The geothermal analog of pumped storage for electrical demand load following

A six-day cyclic load-following experiment, conducted in July 1995 at the Los Alamos National Laboratory´s Fenton Hill hot dry rock (HDR) test site in north-central New Mexico, has verified that an HDR geothermal reservoir has the capability for a significant, and very rapid, increase in thermal power output upon demand. The objective of the load-following experiment was to study the behavior of the Fenton Hill HDR reservoir in a high-production-backpressure (2200 psi) baseload operating condition when there was superimposed a demand for significantly increased power production for a four-hour period each day. In initial tests of this concept, an enhanced thermal power output of 65% for a period of 4 hours each day was obtained. This enhanced power output was obtained from a level of baseload operation that was within only a few percent of the previously determined optimum steady-state reservoir operating conditions. The principal objection to cycling the production from any geothermal reservoir has been the temperature cycling induced in the production wellbore. However, in this present method of surging the production flow, the temperature excursions were limited to only about 19°F. The demonstration of this load-following capability could greatly increase interest in HDR geothermal systems by electric utilities because providing for surges in electric power demand is one of their major concerns at present