BrightSource Energy today announced molten salt energy storage for its heat-driven solar power plants, touting the advantages over flat solar photovoltaic panels.
With the storage, BrightSource solar power plants can deliver electricity to the grid consistently and into the evening hours. That makes the solar power more valuable because utilities pay more for power during peak hours, which continues past nightfall.
BrightSource's solar tower technology generates steam from a field of mirrors called heliostats shining onto a tower. The steam is fed into a conventional turbine to generate electricity. After turning the turbine, the steam is condensed into water and fed back to the tower to be heated again.
In a plant with solar storage, the steam from the tower is fed into a heat exchanger that raises the temperature of so-called "solar salts" stored in large tanks. When electricity is needed, that heat stored in the salt is converted into steam and run through the turbine.
It would be possible to build a plant with round-the-clock power delivery but BrightSource thinks that two to six hours of storage will have the broadest appeal, according to company representative Keely Wachs
Adding storage to renewable energy at a reasonable cost is one of the toughest technical challenges for wide adoption of solar and wind. Molten salt is already being used in solar plants in Spain and one project in Nevada is in the planning stages.
Coupling solar photovoltaic panels, which generate electricity from sunlight, with batteries for storage is more expensive than using molten salt, according to BrightSource Energy. The high-temperature, high-pressure steam its towers generate work better than competing trough-based solar thermal technology as well, it said.
The salt storage system actually lowers the cost of solar plant operation because it raises the plant's capacity factor, or the amount of time over the course of a year it's delivering electricity to the grid, Wachs said. "By adding 6 hours of storage, the capacity factor increases to 50 percent and produces for approximately 4,300 hours, or twice as much as a PV farm," he said.
Updated at 3:10 p.m. PT with additional details.