GANDHINAGAR (India) • Air pollution is diminishing India's capacity to harness power from the sun, experts say, undermining billions of dollars being invested in renewables as the energy-hungry giant emerges as a solar superpower.

New research has found that the smog that sickens millions across India every year is also sapping solar power generation by more than 25 per cent, far beyond levels previously thought.

In the first study of its kind, US and Indian scientists measured how man-made particles floating in the air and deposited as grime on solar panels combined to seriously impair sunlight from being converted into energy. This interference causes steep drops in power generation, they found.

At present levels in India, it could amount to about 3,900 megawatts of lost energy - six times the capacity of its largest solar farm, a gigantic field of 2.5 million panels. "A simple calculation shows that this is a big amount of energy we are going to lose," Professor Chinmay Ghoroi, who co-authored the paper, said at the Indian Institute of Technology in Gandhinagar.

These huge losses will only compound as India realises its grand solar ambitions, experts say.

India, the world's third-largest polluter, is banking on solar power to electrify homes for hundreds of millions of its poorest citizens without adding to its sizeable carbon footprint. At the Paris climate summit in 2015, it pledged cuts to emissions and vowed to source at least 40 per cent of its energy from renewables by 2030 - a target it is well on track to exceed.

New panels are being installed so fast that India is expected to more than double its capacity this year, overtaking Japan as the world's third-largest solar market.

But with this spectacular growth comes "an exponential rise in the total amount of money lost" because of air pollution, said Professor Mike Bergin from Duke University in North Carolina, who led the research published in June. "We're talking billions of dollars here, easy," he said.

This bodes ill as the government seeks 40 per cent of its solar energy from rooftop panels atop industrial zones and urban centres by 2022.

But there is little appetite for gloomy projections as India's solar sector undergoes an unprecedented boom.

Dr André Nobre, an expert on the effect of haze on solar generation, found little interest when he presented his findings at a solar summit in Delhi last month.

"People didn't pay much attention," said Dr Nobre, who is head of operations and maintenance at Singapore-based Cleantech Solar, which invests heavily in India.

The putrid skies blocking out the sun also have a more sinister impact: premature deaths from smog steadily climbed in India to nearly 1.1 million in 2015. Prof Ghoroi said this shadow cast over India's solar success story should encourage policymakers to redouble efforts to clean the skies.

AGENCE FRANCE-PRESSE

Correction note: This story has been edited to provide the correct name of Dr André Nobre.