Japan is pumping out 23.3 times more solar power than it was a decade ago, with a particularly large generating jump after the introduction of feed-in tariffs, according to estimates by Chiba University and Institute for Sustainable Energy Policies (ISEP) researchers.

Since fiscal 2005, Chiba University and the NGO ISEP have put out a renewable energy generation estimate at the end of March every year. In fiscal 2005, solar power sources produced 1.23 million megawatt-hours, while in fiscal 2014 they produced 28.69 million megawatt-hours, equivalent to the yearly power usage of 5.21 million homes, according to the estimates. Around 80 percent of the jump occurred after the introduction in fiscal 2012 of feed-in tariffs, a system where utilities buy up electricity from private renewable energy producers at fixed rates.

Meanwhile, other alternative energy sources have seen much less growth. Wind power, which requires comparatively large-scale development, grew by 2.2 times over the past 10 years, and biomass power generation grew by 3.5 times. Wind power production rose from 2.25 million megawatt-hours to 5.05 million megawatt-hours, and biomass power production rose from 0.56 million megawatt-hours to 1.96 million megawatt-hours.

Chiba University professor Hidefumi Kurasaka says, "In order to meet the goal of cutting domestic greenhouse gas emissions by 80 percent by 2050, the large-scale introduction of renewable energy is essential. The national government should move forward with frameworks to advance types of renewable energy besides solar. Furthermore, the purchase price for solar energy is being lowered every year, which may weaken the growth of solar power generation."

Under the feed-in tariffs, power companies pay renewable energy producers for a period of up to 20 years at a fixed price. The prices differ per energy type, and are set every year by the economy, trade and industry minister according to factors such as the proliferation of that energy type. In the case of solar power-producing companies, at the start of the tariffs in July 2012 they were paid 40 yen per kilowatt-hour, but with the spread of solar power the price was lowered to 24 yen per kilowatt-hour for fiscal 2016.