The potential of harnessing solar radiation in Iran: Generating solar maps and viability study of PV power plants

Renewable Energy 53 (2013) 193e199

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The potential of harnessing solar radiation in Iran: Generating solar maps and viability study of PV power plants Saeb M. Besarati a, Ricardo Vasquez Padilla a, b, D. Yogi Goswami c, *, Elias Stefanakos d a

Clean Energy Research Center, University of South Florida, 4202 E. Fowler Av., ENB 118, Tampa, Fl 33620, USA Department of Mechanical Engineering, Universidad del Norte, Barranquilla, Colombia c Department of Chemical & Biomedical Engineering, University of South Florida, 4202 E. Fowler Av., ENB 118, Tampa, FL 33620, USA d Department of Electrical Engineering, University of South Florida, 4202 E. Fowler Av., ENB 118, Tampa, FL 33620, USA b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 January 2012 Accepted 14 November 2012 Available online 23 December 2012

This paper assesses the potential of harnessing solar radiation in different regions of Iran. In this regard, solar radiation maps are generated for five different cases: total radiation on a south facing fixed surface tilted at the latitude angle; total radiation on a surface tilted at the latitude angle with EasteWest tracking; total radiation on a surface tilted at the latitude angle with azimuth tracking; direct beam radiation on a horizontal surface with EasteWest tracking; and direct beam radiation on a surface with two axis tracking. The first three cases are generally applicable to photovoltaic (PV) power plants while the last two are generally used for concentrating solar power (CSP) plant design. In the second part of the paper, a 5 MW PV power plant is considered for 50 cities of Iran. Capacity factors, electricity generated and annual greenhouse gases emission reductions are compared. The results show a great potential for central and southern parts of the country. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Solar maps Photovoltaics Energy policy of Iran Renewable energy

1. Introduction Iran, which is located in southwestern part of Asia, is the 18th largest and 17th most populated country in the world. Iran’s population increased dramatically during the latter half of the 20th century, reaching about 75 million [1]. Population growth as well as technological advances has driven the demand for greater electricity production. Today Iran ranks as the 19th largest producer and 20th largest consumer of electricity in the world [2]. According to research conducted by the Iranian Ministry of Energy 15,000e 20,000 MW of capacity must be added over the next 20 years to cover the growing demand [3]. Electricity production in Iran is mainly dominated by its fossil fuel resources. Iran has the fourth largest oil and the second natural gas reserves of the world, 9% and 15.8% of the world’s total respectively [2]. Fig. 1 compares electricity generation by different sources from 1972 to 2009 [4]. As can be seen from the figure natural gas began to increase its share in the 1980s and reached almost 75% of the total by 2009.

* Corresponding author. Tel.: þ1 813 974 0956; fax: þ1 813 974 2050. E-mail addresses: [email protected] (S.M. Besarati), rvasquez@ uninorte.edu.co (R.V. Padilla), [email protected] (D.Y. Goswami), [email protected] (E. Stefanakos). 0960-1481/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.renene.2012.11.012

Using fossil fuels for generating electricity has its own advantages and disadvantages. Capacity to generate huge amounts of electricity in just a single location, and cost effectiveness (especially in countries like Iran which has vast fuel resources) are the main advantages, while greenhouse gas emissions can be considered as the most egregious disadvantage. Increasing demand for electricity, environmental concerns, and finite amounts of world fossil fuel resources have necessitated a greater effort in generating power from renewable energies. Although hydro-power is the only form of renewable energy that is extensively used for power generation in Iran, the potential for other renewable sources is vast. Recently, Iran has paid great attention towards harnessing wind energy from suitable sites. The capacity of wind energy installation in the country was reported to be 92 MW by 2010 [5]. Searching for other energy alternatives, potential geothermal sites selection were conducted by Kyushu University in 2007 using Geographic Information System (GIS) [6]. The results indicated 8.8% of Iran has prospective geothermal areas in 18 fields. The Meshkinshahr Geothermal Power Plant which has a maximum electricity generation capacity of 250 MW, came on-line in 2010, becoming Iran’s first geothermal power plant. Based on the geothermal site selection studies, Sabalan was selected for detailed explorations and a 50 MW geothermal power plant is under construction.

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Nomenclature as Dh Hh i Ib,c Ib,h Id,c Id,h Ih It Ir,c L rd rt

azimuth angle [Degree] long term diffuse radiation on a horizontal surface [W/m2] long term total radiation on a horizontal surface [W/ m2] incident angle [Degree] beam radiation on a tilted surface [W/m2] beam radiation on a horizontal surface [W/m2] diffuse radiation on a tilted surface [W/m2] diffuse radiation on a horizontal surface [W/m2] solar radiation on a horizontal surface [W/m2] total radiation [W/m2] ground reflected radiation on a horizontal surface [W/m2] latitude angle [Degree] daily ratio for diffuse radiation daily ratio for total radiation

Greek symbols a altitude angle [ ] b tilted angle [ ] ds declination angle [ ] u sunrise angle [ ] r reflectivity

Solar energy is also widely available in most regions of the country, especially in the central and southern parts. It is interesting to note that if only 1% of the deserts in Iran were covered by solar collectors, the energy generated would be five times more than the country’s annual gross electricity production [7]. Despite this favorable solar resource there is a little use of solar energy in Iran. The first PV site, with a peak capacity of 5 kW DC, was established in the central region of Iran in Doorbid village Yazd in 1993. After that, a number of PV projects began in Yazd, Semnan, Khorasan, Tehran and Taleghan, however, the capacity of these projects seems to be very low compared to the country’s potential. The first CSP plant became operational in Shiraz in 2008. The capacity of the

power plant was upgraded from 250 kW to 500 kW in 2010. In 2009, the Yazd integrated solar combined cycle power station became operational. The plant has a capacity of 467 MW and uses solar energy to augment steam generation by concentrating solar power technology. It consists of gas turbines and a steam turbine, with a solar contribution of 17 MW. Comparing the present solar power generation capacity with the real potential of the country indicates that a comprehensive program must be developed to harness more solar energy. In order to do so, it is essential to develop a data-base of solar radiation availability for the country, which has been the subject of research for a long time. One of the early studies on calculating solar radiation in Iran was performed by Daneshyar [8] in 1978. He suggested a model based on Paltridge and Proctor’s relation for direct beam [9] and the empirical equation of Lof [10] for the diffuse component. The mean monthly values of direct, diffuse and total solar radiation at 34 locations in Iran were calculated. The predicted values of the model for a horizontal surface were compared with the measured data in Tehran which showed approximately 2 percent error. Jafarpour and Yaghoubi [11] estimated monthly and annual solar radiation for Shiraz and concluded that the city receives as much as 7250 MJ/m2 energy from the sun per year, which makes it one of the most suitable locations in the country. Ashjaee et al. [12] applied the radiation models of Daneshyar [8] and Bird and Hulstrom [13] for estimating the daily solar energy. The results were in good agreement with the measured data of Tehran and Isfahan. Samimi proposed an explicitly height-dependent model to estimate the solar radiation over the country and found close agreement with the 17-year long pyranometric measurements of Tehran [14]. Yaghoubi and Sabzevari published further data on solar radiation in Shiraz and showed that the average maximum radiation and daily mean radiation have decreased from 1979 to1993 by about 10% and 8.6%, respectively [15]. Sabziparvar compared and modified different radiation models and estimated global radiation in central arid deserts [16], south and north coasts [17], and arid and semi-arid climates of east and west Iran [18]. Moini et al. [19] presented the monthly and annual solar maps of Iran for a horizontal surface using Angstrom model [20]. Although all the mentioned papers have studied solar radiation in Iran, none of them have provided comprehensive solar radiation maps for different surface tracking modes, which can be useful for designing PV and CSP power plants. In this paper, solar radiation maps of Iran are developed for five different tracking modes. The

250 000

200 000

GWh

150 000

100 000

50 000

0 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 Coal/peat

Oil

Natural gas

Nuclear

Hydro

Biofuels & waste

Fig. 1. Electricity generation by fuel in Iran [4].

Geothermal/solar/wind

S.M. Besarati et al. / Renewable Energy 53 (2013) 193e199

first three cases estimate the total solar radiation on the a fixed south facing surface tilted at the latitude angle; a surface tilted at the latitude angle with EasteWest tracking; and a surface tilted at the latitude angle with azimuth tracking, respectively. These cases are useful for PV power plant design. The last two cases analyze direct beam radiation on a horizontal surface with EasteWest tracking; and a surface with two axis tracking. These two cases are generally applicable to CSP plant design. Finally, a feasibility study of a 5 MW PV power plant is carried out for 50 cities of Iran using RETScreen [21]. Capacity factor, electricity delivered to the grid, and annual greenhouse gases emission reduction are presented for each city. 2. Methodology of hourly solar radiation calculation Determination of the hourly solar radiation received during the average day of each month is essential for calculating the solar collector performance throughout the year. The long-term models provide the mean hourly distribution of global radiation over the average day of each month. Given the long-term average daily total and diffuse irradiation on a horizontal surface, H h and Dh respectively, it is possible to find the long-term hourly solar radiation: Ih and Id,h. Values of H h and Dh can be obtained from either ground measurement data or satellite data [22]. Satellite data provides information about solar radiation and meteorological conditions, in locations where ground measurement data are not available. For solar radiation calculations, the Daily integration approach (DI Model) [23] was used as the hourly radiation model. Gueymard [23] developed the Daily integration approach to predict the monthly-average hourly global irradiation, by using a large data set of 135 stations with diverse geographic locations (82.58 N to 67.68 S) and climates. Gueymard compared his proposed model with previous hourly radiation models (CollaresPereira and Rabl Model CP&R [24] and Collares-Pereira and Rabl Model modified by Gueymard [25]) and concluded that the daily integration model is the most accurate when compared to the other models. Total instantaneous solar radiation on a horizontal surface, Ih, is the sum of the beam or direct radiation, Ib,h, and the sky diffuse radiation Id,h:

Ih ¼ Ib;h þ Id;h

(1)

Introducing the hourly to daily ratios rd and rt as:

rd ¼

Id;h Dh

rt ¼

Ih Hh

(2)

Then, the beam radiation is:

Ib;h ¼ rt H h  rd Dh

(3)

The value of rd was found by Liu and Jordan [26] and the value of rt was modified by Gueymard [23]. Five different tracking systems were used (See Fig. 2): Case 1: Total radiation on a fixed surface south facing tilted at the latitude angle Case 2: Total radiation on a surface tilted at the latitude angle with EasteWest tracking Case 3: Total radiation on a surface tilted at the latitude angle with azimuth tracking Case 4: Direct beam radiation on a horizontal surface with Easte West tracking Case 5: Direct beam radiation on a surface with two axis tracking

195

The total radiation on a tilted surface is the sum of components consisting of beam (Ib,c), sky diffuse (Id,c) and ground reflected (Ir,c).

It ¼ Ib;c þ Id;c þ Ir;c

(4)

The beam radiation on a tilted surface is given by:

Ib;c ¼ Ib;h

cos i sin a

(5)

The values of cos i, Id,c, and Ir,c for each case are shown in Table 1. 3. Solar radiation maps of Iran Solar radiation maps of Iran for five different tracking modes are shown in Figs. 3e7. Figs. 3e5 can be used for the design of PV power plants as they show total solar radiation. As can be readily seen, the central and southern parts of Iran have higher potential to harness solar energy. On the contrary, the northern parts of Iran, especially Guilan and Mazandaran provinces, do not receive high levels of solar radiation. The effect of using different tracking modes can be seen from the figures. By using tracking modes, the potential to harness solar energy is considerably increased. According to Figs. 4 and 5, the EasteWest tracking (Case 2) is superior to the azimuth tracking mode (Case 3). Figs. 6 and 7 show the maps obtained for direct beam radiation on a surface with EasteWest tracking and two axis tracking, respectively. These maps can be used for designing CSP plants. According to the maps, levels of direct beam radiation increase from the northern to southern part of Iran, though some central regions show maximum beam radiation. This is due to lower humidity in these parts. 4. Viability study of 5 MW photovoltaic power plants In this Section 5 MW PV power plants are considered for 50 cities of Iran using RETScreen software [21]. RETScreen is a powerful analytical tool to assess renewable energy and energy efficiency economics and carbon reduction. The RETScreen climate database includes meteorological data, which are from ground monitoring stations. If climate data is not available from a specific ground monitoring station, data is then provided from the NASA’s satellite derived data. The first step in designing a PV power plant is the selection of PV modules. Many types of PV modules with different characteristics are available on the market. For this study, Crystalline Si panels with a capacity of 205 W per panel were selected. The module has the efficiency of 17.4% and frame area of 1.18 m2. The characteristics of the selected module at the reference condition are given in Table 2. Reference condition is defined as total irradiance of 1000 W/m2, air mass of 1.5, and cell temperature of 25  C. According to the power of each module, 24,391 panels are required to generate the maximum power of 5 MW. This number of units covers an area of 28,737 m2. An inverter with an efficiency of 90% and capacity of 4,750 kW was selected to convert power from DC to AC. Miscellaneous inverter losses were assumed to be 5%. Input solar energy to each power plant was obtained from the meteorological database. One axis tracking was considered for calculation while the slope was fixed at the latitude angle for each city. The analysis was completed for 50 cities and the final results are summarized in Table 3. The first column compares the capacity factor of 5 MW power plant with one axis tracking mode in different cities. Capacity factor is defined as the ratio of the actual output of a power plant over a period of time, and, its potential output if it had operated at full nameplate capacity the entire time. According to the table, the highest capacity factor was obtained in

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Fig. 2. Different tracking modes.

S.M. Besarati et al. / Renewable Energy 53 (2013) 193e199

197

Table 1 Incident angle, diffuse and reflected radiation for different tracking systems. Equations obtained from [27]. Case

cos i

Id,c

Ir,c

1

cos a cos as sin L þ sin a cos L cos ds a þ L  90 j cosj pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1  cos2 a cos2 as 1

rd Dh ð1 þ cos LÞ=2

rt H h rð1  cos LÞ=2

rd Dh ð1 þ cos L cos uÞ=2 rd Dh ð1 þ cos LÞ=2 0 0

rt H h rð1  cos L cos uÞ=2 rt H h rð1  cos LÞ=2 0 0

2 3 4 5

Fig. 5. Total radiation on a fixed surface tilted at latitude angle with azimuth tracking (Case 3). Radiation data source: NASA-SSE [22].

Fig. 3. Total radiation on a fixed surface south facing tilted at latitude angle (Case 1). Radiation data source: NASA-SSE [22].

Fig. 4. Total radiation on a fixed surface tilted at latitude angle with EasteWest tracking (Case 2). Radiation data source: NASA-SSE [22].

Bushehr at 26.1%, while the lowest was only 16.5% in Anzali. It was predictable from the solar maps that the southern parts of Caspian sea, Guilan and Mazandaran provinces, have the least potential for generating power by solar energy. This is due to the large number of cloudy and rainy days and also to the high level of relative humidity. The mean relative humidity for Anzali is estimated as 84% [28]. Although calculations show that Bushehr has the highest potential, it should be noted that the analysis is based on radiation

Fig. 6. Direct beam radiation on a horizontal surface with EasteWest tracking (Case 4). Radiation data source: NASA-SSE [22].

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S.M. Besarati et al. / Renewable Energy 53 (2013) 193e199 Table 3 Comparison of performance of 5 MW PV power plants in 50 cities of Iran.

Fig. 7. Direct beam radiation on a surface with two axis tracking (Case 5). Radiation data source: NASA-SSE [22].

data from NASA. NASA’s data is obtained based on satellite measurement and it may fail to account for some other important parameters, such as the level of dust in the air, which would be a big concern in south west of Iran. The mean capacity factor in these 50 cities is 22.27%. The second column in Table 3 depicts the electricity fed to the grid. The highest values were obtained in Bushehr, Abadeh, Shiraz, Isfahan and Bafq with 11,423.3, 10,770.1, 10,734.6, 10,690.7, and 10,634.8 MWh electricity fed into the to grid, respectively. The lowest values were observed at Anzali, Babol, Chalus, Sari, and Langerood with 7220.6, 7573.8, 7745.1, 7869.1 MWh electricity exported to grid, respectively. It is interesting that all these cities are located south of the Caspian Sea. Mean value for this column is 9753 MWh. The third column is the gross annual greenhouse gases (GHGs) emission reduction(tCO2). The GHG emission factor for all types of fuels in Iran was assumed to be 0.537 tCO2 =MWh, according to RETScreen database. The forth column shows the equivalent liters of gasoline not consumed to provide the same amount of CO2 reduction. The mean values for the third and forth columns are 6112 (tCO2) and 2,616,399 L of gasoline, respectively.

Table 2 Characteristics of mono-Si-HIP-205BA3 at reference condition. Efficiency

17.9%

Maximum power Max power voltage Max power current Open circuit voltage Short circuit current Temp. coefficient (Pmax) Temp. coefficient (Voc) Temp. coefficient (Isc) Material Number of cells Module area

205.074 Wdc 56.7 Vdc 3.617 Adc 68.797 Vdc 3.837 Adc 0.29 0.172 0.88 HIT-Si 96 1.179 m2

City

Capacity factor

Electricity to grid (MWh)

Annual GHG reduction (tCo2)

Liter gasoline

Abadan Abadeh Ahar Ahvaz Arak Anzali Babol Bafq Bam Bandar-Abbas Bandar-Gonaveh Bandar-Lengeh Bandar-Mahshahr Birjand Bojnord Bushehr Chahbahar Chalus Dezful Garmsar Gorgan Hamedan Ilam Isfehan Jiroft Kashan Kazerun Kerman Kermanshah langerood Mashad Masjed-soleyman Minab Neishabur Orumieh Qom Ramsar Sanandaj Sari Semnan Shahre-kord Shahroud Shiraz Tabas Tabriz Tehran Yasuj Yazd Zahedan Zanjan

21.90% 24.60% 20.10% 21.90% 23.10% 16.50% 17% 24.30% 23.90% 22.50% 23.90% 23.40% 22.50% 23.40% 21.50% 26.10% 23% 17.30% 22.50% 22.20% 19.80% 23.50% 22.40% 24.40% 24.10% 23.50% 23.20% 23% 21.90% 18% 22.10% 22.90% 23.10% 22.40% 23.10% 23.40% 19.40% 23.10% 17.70% 22% 22.60% 22.50% 24.50% 23.50% 21.40% 22.30% 24% 22.80% 23% 22.30%

9572.6 10770.1 8823.6 9570.8 10135.9 7220.6 7444.8 10634.8 10468.7 9844.6 10468.1 10255.7 9846.6 10252.1 9398.4 11423.3 10087.3 7573.8 9855 9739.7 8673.5 10308.8 9823.6 10690.7 10565.6 10308.4 10156.8 10059.9 9602.9 7869.1 9685.3 10051 10109.3 9801 10121.6 10269.9 8481.2 10103 7745.1 9632.8 9877.5 9834.2 10734.6 10310.2 9375.3 9749.1 10530.9 9966.3 10067.4 9753.3

5994.4 6744.3 5525.4 5993.3 6374.1 4521.6 4662 6659.6 6555.5 6164.7 6555.2 6422.2 6166 6419.9 5885.3 7153.3 6316.7 4742.8 6171.3 6099.1 5431.4 6655.1 6151.6 6694.6 6616.3 6455.2 6360.2 6299.6 6013.4 4927.7 6065 6294 6330.5 6137.4 6338.2 6431.1 5311 6326.5 4850 6032.1 6191.6 6158.2 6722.1 6456.3 5870.9 6104.9 6594.5 6241 6304.3 6107.6

2,575,644 2,897,848 2,374,110 2,575,151 2,727,184 1,942,785 2,003,128 2,861,443 2,816,733 2,648,817 2,816,567 2,759,441 2,649,362 2,758,455 2,528,755 3,073,579 2,714,121 2,037,837 2,651,620 2,620,604 2,333,722 2,773,721 2,643,165 2,876,468 2,842,822 2,773,618 2,732,812 2,706,749 2,583,774 2,117,295 2,605,964 2,704,356 2,720,041 2,637,087 2,723,341 2,763,251 2,281,988 2,718,336 2,083,926 2,591,837 2,660,369 2,646,008 2,888,293 2,744,090 2,522,555 2,263,112 2,833,486 2,681,567 2,708,769 2,624,255

5. Conclusion The solar maps developed in this paper provide information about the levels of total and direct beam solar radiation which can be used as a database for future investments in the solar sector in Iran. Moreover, energy output of a 5 MW PV power plant was investigated in 50 cities of the country. As might be expected, the central and southern parts of the country have a higher potential while the cities close to Caspian Sea show low capacity factors. The highest capacity factor of 26.1% was obtained in Bushehr, while the lowest one was only 16.5% in Anzali. References [1] Aghajanian A. A new direction in population policy and family planning in the islamic republic of Iran. Asia-pacific Population Journal/United Nations 1995; 10(1):3.

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