Lockdowns have been a controversial aspect of the COVID-19 pandemic. Yes, they undoubtedly save lives, but they also cause major ongoing economic issues – disrupting industries, causing job losses and associated financial pain.

But another thing lockdowns have done all over the world is decrease air pollution, and new research shows an interesting flow-on effect of this.

The new study has looked at solar power in Delhi – one of the most polluted cities in the world – and has found that the reduction in air pollution has allowed significantly more sunlight to get through to solar panels in the city, increasing their output.

"The increase that we saw is equivalent to the difference between what a photovoltaic (PV) installation in Houston would produce compared with one in Toronto," says first author Ian Marius Peters of Helmholtz-Institut Erlangen-Nürnberg for Renewable Energies in Germany.

"I expected to see some difference, but I was surprised by how clearly the effect was visible."

Delhi went into a strict lockdown on the 24 March 2020. The team looked at the PM2.5 particle concentration, a measure of fine particles less than 2.5 micrometres in diameter, in the air at the US embassy in Delhi before and after the lockdown – and compared them to the last few years at the same time of the year.

They also looked at the clear sky irradiance – which is how much sunlight reaches Earth's surface without being scattered or absorbed by particles and gases in the air.

The team found that, overall, the amount of sunlight reaching solar panels in Delhi increased by around 8 percent in late March 2020, and 6 percent in April 2020 compared to similar dates in earlier years.