Push for always-on California North Coast zero-emissions energy advances
California’s quest for more 24/7 renewable power to rapidly replace natural gas and nuclear energy took another step forward in the North Coast’s massive geothermal field.
Boards of supervisors for two of the three counties asked to buy-in on a geothermal opportunity zone, or GeoZone, have now done so, leaving promoters prepping to call for site, technology and project proposals this spring. On Feb. 8, Sonoma County supervisors voted to join the GeoZone, and Mendocino County supervisors did so on Dec. 7.
Lynda Hopkins, whose 5th District covers northwest Sonoma County, at the board meeting called it an “exciting opportunity” to extend power production in The Geysers area, which is the largest producing geothermal energy field in North America. Hopkins represents the county on the board of Sonoma Clean Power, a community choice aggregation utility for Sonoma and Mendocino counties and a key backer of the GeoZone effort.
“One of the biggest challenges with renewable energy is the variability, which requires us to keep traditional fossil fuel plants online to replace the energy when the sun is not shining or when the wind is not blowing,” Hopkins said.
The existing geothermal plants at The Geysers, mostly operated by energy company Calpine Corp., produce a net of 700 megawatts of power around the clock, accounting for 10% of California’s renewable electricity production and one-third of the country’s geothermal power.
The Geysers geothermal resource area covers 45 square miles straddling Lake and Sonoma counties. It produces dry steam, which can directly turn power plant turbines, a resource that only has its equal in the world in Larderello, Italy, according to Calpine. There are currently 13 geothermal power plants operating there with 321 wells into the hot rock.
“It’s a fantastic asset that we have in Sonoma County, but it has struggled with the amount of water that it uses,” Hopkins said.
As power production started to fall off at The Geysers in the 1980s as dry steam in the hot rock decreased, plans were hatched to recharge the hot rock by pumping water down to replace what was lost to stream and not recovered by condensation. A 42-mile pipeline was built in 2003 to carry 39 acre-feet (12.6 million gallons) of treated wastewater daily from a plant west of Santa Rosa to the geothermal field, which includes the northeast edge of the county as well as southeastern Mendocino and southwestern Lake counties.
That’s supplemented by as much as 28 acre-feet (9 million gallons) of treated wastewater pumped 40 miles daily from Lake County communities to The Geysers, a pipeline first built in the late 1990s to shift from pulling water out of Clear Lake.
Lake County supervisors have been less enthusiastic about the GeoZone venture, voicing concerns about more water usage, seismic activity, volcanic gas emissions and local use of power generated. After tabling a vote in November, the supervisors on Jan. 25 rejected the proposal to join the GeoZone on a 3-2 vote but expressed interest in revisiting the concept once projects are identified.
Supervisor Bruno Sabatier said he that in addition to concerns about geothermal quakes, emissions of hydrogen sulfide gas from more wells he was worried about any added use of water beyond treated waste.
“The more we continue to experience droughts, the more that's definitely something of concern, as that would be added pressure on the resources that we have,” Sabatier said.
Geof Syphers, CEO of Sonoma Clean Power, responded at the meeting that among the technologies being courted for the GeoZone is closed-loop geothermal technology. It would use far less water than traditional dry-steam systems in use at The Geysers for the past six decades and could dramatically reduce gas emissions. He noted that existing geothermal plants at The Geysers have worked with the Northern Sonoma County Air Quality District to limit such emissions.
