POWER April 2016 - 56

OPERATIONS & MAINTENANCE
1. Puna Geothermal Venture (PGV). Located in the Puna district on the Big Island in
Hawaii, PGV is the only geothermal power plant in the state. Courtesy: Ormat Technologies Inc.
Geothermal and California:
Mutually Supportive
When it comes to geothermal energy
policies, no state is as supportive as California.
California has the most installed
geothermal capacity of any state in the
U.S. by far-more than 80% of the total.
As a dispatchable resource, geothermal
plays a valuable role in the state's renewable
energy mix.
Although the bulk of the geothermal
2. Automatic generator control (AGC) offers flexibility. Using AGC, 16 MW
of PGV's 38-MW capacity can be dispatched by system operators to match demand. Courtesy:
Ormat Technologies Inc.
capacity is installed in Northern California,
Southern California holds significant
potential. The Geothermal Energy Association
and the Imperial Irrigation District
estimate that the Salton Sea region
of California contains between 1,500 MW
and 2,900 MW of geothermal potential,
which, if fully harnessed, could revitalize
a drying, saline lake that is a hotspot
for tourists and water birds. Dust storms
plague the area due to inhospitable vegetation
conditions, but geothermal plants
could help stabilize the desert sand, potentially
mitigating the storms. In addition,
the geothermal industry would
provide an economic boost to the lagging
local economy, creating employment and
adding capital from new sources.
Brine generated from Salton Sea geothermal
plants would also be high in
lithium, whose rising market value could
make plants a mineral " gold mine " if extraction
technologies improve in coming
years (see " Mining for Lithium in Geothermal
Brine: Promising but Pricey " in
the March 2015 issue).
in April 2013. EGS creates an engineered heat
exchanger that involves " enhancing " the permeability
of deep hot rock " by hydrothermal
fracturing, high-rate water injection, and/or
chemical dissolution of minerals by drilling
production wells to depths of 10,000 feet and
beyond where temperatures reach upwards
of 350F. A cold working fluid-water, typically-is
then allowed to flow through the
deep openings in the rock to further crack it
and to mine its heat energy. When the water
is pumped back to the surface, the resulting
steam is used to power a turbine to generate
power. The water is cooled again into a liquid
and injected back into the ground to repeat
56
the cycle in a closed-loop system. "
Designing for Optimal Operation
One innovative plant that won a 2015 Geothermal
Energy Association (GEA) Honors
Award was Enel Green Power North America
Inc.'s (EGP-NA's) Stillwater Solar Geothermal
Hybrid Project (shown in the opening
photo, and a 2012 POWER Renewable Top
Plant winner). Located in Churchill County,
Nev., Enel's plant integrates the continuous
generation capacity of binary-cycle, medium-enthalpy
geothermal power with solar
photovoltaic (PV) and solar thermal units.
The components all work in tandem in a nevwww.powermag.com
er-before-seen
mix. Enel's advanced technology
produced a generation profile consistent
with the demand for electricity while meeting
strict environmental performance standards
without consuming water or releasing
air emissions during normal operations.
When EGP-NA added a 26.4-MW solar
PV unit to the geothermal plant in 2012, it
was one of the largest PV systems of its kind
in the U.S. Integration of the solar system has
helped to maximize plant capacity and improve
reliability.
Used in tandem, the two technologies
complement each other's strengths, making
up for any gaps in productivity. For example,
when thermal efficiency in the geothermal
unit is lowest-during the hottest and sunniest
times of the day or year-solar PV is at its
most productive, stabilizing production and
enabling a more consistent energy producPOWER
| April 2016

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POWER April 2016

Table of Contents for the Digital Edition of POWER April 2016