04/08/2020

Always look on the bright side

Ranking topics: Most polluted capital cities

Coronavirus-induced lockdowns shuttered factories and halted daily commutes across much of the world in March and April. As a result, global electricity use is expected to drop by 5% this year, according to the Institute for Economic Affairs, a think-tank with its headquarters in London. City-dwellers have enjoyed cleaner air thanks to dramatically lower levels of air pollutants, such as nitrogen dioxide. The clearer, sunnier skies have also helped boost solar generation in many places to record highs.

new study published in Joule, an energy journal, uses data from Delhi, one of the world’s most polluted cities, to measure the impact of reduced air pollution on solar output. The researchers found that, during the roughly six weeks India was in lockdown, levels of PM2.5 (particles smaller than 2.5 microns) in the city fell by half. At the same time, the amount of energy produced at a solar-power facility 10km from the city centre was 8.3% higher, on average, in late March and 5.9% higher in April. Less air pollution meant clearer skies that allowed more sunlight to pass through the atmosphere, thereby increasing solar output.

But the researchers point out that lockdowns probably cannot explain the solar-energy boost elsewhere. With PM2.5 levels that can reach 15 times the limit considered safe by the World Health Organisation, Delhi’s smoggy air can block out the sun’s rays. Although cleaner air may have increased solar-energy generation in other heavily polluted cities, such as London or Los Angeles, in places with less air pollution the lockdown probably had a negligible effect.

Instead, the researchers attribute the high solar output reported across Europe during lockdown to good weather conditions. April was the sunniest on record in Britain and Germany. As economies spring to life again, pollution levels will inevitably rise too. For solar producers, that will be a cloud on the horizon.

This article is from our Graphic detail section.