Japan is one of the world largest energy consumers. It is the world’s largest liquefied natural gas (LNG) importer, and is among the top three largest importers of oil and coal.  After Fukushima nuclear disaster and shut down of nuclear generating capacity, Japan replaced the significant loss of nuclear power with generation from imported natural gas, low-sulfur crude oil, fuel oil, and coal. The energy self-sufficiency ratio of Japan in 2016 was 8.3%. Over reliance on fossil fuels, endangered the energy security in the country. To raise the energy self-sufficiency and energy security, Japan needs to diversify its energy mix from too much reliance on fossil fuels to more reliance on renewable energy. However renewable and green energy projects such as solar and wind power are costly and mainly considered risky from the point of view of banks (financiers). This research project looked at the determinants of renewable energy prices by focusing on solar module prices. In addition, the research proposed two applied frameworks, backed by theoretical models on green finance and investment based on projects size in order to induce the private participation in green finance and investment.