Community Renewable Energy

Community Geothermal

Geothermal Energy is heat derived from the earth.  It is the thermal energy contained in the rock and fluid of the earth’s crust, originating from radioactive decay deep within the earth.

Geothermal energy can be harnessed for a variety of functions including electricity production, direct heat, and heat pump use.  The potential use of geothermal energy depends on the resource’s temperature, generally determined to be in one of three classes:

• Low temperature resources (less than 195 degrees F)
• Moderate temperature resources (195 to 300 degrees F)
• High temperature resources (300 degrees F and greater)

High temperature resources are used almost entirely for electricity generation.  As there are different types of geothermal reservoirs, there are also a variety of geothermal power plant technologies including dry steam, flash steam, and binary cycle.  Each of these technologies emits only steam, and can operate successfully in sensitive environments.

Geothermal stations currently provide power to about 4 million US residents, with a total output of about 2500 MW.  Most of this is provided by power plants over 5 MW in size, but there are a handful of geothermal plants in the US considered to be small or community-scale projects. 

Community-scale geothermal power plants have the potential for widespread application, but achieving cost effectiveness in small plant sizes presents a number of challenges.  The National Renewable Energy Laboratory’s Geothermal Technologies Program is working to determine the performance and value of small-scale geothermal power production through five projects in Western states.  To learn more, visit: http://www.nrel.gov/geothermal/georandd.html#field

Uses for low and moderate temperature resources include direct use and ground-source heat pumps. 

Direct Use: Direct use of a geothermal resource means using the water’s heat (directly) without a heat pump or power plant.  Examples of uses include space heat for buildings, district heating (18 systems in the western states), agriculture (soil and greenhouse warming), industrial (product heating or drying), and bathing (hot springs).

Ground-Source: Ground-source heat pumps use the earth or groundwater as a heat source in the winter and a heat sink in the summer.  Heat pumps are the most universally applicable geothermal technology, as the low temperatures required are available worldwide.

For more information on geothermal energy, visit the Geo-Heat Center.