How Energy Is Produced - The Renaissance of Renewable Energy - page 153

Figure 4.56. A GHP circulates a mixture of water and antifreeze around a loop of pipe
(the ground loop) beneath or next to the building. In winter, heat from the ground is
absorbed into this fluid and is pumped through a heat exchanger (vice versa in summer).
The length of the ground loop depends on the size of your home and the amount of heat
you need - longer loops can draw more heat from the ground but need more space to be
buried in.
The Benefits and Costs of Geothermal Energy
Geothermal energy is classified as a renewable resource because the tapped geothermal
heat is naturally replenished by the ongoing nuclear decay in the Earth's core. Within
a human timescale, this energy is inexhaustible. Geothermal energy has the potential to
provide long-term, secure base-load energy and reductions in greenhouse gas emissions
(Goldstein et al. 2011 ) .
Geothermal projects typically have low operational costs but high initial investment
costs because of the need to drill wells and construct power plants. Cost estimates for
geothermal power installations vary widely between countries, from 3.1 to 13 U.S. cents
(2005) per kilowatt-hour for flash steam plants and 3.3-17 U.S. cents per kilowatt-hour for
binary cycle plants. EGS projects are expected to be more capital intensive, however, since
there are no commercial EGS plants yet in operation (Goldstein et al. 2011 ) .
The Potential of Geothermal Energy
In 1950, geothermal power generation was confined to two countries: Italy and New
Zealand. Today, twenty-four countries generate electricity from geothermal resources and
global installed capacity has risen fiftyfold, from 0.2 to 11 GW (see Table 4.9 ). Yet,
though encouraging, this increase is frightfully modest compared with the spectacular
growth of other renewable energy resources, particularly solar PV and wind. The reason
geothermal power remains marginal is that, although high-grade geothermal resources are
already economically competitive with market energy prices in many locations, they have
restricted geographic distribution, while the use of low-grade geothermal resources and
EGS encounters both cost and technology barriers. That is why commercial exploitation to
date has focused on shallow (less than 400 metres) reservoirs with high fluid temperatures
(more than 180°C).