CSP with thermal energy storage boosts California electric grid
Researchers from the U.S. Department of Energy's National Renewable Energy
Laboratory (NREL) have calibrated the significant value that concentrating
solar power (CSP) plants can add to an electric grid.
The NREL researchers evaluated the operational impacts of CSP systems
with thermal energy storage within the California electric grid managed
by the California Independent System Operator (CAISO). NREL used a commercial
production cost model called PLEXOS to help plan system expansion, to evaluate
aspects of system reliability, and to estimate fuel cost, emissions, and
other operational factors within the CAISO system. The analysis is detailed
in a recent publication, Analysis of Concentrating Solar Power with Thermal
Energy Storage in a California 33% Renewable Scenario, by Paul Denholm,
Yih-Huei Wan, Marissa Hummon, and Mark Mehos.
NREL's analysis was considered within the context of California's renewable
portfolio standard (RPS), which requires 33% of power be supplied by renewables
by 2020. The specific focus was on the "Environmentally Constrained" 33%
RPS scenario, which includes a high contribution of generation from photovoltaic
solar energy systems. By also considering how the state could take advantage
of CSP with thermal storage, NREL used the PLEXOS model to quantify the
value of CSP in reducing the need for conventional power generation from
fossil fuels, and compared this value to other sources of generation, including
photovoltaics, which supply variable energy depending on the amount of
To perform this analysis, NREL Senior Analyst Paul Denholm explains, "We
created a baseline scenario, then added four types of generators--a baseload
generator with constant output, a photovoltaic system, a CSP plant providing
dispatchable energy – or power that can be turned on or off on demand
-- and another CSP plant providing both energy and operating reserves."
The analysis demonstrated several valuable properties of dispatchable
CSP, such as its ability to generate power during high-value periods when
electricity demand is high, and its capability to be turned off during
lower-value periods. Of key interest, NREL found that significant operational
value is derived when CSP is allowed to provide reserve power, including
frequently operating at less than full load, which would be a substantial
change in operational practice.
Mark Mehos, manager of NREL's CSP Program, emphasizes a couple other conclusions
from their analysis: "CSP plants switched on during periods of highest
consumer demand for electricity resulted in very high capacity value. And
the difference in value in CSP plants with and without thermal energy storage
depends greatly on the amount of other variable-generation renewable energy
sources on the grid, such as wind and photovoltaics."
NREL's study has helped to develop approaches that can be used by utilities
and system planners to incorporate CSP in standard planning tools. It has
also quantified the value of adding thermal storage to CSP in a scenario
of high levels of renewable energy in California.
NREL is the U.S. Department of Energy's primary national laboratory for
renewable energy and energy efficiency research and development. NREL is
operated for DOE by the Alliance for Sustainable Energy, LLC.