How the Constellation–Calpine Merger Pushed Geothermal Into the Baseload Spotlight

Power from the Depths: How a 25-MW Expansion at The Geysers is Reshaping California’s Grid Reliability

By: Robert Buluma 

MIDDLETOWN, California – On the verdant, rumpled hills of Sonoma and Lake counties, where steam vents hiss from the earth like dragons breathing just below the surface, a quiet revolution in renewable energy has just reached a critical milestone. On June 8, 2026, Calpine, a business unit of Constellation, officially announced the completion of a 25-megawatt (MW) expansion project at The Geysers geothermal complex—the largest operating geothermal field in the world.

At first glance, 25 MW might seem modest in an era of gigawatt-scale solar farms and massive wind arrays. But this is not a typical power plant. This is baseload, weather-proof, 24/7/365 renewable energy. The new capacity, enough to power over 25,000 homes annually, represents more than just an incremental increase in output. It is a strategic bet on reliability, a testament to the enduring value of geothermal energy, and a lifeline for a California grid increasingly strained by heatwaves, electric vehicle adoption, and the intermittent nature of other renewables.

This expansion—following a 38 MW energy storage system added at the site in 2024—cements The Geysers’ role not as a relic of 1960s ingenuity, but as a cornerstone of 21st-century grid resilience.

Part I: The Beast Below – Why The Geysers Matters More Than Ever

To understand the significance of this expansion, one must first understand the unique geology of The Geysers. Despite its name, you won't find Old Faithful here. There are no dramatic pillars of boiling water. Instead, beneath the Mayacamas Mountains lies a fractured graywacke sandstone reservoir, superheated by a shallow magma chamber. The result is the world’s most potent dry-steam field—a reservoir where water exists not as a liquid, but as pure, high-pressure steam.

Since the Pacific Gas and Electric Company first switched on a 11 MW plant at the site in 1960, The Geysers has been a workhorse. For over six decades, it has provided clean, uninterrupted power. However, by the early 2000s, the field faced a crisis: declining steam pressure. The solution was an ingenious feat of civil engineering—the Santa Rosa Geysers Recharge Project, which began injecting treated wastewater from Santa Rosa and surrounding cities back into the reservoir. Today, that recycled water flows through 45 miles of pipeline, replenishing the steam field and allowing The Geysers to operate at a stable capacity of roughly 725 MW across its 13 power plants (owned by Calpine and others).

Enter the 2026 expansion. Unlike building a new solar farm on a vacant desert lot, expanding a geothermal field at this scale required precision drilling, enhanced gathering systems, and navigating the complex thermal dynamics of a reservoir that has been exploited for 65 years.

"This isn't just turning a valve," explains a senior field engineer on site, speaking on condition of anonymity due to company policy. "We are reaching deeper, tapping pockets we bypassed in the 80s, and using new phase-separation technology to squeeze every Btu out of the fluid."

The result is 25 MW of "new" capacity—steam that was previously inaccessible or untapped, now flowing into the turbines of Calpine’s existing generating units.

Part II: The Expansion – Steel, Steam, and Solidarity

The completion of the project is notable for two distinct reasons: the engineering itself, and the labor framework that built it.

The Infrastructure: The $130 million project (estimated by industry analysts) focused heavily on "critical piping infrastructure." Old steel was replaced with high-alloy materials resistant to the corrosive hydrogen sulfide and chlorides present in geothermal steam. New steam gathering lines were laid across rugged, earthquake-prone terrain. Engineers utilized directional drilling to minimize surface disruption, preserving the oak woodlands that surround the complex.

The expansion involved:

· Deepening injection wells: To handle the increased condensate from the new steam extraction.

· Low-pressure turbine optimization: Because the new steam sources are at a slightly lower pressure than the original field, Calpine retrofitted blades and heat exchangers to capture energy from steam that would have previously been vented.

· Digital controls: A new AI-driven management system now balances steam flow between the older plants and the new capacity, maximizing the longevity of the reservoir.

The Labor Agreement: The expansion was completed under a Project Labor Agreement (PLA) with local labor unions. In an era where "green jobs" are often debated, the Geysers expansion is a concrete example of decarbonization supporting skilled trades. Welders, pipefitters, and heavy equipment operators from Northern California’s building trades worked under strong labor standards, completing the project on time and without major safety incidents.

"We proved that environmental progress and working-class wages are not enemies," said a representative of the Sonoma County Building Trades Council during a ribbon-cutting ceremony earlier this week. "The green grid runs on blue-collar steel."

Part III: The Offtake – Powering the Coast

A power plant is just a hole in the ground that makes noise until someone buys the electrons. In this case, the new output has been meticulously divided to serve two of California’s most aggressive Community Choice Aggregators (CCAs).

18 MW to Clean Power Alliance (CPA)

The lion’s share of the expansion—18 MW—will flow south to the Clean Power Alliance, which serves approximately three million customers across Los Angeles and Ventura counties. CPA is currently the number one green power provider in the United States and the fourth largest electricity provider in California.

For CPA, this is about "firming" their portfolio. CPA has aggressive goals for 100% renewable energy. But for most of the day, their supply mix is dominated by solar. When the sun sets in LA, the demand spikes. The Geysers provides a solution: a steady, dispatchable electron flow that doesn't rely on batteries (though they have those too) or natural gas peakers.

"The sun doesn't always shine, and the wind doesn't always blow, but the steam beneath The Geysers is always rising," said Matthew Langer, chief operating officer of Clean Power Alliance, in the official statement. "Partnerships like this strengthen California's clean energy future while supporting a more resilient and sustainable grid."

7 MW to MCE

The remaining 7 MW—which actually came online a year prior in a staggered rollout—are being supplied to MCE (formerly Marin Clean Energy). As the Bay Area’s first CCA, MCE has long been a champion of geothermal. The 7 MW will support residents and businesses in Napa, Marin, and Contra Costa counties—literally the backyard of The Geysers.

This local/regional split is a microcosm of California’s energy policy: power generated in the rural North Bay, serving the urban Southland and the industrial East Bay, connected by the same wires that have carried hydro power from the Sierras for a century.

Part IV: The Grid Context – Why 25 MW is a Big Deal

In a state with a peak demand often exceeding 45,000 MW, adding 25 MW seems like a drop in the bucket. But capacity factors tell a different story.

· Solar has a capacity factor of roughly 20-25% in California. A 100 MW solar farm delivers about 20-25 MW on average.

· Wind varies, averaging 30-35%.

· Geothermal at The Geysers operates at a capacity factor exceeding 90%.

Therefore, a 25 MW geothermal expansion is the equivalent of building 100 MW of solar (or 75 MW of wind) in terms of actual energy delivered to the grid over 24 hours. Moreover, that energy is dispatchable without carbon emissions.

The Storage Synergy: Notably, this 25 MW expansion follows a 38 MW energy storage system (likely lithium-ion batteries) installed by Calpine at The Geysers in 2024. That storage doesn't generate power; it shifts it. During low-demand overnight hours, when wind is sometimes curtailed, the batteries charge. During the 6 PM to 9 PM "net peak" when Californians return home and crank the AC, the batteries discharge.

The combined package—new baseload steam + batteries—turns The Geysers into a hybrid "always-on" plus "time-shifting" powerhouse. It is a model that Constellation (Calpine's parent) hopes to replicate elsewhere, particularly at their other geothermal holdings in the Imperial Valley.

Part V: Voices from the Field – Executive Perspectives

The official press release offered quotes that, while polished, reveal the strategic anxiety driving this investment. Aimee Blaine, senior vice president of Calpine's geothermal region, noted the urgency: "As California's electricity demand continues to grow, investments in reliable, around-the-clock renewable energy are more important than ever."

This is a subtle nod to the "Duck Curve" problem. For years, California has struggled with the risk of blackouts in the evening when solar production vanishes. Natural gas plants have historically filled the gap, but SB 1020 (California’s clean energy roadmap) requires a 90% clean grid by 2035. You cannot burn gas to meet that standard.

Geothermal is one of the few non-hydro, non-nuclear resources that can run 24/7 with zero emissions. The Geysers alone avoids the emission of roughly 2.5 million tons of CO2 annually—the equivalent of taking nearly 540,000 cars off the road.

"We are committed to investing in innovation and new technologies to drive the transition to a reliable, sustainable and secure energy future," reads the Constellation boilerplate. But the 25 MW expansion isn't an innovation; it's a proven solution finally getting the capital it deserves after decades of being overshadowed by the plummeting costs of silicon and fiberglass.

Part VI: The Economic and Community Impact

Middletown, California, has had a rough quarter-century. The town was devastated by the Valley Fire in 2015 and the Clay Fire in 2020. The Geysers complex, located in the hills above the town, is an economic anchor.

The expansion required a permanent increase in operations staff. While specific hiring numbers were not released, union representatives noted that the new piping and wellfield management systems require five to seven new permanent technicians to monitor steam chemistry and flow rates.

Furthermore, the property taxes paid by Calpine (via Constellation) flow into Sonoma County coffers, funding schools and fire protection districts. In a rural area where wineries dominate the flatlands, the geothermal plants are the industrial heartbeat.

Mark P., a third-generation maintenance worker at The Geysers (whose grandfather worked on the original 1960s build), stood near a new pipeline valve during a media tour. "My granddad used to say the steam was so strong in the 60s you could hear it screaming in the pipes," he recalled. "It's quieter now, but smarter. We aren't just mining steam anymore; we are managing an ecosystem down there. This expansion proves we can do this indefinitely."

Part VII: The Engineering Challenges Overcome

It would be dishonest to paint this expansion as a simple victory. The Geysers is a hostile environment. The steam, while carbon-free, contains high levels of hydrogen sulfide (rotten egg gas), ammonia, and carbon dioxide. The fluid is slightly acidic.

Corrosion: The new piping infrastructure had to be welded using specific low-carbon alloys and coated with advanced epoxies. A single pinhole leak in a high-pressure steam line can cut output and create a dangerous, invisible hazard.

Subsidence: When you remove fluid (steam) from the ground, the ground settles. The Geysers region has experienced minor subsidence (sinking) for decades. The new expansion required injection wells to be drilled deeper—up to 10,000 feet—to ensure that for every pound of steam pulled out, a pound of condensed water (plus the recycled wastewater) is pumped back in. Maintaining this mass balance is physics.

Seismic Activity: The Geysers is located in a seismically active zone. In fact, the injection of wastewater—while necessary—has been known to induce very small magnitude earthquakes (micro-seismicity). The new expansion includes sensitive seismometers connected to a shutdown logic. If the ground shakes beyond a threshold (likely M2.5 or M3.0), the injection pumps reroute, and steam extraction is throttled to prevent triggering a larger event. This "adaptive management" system is a direct result of lessons learned from enhanced geothermal projects in Switzerland and South Korea.

Part VIII: The Future – More Steam, Less Carbon

Looking beyond June 8, 2026, what does this mean for Constellation and the industry?

Constellation is currently the largest producer of clean energy in the U.S., primarily thanks to its nuclear fleet (55 gigawatts of capacity across all sources). However, nuclear comes with regulatory hurdles and public perception battles. Geothermal, by contrast, enjoys bipartisan support. It is renewable, non-intermittent, and occupies a small land footprint.

Calpine's management (now under Constellation's banner) has hinted at "supercritical" geothermal experiments—drilling so deep that water hits a "supercritical" state, containing vastly more energy. While the 25 MW expansion uses conventional dry-steam and flash technology, the data gathered from the new deep wells will inform future supercritical drilling plans, possibly at the Salton Sea or even at The Geysers itself.

Furthermore, the expansion serves as a proof-of-concept for the "Geo-Hybrid" model. By co-locating steam turbines (baseload), solar PV (peak production), and batteries (shifting), a facility like The Geysers could eventually provide a 100% clean, 24/7 power profile that mimics a coal or gas plant but with zero emissions.

Part IX: Critics and Considerations

No energy article is complete without acknowledging the limitations. Environmental groups, while generally supportive of The Geysers due to its long history, have raised concerns about the continued use of the recharge pipeline. The water injected into the reservoir comes from treated municipal waste. While that is a brilliant reuse of water that would otherwise flow to the ocean, some argue that in drought-prone California, that water could be used for agriculture or environmental stream flows.

Calpine counters that the water is "non-potable" and that the steam cycles return a significant portion back to the atmosphere as clean vapor, which eventually falls as rain—a closed loop, albeit a leaky one.

Additionally, the levelized cost of energy (LCOE) for new geothermal is higher than utility-scale solar. The 25 MW expansion likely required a power purchase agreement (PPA) with CPA and MCE that is priced above the wholesale market rate for solar. However, utilities and CCAs are increasingly willing to pay a "reliability premium" for baseload renewables. You can't run an air conditioner on a sunny day if the inverter trips. You can, however, rely on a geothermal turbine that has been spinning for 65 years.

Conclusion: The Eternal Fire

As the sun sets over the Mayacamas range, the new pipelines at The Geysers glow with reflected orange light. But inside the turbine halls, the lights are always on. The machines don't sleep.

The 25 MW expansion completed by Calpine and Constellation is not a revolution. It is an evolution—a quiet, deliberate hardening of the American grid. In the race to decarbonize, society has fallen in love with the novelty of solar roofs and the majesty of offshore wind. But the grit of geothermal is where the deep green of environmentalism meets the grey steel of industrial reality.

For the 25,000 homes powered by this expansion—from the beachfront condos of Malibu served by CPA to the suburban cul-de-sacs of the East Bay served by MCE—the lights will flicker on tonight, and they will stay on, regardless of whether the wind howls or the clouds gather.

The earth is hot. The steam is rising. And thanks to a 25-megawatt bet on an old technology, California’s future just got a little more reliable.

About the Geysers:

The Geysers is located approximately 72 miles north of San Francisco. It spans 30 square miles across the Sonoma, Lake, and Mendocino county lines. It currently supplies nearly 20% of the renewable energy in California’s grid mix, though this fluctuates based on solar and hydro availability.

About the Expansion (Key Data):

· Capacity Added: 25 MW

· Homes Powered: ~25,000

· Offtakers: Clean Power Alliance (18 MW), MCE (7 MW)

· Project Labor Agreement: Yes (Local Unions)

· Related Infrastructure: 38 MW battery storage (2024), new high-alloy steam piping.

See Also: 

How the Constellation–Calpine Merger Pushed Geothermal Into the Baseload Spotlight

Source: Constellation 

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