The Department of Energy (DOE) has just released its 2012 update on the state of geothermal in the U.S. You can download the report here (9.7Mb): http://www1.eere.energy.gov/geothermal/pdfs/geothermalannualreport2012.pdf
The report discusses the state of the U.S. geothermal potential and highlights several projects. The Arizona Geological Survey is a lead agency in coordinating the information. The DOE report also points to another website: “A significant amount of information on exploration techniques, geothermal regions, and related publications has been made available through the National Renewable Energy Laboratory’s OpenEI website.” That site does contain interesting information, but I found its production figures a few years out of date.
The U.S. leads the world in geothermal production. The Geysers plant in California is the largest geothermal plant in the world generating 875 MW. I had thought that volcanic Iceland would have a large geothermal potential, but upon checking found that the five Icelandic plants have a combined capacity of 660 MW, smaller than California’s Geyser operation. However, besides electricity, Iceland’s geothermal plants also provide about 87% of heating and hot water requirements to buildings in the country. Iceland gets 74% of its electricity from hydropower.
The DOE report features a section on Enhanced Geothermal Systems (EGS). They say:
“Enhanced Geothermal Systems are man-made reservoirs, created where there is hot rock but insufficient or little natural permeability or fluid saturation. In an EGS project, fluid is injected into the subsurface under carefully controlled conditions, which cause pre-existing fractures to re-open. Increased permeability allows fluid to circulate throughout the now-fractured rock and to transport heat to the surface via a production well where electricity can be generated. While advanced EGS technologies are young and still under development, EGS has been successfully realized on a pilot scale in Europe and now at a new DOE-funded demonstration project at The Geysers.”
This technique is similar to “fracking” in oil and gas fields. It allows exploitation of areas lower in temperature than the Geysers and also exploitation where there is much less groundwater.
Research is also underway to recover lithium, manganese, and zinc from geothermal brines during the power production process. The map below shows the relative geothermal potential of the U.S.