The global endeavour of reducing reliance on non-renewable fossil fuels as our main energy source has motivated the research and development of various renewable energy sources. Solar (or solar photovoltaic (PV)) power is one such alternative that has seen rapidly growing popularity worldwide (see Figure 1). However, it has also been discovered that air pollution can and will impede the efficiency of systems designed to harvest solar energy, signalling a clear need to redress air pollution to achieve our overarching objective of sustainable energy use.
Figure 1. Global solar PV capacity by year (Song et al., 2021)
Song et al. (2021) explain that the efficiency of solar PV systems is a function of the intensity of solar radiation received at such systems’ surfaces. It follows that solar PV power generation may be undermined by air pollution and soiling (Figure 2). According to the same authors, air pollutants, such as aerosols, directly influence surface solar intensity through directly scattering and absorbing solar radiation coming from the Sun. As seen in Figure 3, solar radiation from the Sun may be attenuated partially through absorption and reflection/scattering back into space by atmospheric aerosols.
Figure 2. (a) Air pollution, (b) Soiling of solar PV systems, (c) Reduced surface solar radiation due to (a) and (b) (Song et al., 2021)
Figure 3. Processes of absorption (absorbed) and scattering/reflection (reflected) as solar radiation from the Sun travels through the Earth’s atmosphere (Ekins-Daukes and Kay, 2019).
Hence, as confirmed by Li et al. (2022), the absorption and scattering of solar radiation lowers the overall incoming solar radiation intensity at Earth’s surface (where solar PV systems are usually at). Consolidating these findings, Bergin et al. (2017) concluded that the effects on “direct and indirect radiative forcing” by atmospheric particulate matter possess significant potential to dampen solar PV power generation. Notably, the authors found that the reduction in surface solar intensity ranges from 16% in northern India to 25% over the Sahara and even up to 50% in parts of northwestern India. Given that India ranks 4th globally in solar power capacity (Ministry of New and Renewable Energy, 2022) I find it a huge pity that so much of that potential is lost to air pollution.
Figure 4. Percent reduction in visible solar energy due to (A) ambient PM, (B) dust PM deposition (soiling), (C) all PM deposition (soiling), (D) ambient PM and deposition combined (Bergins et al., 2017)
Figure 4 also depicts that surface solar intensity experiences a far lower magnitude of impact as a result of PM deposition (soiling). Why might this be so? Bergins et al. (2017) suggest that the cleaning frequency of solar PVs is a key influencer of the amount of solar radiation received. This makes sense because unlike ambient air pollution that is difficult to control, regularly cleaning the surfaces of solar PVs will significantly increase the transmission of solar radiation.
Furthermore, Son et al. (2020) contend that climatic conditions also affect the amount of solar radiation received by solar PVs. Their argument that rainfall in South Korea induced by the East Asian Monsoon can “repeatedly wash off” PM that is deposited on solar panels is again corroborated by Figure 4. The greatest reductions in surface solar intensity caused by PM deposition occur in the extremely dry Sahara and Gobi deserts which are dustier than most other areas, hence experiencing a greater attenuation of incoming solar radiation.
While we now know that solar power generation may be hampered by air pollution, how can we be sure that alleviating air pollution can eliminate, or even reverse this problem? Labordena et al’s (2018) study based in China, the world’s largest producer of solar energy, provides a rather convincing case as the authors found that the increase in surface solar intensity attributed to “clean-air policies” can potentially exceed 20% for parts of China that currently emit large volumes of pollution.
Figure 5. Increase in surface solar intensity for eliminating SO2, black carbon, and organic carbon in China’s provinces (Labordena, 2018)
These findings present hope, not just for China, but also the rest of the world that is striving to harness the economic and environmental benefits of solar power. I believe that there are extensive opportunities to leverage on “clean-air policies” across the world, and it would make sense to reap the benefits of higher surface solar intensity by beginning to redress air pollution in areas with high concentrations of solar PV systems.
Until the next entry, breathe safe and be safe!
References
Bergin, M. H., Ghoroi, C., Dixit, D., Schauer, J. J., & Shindell, D. T. (2017). Large reductions in solar energy production due to dust and Particulate Air Pollution. Environmental Science & Technology Letters, 4(8), 339–344. https://doi.org/10.1021/acs.estlett.7b00197
Ekins-Daukes, N., & Kay, M. (2019). Brighten the dark skies. Nature Energy, 4(8), 633–634. https://doi.org/10.1038/s41560-019-0440-0
Labordena, M., Neubauer, D., Folini, D., Patt, A., & Lilliestam, J. (2018). Blue Skies over China: The effect of pollution-control on solar power generation and revenues. PLOS ONE, 13(11). https://doi.org/10.1371/journal.pone.0207028
Li, J., Carlson, B. E., Yung, Y. L., Lv, D., Hansen, J., Penner, J. E., Liao, H., Ramaswamy, V., Kahn, R. A., Zhang, P., Dubovik, O., Ding, A., Lacis, A. A., Zhang, L., & Dong, Y. (2022). Scattering and absorbing aerosols in the climate system. Nature Reviews Earth & Environment, 3(6), 363–379. https://doi.org/10.1038/s43017-022-00296-7
Ministry of New and Renewable Energy. (2022). Year- end review 2022- Ministry of New and Renewable Energy. Press Information Bureau. Retrieved March 22, 2023, from https://pib.gov.in/PressReleasePage.aspx?PRID=1885147
Son, J., Jeong, S., Park, H., & Park, C.-E. (2020). The effect of particulate matter on solar photovoltaic power generation over the Republic of Korea. Environmental Research Letters, 15(8), 084004. https://doi.org/10.1088/1748-9326/ab905b
Song, Z., Liu, J., & Yang, H. (2021). Air pollution and soiling implications for Solar Photovoltaic Power Generation: A comprehensive review. Applied Energy, 298, 117247. https://doi.org/10.1016/j.apenergy.2021.117247