Japanese power companies are warning a hot summer could bring blackouts for some areas unless nuclear plants are re-started.
Kansai Electric Power, which supplies mid-western Japan, including the commercial hubs of Osaka, Kyoto and Kobe, said Monday it could face an electricity shortfall of almost 20 percent if temperatures soar in July.
And the utility said it could remain up to 16 percent short in August as increased air conditioner usage zaps the electricity produced by its thermal fuel plants.
Kyushu Electric Power, covering an area further west, as well as Hokkaido Electric Power in the north also said they will not be able to meet summer demand without nuclear energy.
The warnings came during the first meeting with a government panel of experts and officials looking into what could happen to the power supply amid a debate over whether to bring idled nuclear plants back online.
The power industry, government and many businesses are pushing for atomic plants to be fired up again, but a lingering public distrust of the technology after last year's tsunami-sparked crisis at Fukushima has polarised opinion.
Last week Prime Minister Yoshihiko Noda's government gave the green light to restarting reactors at the Oi nuclear plant, run by Kansai Electric, but regulators still have to convince those living near the plant.
Public opposition to nuclear energy has intensified since the meltdowns at Tokyo Electric Power Company's Fukushima Daiichi plant when cooling systems were swamped by surging seawater in the worst atomic disaster for 25 years.
Since then, no power plant that has gone offline for regular safety checks has been permitted to restart.
Of Japan's stable of 50 reactors, only one remains in action, and that is due to be shut down on May 5. The four crippled units at Fukushima are no longer classed as reactors.
Supporters say without nuclear power, energy-hungry and resource-poor Japan cannot continue to function normally.
But critics of the technology point to continuing efficiencies that have allowed the world's third largest economy to all but shrug off previous dire warnings of shortages.