POWER December 2012 - 38

top plants
ter facility was something that occurred to
EGP NA management after building the geothermal
component, Venturini said. He also
explained his company's goals related to developing
new synergies between geothermal
and solar energy.
" Having succeeded in proving the concept
in a commercial-scale application, EGP NA
Green Power's Stillwater Solar project paves
the way to address key drawbacks for both
geothermal and solar technologies: resource
risk/parasitic load and generation intermittency,
respectively, " Venturini said. The geothermal
plant also provides auxiliary power to
the solar plant when there is no sunlight, " thus
eliminating the need for backfeeding power
from the utility, " according to Venturini.
Currently, a number of utilities use renewable
energy sources like solar power during
hours of peak consumer demand and combine
it with a baseload coal or natural gas plant to
ensure a steady power supply. In contrast, the
Stillwater facility combines two renewable
energy technologies to produce electricity at
the same location and thereby increases the
generation of zero-emission electricity.
Combining geothermal and solar energy
at the Stillwater plant also makes it possible
to use the same infrastructure, further reducing
environmental impacts. That integration
includes the control system, electrical
protection and island mode capability, fire
detection/protection schemes, electrical interconnection,
and the use of a common operations
and maintenance staff.
" It has to be said that since this geothermal-solar
project is a first of its kind, it met
the regular challenges of everything new in
terms of combining two advanced technologies,
as well as challenges of a regulatory and
administrative nature, " Venturini said.
This innovative hybrid power plant demonstrates
that the strengths of these different
renewable technologies combine to create a
better whole. Together, they:
■ Enhance the thermal efficiency in the geothermal
unit when it is lowest, typically
during the hottest and sunniest times of
the day or year.
■ Stabilize production during the day, enabling
a more load-following production
profile.
■ Reduce investment risk due to the uncertainty
of the geothermal resource and compensate
for geothermal reservoir temperature depletion
without reducing production.
Plant Profile
The solar power component at the Stillwater
facility consists of more than 89,000
polycrystalline premium photovoltaic (PV)
CNPV-295P modules on fixed mounts
(Figure 1). They were manufactured by
CNPV Solar Power SA, an integrated manufacturer
of solar PV products. Las Vegas-
based Bombard Renewable Energy was the
general contractor for the solar project.
The benefit of adding solar to the Stillwater
facility's production capacity has been confirmed
in generation measurements to date.
" Average daily generation in the peak hours
is significantly enhanced by the PV system,
while the geothermal plant begins to reach
optimal generation levels when solar generation
ramps down, " Venturini explained.
" From a source point of view, there were
no development difficulties, as the geother1.
Some like it hot. The Stillwater facility integrates 26 MW of photovoltaic solar generating
capacity with 33 MW of baseload geothermal power. In the geothermal plant's binary system,
hot water from underground wells heats isobutane and causes it to flash into vapor, which
then turns the turbines to generate electricity. Courtesy: Enel Green Power North America
mal plant (operational since 2009) was already
positioned in an area with good solar
irradiation levels, so EGP NA just had to
install the PV facility and connect it to the
grid, " Venturini said. " It also helped that Enel
Green Power was finishing construction of its
pilot project in Italy integrating a solar thermal
system to boost efficiency of a combined
cycle natural gas power plant. "
EGP NA employs approximately 50 staff
members in the state of Nevada. The company
has roughly 30 employees who operate
and maintain the Stillwater Solar Geothermal
Hybrid Plant and EGP NA's Salt Wells Geothermal
Plant (which also became operational
in Nevada in 2009).
Venturini noted that the project's success
derives from a number of factors:
■ The hard work and commitment of the engineers
and staff at EGP NA.
■ The collaboration with and support of NV
Energy, state and local government agencies,
and the local communities-all of
which were essential in completing the
project.
■ Federal and state energy policies supporting
renewable energy that were critical in
EGP NA's decision to commit to this successful
investment.
Looking Ahead
The Stillwater hybrid plant is already being
recognized as a trendsetter in the renewable
energy sector that will probably encourage
future hybrid projects. On June 28, 2012,
the Geothermal Energy Association (GEA)
recognized the Stillwater Solar-Geothermal
Hybrid Project for advancing geothermal
technology. The GEA singled out the Stillwater
facility for being the first hybrid power
plant of its kind. The association pointed out
that " this technology may help to allow future
projects that would otherwise have been
unfeasible as stand-alone geothermal or solar
projects to be more economically and technologically
viable. "
In his remarks at the dedication ceremony
for the Stillwater Solar Plant in May, Nevada
Governor Brian Sandoval praised EGP NA
for its innovation and leadership and looked
forward to future growth in the Nevada renewable
energy sector. " Clean energy is a key sector
for Nevada. It provides energy from local
sources, drives innovation, and most importantly,
brings high-quality jobs and economic
growth to the local communities. Enel Green
Power's first-of-a-kind solar geothermal hybrid
project is a living example of these benefits
and I support the further growth of this
industry in Nevada, " Sandoval said. ■
-Angela Neville, JD is POWER's
senior editor.
36
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