GEOTHERMAL ENERGY CONVERSION TECHNOLOGIES
There are three principle ways that have been developed for converting geothermal energy into electricity. Each is designed to exploit a specific type of geo- thermal resource. The most straightforward of the three is only feasible when a geothermal reservoir produces high-temperature dry steam alone. Under these circumstances it is possible to use a direct steam power plant, which is analogous to the power train of a steam turbine power station, with the boiler of the plant replaced by the geothermal steam source. Provided the steam exiting the reservoir is of suitable quality, this provides an extremely cheap and effective means of generating electricity.
Most high-temperature geothermal fields produce a mixture of steam and hot brine. This mixture cannot be utilized quite so simply and is most effectively
exploited using a configuration called a flash-steam geothermal plant. The flash process converts part of the hot, high-pressure liquid to steam and this steam, together with any steam extracted directly from the borehole, is used to drive a steam turbine.
Where the geothermal resource is of a relatively low temperature a third sys- tem called a binary plant is more appropriate. This uses the lower-temperature geothermal fluid to vaporize a second low–boiling point fluid contained in a sep- arate, closed system. The vapor then drives a turbine that turns a generator to pro- duce electricity. Although overall efficiency of such binary systems is low, the availability of a cheap heat source makes the system economical to operate.