The Geysers: World's Largest Geothermal Power Complex (Since 1960)

Located in the Mayacamas Mountains of Sonoma County, Northern California, The Geysers is the planet's premier geothermal energy facility.

Key Facts

• Operational since: 1960 (first commercial plant).
• Installed capacity: ~1,517 MW (net ~900 MW delivered to grid).
• Power plants: 13 active units (down from 21 peak; some retired, some repurposed).
• Operator: Calpine Corporation (majority), with NCPA and others.
• Annual generation: ~6.5 TWh — powers ~750,000 homes, ~20% of California's renewable output.

How It Works

Natural steam reservoirs (240–340°C) at 2–3 km depth are tapped via 350+ production wells. Steam drives turbines directly (dry steam). Condensate is reinjected to sustain pressure—a pioneering enhanced geothermal system (EGS) since 1997 using treated wastewater from Santa Rosa and Lake County.

Significance

• Baseload renewable (95% capacity factor) — complements intermittent solar/wind.
• Largest single geothermal field globally.
• Model for EGS replication worldwide (e.g., Utah FORGE, Germany, Japan).

The Geysers remains the gold standard for commercial geothermal power.