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GEOTHERMAL POWER
Delving Deeper: New
Optimism for Enhanced
Geothermal Systems
Enhanced geothermal systems (EGS) have long held promise. New developments
suggest dramatic progress may be on the horizon. Can innovation feasibly overcome
technical and economic hurdles that have consistently challenged EGS?
Sonal Patel
n February 2024, the U.S. Department
of Energy (DOE) unveiled the
first round of its much-awaited enhanced
geothermal systems (EGS) pilot
demonstration selections. The agency's
Geothermal Technologies Office (GTO)
at first announced three projects, but
by March 2024, it appeared to have narrowed
them down to two. One pilot will
be spearheaded by California-headquartered
Chevron New Energies and will
use " innovative drilling and stimulation
techniques to access geothermal energy
near an existing field in Sonoma
County in northern California. The other,
led by Fervo Energy, will develop the Milford
Renewable Energy Corridor on the
western flank of the Mineral Mountains
in Utah, next to the Frontier Observatory
for Research in Geothermal Energy
(FORGE), the DOE's 2015-opened dedicated
EGS underground field laboratory.
The GTO said the two projects will
I
1. Much like fracking, an enhanced geothermal system (EGS) pumps liquid (often water) at
high pressures into the ground in order to create a network of fissures. The water is superheated
by the natural hot dry rock and then pumped to the surface. Source: U.S. Department of
Energy
receive up to $40 million of the $84 million
designated for the EGS pilot projects
under the November 2021-enacted Infrastructure
Act. (A third project unveiled
in February, Mazama Energy's " first-ofits-kind
super-hot EGS, " would have leveraged
temperatures above 375C near
Newberry Volcano in Oregon and had
been slated to receive $20 million; however,
its status remains unclear.) GTO
told POWER in March that details of its
selected projects were still under wraps,
given that " project details and funding
amounts are subject to change. " Negotiations,
which will precede the final awards,
could run between three to five years,
which will entail " one or more budget
periods. " At the same time, " Project continuation
beyond the first budget period
will be contingent upon several elements,
including satisfactory performance and
DOE's Go/No-Go decision, " it said. However,
the funding opportunity issued to
April 2024 | POWER
select the projects will remain " rolling, "
meaning that it may remain open for up
to 48 months and provide more opportunities
for the DOE's original intention to
select up to seven EGS pilots, depending
on funding available. A second round of
applications is in the works and should be
issued soon, it noted.
An Ambitious Goal: Shave EGS Costs
by 90%
Still, the GTO's initial selections mark a
crucial step forward for EGS, a long-pursued
subset of geothermal technology.
EGS are advanced engineered geothermal
reservoirs that involve drilling deep
wells underground in hot rock at temperatures
of 175C to more than 300C
but where there is little to no natural permeability
or fluid saturation. Compared
to other approaches, EGS distinctly enhances
subsurface permeability via safe,
well-engineered stimulation processes
" that re-open preexisting fractures, create
new ones or a combination of both, "
explains the GTO. " These open conduits
increase permeability and allow fluid to
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circulate throughout the hot rock. The
fluid transports the otherwise stranded
heat to the surface where clean, renewable
electricity can be generated with
current power generation technologies. "
According to the DOE, EGS (Figure
1) is generally categorized as near-field
resources-areas around hydrothermal
sites that are elevated in temperatures
but lack sufficient permeability and/
or in-situ fluids to be economically produced
as a conventional hydrothermal
resource-and deeper man-made reservoirs
drilled to depths of 3 kilometers
(km) to 10 km. They are thought to occur
naturally everywhere on Earth.
However, although EGS has been explored
since the 1970s, efforts to develop
it have remained small in scale, owing
mainly to insufficient reservoir volume,
difficulty with drilling, and induced seismicity.
Since the first EGS pilot installation
at Fenton Hill in the U.S. (which ran
from 1974 to 1995), experimental projects
have operated at Rosemanowes
in the UK; Basel in Switzerland (which,
at 3 MW, has so far been the largest in
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