The solar yield, i.e. the product of specific solar radiation per square metre and the peak power of a solar module, decreases on the one hand because air particles absorb radiation at high altitudes, as a new study now shows. On the other hand, because particulates particles settle on the photovoltaic modules themselves and pollute them. Frequent cleaning of solar modules, however, is associated with the risk of minute damage to the surface. So how do air pollution and particulates reduce the power generation of solar modules?
Less specific solar radiation due to polluted air
Chinese scientists from the Institute of Atmospheric Physics of the Chinese Academy of Sciences have now confirmed in their study that polluted air scatters or absorbs sunlight. As a result, less sunlight reaches the earth's surface - and there is less specific solar radiation.
It is particularly tricky that the smaller the particulates particles are, the more harmful the effects become. It is true that the intensity of solar radiation varies over time. But in addition to cloud cover, released aerosol particles, ash or dust can refract or scatter sunlight.
The researchers note that with increasing air pollution, the ratio of scattered to global radiation also increases and thus ultimately less sunlight penetrates to the Earth's surface. Furthermore, the higher the particle concentration, the more the direct penetration of solar radiation to the Earth's surface is reduced. At the same time, more air pollution also increases the scattering potential.
Under different weather and light conditions, research was carried out into the effect of air pollution on solar radiation. The solar radiation hitting the earth's surface - the SSR (surface solar radiation) - is the actual energy source for photovoltaic systems.
Especially for urban photovoltaic systems, the solar yield is lower
Thus, the findings of this study point to potential difficulties that solar power generation will face, by no means only in China, and does not make the switch to renewable energy any less challenging.
Back in 2017, scientists from the American Chemical Society studied the effects of particulates in the atmosphere on the specific solar radiation per square kilometre. In China and India, the researchers found 17 to 20 % less energy production through photovoltaics. Extrapolated, this means: particulates is currently responsible for a reduction in solar yield of up to 1 gigawatt in India. In China, it is even up to 10 gigawatts of non-generated solar power due to polluted air. The solar yield is correspondingly lower.
particulatesfrom human activity is particularly dramatic
Although much of the deposited particles come from dust and dirt, the particulates resulting from human activities such as the burning of fossil fuels is infinitely more problematic. These particles are often very small. They are also difficult to clean because they are often sticky. But the more frequently solar modules are cleaned, the greater the risk of damaging these highly sensitive surfaces.
The researchers are by no means alone in their findings: In the journal Energy & Environmental Science in 2018, scientists from the Massachusetts Institute of Technology (MIT) confirm that the effects are indeed enormous. In some cases - the MIT scientists also studied the situation in India and China - it can mean the difference between a successful solar power plant and one that ends up not reaching the expected production level; and possibly incurring losses.
Among others, MIT professor Tonio Buonassisi from the mechanical engineering faculty was involved in the study. Over two years, the scientists collected measurements of solar radiation and pollution - and confirmed a significant reduction in the specific solar radiation on the solar modules. This showed that there is not a day without polluted air in Delhi (India).
Economic damage in the billions?
Result: The researchers finally determined an annual, average degree of damping of the solar cell output of about 12 percent. Exactly this 12 percent not infrequently exceeds the profit margins and thus makes photovoltaic systems less lucrative.
Extrapolated, the economic damage is immense: in Delhi alone, the loss of power generation revenue could be as much as $20 million a year, in Kolkata about $16 million, and in Beijing and Shanghai about $10 million a year each, the team estimates. Planned installations in Los Angeles could lose between $6 million and $9 million. Overall, they predict that the potential losses "could easily be hundreds of millions, if not billions, of dollars annually".
According to the MIT scientists, another finding leads to less solar yield: global warming. In another study, Ian Peters and Tonio Buonassisi come to the conclusion that on average the solar yield decreases by 0.45 percent per degree of temperature increase. This figure certainly differs depending on the type of solar module used, but it is a risk that must be taken into account.
With these findings in mind, it becomes even clearer that the limitation of pollutant emissions is also indispensable in terms of the energy transition.
(Image: Mariana Proenca/ unsplash)
