NREL report finds “significant value” for CSP with TES when allowed to operate at less than full load

Published on: Friday, 26 April 2013
Thermal storage tanks in a CSP plant under construction

NREL has conducted a report that quantifies the significant value that Concentrated Solar Power plants can add to the grid. 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). A commercial production cost model called PLEXOS, has been used 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 –available to download from CSP World- 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, however, this would require substantial changes in operational practice of CSP plants.

When CSP is allowed to provide operating reserves, its operational value increased by about $17/MWh (producing a total difference of $22/MWh compared to the base-load resource and $29/MWh compared to the PV generator).

Combined, the operational and capacity value of CSP calculated in this analysis ranges from about $80/MWh to about $135/MWh. This represents an incremental value of $13/MWh to $51/MWh compared to a base-load resource, or $15/MWh to $40/MWh compared to PV.

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 photovoltaic”. In a previous report, available at CSP World Library, NREL noted that CSP with TES could provide a greater penetration of solar power to the grid.

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 sunlight available.

To perform this analysis, NREL Senior Analyst Paul Denholm explains, “We created a baseline scenario, then added four types of generators—a base-load 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 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.

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