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Hydrogen production horizon using solar energy in Biskra, Algeria
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 4
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Hydrogen production horizon using solar energy in Biskra, Algeria A. Saadi a,*, M. Becherif b,**, H.S. Ramadan b,c a
University of Mohamed Kheider, Faculty of Engineering, Biskra, Algeria University of Bourgogne Franche-Comte/UTBM, FC Lab, FEMTOeST, 90010 Belfort Cedex, France c Zagazig University, Faculty of Engineering, 44519 Zagazig, Egypt b
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abstract
Article history:
This paper aims at studying the hydrogen production from solar energy available in Biskra
Received 22 February 2016
region in the east of Algeria by the Proton Exchange Membrane (PEM) electrolyzer. The
Received in revised form
electrolyzer is supplied by solar photovoltaic (PV) system. Three kinds of PV generator with
31 July 2016
rated power up to 6 kW are used for producing hydrogen. The PV panel characteristics are
Accepted 30 August 2016
experimentally validated. The instantaneous effects of temperature and solar radiation on
Available online xxx
PV characteristics are shown. Moreover, a comprehensive study is devoted to validate two different models for the areas solar radiation. The simulation results are compared to the
Keywords:
experimental measurements using statistical analysis. The solar radiation model on a
(PEM) electrolyzer
horizontal and on a tilted and oriented PV panel give sufficient results. The adequate
Hydrogen
agreement between the simulation results and the experimental data verifies the effec-
Photovoltaic panel
tiveness of the proposed models.
Solar radiation model
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Hydrogen, almost the cleanest fuel of the future, is considered the lightest, simplest and most plentiful of all chemical elements in the universe. It can be a source of new and renewable/new energy. In comparison with other options, it is an ideal candidate as a clean energy carrier particularly for both transportation and stationary applications in favor of its less pollution, better urban air quality of near-zero carbon, besides minimum hydrocarbon, GHG and NOx emissions. Owing to its excellent energy storage capacity, hydrogen can be used for solving the problem of electric power stored in the batteries, application of vehicles, computers and mobiles. Therefore, it can present an affordable alternative for the potential shaping
of the future global energy markets. Long term hydrogen production using Renewable Energy (RE) is among the environmentally benign methods in both energy and transport sectors. The future energy economy will consist of many diversified and combined RE technologies based on photovoltaic cells, wind, hydro and geothermal, etc. Hydrogen, as one of the most powerful fuels, can be extracted from steam reforming natural gas, coal, nuclear power, biofuels or even waste products through the process of electrolysis [1]. The hydrogen can be used either for storing or generating electricity in power systems as shown in Fig. 1 [2,3]. As the electrolyzer model shown in Fig. 1 is not suitable for the efficiency analysis of the studied system, the model of the
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (A. Saadi), [email protected] (M. Becherif). http://dx.doi.org/10.1016/j.ijhydene.2016.08.224 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
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Fig. 1 e Hydrogen storage/production in power systems.
electrolyzer presented by Khan and Iqbal [4] is used where the voltage is involved and validated at a standard temperature. Among the different electrolyzers introduced in the literature [5e9], the study mainly focuses on hydrogen production in Biskra region of Algeria from solar panels where a simple electrolyzer model is adequate. In order to successfully have a society based upon RE, a way to store such intermittent RE from both solar and wind energy are excellent methods of obtaining energy from natural resources [10]. However, the levels of sunshine, and the intensity of wind varies. When these sources are not available electricity cannot be generated. When a large amount of energy is being produced, hydrogen can be created from water then stored for later use. The electrolysis of water is a mature technology that can be developed for efficient hydrogen production. However, large amounts of electricity is required. Therefore, solar or wind energy can be properly used for producing the necessary electricity for releasing hydrogen [11]. Most regions of Algeria receive an enormous amount of solar radiation like other Mediterranean countries. Hence, solar technology can be applied and utilized in these countries. Only few stations measure the daily solar radiation on consistent basis. In the absence and/or shortage of reliable solar radiation data, it is necessary to estimate solar radiation using the models in order to predict the global solar radiation in the area under study [12]. The main contribution of this study is verifying theoretically the possibility of producing hydrogen from solar energy production in Biskra region of Algeria. The experimental validation of two different models on a horizontal and on a tilted surface are performed in order to clarify the importance of considering the hydrogen production from solar energy as a horizon potential for regions of similar geographical characteristics. The rest of paper is organized as follows: A brief description of Biskra area is given in Section Biskra area at first. In the second, a description presentation of test bench is introduced in Section test bench description. After, solar radiation is described in Section solar radiation. Then, a presentation of
solar radiation models is exhibited in Section modeling of solar radiation. The experimental study of PV panel is presented in Section PV panel. And Modeling of electrolyzer is described in Section electrolyzer. Finally the concluding remarks and perspectives are stated in Section conclusion.
Biskra area Bordering on the Mediterranean Sea, Algeria lies in the northwest of Africa between the Sahel countries in the south, Western Sahara and Morocco in the west, Tunisia and Libya in the east. It is located between the 18 and 38 of North latitude and between meridians 9 of West longitude and 12 of East longitude. It covers an area of about 2,381,741 km2 Its coastal line on the Mediterranean sea extends over about 1200 km and the aerial space stretches out southward on 1800 km as far as the tropic of cancer [13]. The Algerian population is around 38.5 million citizen, including 849 672 people in Biskra area, according to the statistics in 2014 [14]. More than 50% of the population are young, less than 19 years old. The population is not well distributed; more than 60% live on the coastal area. The population growth and the rapid urbanization have a considerable impact on the demand for energy and the environment [13]. Algeria is the leading natural gas producer in Africa, the second-largest natural gas supplier to Europe outside of the region, and is among the top three oil producers in Africa [15]. Oil occupies an important place in the country's economic development. The total energy consumption of Algeria in 2012 was about 50.9 million Tons of Oil Equivalents (TOE) and should increase to 91.54 million TOE in 2030 [15]. The revolution in RE (wind and solar power) in terms of technological development and costs may help to reduce the consumption of fossil fuels. It encourages the use of RE. Within the framework of the national RE program development and energy efficiency in Algeria, Sonelgaz company has carried out many projects of electricity production based on wind and solar energy to power the isolated villages and
Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 4
remote houses of south Algeria. By 2030, a share of RE in the national energy between 30% and 40% should be reached. The share of renewable power by 2023 will represent about 17% of installed capacity (5539 MW) compared to 4.74% in 2011 (540 MW) [15]. By its position in the heart of the Sun Belt, Algeria enjoys both qualitative and quantitative important solar energy potential. Going from north to south, the country presents significant variations in its topographic, climatic and socioeconomic characteristics. Biskra city has a strategic position because it connects the north and south, it harbors full of joyful whose north rocky and mountainous as the Aures and south and east the Sahara desert, and full of magnificent oasis round. It covers an area of about 21 509.80 km2. It is thus one of the largest southern states [14]. Biskra site characterized by a hot, dust and dry climate as shown in Fig. 2. The city of Biskra is situated at latitude 34 480 North and longitude 5 440 east, its elevation is above 85 m sea level, atmospheric pressure at this Bar height is 1.004. The city is characterized by very high monthly average solar radiation throughout the year [16]. In Ref. [17], the global solar irradiation at different Algerian locations (Algiers, Oran, Bechar and Tamanrasset) using the available climatological measured data has been studied. Biskra region, that is considered as a north-south connection zone in Algeria, has at least similar characteristics to such areas. Owing to its special climate and annual solar irradiation, Biskra region specimen is proposed for hydrogen energy production in this study. Biskra is a town rich of a wide range of natural resources like biomass, solar and wind energy and water for electrolysis. This will offer the area a full range of options for the development of a hydrogen industry. If the Sahara is the driest region in the world, it contains nonetheless a huge underground aquifer. Stretching from west of Libya and Tunisia to Adrar and Biskra, and from Laghouat to Illizi, this aquifer covers an area of 800,000 km2. Reserves are estimated at 6.1013 m3. Furthermore, the water used in the electrolysis could be taken from
3
different sources [13]. The aquifer, one of the largest sequestration and storage fields could be used. Biskra is the main natural compound surface water in the region. It is characterized by surface, groundwater and famous by the thermal spa [18]. The water quantity available in Biskra estimated 1017 million m3, of which 22 million m3 any surface water 2.16%, and 995 million m3 of underground water, an increase of 97.84%. The total area of agricultural is about 1,652,751 ha or approximately 77% of the total area of the state. Basic agricultural wealth is palm around 4286 354 date-palm. The total area of nature forest is 97,729 ha. It represents only 4.54% of total area. There are two dams, the first one «Foum-ElGhorza on the Oued El-Abiod with initial storage capacity is estimated at 47 million m3. A second dam, “Fountains of Gazelles” in El Oued Hai, the annual mean input of wadis crossed is estimated at 41,106 m3 (21,106 m3 and 20,106 m3) [19] Modeling of underground, Ouerdachi. The region is available on the important energy network, covered in four lines of electric power of 220 kVA. In the future, the hydrogen could join electricity as an important energy carrier. An energy carrier moves and delivers energy in a usable form to consumers. Hydrogen's potential production from RE resources such as solar, wind, geothermal energy, hydrogen production from oil palms biomass as a potential source became vital. The sun and wind can not produce energy all the time. They could produce electric energy and hydrogen which can be stored when needed. Hydrogen can also be transported like electricity to locations where it is needed [20]. The transport of hydrogen towards potential national and international consumers could be insured via the existing dense of pipeline network [21]. Prospect of geothermal energy use for hydrogen production is good, particularly for the supply of heat, through the hot water, for high temperature electrolysis. Efficiency of electrolysis systems can be improved by operating at high temperature. This reduces the energy needed to activate the electrolysis process. It has been suggested that heat could be obtained from geothermal sources [22].
Test bench description To achieve the paper goal, a simple and reliable PV panel test bench of Fig. 3 is performed, with acceptable accuracy for achieving the experimental performance of the PV generator in the climatic conditions of the region. PV generator 1: SUNTECH 190W Monocrystalline Solar Module (STP 190S-24/Adþ) of high conversion efficiency (up to 14.9%), is structure of test bench test built in Fig. 3a.
Fig. 2 e Solar radiation in Algeria.
The module can be moved and oriented to receive a solar irradiation and change the angle of inclination according to the dimensions as shown in Fig. 3b. Devices are required as a solar pyranometer, anemometer, thermometer and Compass. According to this test bench, experimental tests are verified and then explained. The obtained data distinguish the PV array installed on the site of the Faculty of Science and Technology of the University of Biskra. The PV panel presents a basic element of exist generator systems feeding several
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Fig. 3 e Structure test bench of PV panel.
loads such as lamps, batteries and motors, through DC/DC converters and DC/AC controllers and regulators. Some PV systems are supported by “tracking” technology. It is possible to orient the modules according to angle and orientation of the sun during the year. Two of them available: two-axis tracker and a fixed system.
with two axes is six panels (3 series and 2 parallel) supplying a small water pump. PV generator 3: The PV generator is installed to have fixed inclined array by an angle of 45 and oriented (South). 8 individual PV modules are connected in series and 4 panels are in parallel.
PV generator 2: When productivity is sought, the tracker systems should be moved to improve performance, but they have low wind resistance. PV generator for tracker
Fig. 4a shows the incident variation of solar flux irradiation on the PV panel. In order to achieve the maximum energy yield of the PV system, the modules will be mounted towards
Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
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Fig. 4 e Experimental characteristics based on Tilt angle. south with an optimal tilt angle [23]. After several experimental tests on the site, have been concluded, the optimum depends on the sun height and the annual distribution of irradiation. For this area, the adequate tilt angle is between 30 and 50 . During the year, the optimum is approximately 34.8 . The PV panel efficiency is the ratio between the energy supplied and the incident light energy. In practice, the performance of the solar module is always less than that of a cell. The associated cells result in adaptation losses, as shown in Fig. 4b. The average efficiency is about 13% South.
Solar radiation Solar energy is a sustainable, safe and abundant energy resource. Estimating solar irradiation incident on inclined surfaces of various orientations is necessary for PV applications. The total radiation incident on a tilted plane consists of three components: beam radiation, diffuse radiation and reflected radiation from the ground. The beam component can
be calculated by the ratio of the incidence angle to the solar zenith angle. The reflected component has a small effect on calculations and may be calculated with an isotropic model. In contrast, models for estimating the diffuse component show major differences. There are a lot of models have justified the interest in this field, twelve of them studied in Ref. [24]. Previous studies have shown many mathematical methods for the relation between the solar radiation on an inclined surface and on the horizontal plane with different accuracies. The trajectory of the Earth around the Sun is an ellipse with the Sun at one of the focus. The mean Earth-Sun distance varies from 144 million Km (21 December) to 154 million km (21 June). The solstices and equinoxes divide the year up into four approximately equal parts. In the northern hemisphere winter solstice occurs on about December 21, summer solstice is near June 21, spring equinox is around March 20 and autumnal equinox is about September 23. Therefore, the measurements shown in Fig. 5a and Fig. 5 have been taken into special days. On Friday, March 20, 2015 the three phenomena passed on Earth; the equinox, the sun
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Fig. 5 e Solar radiation incident for different measurement days.
eclipse and the supermoon. The region is exposed to a partial eclipse. The weather was very windy and cloudy. The solar radiation was very weak. Very low temperatures were measured the moment of the eclipse and obscured the sun shown in Fig. 6a. Natural changes in climate such as heating due to volcanic activity, radiation from the sun, and changes in the chemistry of the atmosphere sometimes take thousands of years to change only 1 C. Nowadays, because of pollution, the earth temperature is increasing which is confirmed in Fig. 6a. In this area, hot days have become more frequent, than the cold days which become less severe. The temperature reaching 47 C in the month of May and it is not cold at all in the winter. The temperature is an important factor for the implementation of systems using RE. The temperature affects on both the PV panel and the electrolysis.
Modeling of solar radiation Modeling of solar radiation provides an understanding of its dynamics which is of great interest in the design of solar energy conversion systems. The method for the calculation of the solar
irradiance on a surface with any orientation and tilt is not accurate enough because of the sky isotropic consideration. In order to account for the sky cloudy clear periods, it's necessary to calculate the mean hourly, daily, monthly values. The daily radiation has to be considered instead of the instantaneous irradiance. Then its monthly values can be obtained as the average of irradiances for each day of the month [25]. In order to determine the angle of incidence of the sun rays on a surface, the following parameters should be known: the latitude of the site L, the position of the sun through u and d, the tilt angle b of the surface on the horizon and the azimuth of the surface g that is the angle calculated on the horizontal plane between the projection of the surface normal to the to the horizontal plane and the south direction. d (degrees) is the solar declination that can be calculated by the approximate formula [26]. The angle of declination is given by: d ¼ 23:45sin ½0:980ðj þ 284Þ
(1)
where j is the day number of the year, j ranges from 1 (1st January) to 365, or 366 in case of a leap year, when precision is required [27]. The Developing Fourier series can be considered, then:
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Fig. 6 e Annual temperature and ET time.
With: J ¼ 0:984*j
ET ¼ 0:0072*cosJ 0:0528*cos2J 0:0012*cos3J 0:1229*sinJ 0:1565*sin2J 0:0041*sin3J
d ¼ 0:33281 22:984cosJ 0:3499cos2J 0:1398cos3J þ 3:7872sinJ þ 0:03205sin2J þ 0:07187sin3J
The orbit of the earth an ellipse. Thus, the earth's angular speed varies slightly throughout the year [27]. Combined with the regular rotation of the earth about itself, the sun does not reach its highest position in the sky named the solar noon at 12h mean solar time (MST) every day. The time of solar noon may differ from 12 h MST by up to 17 min. The time determined every day by the actual position of the sun in the sky is called true solar time (TST), or local apparent time. The difference between TST and MST called “equation time (ET)” is defined as: ET ¼ 360=24ðTST 12Þ
where, J ¼ 0:984*j , and j is the day number of the year. The evolution of both the solar declination and the time equation during the year are shown in Fig. 6b. The equation time is the variation of the difference between MST and TST as a function of the day in the year is depicted. The maximum variation is reached on 31st October of about 15.67 s. The minimum variation is equal to 13.79 s on 13th February. (h) is the height of the sun in degrees, can be calculated by: sinh ¼ sinL$sind þ cosL$cosd$cosu
(6)
(3)
u: is the hour angle of the sun in degrees. The calculation of the solar angle at sunrise (-u) and sunset (u) is obtained by proposing sinh ¼ 0, then:
(4)
cosu ¼ tgd$tgL
TST in (hours) is determined by: TST ¼ MST ET
(5)
(2)
ET that refers to the time uniform rotation of the earth around the sun is given by Ref. [27]:
(7)
The solar time at sunrise and sunset (tSR and tSS ) respectively will be:
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tSR ¼ 12 þ
u 15
(8)
tSS ¼ 12
u 15
(9)
The day length d in hours is: d ¼ ðu ð uÞÞ=15 ¼ 2$u=15
(10)
The component of the diffuse radiation on an inclined plane Dc(b) is given by: Dc ðbÞ ¼ Dh
1 þ cosð b Þ 2
(19)
where Dh is the diffused solar radiation.
Solar radiation model on a horizontal PV panel The total radiation received on the horizontal is a summation of the direct and diffuse radiation. Gh ¼ Ih $sinh þ Dh
(11)
where: Ih is a direct radiation, calculated by: Ih ¼ A$exp
1 B$sinðh þ CÞ
(12)
Dh is a diffuse solar radiation expressed as: Dh ¼ D$sinh0:4
(13)
A, B, C and D parameters depend to the kind of sky. Selecting throughout the year, a number of types of clear weather days, where the energy distribution has asymmetry axis located 12 h and true solar time. The global illumination can be obtained directly from: Gh ¼ E$ sinhF
(14)
From the experimental values of Gh, Equation (14) can present best possible variations where E and F values are determined by the least squares method through the following linear: logGh ¼ logðEÞ þ F$logðsinhÞ
(15)
f0 ¼ logGh , the linear slope fit can then be beAssuming G tween (F) and (log E).
Solar radiation model on a tilted and oriented PV panel The solar radiation is the sum of three components: beam radiation, diffuse radiation by the sky and diffuse reflected by the ground (albedo) r. Global solar radiation is the sum of the direct, refracted and diffuse solar radiation [28]. It can be calculated by: Gi ¼ Rd ðbÞ þ Dc ðbÞ þ Ds ðbÞ
(16)
The direct radiation component is given by: Rd ¼ Ih $Rb
(17)
where Rb is the inclination factor, estimated by: Rb ¼
cosðL bÞ $cosd cosu þ sinðL bÞ$sind cosL cosd cosu þ sinL sind
(18)
where b is tilted angle. L is the latitude of the site. d is declination angle. It is the angle between earth-sun line and the equatorial plane.
Fig. 7 e Simulation/experimental results of solar radiation models.
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The ground reflected components Dc ðbÞ of solar radiation
Statistical analysis
is: Ds ðbÞ ¼ Gh
1 cosð b Þ $r 2
(20)
where r is the foreground's albedo and Gh is the global illumination. To validate the propose model, Matlab™ simulations are used for designing all days programs. From each of these programs, for the diagrams, curves representative of the measured and estimated values are prepared by the proposed model. The data of the global solar radiation are measured w/m2. The data is collected for the period of December 2014 to May 2015. The time of recording was often between 5 min and 10 min. The simulation results provide the evolution of the solar radiation on a horizontal and tilted PV panel depending on climatic conditions and for the days shown in Fig. 7. Fig. 7(a) and (b) are two different cases in December 22 and February 18, to present different seasons (winter and spring). Clearly, the graph that the values of the amount of solar radiation are the least possible during the first daylight hours in December. It is due to the different position of the sun relative to the earth's surface. Day grow taller in summer. Experimental values of solar radiation prove that, the middle of day is not at 12 pm. The radiation is not symmetrical contrary to what the proposed models assume. That causes a small difference between the measured results and proposed models. In May, the solar radiation incident on horizontal and tilted surface has the same value. However in December, solar radiation on tilted PV panel is twice the value of solar radiation on a horizontal PV panel. Starting from spring, the maximum value of solar radiation higher than 1000 w/m2. In the winter, this value becomes less as shown in Fig. 7 (b) and (c) respectively. According to Fig. 7 (a) and (c), the model on a horizontal PV panel gives good results for clear and bit cloudy sky. The results indicate that the model on a tilted PV panel favorably with the observed values in the whole seasons. The reasonable discrepancy between the model and experimental results is because of the sky condition at the measurement. Obviously, better results are found for clearer sky. The use of high digital programs to record measurements permits the negative impact of different several factors such as: the dispersion of solar radiation, wind, steam, air humidity, dust, reflective quality of the ground solar radiation in addition to the pollution and global warming influence.
In this study, the performance of the models is evaluated using the different statistical errors or indicators such as: the percentage error (PE), absolute percentage error (APE), mean bias error (MBE), and root-mean-square error (RMSE) defined as [29]: Pn PE ¼
ðx xm Þ Pn i¼1 x
i¼1
Pn APE ¼
MBE ¼
(21)
jx xm j Pn i¼1 x
(22)
n 1 X $ ðx xm Þ n i¼1
(23)
i¼1
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Pn 2 i¼1 ðX Xm Þ RMSE ¼ n
(24)
where x and xm are the ith calculated and measured values on a tilted surface respectively. n is the total number of observations for a specific period of time. The Percentage Error (PE) is the relative error between the x and xm values shown as a percentage. APE is the absolute value of the PE. The MBE values give information about the long-term model performance. A small MBE value is a desired condition. A negative and positive value refers to underestimation and overestimation respectively. The RMSE determines the model's accuracy by comparing the deviation between the predicted/ calculated and measured values. The RMSE values, which are always positive, denote information about the model shortterm performance. A smaller value indicates better model performance while zero represents the ideal case [30,31]. Table 1 summarizes the statistical errors (PE, APE, MBE and RMSE), which are calculated using Equations (25)e(28). It shows those statistics associated with the results of Fig. 7. From Table 1, the PE, APE, MPE and RMSE are estimated in four different dates for two solar radiation models (horizontal and inclined surface). The results show that the maximum RE and APE values are 17.46% and 24.34% at February 18th, 2015 for the inclined surface model. The minimum RMSE value 94.75 W/m2 results at March 22nd, 2015 for the horizontal surface model. The errors are acceptable. The results, in general, shows adequate agreement between both models under different sky conditions. The high values is due to the
Table 1 e Statistics errors of solar radiation models. Solar radiation model Horizontal surface
Inclined surface
Date
PE (%)
APE (%)
MBE (W/m2)
RMSE (W/m2)
December 22nd, 2014 February 18th, 2015 March 22nd, 2015 May 6th, 2015 December 22nd, 2014 February 18th, 2015 March 22nd, 2015 May 6th, 2015
12.40 11.60 3.16 12.92 0.52 4.36 17.46 0.08
23.38 19.08 14.40 17.82 16.16 11.66 24.34 11.35
44.69 98.82 77.19 153.02 99.02 32.40 150.91 99.14
105.41 125.75 94.75 181.18 151.33 112.54 186.48 121.68
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Fig. 8 e Experimental characteristics of the PV panel.
measurement equipment and manual measure's operator. In addition, the limited number of experimental tests negatively affects on the results.
PV panel PV panels capture the sun's energy using photovoltaic cells. These cells do not need direct sunlight to work. Electricity may be generated during cloudy days. Algeria is characterized by its good geographical situation, it receives important quantity of solar radiation during the years and seasons [32]. The application of the PV systems becomes more important
Fig. 10 e Effect of temperature on the PV panel characteristics.
practically for isolated areas and local to extend domestic level. Being a semiconductor device, the PV system is static, quiet, free of moving parts, and has little operation and maintenance costs. The main characteristics of the PV module are shown in Fig. 8 and Fig. 9 respectively. The IeV output characteristic of a PV module is highly non-linear. The output characteristics of the panel depend on the solar radiation and the ambient temperature. The IeV curve of PV panel has three important points: the short circuit (0, Isc), the open circuit (Voc, 0) and the maximum power (Pmpp1, Pmpp2 and Pmpp3). The points M1, M2 and M3 respectively represent with optimal voltage and current (Vmp, Impp) at different conditions. In Fig. 8, the IeV output characteristics duration of PV panel is 20 min. The starting solar radiation is about 701 w/m2 at fixed temperature of about 36 C. After 10 min the value of solar radiation rised to 805 w/m2. This increase lead to an increase in both; current and voltage outputs. These results increase in
Fig. 9 e Instantaneous variation of solar radiation and temperature on PV panel.
Fig. 11 e One-diode equivalent circuit for a PV panel.
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Table 2 e Photovoltaic panel specification. Parameter
Pmax
Vmp
Imp
Voc
Isc
Rs
M
Value
190w
5.2
36.6
45.2
5.62
0.11
1.54
power output. The temperature influences on the characteristics of PV panel. The power decreases if the temperature increases more than 25 C. The instantaneous effect of these parameters are shown in Fig. 9a and b [33]. As the RE systems are non-linear power sources by nature; the Wind, the PV generator and the Proton Exchange Membrane Fuel Cell (PEMFC) need accurate on-line identification of the optimal operating point [34,35]. The power generated by PV panel depends on environmental factors such as solar radiation and cell temperature. The direct link with a load often forced the system to operate very low. Aiming at optimizing such systems to ensure optimal functioning of the unit; modern control approaches based on Genetic Algorithm (GA), Artificial Neural Network (ANN) and Fuzzy Logic (FL) have proposed in Ref. [34]. Various MPPT control techniques in Ref. [32] have been presented in order to ameliorate the PV efficiency and to maximize the energy captured by the PV panel. For producing an adequate quantity of solar hydrogen, the electrolysis are supplied with
11
an optimal current, voltage and power as shown in Fig. 9a and b. However, 13% of global solar radiation incidents on PV panel can be exploited. The boost DC/DC converter is used mainly for permitting a maximum power tracking of PV panel and to increase the PV voltage to be compatible with the electrolyzer. The effect of temperature and irradiance is studied using the test bench PV panel. The solar radiation has three values around 910 W/m2, and the temperature increases from 25 C to 47 C. Fig. 10 (a) illustrates the currentevoltage (IeV) characteristics of the PV panel. It can be clearly observed that the open-circuit voltage (Voc) decreases with the temperature rise. The short circuit current (Isc) has a proportional relation with the temperature in both cases. Fig. 10 (b) illustrates the powerevoltage (PeV) characteristics where the negative influences of the temperature influences on the power provided by the PV panel are depicted.
PV panel modeling Single diode equivalent circuit of PV panel in both ideal and practical cases is given in Fig. 11 [36]. In this paper, the practical PV panel model is analyzed where the relation between the output current I and voltage V is defined as: I ¼ Iph ID Ish
(25)
Fig. 12 e Comparison between the experimental data and the model results. Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
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where Iph is the irradiance current (photocurrent) (A), which is proportional to solar radiation. ID is the current of diode (A). Ish is the current of parallel resistor (A) such that:
ID ¼ I0 e
Ish ¼
q
Vþ Rs I m K T
!
1
(26)
V þ Rs I Rsh
(27)
For the PV panel, the output current is given by:
q
I ¼ Iph I0 e
Vþ Rs I m K T
! 1
V þ Rs I Rsh
The production rate of hydrogen mH2 in an electrolyzer cell is directly proportional to the transfer rate of electrons at the electrodes, which in turn equivalent to the electrical current in the circuit, then: mH2 ¼
hF N ie 2F
where ie is the electrolyzer current, N is the number of electrolyzer cells in series, F is the faraday constant and hF is the Faraday efficiency, the ratio between the actual and theoretical maximum amount of hydrogen produced in the electrolyzer can be [4,40].
(28) hF ¼ 96:5 exp
I0 is the cell reverse saturation current (diode saturation current), q is the electron charge q ¼ 1:602 1019 C, m is the cell ideality factor, k is the Boltzmann constant k ¼ 1:3806503 1023 J=K T is the cell temperature; Rs and Rsh represent the cell series and shunt resistance, respectively [37]. Datasheet values are given at Standard Test Conditions (STC). STC means irradiation level is 1000 W/m2, with a panel temperature of 25 C and air mass of 1.5 solar spectral irradiance distributions [38]. Different methods in literature have been studied to identify the one-diode model for PV modules either by introducing simplifications/approximations techniques or by considering suitable data interpolations/experimental from the panel characteristic curves [38]. The PV panel is used defined block in MATLABTM/Simulink. The circuit based simulation model for a PV cell for estimating the IV characteristic curves of the PV panel with respect to changes on environmental parameters (temperature and solar radiation) and cell parameters (parasitic resistance and ideality factor) [39]. The study based on the use of measurements and specific fitting procedure for finding Rs and m ideality factor value using the parameters given in Table 2. Using sufficient experimental data leads to obtaining better fitness by the optimum values of the parameters. The comparison between the simulation results and the experimental curves is presented in Fig. 12 through the nonlinear IeV and PeV characteristic curves respectively. The model calculates the points with acceptable accuracy under any temperature and solar radiation values.
(30)
0:09 75:5 2 ie ie
! (31)
On a daily period te is the duration for which the electrolyzer will produce the quantity of hydrogen QH2 , therefore: QH2 ¼ mH2 te
(32)
Equations (31) and (33) represent the simple electrolyzer model are used for the electrolyzer system design via MATLAB™/Simulink. In Equation (30), the ideal electrolyzer is considered although several research works have indicated that the quality of produced H2 depends on the magnitude of the current used during the process [4]. This confirms the importance and originality of the paper idea. As the use of solar panels particularly provides very high electric currents,
Electrolyzer The water electrolysis operation is an electrolytic process which decomposes water H2 O molecule into oxygen O2 and hydrogen H2 gases by applying a DC voltage PV panel. Protons flow through the PEM membrane from the anode to the cathode while the electrons move to the cathode via the outer electrical circuit. At the cathode, hydrogen is formed by the recombination of electrons and protons [8,9]. The overall chemical reaction of water electrolysis is given by: H2 O þ electricity/2H2 þ O2 þ heat
(29)
Fig. 13 e (a) Electrolyzer hydrogen according to the current, (b) flow hydrogen production by 3 PV generators during 1 day.
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the solar energy lost per day can be properly stored in hydrogen form in certain areas. Thereafter, the Fuel Cell (FC) can be used to generate energy from the stored Hydrogen [41]. Fig. 13a shows the production of hydrogen (mol/s) to the change in current provided by the PV panel assuming that, the molar volume of an ideal gas measured in normal conditions of pressure and temperature is Vm ¼ 22.4 L/mol. Fig. 13 illustrates the production of hydrogen by (m3/s). Notably, the average solar radiation is about 900 w/m2 over five hours of the day, (between 10:00 to 15:00). The three PV generators produce maximum powers to the PEM electrolyzer which is sized for each generator. The hydrogen flow by three PV generators is shown in Fig. 13b.
[6]
[7]
[8]
[9]
Conclusion The two proposed models take into account several climatic parameters (humidity of the site, slope of the collector, latitude of the city, longitude). It is possible to determine the various solar radiations: total, diffuse and direct receipt by a horizontal or a tilted surface and orientation. The models present solar radiation with an adequate accuracy. According to the simulation results, the model on a horizontal surface is best suited to a clear sky. The three PV generators are chosen to feed the electrolyzer. The PV panel test bench structured can achieve several experiments and the hydrogen flow is satisfactory. Incident solar radiation can be used for producing hydrogen. The dates residue is the most significant resources of feedstock for hydrogen production by biomass. Heat and water are the feedstock for hydrogen producing by electrolysis using solar energy and wind. Therefore, Biskra can be proposed an appropriate region for hydrogen production, not only in Algeria but also in North Africa contrites. The Production of hydrogen can be a great perspective in Biskra area. In the forthcoming research, the authors will study the techno-economic impact of the different electrolyzer modeling on Hydrogen production in Biskra region of Algeria. The Maximum Power Point Tracking (MPPT) will be experimentally implemented to maximize the captured energy for feeding the electrolyzer.
references
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[27] Blanco J, Malato S. Solar energy conversion and photoenergy system - volume I. EOLSS Publications; 2009. [28] Yang D. Solar radiation on inclined surfaces: corrections and benchmarks. Sol Energy 2016;136:288e302. [29] Xie Y, Sengupta M, Dudhia J. A fast all-sky radiation model for solar applications (FARMS): Algorithm and performance evaluation. Sol Energy 2016;135:435e45. [30] Mohammadi K, Shamshirband S, Kamsin A, Lai PC, Mansor Z. Identifying the most significant input parameters for predicting global solar radiation using an ANFIS selection procedure. Renew Sustain Energy Rev 2016;63:423e34. [31] Hassan GE, Youssef ME, Mohamed ZE, Ali MA, Hanafy AA. New temperature-based models for predicting global solar radiation. Appl Energy 2016;179:437e50. [32] Saadi A, Moussi A. Optimisation of chopping ratio of backboost converter by MPPT technique with a variable reference voltage applied to the photovoltaic water pumping system. IEEE Ind Electron 2010;3:1716e20. [33] Saadi A, Moussi A. Optimisation of back-boost converter by MPPT technique with a variable reference voltage applied to photovoltaic water pumping system under variable weather conditions. Asian J Inf Technol 2007;6(2):222e9. [34] Becherif M, Hissel D. MPPT of a PEMFC based on air supply control of the motocompressor group. Int J Hydrogen Energy 2010;35(22):12521e30. [35] Tabanjat A, Becherif M, Hissel D. Reconfiguration solution for shaded PV panels using switching control. Renew Energy 2015;82:4e13. [36] Khalilnejad A, Abbaspour A, Sarwat AI. Multi-level optimization approach for directly coupled photovoltaicelectrolyser system, vol. 41; 2016. p. 11884e94. [37] Bandou F, Hadj Arab A, Belkaid MS, Logerais PO, Riou O, Charki A. Evaluation performance of photovoltaic modules after a long time operation in Saharan environment. Int J Hydrogen Energy 2015;40:13839e48. [38] Yildiran N, Tacer E. Identification of photovoltaic cell single diode discrete model parameters based on datasheet values. Sol Energy 2016;127:175e83. [39] Laudani A, Fulginei FR, Salvini A. Identification of the onediode model for photovoltaic modules from datasheet values. Sol Energy 2014;108:432e46. [40] Pachauri RK, Chauhan YK. Hydrogen generation/pressure enhancement using FC and ANN based MPPT Assisted PV system. IEEE conference on computational intelligence on power, energy and controls with their impact on humanity (CIPECH), pp. 427e432, 2014. [41] Brahim Laoun B, Khellaf A, Naceur MW, Kannan AM. Modeling of solar photovoltaic-polymer electrolyte
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Nomenclature d: Length day, hour Dh: Diffuse solar radiation, w/m2 ET: Equation time, hour F: Faraday constant Gh: Total radiation received on the horizontal surface, w/m2 Gi: Total radiation received on the tilted surface, w/m2 h: Height of the sun, deg ie: Electrolyzer current, A I: PV panel current, A ID: Current of diode, A Ih: Direct radiation, w/m2 I0: Diode saturation current, A Iph: Photocurrent, A Isc: Short circuit current, A Ish: Current of parallel resistor, A j: day number of the year k: Boltzmann constant, J/K L: Latitude of the site and positive for the northern hemisphere, deg. m: Ideality factor mH2 : Hydrogen production rate, mol/s MST: Mean solar time, hours N: Number series electrolyzer cells q: Electron charge, C QH2 : Hydrogen flow, m3/s Rb: Ratio of the daily direct solar radiation incident on a tilted surface to that on a horizontal surface Rd: Ratio of the daily diffuse solar radiation incident on a tilted surface to that on a horizontal surface Rs: Cell series resistance, U Rsh: Cell shunt resistance, U T: Cell temperature, C TST: True solar time of the study site, hours tSR : Sunrise solar time, hours tSS : Sunset solar time, hours V: PV panel, V Voc: Open-circuit voltage, V u: Solar hour angle, deg b: Tilt angle, deg d: Solar declination, deg g: Azimuth of the surface hF: Faraday efficiency
Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Hydrogen production horizon using solar energy in Biskra, Algeria A. Saadi a,*, M. Becherif b,**, H.S. Ramadan b,c a
University of Mohamed Kheider, Faculty of Engineering, Biskra, Algeria University of Bourgogne Franche-Comte/UTBM, FC Lab, FEMTOeST, 90010 Belfort Cedex, France c Zagazig University, Faculty of Engineering, 44519 Zagazig, Egypt b
article info
abstract
Article history:
This paper aims at studying the hydrogen production from solar energy available in Biskra
Received 22 February 2016
region in the east of Algeria by the Proton Exchange Membrane (PEM) electrolyzer. The
Received in revised form
electrolyzer is supplied by solar photovoltaic (PV) system. Three kinds of PV generator with
31 July 2016
rated power up to 6 kW are used for producing hydrogen. The PV panel characteristics are
Accepted 30 August 2016
experimentally validated. The instantaneous effects of temperature and solar radiation on
Available online xxx
PV characteristics are shown. Moreover, a comprehensive study is devoted to validate two different models for the areas solar radiation. The simulation results are compared to the
Keywords:
experimental measurements using statistical analysis. The solar radiation model on a
(PEM) electrolyzer
horizontal and on a tilted and oriented PV panel give sufficient results. The adequate
Hydrogen
agreement between the simulation results and the experimental data verifies the effec-
Photovoltaic panel
tiveness of the proposed models.
Solar radiation model
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Hydrogen, almost the cleanest fuel of the future, is considered the lightest, simplest and most plentiful of all chemical elements in the universe. It can be a source of new and renewable/new energy. In comparison with other options, it is an ideal candidate as a clean energy carrier particularly for both transportation and stationary applications in favor of its less pollution, better urban air quality of near-zero carbon, besides minimum hydrocarbon, GHG and NOx emissions. Owing to its excellent energy storage capacity, hydrogen can be used for solving the problem of electric power stored in the batteries, application of vehicles, computers and mobiles. Therefore, it can present an affordable alternative for the potential shaping
of the future global energy markets. Long term hydrogen production using Renewable Energy (RE) is among the environmentally benign methods in both energy and transport sectors. The future energy economy will consist of many diversified and combined RE technologies based on photovoltaic cells, wind, hydro and geothermal, etc. Hydrogen, as one of the most powerful fuels, can be extracted from steam reforming natural gas, coal, nuclear power, biofuels or even waste products through the process of electrolysis [1]. The hydrogen can be used either for storing or generating electricity in power systems as shown in Fig. 1 [2,3]. As the electrolyzer model shown in Fig. 1 is not suitable for the efficiency analysis of the studied system, the model of the
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (A. Saadi), [email protected] (M. Becherif). http://dx.doi.org/10.1016/j.ijhydene.2016.08.224 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
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Fig. 1 e Hydrogen storage/production in power systems.
electrolyzer presented by Khan and Iqbal [4] is used where the voltage is involved and validated at a standard temperature. Among the different electrolyzers introduced in the literature [5e9], the study mainly focuses on hydrogen production in Biskra region of Algeria from solar panels where a simple electrolyzer model is adequate. In order to successfully have a society based upon RE, a way to store such intermittent RE from both solar and wind energy are excellent methods of obtaining energy from natural resources [10]. However, the levels of sunshine, and the intensity of wind varies. When these sources are not available electricity cannot be generated. When a large amount of energy is being produced, hydrogen can be created from water then stored for later use. The electrolysis of water is a mature technology that can be developed for efficient hydrogen production. However, large amounts of electricity is required. Therefore, solar or wind energy can be properly used for producing the necessary electricity for releasing hydrogen [11]. Most regions of Algeria receive an enormous amount of solar radiation like other Mediterranean countries. Hence, solar technology can be applied and utilized in these countries. Only few stations measure the daily solar radiation on consistent basis. In the absence and/or shortage of reliable solar radiation data, it is necessary to estimate solar radiation using the models in order to predict the global solar radiation in the area under study [12]. The main contribution of this study is verifying theoretically the possibility of producing hydrogen from solar energy production in Biskra region of Algeria. The experimental validation of two different models on a horizontal and on a tilted surface are performed in order to clarify the importance of considering the hydrogen production from solar energy as a horizon potential for regions of similar geographical characteristics. The rest of paper is organized as follows: A brief description of Biskra area is given in Section Biskra area at first. In the second, a description presentation of test bench is introduced in Section test bench description. After, solar radiation is described in Section solar radiation. Then, a presentation of
solar radiation models is exhibited in Section modeling of solar radiation. The experimental study of PV panel is presented in Section PV panel. And Modeling of electrolyzer is described in Section electrolyzer. Finally the concluding remarks and perspectives are stated in Section conclusion.
Biskra area Bordering on the Mediterranean Sea, Algeria lies in the northwest of Africa between the Sahel countries in the south, Western Sahara and Morocco in the west, Tunisia and Libya in the east. It is located between the 18 and 38 of North latitude and between meridians 9 of West longitude and 12 of East longitude. It covers an area of about 2,381,741 km2 Its coastal line on the Mediterranean sea extends over about 1200 km and the aerial space stretches out southward on 1800 km as far as the tropic of cancer [13]. The Algerian population is around 38.5 million citizen, including 849 672 people in Biskra area, according to the statistics in 2014 [14]. More than 50% of the population are young, less than 19 years old. The population is not well distributed; more than 60% live on the coastal area. The population growth and the rapid urbanization have a considerable impact on the demand for energy and the environment [13]. Algeria is the leading natural gas producer in Africa, the second-largest natural gas supplier to Europe outside of the region, and is among the top three oil producers in Africa [15]. Oil occupies an important place in the country's economic development. The total energy consumption of Algeria in 2012 was about 50.9 million Tons of Oil Equivalents (TOE) and should increase to 91.54 million TOE in 2030 [15]. The revolution in RE (wind and solar power) in terms of technological development and costs may help to reduce the consumption of fossil fuels. It encourages the use of RE. Within the framework of the national RE program development and energy efficiency in Algeria, Sonelgaz company has carried out many projects of electricity production based on wind and solar energy to power the isolated villages and
Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
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remote houses of south Algeria. By 2030, a share of RE in the national energy between 30% and 40% should be reached. The share of renewable power by 2023 will represent about 17% of installed capacity (5539 MW) compared to 4.74% in 2011 (540 MW) [15]. By its position in the heart of the Sun Belt, Algeria enjoys both qualitative and quantitative important solar energy potential. Going from north to south, the country presents significant variations in its topographic, climatic and socioeconomic characteristics. Biskra city has a strategic position because it connects the north and south, it harbors full of joyful whose north rocky and mountainous as the Aures and south and east the Sahara desert, and full of magnificent oasis round. It covers an area of about 21 509.80 km2. It is thus one of the largest southern states [14]. Biskra site characterized by a hot, dust and dry climate as shown in Fig. 2. The city of Biskra is situated at latitude 34 480 North and longitude 5 440 east, its elevation is above 85 m sea level, atmospheric pressure at this Bar height is 1.004. The city is characterized by very high monthly average solar radiation throughout the year [16]. In Ref. [17], the global solar irradiation at different Algerian locations (Algiers, Oran, Bechar and Tamanrasset) using the available climatological measured data has been studied. Biskra region, that is considered as a north-south connection zone in Algeria, has at least similar characteristics to such areas. Owing to its special climate and annual solar irradiation, Biskra region specimen is proposed for hydrogen energy production in this study. Biskra is a town rich of a wide range of natural resources like biomass, solar and wind energy and water for electrolysis. This will offer the area a full range of options for the development of a hydrogen industry. If the Sahara is the driest region in the world, it contains nonetheless a huge underground aquifer. Stretching from west of Libya and Tunisia to Adrar and Biskra, and from Laghouat to Illizi, this aquifer covers an area of 800,000 km2. Reserves are estimated at 6.1013 m3. Furthermore, the water used in the electrolysis could be taken from
3
different sources [13]. The aquifer, one of the largest sequestration and storage fields could be used. Biskra is the main natural compound surface water in the region. It is characterized by surface, groundwater and famous by the thermal spa [18]. The water quantity available in Biskra estimated 1017 million m3, of which 22 million m3 any surface water 2.16%, and 995 million m3 of underground water, an increase of 97.84%. The total area of agricultural is about 1,652,751 ha or approximately 77% of the total area of the state. Basic agricultural wealth is palm around 4286 354 date-palm. The total area of nature forest is 97,729 ha. It represents only 4.54% of total area. There are two dams, the first one «Foum-ElGhorza on the Oued El-Abiod with initial storage capacity is estimated at 47 million m3. A second dam, “Fountains of Gazelles” in El Oued Hai, the annual mean input of wadis crossed is estimated at 41,106 m3 (21,106 m3 and 20,106 m3) [19] Modeling of underground, Ouerdachi. The region is available on the important energy network, covered in four lines of electric power of 220 kVA. In the future, the hydrogen could join electricity as an important energy carrier. An energy carrier moves and delivers energy in a usable form to consumers. Hydrogen's potential production from RE resources such as solar, wind, geothermal energy, hydrogen production from oil palms biomass as a potential source became vital. The sun and wind can not produce energy all the time. They could produce electric energy and hydrogen which can be stored when needed. Hydrogen can also be transported like electricity to locations where it is needed [20]. The transport of hydrogen towards potential national and international consumers could be insured via the existing dense of pipeline network [21]. Prospect of geothermal energy use for hydrogen production is good, particularly for the supply of heat, through the hot water, for high temperature electrolysis. Efficiency of electrolysis systems can be improved by operating at high temperature. This reduces the energy needed to activate the electrolysis process. It has been suggested that heat could be obtained from geothermal sources [22].
Test bench description To achieve the paper goal, a simple and reliable PV panel test bench of Fig. 3 is performed, with acceptable accuracy for achieving the experimental performance of the PV generator in the climatic conditions of the region. PV generator 1: SUNTECH 190W Monocrystalline Solar Module (STP 190S-24/Adþ) of high conversion efficiency (up to 14.9%), is structure of test bench test built in Fig. 3a.
Fig. 2 e Solar radiation in Algeria.
The module can be moved and oriented to receive a solar irradiation and change the angle of inclination according to the dimensions as shown in Fig. 3b. Devices are required as a solar pyranometer, anemometer, thermometer and Compass. According to this test bench, experimental tests are verified and then explained. The obtained data distinguish the PV array installed on the site of the Faculty of Science and Technology of the University of Biskra. The PV panel presents a basic element of exist generator systems feeding several
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Fig. 3 e Structure test bench of PV panel.
loads such as lamps, batteries and motors, through DC/DC converters and DC/AC controllers and regulators. Some PV systems are supported by “tracking” technology. It is possible to orient the modules according to angle and orientation of the sun during the year. Two of them available: two-axis tracker and a fixed system.
with two axes is six panels (3 series and 2 parallel) supplying a small water pump. PV generator 3: The PV generator is installed to have fixed inclined array by an angle of 45 and oriented (South). 8 individual PV modules are connected in series and 4 panels are in parallel.
PV generator 2: When productivity is sought, the tracker systems should be moved to improve performance, but they have low wind resistance. PV generator for tracker
Fig. 4a shows the incident variation of solar flux irradiation on the PV panel. In order to achieve the maximum energy yield of the PV system, the modules will be mounted towards
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Fig. 4 e Experimental characteristics based on Tilt angle. south with an optimal tilt angle [23]. After several experimental tests on the site, have been concluded, the optimum depends on the sun height and the annual distribution of irradiation. For this area, the adequate tilt angle is between 30 and 50 . During the year, the optimum is approximately 34.8 . The PV panel efficiency is the ratio between the energy supplied and the incident light energy. In practice, the performance of the solar module is always less than that of a cell. The associated cells result in adaptation losses, as shown in Fig. 4b. The average efficiency is about 13% South.
Solar radiation Solar energy is a sustainable, safe and abundant energy resource. Estimating solar irradiation incident on inclined surfaces of various orientations is necessary for PV applications. The total radiation incident on a tilted plane consists of three components: beam radiation, diffuse radiation and reflected radiation from the ground. The beam component can
be calculated by the ratio of the incidence angle to the solar zenith angle. The reflected component has a small effect on calculations and may be calculated with an isotropic model. In contrast, models for estimating the diffuse component show major differences. There are a lot of models have justified the interest in this field, twelve of them studied in Ref. [24]. Previous studies have shown many mathematical methods for the relation between the solar radiation on an inclined surface and on the horizontal plane with different accuracies. The trajectory of the Earth around the Sun is an ellipse with the Sun at one of the focus. The mean Earth-Sun distance varies from 144 million Km (21 December) to 154 million km (21 June). The solstices and equinoxes divide the year up into four approximately equal parts. In the northern hemisphere winter solstice occurs on about December 21, summer solstice is near June 21, spring equinox is around March 20 and autumnal equinox is about September 23. Therefore, the measurements shown in Fig. 5a and Fig. 5 have been taken into special days. On Friday, March 20, 2015 the three phenomena passed on Earth; the equinox, the sun
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Fig. 5 e Solar radiation incident for different measurement days.
eclipse and the supermoon. The region is exposed to a partial eclipse. The weather was very windy and cloudy. The solar radiation was very weak. Very low temperatures were measured the moment of the eclipse and obscured the sun shown in Fig. 6a. Natural changes in climate such as heating due to volcanic activity, radiation from the sun, and changes in the chemistry of the atmosphere sometimes take thousands of years to change only 1 C. Nowadays, because of pollution, the earth temperature is increasing which is confirmed in Fig. 6a. In this area, hot days have become more frequent, than the cold days which become less severe. The temperature reaching 47 C in the month of May and it is not cold at all in the winter. The temperature is an important factor for the implementation of systems using RE. The temperature affects on both the PV panel and the electrolysis.
Modeling of solar radiation Modeling of solar radiation provides an understanding of its dynamics which is of great interest in the design of solar energy conversion systems. The method for the calculation of the solar
irradiance on a surface with any orientation and tilt is not accurate enough because of the sky isotropic consideration. In order to account for the sky cloudy clear periods, it's necessary to calculate the mean hourly, daily, monthly values. The daily radiation has to be considered instead of the instantaneous irradiance. Then its monthly values can be obtained as the average of irradiances for each day of the month [25]. In order to determine the angle of incidence of the sun rays on a surface, the following parameters should be known: the latitude of the site L, the position of the sun through u and d, the tilt angle b of the surface on the horizon and the azimuth of the surface g that is the angle calculated on the horizontal plane between the projection of the surface normal to the to the horizontal plane and the south direction. d (degrees) is the solar declination that can be calculated by the approximate formula [26]. The angle of declination is given by: d ¼ 23:45sin ½0:980ðj þ 284Þ
(1)
where j is the day number of the year, j ranges from 1 (1st January) to 365, or 366 in case of a leap year, when precision is required [27]. The Developing Fourier series can be considered, then:
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Fig. 6 e Annual temperature and ET time.
With: J ¼ 0:984*j
ET ¼ 0:0072*cosJ 0:0528*cos2J 0:0012*cos3J 0:1229*sinJ 0:1565*sin2J 0:0041*sin3J
d ¼ 0:33281 22:984cosJ 0:3499cos2J 0:1398cos3J þ 3:7872sinJ þ 0:03205sin2J þ 0:07187sin3J
The orbit of the earth an ellipse. Thus, the earth's angular speed varies slightly throughout the year [27]. Combined with the regular rotation of the earth about itself, the sun does not reach its highest position in the sky named the solar noon at 12h mean solar time (MST) every day. The time of solar noon may differ from 12 h MST by up to 17 min. The time determined every day by the actual position of the sun in the sky is called true solar time (TST), or local apparent time. The difference between TST and MST called “equation time (ET)” is defined as: ET ¼ 360=24ðTST 12Þ
where, J ¼ 0:984*j , and j is the day number of the year. The evolution of both the solar declination and the time equation during the year are shown in Fig. 6b. The equation time is the variation of the difference between MST and TST as a function of the day in the year is depicted. The maximum variation is reached on 31st October of about 15.67 s. The minimum variation is equal to 13.79 s on 13th February. (h) is the height of the sun in degrees, can be calculated by: sinh ¼ sinL$sind þ cosL$cosd$cosu
(6)
(3)
u: is the hour angle of the sun in degrees. The calculation of the solar angle at sunrise (-u) and sunset (u) is obtained by proposing sinh ¼ 0, then:
(4)
cosu ¼ tgd$tgL
TST in (hours) is determined by: TST ¼ MST ET
(5)
(2)
ET that refers to the time uniform rotation of the earth around the sun is given by Ref. [27]:
(7)
The solar time at sunrise and sunset (tSR and tSS ) respectively will be:
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tSR ¼ 12 þ
u 15
(8)
tSS ¼ 12
u 15
(9)
The day length d in hours is: d ¼ ðu ð uÞÞ=15 ¼ 2$u=15
(10)
The component of the diffuse radiation on an inclined plane Dc(b) is given by: Dc ðbÞ ¼ Dh
1 þ cosð b Þ 2
(19)
where Dh is the diffused solar radiation.
Solar radiation model on a horizontal PV panel The total radiation received on the horizontal is a summation of the direct and diffuse radiation. Gh ¼ Ih $sinh þ Dh
(11)
where: Ih is a direct radiation, calculated by: Ih ¼ A$exp
1 B$sinðh þ CÞ
(12)
Dh is a diffuse solar radiation expressed as: Dh ¼ D$sinh0:4
(13)
A, B, C and D parameters depend to the kind of sky. Selecting throughout the year, a number of types of clear weather days, where the energy distribution has asymmetry axis located 12 h and true solar time. The global illumination can be obtained directly from: Gh ¼ E$ sinhF
(14)
From the experimental values of Gh, Equation (14) can present best possible variations where E and F values are determined by the least squares method through the following linear: logGh ¼ logðEÞ þ F$logðsinhÞ
(15)
f0 ¼ logGh , the linear slope fit can then be beAssuming G tween (F) and (log E).
Solar radiation model on a tilted and oriented PV panel The solar radiation is the sum of three components: beam radiation, diffuse radiation by the sky and diffuse reflected by the ground (albedo) r. Global solar radiation is the sum of the direct, refracted and diffuse solar radiation [28]. It can be calculated by: Gi ¼ Rd ðbÞ þ Dc ðbÞ þ Ds ðbÞ
(16)
The direct radiation component is given by: Rd ¼ Ih $Rb
(17)
where Rb is the inclination factor, estimated by: Rb ¼
cosðL bÞ $cosd cosu þ sinðL bÞ$sind cosL cosd cosu þ sinL sind
(18)
where b is tilted angle. L is the latitude of the site. d is declination angle. It is the angle between earth-sun line and the equatorial plane.
Fig. 7 e Simulation/experimental results of solar radiation models.
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The ground reflected components Dc ðbÞ of solar radiation
Statistical analysis
is: Ds ðbÞ ¼ Gh
1 cosð b Þ $r 2
(20)
where r is the foreground's albedo and Gh is the global illumination. To validate the propose model, Matlab™ simulations are used for designing all days programs. From each of these programs, for the diagrams, curves representative of the measured and estimated values are prepared by the proposed model. The data of the global solar radiation are measured w/m2. The data is collected for the period of December 2014 to May 2015. The time of recording was often between 5 min and 10 min. The simulation results provide the evolution of the solar radiation on a horizontal and tilted PV panel depending on climatic conditions and for the days shown in Fig. 7. Fig. 7(a) and (b) are two different cases in December 22 and February 18, to present different seasons (winter and spring). Clearly, the graph that the values of the amount of solar radiation are the least possible during the first daylight hours in December. It is due to the different position of the sun relative to the earth's surface. Day grow taller in summer. Experimental values of solar radiation prove that, the middle of day is not at 12 pm. The radiation is not symmetrical contrary to what the proposed models assume. That causes a small difference between the measured results and proposed models. In May, the solar radiation incident on horizontal and tilted surface has the same value. However in December, solar radiation on tilted PV panel is twice the value of solar radiation on a horizontal PV panel. Starting from spring, the maximum value of solar radiation higher than 1000 w/m2. In the winter, this value becomes less as shown in Fig. 7 (b) and (c) respectively. According to Fig. 7 (a) and (c), the model on a horizontal PV panel gives good results for clear and bit cloudy sky. The results indicate that the model on a tilted PV panel favorably with the observed values in the whole seasons. The reasonable discrepancy between the model and experimental results is because of the sky condition at the measurement. Obviously, better results are found for clearer sky. The use of high digital programs to record measurements permits the negative impact of different several factors such as: the dispersion of solar radiation, wind, steam, air humidity, dust, reflective quality of the ground solar radiation in addition to the pollution and global warming influence.
In this study, the performance of the models is evaluated using the different statistical errors or indicators such as: the percentage error (PE), absolute percentage error (APE), mean bias error (MBE), and root-mean-square error (RMSE) defined as [29]: Pn PE ¼
ðx xm Þ Pn i¼1 x
i¼1
Pn APE ¼
MBE ¼
(21)
jx xm j Pn i¼1 x
(22)
n 1 X $ ðx xm Þ n i¼1
(23)
i¼1
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Pn 2 i¼1 ðX Xm Þ RMSE ¼ n
(24)
where x and xm are the ith calculated and measured values on a tilted surface respectively. n is the total number of observations for a specific period of time. The Percentage Error (PE) is the relative error between the x and xm values shown as a percentage. APE is the absolute value of the PE. The MBE values give information about the long-term model performance. A small MBE value is a desired condition. A negative and positive value refers to underestimation and overestimation respectively. The RMSE determines the model's accuracy by comparing the deviation between the predicted/ calculated and measured values. The RMSE values, which are always positive, denote information about the model shortterm performance. A smaller value indicates better model performance while zero represents the ideal case [30,31]. Table 1 summarizes the statistical errors (PE, APE, MBE and RMSE), which are calculated using Equations (25)e(28). It shows those statistics associated with the results of Fig. 7. From Table 1, the PE, APE, MPE and RMSE are estimated in four different dates for two solar radiation models (horizontal and inclined surface). The results show that the maximum RE and APE values are 17.46% and 24.34% at February 18th, 2015 for the inclined surface model. The minimum RMSE value 94.75 W/m2 results at March 22nd, 2015 for the horizontal surface model. The errors are acceptable. The results, in general, shows adequate agreement between both models under different sky conditions. The high values is due to the
Table 1 e Statistics errors of solar radiation models. Solar radiation model Horizontal surface
Inclined surface
Date
PE (%)
APE (%)
MBE (W/m2)
RMSE (W/m2)
December 22nd, 2014 February 18th, 2015 March 22nd, 2015 May 6th, 2015 December 22nd, 2014 February 18th, 2015 March 22nd, 2015 May 6th, 2015
12.40 11.60 3.16 12.92 0.52 4.36 17.46 0.08
23.38 19.08 14.40 17.82 16.16 11.66 24.34 11.35
44.69 98.82 77.19 153.02 99.02 32.40 150.91 99.14
105.41 125.75 94.75 181.18 151.33 112.54 186.48 121.68
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Fig. 8 e Experimental characteristics of the PV panel.
measurement equipment and manual measure's operator. In addition, the limited number of experimental tests negatively affects on the results.
PV panel PV panels capture the sun's energy using photovoltaic cells. These cells do not need direct sunlight to work. Electricity may be generated during cloudy days. Algeria is characterized by its good geographical situation, it receives important quantity of solar radiation during the years and seasons [32]. The application of the PV systems becomes more important
Fig. 10 e Effect of temperature on the PV panel characteristics.
practically for isolated areas and local to extend domestic level. Being a semiconductor device, the PV system is static, quiet, free of moving parts, and has little operation and maintenance costs. The main characteristics of the PV module are shown in Fig. 8 and Fig. 9 respectively. The IeV output characteristic of a PV module is highly non-linear. The output characteristics of the panel depend on the solar radiation and the ambient temperature. The IeV curve of PV panel has three important points: the short circuit (0, Isc), the open circuit (Voc, 0) and the maximum power (Pmpp1, Pmpp2 and Pmpp3). The points M1, M2 and M3 respectively represent with optimal voltage and current (Vmp, Impp) at different conditions. In Fig. 8, the IeV output characteristics duration of PV panel is 20 min. The starting solar radiation is about 701 w/m2 at fixed temperature of about 36 C. After 10 min the value of solar radiation rised to 805 w/m2. This increase lead to an increase in both; current and voltage outputs. These results increase in
Fig. 9 e Instantaneous variation of solar radiation and temperature on PV panel.
Fig. 11 e One-diode equivalent circuit for a PV panel.
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Table 2 e Photovoltaic panel specification. Parameter
Pmax
Vmp
Imp
Voc
Isc
Rs
M
Value
190w
5.2
36.6
45.2
5.62
0.11
1.54
power output. The temperature influences on the characteristics of PV panel. The power decreases if the temperature increases more than 25 C. The instantaneous effect of these parameters are shown in Fig. 9a and b [33]. As the RE systems are non-linear power sources by nature; the Wind, the PV generator and the Proton Exchange Membrane Fuel Cell (PEMFC) need accurate on-line identification of the optimal operating point [34,35]. The power generated by PV panel depends on environmental factors such as solar radiation and cell temperature. The direct link with a load often forced the system to operate very low. Aiming at optimizing such systems to ensure optimal functioning of the unit; modern control approaches based on Genetic Algorithm (GA), Artificial Neural Network (ANN) and Fuzzy Logic (FL) have proposed in Ref. [34]. Various MPPT control techniques in Ref. [32] have been presented in order to ameliorate the PV efficiency and to maximize the energy captured by the PV panel. For producing an adequate quantity of solar hydrogen, the electrolysis are supplied with
11
an optimal current, voltage and power as shown in Fig. 9a and b. However, 13% of global solar radiation incidents on PV panel can be exploited. The boost DC/DC converter is used mainly for permitting a maximum power tracking of PV panel and to increase the PV voltage to be compatible with the electrolyzer. The effect of temperature and irradiance is studied using the test bench PV panel. The solar radiation has three values around 910 W/m2, and the temperature increases from 25 C to 47 C. Fig. 10 (a) illustrates the currentevoltage (IeV) characteristics of the PV panel. It can be clearly observed that the open-circuit voltage (Voc) decreases with the temperature rise. The short circuit current (Isc) has a proportional relation with the temperature in both cases. Fig. 10 (b) illustrates the powerevoltage (PeV) characteristics where the negative influences of the temperature influences on the power provided by the PV panel are depicted.
PV panel modeling Single diode equivalent circuit of PV panel in both ideal and practical cases is given in Fig. 11 [36]. In this paper, the practical PV panel model is analyzed where the relation between the output current I and voltage V is defined as: I ¼ Iph ID Ish
(25)
Fig. 12 e Comparison between the experimental data and the model results. Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224
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where Iph is the irradiance current (photocurrent) (A), which is proportional to solar radiation. ID is the current of diode (A). Ish is the current of parallel resistor (A) such that:
ID ¼ I0 e
Ish ¼
q
Vþ Rs I m K T
!
1
(26)
V þ Rs I Rsh
(27)
For the PV panel, the output current is given by:
q
I ¼ Iph I0 e
Vþ Rs I m K T
! 1
V þ Rs I Rsh
The production rate of hydrogen mH2 in an electrolyzer cell is directly proportional to the transfer rate of electrons at the electrodes, which in turn equivalent to the electrical current in the circuit, then: mH2 ¼
hF N ie 2F
where ie is the electrolyzer current, N is the number of electrolyzer cells in series, F is the faraday constant and hF is the Faraday efficiency, the ratio between the actual and theoretical maximum amount of hydrogen produced in the electrolyzer can be [4,40].
(28) hF ¼ 96:5 exp
I0 is the cell reverse saturation current (diode saturation current), q is the electron charge q ¼ 1:602 1019 C, m is the cell ideality factor, k is the Boltzmann constant k ¼ 1:3806503 1023 J=K T is the cell temperature; Rs and Rsh represent the cell series and shunt resistance, respectively [37]. Datasheet values are given at Standard Test Conditions (STC). STC means irradiation level is 1000 W/m2, with a panel temperature of 25 C and air mass of 1.5 solar spectral irradiance distributions [38]. Different methods in literature have been studied to identify the one-diode model for PV modules either by introducing simplifications/approximations techniques or by considering suitable data interpolations/experimental from the panel characteristic curves [38]. The PV panel is used defined block in MATLABTM/Simulink. The circuit based simulation model for a PV cell for estimating the IV characteristic curves of the PV panel with respect to changes on environmental parameters (temperature and solar radiation) and cell parameters (parasitic resistance and ideality factor) [39]. The study based on the use of measurements and specific fitting procedure for finding Rs and m ideality factor value using the parameters given in Table 2. Using sufficient experimental data leads to obtaining better fitness by the optimum values of the parameters. The comparison between the simulation results and the experimental curves is presented in Fig. 12 through the nonlinear IeV and PeV characteristic curves respectively. The model calculates the points with acceptable accuracy under any temperature and solar radiation values.
(30)
0:09 75:5 2 ie ie
! (31)
On a daily period te is the duration for which the electrolyzer will produce the quantity of hydrogen QH2 , therefore: QH2 ¼ mH2 te
(32)
Equations (31) and (33) represent the simple electrolyzer model are used for the electrolyzer system design via MATLAB™/Simulink. In Equation (30), the ideal electrolyzer is considered although several research works have indicated that the quality of produced H2 depends on the magnitude of the current used during the process [4]. This confirms the importance and originality of the paper idea. As the use of solar panels particularly provides very high electric currents,
Electrolyzer The water electrolysis operation is an electrolytic process which decomposes water H2 O molecule into oxygen O2 and hydrogen H2 gases by applying a DC voltage PV panel. Protons flow through the PEM membrane from the anode to the cathode while the electrons move to the cathode via the outer electrical circuit. At the cathode, hydrogen is formed by the recombination of electrons and protons [8,9]. The overall chemical reaction of water electrolysis is given by: H2 O þ electricity/2H2 þ O2 þ heat
(29)
Fig. 13 e (a) Electrolyzer hydrogen according to the current, (b) flow hydrogen production by 3 PV generators during 1 day.
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the solar energy lost per day can be properly stored in hydrogen form in certain areas. Thereafter, the Fuel Cell (FC) can be used to generate energy from the stored Hydrogen [41]. Fig. 13a shows the production of hydrogen (mol/s) to the change in current provided by the PV panel assuming that, the molar volume of an ideal gas measured in normal conditions of pressure and temperature is Vm ¼ 22.4 L/mol. Fig. 13 illustrates the production of hydrogen by (m3/s). Notably, the average solar radiation is about 900 w/m2 over five hours of the day, (between 10:00 to 15:00). The three PV generators produce maximum powers to the PEM electrolyzer which is sized for each generator. The hydrogen flow by three PV generators is shown in Fig. 13b.
[6]
[7]
[8]
[9]
Conclusion The two proposed models take into account several climatic parameters (humidity of the site, slope of the collector, latitude of the city, longitude). It is possible to determine the various solar radiations: total, diffuse and direct receipt by a horizontal or a tilted surface and orientation. The models present solar radiation with an adequate accuracy. According to the simulation results, the model on a horizontal surface is best suited to a clear sky. The three PV generators are chosen to feed the electrolyzer. The PV panel test bench structured can achieve several experiments and the hydrogen flow is satisfactory. Incident solar radiation can be used for producing hydrogen. The dates residue is the most significant resources of feedstock for hydrogen production by biomass. Heat and water are the feedstock for hydrogen producing by electrolysis using solar energy and wind. Therefore, Biskra can be proposed an appropriate region for hydrogen production, not only in Algeria but also in North Africa contrites. The Production of hydrogen can be a great perspective in Biskra area. In the forthcoming research, the authors will study the techno-economic impact of the different electrolyzer modeling on Hydrogen production in Biskra region of Algeria. The Maximum Power Point Tracking (MPPT) will be experimentally implemented to maximize the captured energy for feeding the electrolyzer.
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Nomenclature d: Length day, hour Dh: Diffuse solar radiation, w/m2 ET: Equation time, hour F: Faraday constant Gh: Total radiation received on the horizontal surface, w/m2 Gi: Total radiation received on the tilted surface, w/m2 h: Height of the sun, deg ie: Electrolyzer current, A I: PV panel current, A ID: Current of diode, A Ih: Direct radiation, w/m2 I0: Diode saturation current, A Iph: Photocurrent, A Isc: Short circuit current, A Ish: Current of parallel resistor, A j: day number of the year k: Boltzmann constant, J/K L: Latitude of the site and positive for the northern hemisphere, deg. m: Ideality factor mH2 : Hydrogen production rate, mol/s MST: Mean solar time, hours N: Number series electrolyzer cells q: Electron charge, C QH2 : Hydrogen flow, m3/s Rb: Ratio of the daily direct solar radiation incident on a tilted surface to that on a horizontal surface Rd: Ratio of the daily diffuse solar radiation incident on a tilted surface to that on a horizontal surface Rs: Cell series resistance, U Rsh: Cell shunt resistance, U T: Cell temperature, C TST: True solar time of the study site, hours tSR : Sunrise solar time, hours tSS : Sunset solar time, hours V: PV panel, V Voc: Open-circuit voltage, V u: Solar hour angle, deg b: Tilt angle, deg d: Solar declination, deg g: Azimuth of the surface hF: Faraday efficiency
Please cite this article in press as: Saadi A, et al., Hydrogen production horizon using solar energy in Biskra, Algeria, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.08.224