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Renewable Energy: Scaling Deployment in the United States Chapter j 5 95

constant temperature nature of subsurface Earth, cooling warm summer air in
the underground or, in the winter, drawing heat up from the relatively warm
ground. As this technology does not require the presence of hydrothermal
resources, its adoption is feasible in all regions of the country. In the domain of
electricity production, next-generation “enhanced geothermal systems” are
being designed to access the hot, dry rocket at several miles’ depth and,
through the injection of water, artificially create a hydrothermal resource
(Annual U.S. and Global Geothermal, 2016).
One key feature of geothermal energy is that it is continuously available, as
opposed to intermittent resources like sunshine and wind. As such, geothermal
power is one of the leading options for renewable resource-based base load
electricity generation and provides a technically viable option for supplanting
coal power plants, which are arguably the most environmentally pernicious
class of generators currently operating.
Although in the late 19th century numerous communities in the United
States made use of surface-level hydrothermal resources for residential and
commercial heating services, it was not until 1922 that the first geothermal
electricity generator was brought online at The Geysers near San Francisco,
California. In 1960, the first US utility-scale geothermal plant, an 11-MW
facility, was completed. After rapid expansion in the 1980s, spurred in part
by California’s Geothermal Grant and Loan Program, growth in total capacity
and output has slowed. In the past decade, the average growth rate of electrical
output from the geothermal industry was about 1% per year (Annual U.S. and
Global Geothermal, 2016).
In 2014, geothermal energy resources provided about 5% of US renewable
electricity generation, and as of 2009, there were more than 3700 MW of
geothermal electricity generators online. Owing to its location on a series of
tectonic plate conjunctions, California enjoys considerable hydrothermal
resources and, at 2700 MW of installed capacity, is the premier geothermal
power producer in the country. With 600 MW of installed capacity and more
projects under development than other states, Nevada’s fleet is also a signifi-
cant component of the US geothermal power plant stock. As of 2016, reported
projects currently under development are set to add 1200 MW of generation
capacity. In addition, it is estimated that about 50,000 homes have geothermal
heat pumps installed each year (Geothermal Heat Pumps).

BIOPOWER

Biomass resources exist where solar energy is stored in an organic form as
plant matter or other biological material. Biopower technologies utilize
biomass to generate electricity.
Direct-combustion steam production is the most common mode for gener-
ating biopower, although the scale and thermal efficiency of those boilers tend
to be smaller and lower, respectively, than their coal counterparts. Cofiring