Sanyo has announced plans to double its annual investment in solar power and rechargeable batteries, according to reports from Japan.

The company has pledged $1.81bn over the next three years aimed at doubling output. Slightly more than half of the spending is expected to go on solar power.

Sanyo is already among the world's largest manufacturers of solar panels and rechargeable batteries, and is expected to spend $335m in fiscal 2007.

Japan's solar market is expected to grow at more than 20 per cent per year, according to the Nikkei Daily.

Matsushita, the world's third largest rechargeable lithium ion battery maker, is also expanding its output in Japan.

The company plans production increases and a new factory that will raise output by 50 per cent to 37 million units a month by April 2010, according to local press.

The burgeoning solar power market has attracted new investment from other Japanese firms, such as Honda which this week announced the opening of a new solar cell manufacturing plant in Japan.

"To reduce its environmental footprint, Honda has been proactively pursuing voluntary targets to make its automobiles, motorcycles and power products cleaner and to reduce CO2 emissions," said the firm in a statement.

"At the same time, Honda has been committed to developing technology for a clean energy source which does not use fossil fuels."