howzit work? | answered here with pictures
geothermal electricity
Volcanic heat can be
found almost anywhere.
by SETH MASIA
ILLustratION by kurt struVe
Seth Masia ( smasia@solartoday.org)
is deputy editor of SOLAR TODA Y.
Chuck Kutscher assisted in preparing
this article.
Geothermal is a misunderstood word. It’s often applied to ground-source heating and cooling systems, a very efficient echnology to replace traditional furnaces and air conditioners in homes and commercial buildings. But here, we reserve the term
geothermal to refer to energy derived from water heated naturally from
volcanic processes.
Historically, geothermal energy has been used to heat buildings and
pools in volcanically active regions. The Romans built public baths over
natural hot springs, and a number of American towns, notably Klamath
Falls, Ore., and Boise, Idaho, sell natural steam as a public utility. The
first use of geothermal steam to drive an electric generator occurred in
Larderello, an old Roman sulphur spa in Tuscany, in 1904. A commercial electric plant was producing 250 kilowatts there by 1913, and today
Larderello steam plants put about 550 megawatts (MW) into the
Italian grid.
The United States, with about 3,100 MW
nominal capacity of operating geothermal plants,
produces about one-third of the world’s total geothermal electric power. (About 750 M W comes from
The Geysers, a cluster of plants in Northern California
that has been selling power since 1921. Another 450
MW comes from 21 smaller plants in Nevada.) American companies have filed for permits to build another
4,000 MW in the next few years. Philippine geothermal
plants produce about 1,900 MW (about 27 percent of
the nation’s power), and Indonesia produces about 1,200
MW, with another 4,000 MW projected.
2-3 miles deep
Geothermal power is potentially available anywhere.
Drill deep enough anyplace in the country, and eventually,
The trick is economically drilling that deep and fracturing
just enough rock to create a successful reservoir. An enhanced
geothermal plant needs at least two wells: one or more to extract
hot water and another to pump the cooled water back down into
the rock for reheating. In a future binary-circuit plant, the hot
water would be flashed to steam (by lowering its pressure) or used
to boil a hydrocarbon fluid, either of which would drive a power turbine
in a closed circuit. In Nevada, it typically costs about $10 million to drill
the two bores and build the binary turbine circuit. In general, a new
geothermal power plant costs $2 to $5 per watt to install and produces
power at a levelized cost of 4 to 11 cents per kilowatt-hour.
A big advantage of geothermal electricity is reliability. Plants typically
operate at 90 to 95 percent capacity, compared to about 75 percent for
the typical coal-fired plant.
Over decades, a geological hotspot can cool. To keep power up, more
water can be injected. At The Geysers, 71 miles (115 km) of pipeline now
bring in treated effluent from surrounding communities for injection
down the “cold” wells. ST
