The process of producing electricity from a geothermal source is a two-step process. Heat from a geothermal source is first converted into mechanical energy, usually in the form of steam or a specialized “working fluid” that turns a turbine. The turbine is connected to a generator to produce electricity.
Since there are different kinds of geothermal sources that range from pure steam to simply hot water, the geothermal source type will largely dictate the type of power generation plant that will work best. There are four main types of geothermal power generation plants being used today: 1) flash 2) dry steam 3) binary and 4) flash/binary combined power plants. Gradient Resources is currently engaged in the use of the following power generation technologies:
In geothermal sites that produce a combination of steam and hot water a flash power plant separates the steam from the hot water (called brine) and uses the steam to power the turbine generators. The hot water is collected and re-injected into the geothermal site to minimize water loss. Power plants in Dixie Valley, Nevada and Coso, California are examples of flash power plants.
Binary power plants are complete “closed loop” systems and can be utilized at any geothermal site including lower temperature geothermal sites. Geothermal steam and/or hot water is used to heat an organic fluid that boils at a lower temperature than water. This heated working fluid then turns the power generating turbines. The working fluid is cooled and used over and over again while the hot water is then condensed and re-injected into the site to close the loop resulting in zero emissions. Binary power plants exist in Steamboat and Patua, Nevada.