Solar power is in the news — sunshine hours matter. Mega-solar belongs where skies are clearest longest.
Japan's sunniest prefecture? Surprisingly Yamanashi — 2,183.0 hours in 2010, 11%+ above the 1,897.4 average. Kochi, Miyazaki, Gunma, Shizuoka follow.
Darkest: Akita 1,526.0, Aomori, Toyama, Yamagata, Fukui — Japan Sea snow country.
Tokyo (Palaceside Building's home): 1,881.3 hours, rank 27 — slightly below average despite winter sun. Osaka 1,996.4 at 18 surprises.
Bottom-six Niigata got Showa Shell's 2010 "Snow Country Mega-Solar" on a former refinery — CIS thin cells boost efficiency; 1,000 kW (~300 homes) via Tohoku Electric.
Ideal sites are equatorial high drylands — Japan's seasons, rain, and typhoons are less ideal; we hope technology improves efficiency.