Onuma Plant is a 10 MW geothermal power plant in Akita, Japan. It is operated by HOKKAIDO ELECTRIC POWER CO INC. Based on its capacity (estimated), it can supply roughly 17,832 homes (estimated). It ranks #518 of 659 Japan power plants by installed capacity. Commissioned in 1973, it is around 53 years old — an older, legacy facility. As a non-combustion source, it has no direct CO₂ emissions from generation. In context, the national grid averages 477 gCO₂/kWh (32.7% low-carbon) (2025).
Plant data: WRI Global Power Plant Database (CC BY 4.0), id WRI1020123.
Installed capacity (MW), WRI Global Power Plant Database (CC BY 4.0).
Operated by HOKKAIDO ELECTRIC POWER CO INC. All plants by this company →
This geothermal plant taps underground heat to raise steam that drives a turbine. It sits in a warm-summer humid continental climate (Köppen Dfb) — Northern Hemisphere, latitude 40.0°N — which shapes how much energy it can produce and how its output varies through the year.
Monthly mean temperature
Heating degree-days here run 93% above the median power plant in this dataset — a proxy for how much extra energy heated equipment must replace through its surfaces in winter.
Climate heat-demand index: 93/100 — this site sits in the top third of the power plants we cover by heating degree-days.
In colder climates, uninsulated hot equipment (boilers, turbines, valves, steam lines) loses proportionally more heat to ambient air — exactly the loss Inzonex modular insulation is designed to cut.
Climate normals: WorldClim 2.1 (1970–2000 monthly normals, 10 arc-min, CC BY 4.0); zone: Köppen-Geiger world climate classification (Kottek et al. 2006, 0.5° grid). Degree-days & heat-demand index computed by PowerAtlas — a modelled heat-demand proxy, not a measured site figure.
The #13 largest geothermal power plant of 14 in Japan by capacity.
Japan has 14 geothermal power plants in this dataset, together about 536 MW of capacity.
Coordinates 39.9813, 140.7819 from WRI Global Power Plant Database (CC BY 4.0). View on OpenStreetMap.
