The sunniest region had the cheapest power — Japan, 22 Oct 2026
公開日：2026-10-23
On 22 October, the sunniest place in Japan was Shikoku. It also had the cheapest daytime wholesale power in the country, at 2.00 JPY/kWh. The national average fell 51.5% from the previous day to 15.78, widening the spread between regions to 13.8x.
Price: regional gaps are revenue gaps
Daytime average by area: Tokyo 27.65, Chubu 23.03, Hokuriku 23.03, Kansai 23.03, Tohoku 9.40, Hokkaido 6.58, Chugoku 6.48, Kyushu 6.48, Shikoku 2.00.
High-voltage areas in eastern Japan cluster above 20 JPY while western regions sit mostly below 10. The same kilowatt-hour, sold from a different location, is worth more than ten times as much.
Time of day: prices recover at the edges
The daytime high was 36.76 JPY (around 17:30) and the low 8.34 JPY (around 12:30). Prices still fall when solar output peaks.
Irradiance: the west leads
National average irradiation was 12.7 MJ/m². Against a seven-day baseline of 100, Shikoku led at 124 and Hokuriku trailed at 84.
The index is not generation. It captures weather only — no installed capacity, no inverter efficiency.
The sunniest region had the cheapest power. In Shikoku, an index of 124 and a price of 2.00 JPY describe the same place on the same day.
Why it matters
Revenue for a FIP plant is the market price plus the premium. In the hours when the market price collapses, the premium is nearly all of the income.
That makes regional price gaps into revenue gaps: identical equipment and identical output can earn very different amounts. Output data alone will not show you this.
Data and method
Prices are averages of 30-minute JEPX day-ahead slots between 08:00 and 17:00. The irradiance index compares Open-Meteo daily irradiation (MJ/m²) with the trailing seven-day average; it is an estimate, not metered generation.