For months, Ukraine’s electricity grid has faced repeated Russian missile and drone attacks that have knocked out power plants and gutted substations. Now, it is contending with another, more unexpected threat: a sizzling heat wave.

Most of the country is experiencing unusually hot summer weather, with temperatures reaching 104 degrees Fahrenheit, or 40 degrees Celsius. It has strained an already hobbled grid, as residents turn on air-conditioners and food businesses use more electricity to cool products. Ukrenergo, the country’s national electricity operator, said Monday that current consumption largely exceeds Ukraine’s generating capacity.

To prevent a collapse of the grid, the authorities have imposed widespread rolling blackouts across the country. In Kyiv, the capital, most buildings are now without power for at least 10 hours a day, including during long periods in the daytime.

On Tuesday, Valerii Kalinichenko, a waiter at Shibuya Sushi Kiosk, a Japanese restaurant in central Kyiv, said his managers had bought a 15-kilowatt gas generator to provide power and keep their food fresh. “Power outages — we are ready for them,” he said.

The roar of generators installed by cafes and restaurants has become a soundtrack of the Ukrainian capital since the heat wave began last week.