Japan Solar & Battery CalculatorJapan Home Solar and Battery Calculator: Output, Self-Consumption and Payback
Enter your prefecture, system size, roof direction and electricity bill. The calculator estimates annual output from JMA climate normals, simulates hour-by-hour self-consumption, exports and battery use, and shows the payback period, with Japan's FY2026 feed-in tariff (¥24 then ¥8.3). Free, nothing is sent.
Figures on this site are estimates from JMA climate normals and published averages for rules and costs. They are not quotes and do not guarantee output or savings. Roof shape, shading, equipment, how you use electricity and your tariff change the results a lot. Before buying, get site surveys and quotes from several installers and check your utility tariff and local subsidies.
How it works
- Monthly horizontal radiation and temperature normals are converted to radiation on your roof and output after temperature and equipment losses.
- Each month is split into sunny, average and cloudy days, and every hour the solar output is used at home first, surplus charges the battery, the battery covers shortfalls, and the rest is exported or imported.
- Bill savings plus export income minus maintenance are compared with the upfront cost after subsidies. Panels lose 0.5% and batteries 1.5% of capacity per year.
FAQ
How much does 1 kW of solar generate in Japan per year?
Using JMA climate normals, a south-facing panel on a 4-sun (22°) roof produces about 1,100–1,400 kWh per kW per year. Yamanashi, Nagano, Shizuoka and Aichi are among the highest; the Sea of Japan side is lower. See "Output by prefecture".
What is the FY2026 feed-in tariff for home solar?
Under the "initial investment support scheme", residential systems under 10 kW get ¥24/kWh for the first 4 years and ¥8.3/kWh for years 5–10 (approvals from late FY2025 to FY2027). After that you sign a contract with a utility, often at around ¥7–10/kWh.
Does a home battery pay for itself?
It depends on the gap between what you pay for electricity and what you get for exports, the battery price and subsidies. The simulator shows the battery's effect compared with solar alone and whether it pays back. Backup during blackouts is not counted in money.
What is the self-consumption rate?
The share of solar output you use at home instead of exporting. For households that are out during the day it is around 30% with solar alone and rises with a battery.
Is my input sent anywhere?
No. Everything is calculated in your browser.
Sources: radiation and temperature from JMA climate normals (1991–2020); feed-in tariff and renewable surcharge from METI (March 19, 2026); PV system and O&M costs from the Procurement Price Calculation Committee (110th meeting); battery cost from METI (March 2025); default electricity price from the appliance fair trade council. Calculated by this site (checked 2026-11-01). Links are in Japanese.