New Delhi, May 29 -- India's power grid has developed a new weak spot. As heatwave temperatures climb past 45degC and electricity demand surges, solar power is helping the grid meet demand during the day. But night is becoming a different story.

After sunset, several parts of the country are witnessing power outages as the grid struggles to meet evening demand once solar supply fades, according to three people aware of the matter and grid data reviewed by Mint.

According to Sanjeev Aggarwal, founder and chairman, Hexa Climate, a renewable power generator, the challenge is now faced from 6-10 pm, when the sun is gone and demand is still high. "That gap is now the defining problem of India's grid," he said.

The supply crunch has been agg...