The Impact of Dust on Solar Panel Efficiency

Introduction

Fig. 1: Array of giant photovoltaic cells (Source: Wikimedia Commons)

Solar panels are known as one of the leading sources of renewable energy, and they work by converting sunlight into electrical energy. Governments of more and more countries are pushing for usage of solar panels in lieu of non-renewable energies such as coal and petroleum. While their low environmental impact is a strong incentive for increased implementation, solar panels still face some challenges which hinder their ability to reach their full potential. One of those challenges is dust accumulation on the solar panel, which acts as a layer of shade preventing sunlight from penetrating the cell and being converted to electrical current. Dust conditions vary around the world, with desert regions such as the Middle East and North Africa having some of the most elevated dust concentrations in the world; interestingly, these regions also receive the most solar irradiation. [1] The giant array of photovoltaic panels in Fig. 1 is present in a desert in Nevada, suggesting the high solar irradiation in deserts.

Variables Affecting Power Output

The first key term to define is dust. Dust may be defined as minute particles with a diameter of under 500 μm. [2] It comes from solid material and can be visible or invisible, floating or settled. To evaluate the impact of dust deposition on the solar panels, it is necessary to first determine how much dust accumulates on the panels. We can define the thickness of dust on the solar panel, which we can define by the formula [3]

Most research papers define the amount of dust on the panel by grams per meter squared, and therefore determine the power lost from the solar panel per grams per meter squared of dust. The amount of dust that accumulates on the panel varies geographically. For example, an experiment performed in Tehran, Iran shows that the dust concentration on a local solar panel (accumulated over a period of 70 days) ranges from 4.0599 g/m² to 10.3129 g/m². [4] In the Middle East and North Africa, the dust accumulation rate was said to be around 0.3 g m^-2 day^-1. [5] If we want to compare that value to Tehran's, 0.3 × 70 = 21 g/m², which is a reasonable amount, considering that these regions have the highest dust concentrations on Earth.

Performance Degradation

While all research on the topic suggests that dust settlement on the solar panel significantly reduces solar power, different reports present different values to the extent of impact of dust settlement. For instance, one report states that one gram of dust accumulated on a photovoltaic panel of size 12 cm × 8 cm (hence 1/96 g/cm² ≈ 0.01 g/cm²) reduces efficiency by 60%. [6] However, another study carried out in the United Arab Emirates finds that the power decrease in photovoltaic cells is linear, with a value of 1.7% per g/m². Interestingly, most research has reached a consensus that solar panels can lose up to 40-50% power due to dust accumulation. [2,6,7] It is also important to note that other variables can affect the impact of dust settlement on solar panels, and they include humidity, size of dust particles, wind, and tilt of the solar panel. Increased humidity leads to more severe effects of dust settlement, because it binds dust particles to the surface of the panel, preventing them from being carried away by wind. [8] Furthermore, wind speed and panel tilt come hand-in-hand in affecting dust settlement. Horizontal panels tend to accumulate more dust because of gravity, but wind plays a big role. Excessively low wind speeds typically encourage suspended dust particles to settle onto the panel, but high wind speeds are capable of blowing dust off the panel, thus cleaning the PV. [9] Moreover, the smaller the size of the dust particle, the more it decreases PV power output, because small particles block more light with fewer holes given the uniform distribution of particles. [4]

Cleaning Solar Panels

There are a few prominent methods to clean solar panels. One of them, carried out by the Adani group in India, involves the use of tractors that clean the panels with water, cleaning wipers, and brushes. [10] However, this technique requires heavy usage of water and manual labor, which is both unsustainable and economically unviable. Another technique to remove dust from solar panels is called electrostatic dust removal, which applies a high AC voltage to repel dust particles from soiled solar panels. This has a maximum cleaning efficiency of 100% when dust settled is roughly 1 g/m², which corresponds to dust accumulation over a period of three days in the Middle East and North Africa. [11] The power consumption of this cleaning system is very low compared to the solar cell's power output. It takes around 5 minutes to clean a 1 m × 1 m solar panel with an electricity consumption of roughly 0.9 Wh. [11,12] If we assume that the power generated by the panel averages 300 W/m² over 7 hours, then the fraction of the energy collected by the panel that must be used for cleaning is

This cleaning method is especially useful in increasing the efficiency of mega solar panels in deserts. [11] Overall, while more and more power plant companies are cleaning their solar panels to reduce the dust settlement, multiple techniques are still being explored and optimized to keep a net positive power generation and to remain sustainable for the future.

© Jad Fidawi. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. 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.

References

[1] I. Al Siyabi et al., "Effect of Soiling on Solar Photovoltaic Performance under Desert Climatic Conditions," Energies 14, 659 (2021).

[2] A. Hussain, A. Batra, and R. Pachauri, "An Experimental Study on Effect of Dust on Power Loss in Solar Photovoltaic Module," Renewables 4, 9 (2017).

[3] R. Siddiqui and U. Bajpai, "Correlation Between Thicknesses of Dust Collected on Photovoltaic Module and Difference in Efficiencies in Composite Climate," Int. J. Energy Environ. 3, 26 (2012).

[4] A. A. Hachicha, I. Al-Sawafta and Z. Said, "Impact of Dust on the Performance of Solar Photovoltaic (PV) Systems Under United Arab Emirates Weather Conditions," Renew. Energy 141, 287 (2019).

[5] H. Kawamoto and M. Kato, "Electrostatic Cleaning Equipment for Dust Removal from Solar Panels of Mega Solar Power Generation Plants," 7th World Conf. on Photovoltaic Energy Conversion, Waikoloa, HI, IEEE 8547468, 10 Jun 19.

[6] S. P. Aly et al., "Novel Dry Cleaning Machine for Photovoltaic and Solar Panels," 3rd Int. Renewable and Sustainable Energy Conference, Marrackech, Morocco, IEEE 7455112, 10 Dec 15.

[7] M. A. M. Ramli et al., "On the Investigation of Photovoltaic Output Power Reduction Due to Dust Accumulation and Weather Conditions," Renew. Energy 99, 836 (2016).

[8] B. Guo et al., "Effect of Dust and Weather Conditions on Photovoltaic Performance in Doha, Qatar," 1stt Workshop on Smart Grid and Renewable Energy, Doha, Qatar, IEEE 7208718, 22 Mar 15.

[9] M. Mani and R. Pillai, "Impact of Dust on Solar Photovoltaic (PV) Performance: Research Status, Challenges and Recommendations," Renew. Sustain. Energy Rev. 14, 3124 (2010).

[10] S. Tiwari, P. Rani and R. N. Patel, "Examining the Economic Viability of a Solar Panel Dust Cleaning," 2019 IEEE Int. Conf. on Electrical, Computer and Communication Technologies (ICECCT), IEEE 8869011, 20 Feb 19.

[11] H. Kawamoto and M. Kato, "Electrostatic Cleaning Equipment for Dust Removal from Solar Panels of Mega Solar Power Generation Plants," 7th World Conference on Photovoltaic Energy Conversion (WCPEC), IEEE 8547468, 10 Jun 18.

[12] M. R. Maghami et al., "Power Loss Due to Soiling on Solar Panel: A Review," Renew. Sustain. Energy Rev. 59, 1307 (2016).