Japanese companies are building some of the world's biggest battery systems to address one of solar power's biggest problems--its volatility.

Handling the surges in power when the sun shines and storing that energy for use when it is cloudy or dark is a major headache for solar power producers and the utilities they supply.

Mitsubishi Electric Corp. and NGK Insulators Ltd. are assembling a 50,000 kilowatt battery system for Kyushu Electric Power Co. to study ways to better accommodate solar power.

A slightly smaller, 40,000 kilowatt battery system is under construction in Minami Soma, north of the Fukushima Daiichi nuclear power plant, for Tohoku Electric Power Co. to conduct similar research.

The government is financing both projects at a total cost of ¥31.7 billion ($257 million), a government official said.

Power companies have cited the volatility of supply as a reason for refusing to accept new solar power suppliers, effectively putting a brake on efforts to increase use of this renewable power in Japan.

Part of the problem lies in the relatively small size of Japan's power grids, due to the geography of the archipelago and the lack of compatibility between regional power utility grids.

In Europe, where renewable energy is widely adopted, power grids are connected across the continent enabling surges in electricity generation in one location to be sent elsewhere relatively easily.

During a boom in solar power investment in the two years after Japan’s renewable energy law took effect in July 2012, the southern island of Kyushu saw an especially large number of solar projects due to its relatively high levels of sunshine.

Kyushu Electric suspended making contracts with new projects last September, citing problems with its grid capacity.

The utility will use the new battery system to study how to stabilize electricity flows when solar power generates a large amount of power on a low demand day, a company spokesman said.

Tohoku also enjoyed a solar investment boom because of its large areas of unused land. Tohoku Electric's research into improved handling of solar electricity will start in February.