POWER December 2016 - 26

TOP PLANTS
Crescent Dunes Solar Energy
Project, Tonopah, Nevada
Owner/operator: SolarReserve
Courtesy: SolarReserve
Three-and-a-half hours north of Las Vegas, in a rocky, desolate stretch of Nevada
desert, an innovative solar-storage plant has nearly completed a year of commercial
operations. It also may have delivered proof of round-the-clock dispatchable solar
energy.
Thomas W. Overton, JD
T
he Crescent Dunes Solar Energy Project,
a concentrating solar power (CSP)
plant built by Santa Monica, Calif.-
based SolarReserve outside Tonopah, Nev.,
shares a lot of similarities with other solartower
CSP plants like Ivanpah (POWER's
2014 Plant of the Year). Just over 10,000
billboard-sized heliostats, each about 1,200
square feet, focus sunlight on a central receiver
at the top of a 640-foot tower. The
plant uses the heat collected to generate
steam and drive a turbine generator.
CSP is a straightforward and fairly well
understood technology that's been around
for more than a decade. The first utility-scale
CSP plant came online in 2008, and several
dozen of them are in operation around the
world, mostly in Spain. Crescent Dunes isn't
the largest CSP plant by any means-at 110
MW, it's less than a third the size of Ivanpah,
the current leader.
What sets Crescent Dunes apart from its
predecessors is that it incorporates 10 hours
of full-power thermal energy storage-a total
26
of 1.1 GWh. In terms of duration, that's more
than earlier CSP-plus-storage plants like the
Solana Generating Station in Arizona (a 2014
POWER Top Plant) that store around five to
seven hours of generation, and far more than
the largest battery projects currently in development,
which top out at around 400 MWh.
And unlike Solana, which circulates a heattransfer
fluid that is then used to heat molten
salt, the receiver at Crescent Dunes heats the
salt directly.
The molten salt system circulates the salt
from a cold tank, through the solar tower,
where it's heated from 550F to 1,050F, and
then to a hot tank (Figure 1). Molten salt from
the hot tank is then sent through a Nooter/Eriksen
steam generator. The steam is sent through
a turbine-generator, then to an air-cooled condenser,
and back to the steam generator.
Round the Clock
The plant sells its power to Nevada utility
NV Energy under a 25-year power purchase
agreement (PPA). Since reaching commerwww.powermag.com
cial
operations in November 2015, Crescent
Dunes has-unlike Ivanpah-quietly exceeded
its obligations, delivering 105% of
contracted output. The molten salt receiver
has achieved 100% availability through 2016,
and performance data show that it's operating
2% above its expected efficiency.
On a normal day, Crescent Dunes begins
generating power around 10 a.m., reaches
full power around noon, and stays there until
10 p.m. to midnight per the terms of its PPA,
which calls for 12 to 14 hours of generation
a day. This helps NV Energy meet peak
evening demand, and Crescent Dunes shuts
down as that demand falls late at night.
But that's only what it's contracted to do
for the utility. The PPA, in fact, doesn't exploit
the plant's full capabilities. By reducing
its net output slightly, Crescent Dunes
can actually operate 24 hours a day, banking
excess thermal energy while the sun shines
and using it to generate steam all night. As
a proof of concept, SolarReserve ran the
plant for a continuous 120-hour period durPOWER
| December 2016
http://www.powermag.com
POWER December 2016

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