The benefits of this combination include:
- Extending the production of electricity into later parts of the day and after the sun sets when it is most valued by utilities
- Reducing the cost of renewable power for utilities’ customers by increasing a plant’s capacity factor and offering higher efficiencies than competing solar thermal power plants
- Providing utilities with greater operational flexibility to shape production to meet changing utility customer demand
- Offering utilities and grid operators additional operational and market value, by providing balancing and shaping capabilities, as well as ancillary services to support a reliable grid.
Adding storage to a solar thermal power plant reduces the cost of energy produced at a plant by increasing its capacity factor - how much power a plant produces – by extending the production of electricity into later parts of the day when it is most needed by utilities. The ability to increase capacity factors by adding proven storage represents a significant advantage for solar thermal over other renewable resources like photovoltaics (PV) and wind that do not yet have economical storage capabilities.
According to BrightSource, its SolarPLUS plants also have efficiency and cost advantages over competing parabolic trough solar thermal technologies because of the LPT solar thermal power generating technology’s ability to reach higher temperature and higher pressure operating levels. Today, BrightSource’s LPT solar thermal power generating technology is producing the world’s highest temperature (540 degrees Celcius) and pressure (140 Bar) steam from solar. In contrast, parabolic trough plants are limited to approximately 400 degrees Celcius and 100 bar pressure. The ability to reach higher temperature and pressure operating levels allows for more improved economics in pure solar generation and in storage mode relative to parabolic troughs due to higher operating efficiencies.
The company notes that, in addition to producing firm and dispatchable power, storage also provides operational flexibility, balancing and shaping capabilities, and ancillary benefits to help support a reliable grid, reducing the need for additional fossil fuel units necessitated by the intermittency of PV and wind.
“Electricity markets with high penetration levels of intermittent resources are starting to place significant value on those resources that can provide clean energy as well as operational flexibility and reliability services to the grid,” said Dr. Udi Helman, Director of Economic and Pricing Analysis for BrightSource Energy. “BrightSource’s SolarPLUS solar thermal power plants will empower utilities with a flexible power source that meets electricity demand at peak, can be used to further lower wholesale power costs, and supports grid reliability by providing ancillary services and improved resource adequacy.”
Today, molten salt storage – “solar salts”– is used widely in solar thermal plants in Spain. The solar salts- composed of 60% sodium nitrate (NaNO3) and 40% potassium nitrate (KNO3) - are commonly available materials.
A traditional LPT power tower solar thermal system uses a field of software-controlled mirrors called heliostats to reflect the sun’s energy to a boiler atop a tower to produce high temperature and high pressure steam. The steam is used to turn a conventional steam turbine to produce electricity. In a BrightSource SolarPLUS plant, the steam is directed to a heat exchanger, where molten salts are further heated to a higher temperature, thus efficiently storing the heat energy for future use. Later, when the energy in storage is needed, the heat stored in the molten salts is used to generate steam to run the steam turbine.
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