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GEOTHERMAL POWER
3. Fervo Energy's enhanced geothermal system drilling learning curve, from project start
( " spud " ) to reaching the target depth (TD), suggests the company planned an 18% learning
curve, but it has realized a 35% learning curve across all EGS projects. Courtesy: Fervo Energy
The achievements have garnered Fervo
a new slate of heavyweight backers,
including shale oil and gas pioneer Devon
Energy, Mitsubishi Heavy Industries,
and several other investors. According to
Fervo CEO and Co-Founder Tim Latimer,
the company's appeal lies in a unique
combination of favorable factors. " Demand
for around-the-clock clean energy
has never been higher, and next-generation
geothermal is uniquely positioned
to meet this demand, " he said. " Our
technology is fully de-risked, our pricing
is already competitive, and our resource
pipeline is vast. "
Challenges Remain for Wider
Deployment
However, EGS's wider deployment may
still be challenged. Experts generally
agree that, as with most other emerging
power technologies, EGS power
costs are currently not adequately characterized.
The NREL in 2023 suggested
average overnight capital costs for nearhydrothermal
field EGS range widely, between
$7,770/kW and $22,501/kW, and
for deep EGS (3 km to 6 km), between
$20,848/kW and $49,155/kW.
For the most part, cost uncertainty
still appears rooted in unknowns related
to well flow rates and the cost of deep
geothermal drilling. " Drilling a single
geothermal well can cost millions of
dollars, and drilling can exceed 50% of
a project's total costs, " the GTO noted.
" In addition, EGS depths are 4,000 to
more than 10,000 feet in the subsurface,
meaning longer and harsher drilling conditions.
Improving drilling times, reducing
drilling costs, and refining stimulation
approaches are critical, " it said.
Other
challenges
include
inherent
risks in the time and cost involved in
identifying resources and drilling to acApril
2024 | POWER
cess them. The emergence of closedloop
systems may reduce this risk
" because inherent geologic risks can
be addressed through engineering improvements, "
the GTO said. Protracted
permitting timelines for EGS may also
prolong project development, which
poses hurdles for financing.
In addition, EGS projects depend on
the time needed for development and the
cost of associated materials. " EGS environments
are hot, hard, corrosive, and
abrasive, requiring improved or innovative
materials and components that can
withstand the subsurface environment, "
the GTO noted. " Drilling improvements
are showing a marked improvement in
drilling times; however, material costs
remain an important topic and can be
addressed through improved materials
or alternative development methods, "
it said. Over the longer term, more and
larger wells will play a significant role in
reducing EGS costs, " so continuing to
reduce casing and cement costs is vital. "
Cost considerations are especially paramount
given that EGS's future role in a
decarbonized power system will likely be
as baseload generation. EGS has been
mostly viewed as baseload because
" these plants tend to have high fixed
costs and near-zero variable costs, and
derive few if any benefits from curtailing
output, " wrote researchers from Princeton
University and Fervo in a January
2024 article published in the journal Nature.
However, even with well-designed
and successfully engineered reservoirs,
EGS power plants could achieve capital
costs on the order of $5,000/kW to
$6,000/kW using current state-of-the-art
drilling and power plant technology, they
said. Major advances in deep drilling and
high-temperature reservoir engineering
could enable a better cost profile of as
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low as $3,000/kW, but even in that case,
EGS deployment could still be limited to
about 100 GW in " cost-optimized systems, "
they added.
A more feasible pathway by which
EGS could increase the average value of
energy is through flexible operation, the
researchers argued. While a flexible EGS
plant will likely have a higher LCOE than
an inflexible one, the " increased cost is
more than made up for by an increase
in system value, and by extension revenue, "
they said. " The added value from
flexibility can enable EGS deployment
in scenarios where it would otherwise
fail to find a market, including in partially
decarbonized electricity systems where
round-the-clock clean power is not yet
fully valued. The ability to gain an early
commercial foothold will be critical for an
emerging technology like EGSs, which
could see large cost reductions through
learning by doing as adoption increases. "
Some EGS startups are already exploring
a pronounced role for flexibility.
In February, Houston-based Sage Geosystems
outlined plans to build and begin
operating its first 3-MW EarthStore
facility by November. Sage's EarthStore
system is a Geopressured Geothermal
System (GGS), which means it uses
mechanical energy storage technology
that harvests the pressure energy of the
fluid and is also enhanced by the heat
of an EGS well design, Sage CEO Cindy
Taff explained to POWER. The facility
will be based on a full-scale commercial
pilot that Sage demonstrated in Texas
last year. The pilot produced 200 kW for
more than 18 hours (long-duration) and 1
MW for 30 minutes (load-following) with
Pelton turbines, with a round-trip efficiency
of up to 75% and water losses of
less than 2%.
" The depths of the energy storage are
going to be between 7,000 and 12,000
feet (2.1 km to 3.7 km), " she said. " It's
applicable for depths around 16,000 feet
to 20,000 feet, and we're really looking
for the temperature of the formation,
150C or greater, " she explained. " What
differentiates the GGS is not only are we
harvesting that heat from the system
from the water that we pump into the
ground, but we're also harvesting the
pressure. All other geothermal systems
vent the pressure, but that pressure is
an energy component. Our modeling
says that if you don't vent the pressure,
you're going to have a net output that's
25% to 50% higher. " ■
-Sonal Patel is a POWER senior
associate editor.
23

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