjun (n.d.) [cited 02.02.2012]. URL http://www.or.is/UmOR/ Veiturogveitusvaedi/Virkjanir/Nesjavallavirkjun/. [16] Grid IE. Map of Nesjavellir and relevant power lines. Landsnet. [17] Rafnsson K. E-mail communication; 2012. [18] T K, Jonsdottir H. Life cycle analysis of Nesjavellir geothermal power plant. Tech. Rep.. Technological Institute of Iceland; 2008 [19] Eimskip, Siglingaaaetlun (n.d.) [cited 07.03.2012]. URL http://eimskip.is/IS/ Um-Eimskip/siglingar/default.html. [20] EHO/MAO, M/v Dettifoss datasheet. Tech. Rep., Eimskip (n.d.). [21] Energy units (n.d.) [cited 15.02.2012]. URL http://www.aps.org/policy/reports/ popa-reports/energy/units.cfm. [22] Linuhonnun. 132 kv nesjavallalina 1, bygging og rekstur. Tech. Rep.. Orkuveita Reykjavikur; 2002 [23] VGK. Nesjavallavirkjun afangi 4b stækkun rafstodvar ur 76 í 90 mw. Tech. Rep.. Orkuveita Reykjavíkur; 2000 [24] Gonçalves da Silva C. The fossil energy/climate change crunch: can we pin our hopes on new energy technologies? Energy 2010;35(3):1312e6. [25] Kreith F. Bang for the buck e energy return on investment is a powerful metric for weighing which energy systems are worth pursuing. Journal of Mechanical Engineering May 2012:26e31.
280
R.S. Atlason, R. Unnthorsson / Energy 51 (2013) 273e280
[26] Gagnon L, Belanger C, Uchiyama Y. Life-cycle assessment of electricity generation options: the status of research in year 2001. Energy Policy 2002; 30(14):1267. [27] Cleveland CJ. Energy quality and energy surplus in the extraction of fossil fuels in the U.S. Ecological Economics 1992;6(2):139e62.
[28] Guilford MC, Hall CA, O’Connor P, Cleveland CJ. A new long term assessment of energy return on investment (EROI) for U.S. oil and gas discovery and production. Sustainability 2011;3(10):1866e87. [29] Manfred L. Life cycle energy and greenhouse gas emissions of nuclear energy: a review. Energy Conversion and Management 2008;49(8):2178e99.