San Diego Gas and Electric Company
Heber, CA, U.S.

Heber Binary Geothermal Demonstration Power Plant

Fluor provided engineering, procurement and construction liaison services for the 70-megawatt electrical Heber Binary Geothermal Demonstration Power Plant in Southern California. This was the world's first commercial-sized geothermal power plant utilizing the binary-cycle energy conversion method.

Fluor also conducted a feasibility study and major equipment identification to prove plant operability and economics, and selected the working fluid best suited to the geothermal resource characteristics.

Client's Challenge

This conversion system permits exploitation of moderate temperature geothermal resources considered non-recoverable by the more conventional flash steam cycle. This working fluid is a mixture of hydrocarbons, 90 percent isobutane and 10 percent isopentane. The Heber plant uses geothermal brine at 360 degrees Fahrenheit, which is pumped to the surface by use of downhole pumps.

Upon completion, Heber was the largest geothermal plant of its type in the United States at the time.

Fluor's Solution

The brine is retained under pressure and in the liquid state as it is pumped to brine/hydrocarbon heat exchangers. The tube-side flow of brine through the exchanger transfers heat energy to the shell-side hydrocarbon prior to re-injection. The brine loop is a closed system making no contribution to environmental pollution.

The Heber hydrocarbon turbine required special tooling for the blading because of the high mole weight of the hydrocarbon, and in the casing to accommodate the no-leak, compressor type of seals. These special design features and the non-corrosive nature of the working fluid will help ensure that the turbine provides high reliability and exceptional durability. These were further enhanced by the incorporation of a plant-wide distributed control and monitoring system.


​In cooperation with the Energy Research & Development Administration (ERDA), the Heber Geothermal Demonstration Power Plant began operations in 1980.​