Pacific Gas and Electric Company’s Geysers Unit 21 (Geysers 21)

Docket No. 84-AFC-1

Certification Granted on June 12, 1985, but the project was never constructed.

Staff Counsel: Gary Fay

Hearing Officer: Garret Shean

Presiding Member: Barbara Crowley


Project Summary


AFC Filing and Data Adequacy

Pacific Gas and Electric Company (PG&E) filed an AFC for its 140 MW Geysers Unit 21 Geothermal Project on April 5, 1984. With the submission of additional data, the Geysers 21 AFC was accepted as data adequate by the Energy Commission, effective June 8, 1984.

Geysers Overview and Project Description

Geothermal power was the CEC’s most successful preferred technology during the late 1970s and early 1980s, with a total of twelve powerplants certified in the Geysers Known Geothermal Resource Area (KGRA) of Lake and Sonoma Counties, making it the world’s largest geothermal field. Geothermal, followed later by cogeneration, was the Energy Commission’s chosen alternative to the large coal and nuclear plants long favored by utilities.

PG&E had pioneered in the geysers many years earlier, long before the Energy Commission was created. Well over a dozen PG&E geothermal plants were already operating before the CEC started licensing geysers facilities, starting with AFCs for PG&E Units 16, 17, and 18. PG&E produced more geothermal power than any other utility in the geysers (if not the planet).

Projections had indicated that a vast potential of close to a thousand megawatts existed for additional geothermal plants, many of which already had proposed sites. Municipal utilities and even qualifying facilities (QFs) wanted their share of the geothermal bonanza.

But by the mid 1980s, the geysers boom was coming to an end, as other, more reliable/cheaper options, such as the purchase of energy from outside California, became available. Meanwhile, contrary to projections, the geothermal steam supply unexpectedly started to decline. As a result, electricity production fell at many existing plants, and proposals for new facilities were virtually all canceled.

The PG&E service area developed a surplus of electricity, in large part due to an influx of QF projects with a capacity below 50 MW, and thus not subject to CEC jurisdiction. PG&E then stopped building its own powerplants altogether.

Geysers 21 would thus be PG&E’s biggest and last geothermal AFC. Although certified, Geysers 21 would not be constructed.

The Geysers 21 site was located in Lake County, on the east slope of the Mayacamas Mountains, west of the small town of Cobb. Approximately 485,000 cubic yards of soil and rock material would have to be cleared from the site and disposed of to establish 8 acres of flat, graded surface for the powerplant. As usual, Union Oil (now UNOCAL, was PG&E’s steam supplier. It was expected that up to 80 geothermal wells would be drilled to provide steam for the plant’s turbines over the projected 30-year life of the facility.

Steam Sufficiency Hearing

Under Public Resources Code section 25540.2(a), a 12-month geothermal AFC, without an NOI, can be reviewed by the Energy Commission only if, at the outset of the proceeding, the applicant can reasonably demonstrate that the site is capable of providing geothermal resources in commercial quantities.

The Committee conducted steam sufficiency hearings for Geysers 21 on July 27 and October 9, 1984. On November 2, 1984, the Committee issued an order determining that the facility had adequate steam resources in accordance with Public Resources Code section 25540.2(a).


There were no major disputed issues in the Geysers 21 case. Air Quality and Demand Conformance were not contested. PG&E entered into agreements with the Sonoma and Lake County schools to compensate for new students brought into overcrowded districts by PG&E’s workforce. (Page 125 of the CEC Decision, Finding #36 on page 129 of the CEC Decision, and Requirement R52 (Socioeconomics) on page 130 of the CEC Decision.)

Fine tuning PG&E’s proposed mitigation measures in areas such as biological monitoring, noise, visual impacts, and structural engineering (design criteria for surviving earthquakes), plus consideration of alternative transmission tapline routes, was the major activity of the CEC staff, intervenors, and the Committee.

Trying to minimize this industrial project’s visual effect upon a mostly natural area (except for other geothermal plants) was a challenge, since the Committee declared the powerplant to constitute "a significant adverse visual impact." (Page 144 of the CEC Decision.) Many approaches were considered, but the most drastic re-design alternatives were found to be infeasible by the Committee. (Pages 147-154, 159-167 of the CEC Decision.) In the end, the Committee had to rely upon traditional screening methods, planting vegetation and large trees, plus using paint colors that blend in with the environment. PG&E also proposed limited night lighting to reduce impacts upon nearby residences. (Pages 167-172 of the CEC Decision.)


The Energy Commission certified PG&E Geysers Unit 21 at its June 12, 1985 Business Meeting. This facility was never built.