Onuma Plant is a 9.5 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 18k homes (estimated). It ranks #562 of 692 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.
Data status
Known data
Calculated from dataset
Not available
Known, modelled and calculated values are kept separate. Missing fields are shown as unavailable.
Data provenance
Capacity and fuel are the upstream open-dataset record, not yet matched to a 2026 registry or GEM entry.
capacity: WRI GPPD; fuel: WRI GPPD
In context: how this plant compares
At 9.5 MW, Onuma Plant is below the median geothermal plant in Japan (30 MW). Geothermal plants tap underground heat to raise steam for a turbine; they provide steady, low-carbon baseload but are limited to geologically active regions.
Capacity comparison computed from the WRI Global Power Plant Database; fuel-type context is general engineering background.
Key facts
- Share of Japan geothermal capacity
- 1.8% of 536 MW across 14 plants in this dataset
- Age among peers
- 2 of 12 dated geothermal plants in Japan are older
Calculated from the capacity and generation records in this dataset (WRI Global Power Plant Database (CC BY 4.0)).
Capacity vs largest geothermal plants in Japan
Installed capacity (MW), WRI Global Power Plant Database (CC BY 4.0).
Owner
Operated by HOKKAIDO ELECTRIC POWER CO INC. All plants by this company →
Local climate & thermal context
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.
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.
Site climate & environmental severity
This site sits in a mild atmospheric environment (estimated ISO 9223 class C2 — Low), with thermal cycling the leading environmental stress.
Indicative estimate via the ISO 9223:2012 informative method (atmospheric corrosivity from temperature, time-of-wetness and airborne salinity), using WorldClim climate normals, the Köppen-Geiger class and coast distance. Indicative, not a measured corrosion rate.
How it compares & nearby plants
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.
Nearby power plants
- Sumikawa Akita · Geothermal · 50 MW · Akita
- Matsukawa Geothermal · Geothermal · 23.5 MW · Iwate
- Kakkonda · Geothermal · 80 MW · Iwate
- Shizukuishi · Solar · 24.8 MW · Iwate
- Ikawa - Juwi Solar Power Plant · Solar · 1.5 MW · Akita
- Akita · Oil · 1,300 MW · Akita
Location
Coordinates 39.9813, 140.7819 from WRI Global Power Plant Database (CC BY 4.0). View on OpenStreetMap.
Frequently asked questions
What type of power plant is Onuma Plant?
Onuma Plant is a 9.5 MW geothermal power plant in Akita, Japan, commissioned in 1973.
Who operates Onuma Plant?
Onuma Plant is operated by HOKKAIDO ELECTRIC POWER CO INC.