Western GeoPower Unit 1 – The Geysers


Project History
The Geysers Geothermal Field has produced commercial geothermal power continuously since 1960 and is one of only five geothermal fields in the world that produce “dry’ steam – a feature that reduces both capital and operating costs of power generation. Present generation from the two operating companies in the field – Calpine Corporation and Northern California Power Agency – is about 900 megawatts (MW).

A commercial power plant of 62 MW (gross) capacity, known as PG&E Unit 15, operated at the WGP leasehold between 1979 and 1989. It is now recognized that the Unit 15 plant was oversized for the available resource. For this reason, the wells supplying the plant experienced a rapid decline in productivity, similar to the decline experienced throughout The Geysers at that time. The plant was shut down in 1989 and eventually dismantled; and the wells were plugged and abandoned.

Since the mid-1990s, the rate of decline in well productivity at The Geysers has eased substantially and reservoir pressure has stabilized. In large part, this is due to increased injection of treated municipal waste water into the reservoir. Reservoir pressure under the Unit 15 leasehold has substantially recovered since the wells stopped production.

There is a demonstrated production history and a large database of resource information available from the Unit 15 leasehold, minimizing the resource-related risks of new development. GeothermEx, Inc. of Richmond, California projects that the Unit 15 leasehold will commercially support a 25.5 MW (net) power plant for a minimum of 20 years, with generation continuing at a slightly reduced output factor through 30 years.

GeothermEx is a recognized international authority in the evaluation of geothermal resources and has been involved in the development of all the geothermal fields in the United States and over 750 projects worldwide. The company has been associated with the development of The Geysers Geothermal Field for over 30 years.

Project Facilities
The project involves the design, construction and operation of physical facilities comprising production and injection wells, a gathering and injection system, a power generation plant and a transmission line and inter-tie.  Capital costs of design, construction, finance charges and drilling construction are estimated at US $100 million. A general description of the facilities follows:

Production and Injection Wells
Western GeoPower anticipates drilling 8 new production wells and one injection well on the property it controls by way of leases with the private land and mineral owners. The drill pads will require little work since the pads existing from the previous Unit 15 operations are still in good condition and the site is well served by existing access roads. The design envisions two pads with four wells each.

Power Plant
The power plant will consist of a 25.5 MW (net) nominal turbine-generator unit using a dual-inlet, single-flow, top-exhausting geothermal steam turbine, a conventional turbine approach proven in geothermal service worldwide. The generator will be air-cooled and generate at 13.8 kV which will be stepped up to transmission voltage. Principal plant ancillary systems will include a direct-contact condenser and wet cooling tower, with cooling water make-up supplied by condensate.

Transmission Line
An existing 115 kV transmission line that runs adjacent to the location of the proposed power plant can be accessed by tapping the line. No transmission upgrades are anticipated since the lines have been operating below capacity for a number of years.