Renewable energy companies are betting that a leading contender in the race to become Japan's next prime minister, Taro Kono, will unleash changes allowing more market access and a fairer playing field after years of neglect.

The 58-year-old has long championed more renewable supplies in Japan's roughly $150 billion electricity sector, the world's biggest national power market outside China, and has promised an economic stimulus package focused on renewables if he wins.

Investors have been buying renewable energy shares hoping the popular Kono wins the Sept. 29 vote for the Liberal Democratic Party's (LDP) next leader and — by virtue of its majority in the Diet — Japan's next prime minister.