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| Fig. 1: Correlation between efficiency and module's temperature. The increase in module's temperature is associated with reduction in efficiency. [7] |
Saudi Arabia is the largest oil producer and it has the second highest proven oil reserves, after Venezuela. In 2012, oil production was more than 11 million barrels per day, which accounts for 13.3 of the world's production, and the remaining proven oil reserves are estimated to be 265.9 billion barrels, 15.9% of the world's reserves. [1] Recently, the country has embarked on an ambitious initiative to diversify its energy supplies with more focus on renewable energy. The new plan is aimed to lower the country's dependance on fossil fuel and meet the anticipated increase in domestic energy demand. Electricity consumption is expected to increase from 51 GW in 2011 to 120 GW by the year 2030. [2] King Abdullah City for Atomic and Renewable Energy (K.A.CARE) plans to increase renewable energy contribution to 54 GW by 2032 and Solar photovoltaic (PV) will add 16 GW to the energy mix. [3,4]
Energy from photovoltaic (PV) could be an obvious excellent alternative energy source for Saudi Arabia since it is sunny and has one of the highest direct normal irradiation (DNI) resources in the world. However, other climate conditions such as temperature and dust add more challenges to the already existing struggle to compete economically with fossil fuel even under controlled optimum conditions. Sunny weather increases power output from solar panels while dust and high temperature reduce the efficiency leading to lower power output. [5]
The temperature of PV surface rises with longer exposure period to sunlight and high ambient temperature. The elevated temperatures directly impact the PV efficiency. Atom vibrations (photons), in a p-n junction cell, increase and obstruct charge carrier movement which decreases cell efficiency. [5] As part of Power System Program of the International Energy Agency (EIA), a study was conducted to analyze data from 18 grid connected PV plants located on different geographic locations and it showed a direct relation between temperature and PV module efficiency. The plants were located in Austria, German, Italy, Japan and Switzerland. The study concluded that 17 out of the 18 systems showed annual losses in efficiency due to temperature changes by 1.7% to 11.3%. The highest efficiency reduction was observed at a relatively high ambient temperature of 30°C. [6]
A study was conducted on a ploycrystaline PV module with solar tracker on Dhahran- east of Saudi Arabia showed similar temperature effect. The data were compared based on daily peak power output. PV module efficiency decreased from 11.6% to 10.4% when module temperature increased from 38°C to 48°C, which corresponds to 10.3% losses in efficiency and a temperature coefficient of -0.11 ΔE/%°C, Fig. 1. [7]
Saudi Arabia is located on a very arid region that has frequent dust storms and dusty conditions. Deposits of dust on the surface of PV module blocks the solar irradiation from reaching cells through the glass cover. The density of deposited dust, its composition and particle distribution, can have an impact on the power output and current voltage and characteristics of PV modules. The objective of the aforementioned PV study in Dhahran was to investigate the effect of dust accumulation on the power output of solar PV. Four mono-crystalline PV modules and 2 polycrystalline modules were tested at outdoor conditions for several months and power output was monitor daily. [7]
During the course of the study, it was observed that there was atmospheric dust that scatters the solar radiation, in addition to dust deposits on PV surface, which also blocks PV module from direct solar radiation. The study concluded that long period of PV module exposure to real outdoor conditions gradually decreases power output if no cleaning is performed to remove the dust. More than 50% power output reduction was observed over six moths of no cleaning. It was also observed that a single dust storm in the month of March decreased the power output by 20% for all modules. The dust density was measured to be 0.0618 milligram/cm2/month. Another observation is that rainfall helps to clean the panels and restore its power output to higher levels. Rainfall, however, is not frequent in Saudi Arabia so it can't be relied on for PV surface clean up. The study also showed that power output was sustained at high levels when it was cleaned up routinely once a week. [7]
The high summer temperature in Saudi Arabia is very often associated with very high humidity along the east and west coasts. Humidity affects solar PV in ways comparable to dust accumulation. Water vapor particles might reduce the irradiance level of sunlight that is required for PV panels to reach high efficiency. PV surface could be moist and light is scattered either by refraction, reflection or diffraction when it hits water droplets. [8] A study was conduced on Qatar for two commercial PV modules, mono-crystaline and amorphous, to evaluate the effect of humidity. Both modules were installed in a fixed position relative to the sun. Relative humidity, temperature and power output were recorded. The study found that when the temperature or relative humidity increases, PV efficiency decreases and that decrease was more significant when there was a change in relative humidity. Impact of relative humidity was 50% higher than the impact of temperature. The effect was assessed by finding the change in maximum power efficiency with respect to temperature change and comparing it to the same efficiency with respect to humidity change, Table 1. [9]
| Table 1: Efficiency variation for two PV modules with respect to relative humidity and temperature on Qatar. [9] |
Hight Temperatures, dust and humidity are the main obstacles that reduce the efficiency of PV modules and overcoming them completely might be very costly. The challenge for Saudi Arabia is to find economically feasible ways to reduce their effects. More evaluations of optimum site locations might reveal better candidates for deploying solar PV. The west cost of Saudi Arabia, for instance, has relatively less dust storms and lower temperatures.
More research is needed to investigate potential technologies that can be used to improve PV performance. Some of the potential technologies that provide cooling mechanisms are fins, ducts and water coolers. Cooling down the PV module could limit efficiency losses to less than 3%. Air ducts attached to backside of the PV panels could reduce the module temperature by more than 10°C. Installing water tanks at the bottom of the PV panels or flowing cold water were shown to be able to reduce the module temperature by 22°C. [5] The effect of dust accumulation on the PV panel surface can be minimized by implementing cost effective cleaning methods. It could also involve additional coating to avoid sticking of sand and dust particles on the PV panel surface.
© Mohammed Alshakhs. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] BP Statistical Review of World Energy 2013," British Petroleum, June 2013.
[2] R. Shamseddine, "Saudi Signs Deal to Build 4-GW Gas Power Plant," Reuters, 21 Sep 11.
[3] A. McDowall, "Saudi Sets Out Roadmap for Major Renewable Energy Programme," Reuters, 23 Feb 13.
[4] A. McDowall and N. Shamseddine, "Saudi Battles Excess Heat, Dust to Build Solar Power," Reuters, 23 May 12.
[5] A. Baras et al., "Opportunities and Challenges of Solar Energy in Saudi Arabia," in Proc. World Renewable Energy Forum (WREF) 2012, ed. by C. Fellows (Curran Associates, 2012), p. 4721.
[6] T. Nordmann and L. Clavadetscher, "Understanding Temperature Effects on PV System Performance," Proc. 3rd World Conf. on PV Energy Conversion, 3, 2243 (2003).
[7] M. J. Adinoyi and S. A. M. Said, "Effect of Dust Accumulation on the Power Outputs of Solar Photovoltaic Modules," Renewable Energy 60, 633 (2013).
[8] S. Mekhilef, R. Saidur and M. Kakalisarvestani, "Effect of Dust, Humidity and Air Velocity on Efficiency of Photovoltaic Cells," Renew. Sustain. Energy Rev. 16, 2920 (2012).
[9] F. Touati et al., "Effects of Environmental and Climatic Conditions on PV Efficiency in Qatar," Renewable Energy and Power Quality Journal, No. 11, 275 (2013).