Shifting away from nuclear power and replacing it with wind and solar energy would cost Japan around $280 billion in new investment by 2020, Greenpeace said on Monday, calling on Tokyo to ensure safety for future power generations.

The report comes as Japan debates the future of nuclear energy after the March quake and tsunami triggered the world's worst nuclear crisis in 25 years at the Fukushima Daiichi plant.

Prime Minister Yoshihiko Noda, who took office early this month, has said the government wants to restart off-line nuclear reactors once safety checks were cleared, with the understanding of local communities.

Some 70 percent of people in Japan oppose nuclear energy and think it is necessary to pursue alternative sources of power despite its potential cost.

Currently, only 11 out of 54 reactors are operating in Japan following maintenance checks due to heightened public worries. That means only 20 per cent of the nation's total nuclear power capacity is in use. Solar and wind power account for about one percent of the country's electricity.

In a green energy scenario that includes a small increase in gas-fired power generation, the environmental lobby proposed raising generating capacity from wind turbines to 56 gigawatts from 2.1 GW and that from solar panels to 57 GW from 3.6 GW.

Greenpeace also says the cost of electricity from solar power, which is now higher than that from fossil fuels, should fall to competitive levels as technology advances.

"The price (of solar energy) dropped more than 50 per cent in the last year in Europe and will go down another 20 per cent in the next 12 months," said Sven Teske, senior energy expert at Greenpeace International.

"There are a lot of Chinese companies that manufacture solar panels and competition is enormous," he added.

Greenpeace wants Japan to cut its capacity for coal-fired energy by 60 per cent to 19.3 GW within 10 years. Japan should also cut its capacity from oil-fired power stations by 16 per cent, while increasing slightly the capacity of power generated from natural gas, it added. – Reuters