Solar thermal power station will realize night power supply

There are various signs that solar energy is moving in the direction of mainstream power generation. Recently, BrightSource Energy, a solar energy project developer in the United States, said that it is developing new storage technologies that will enable solar power stations to continue generating electricity after the sun goes down without sunlight.

At present, many solar thermal power stations have deployed large-area-range mirrors, commonly known as heliostats, to concentrate the sunlight, put them into a boiler filled with water, and place them on a 459-foot tall tower. The steam will drive the turbines to generate electricity. Right now, BrightSource will install a molten salt system for these power stations, which can store heat so that it can freely release heat during the night or during peak electricity demand to generate steam.

BrightSource CEO John Woodrad said that this flexibility can integrate intermittent renewable energy into the grid more efficiently and cheaply. "This is a very important economic issue." John Woodard said, "How long does electricity last during the night and how much electricity is generated? The beauty of this molten salt system is that it can generate energy flexibly." In addition, he It also claims that this technology can reduce the cost of solar power generation, make it more reliable, and help increase its competitiveness compared to traditional power sources.

According to BrightSource, one of the advantages of solar thermal technology compared to traditional photovoltaics that convert sunlight directly into electrical energy is that the heat can be stored cheaply and used to generate electricity when needed. This so-called storage method has been in existence for more than 10 years, namely heating molten salt, usually a mixture of sodium and potassium nitride, and storing it in a container. When generating electricity, molten salt is pumped through a heat exchanger to produce steam.

"Storage can make thermal power plants run longer in the daytime, so that we can recover the cost of expensive turbines and generators faster," said John Woodard. In fact, a solar thermal power station without storage capabilities can generate about 2,700 hours of electricity a year, and BrightSource's storage system increases this time to 4,300 hours. The increase in production far exceeds the increased storage costs.

According to a study by the National Renewable Energy Laboratory in Golden, Colorado, a storage system can reduce the cost per kilowatt-hour by 25% to 30%.

BrightSource explained that in addition to reducing costs, the storage system also improves the economics of solar thermal power generation. Utilities no longer need to invest in back-up power supplies to eliminate power supply fluctuations. They can rely on these powers to meet increased demand at any given moment.

However, there are also questions about the price of BrightSource's storage system. Mark Metz, a researcher at the National Renewable Energy Laboratory (NREL), said that if solar heat utilization technology is to compete with photovoltaic solar panels, then storage technology can be crucial. He believes that panel prices are declining. BrightSource's storage system may not provide electricity at a lower price. Everything is equal.

In addition, except for BrightSource, Torresol Energy of Spain and Solar Reserve of the United States plan to use molten salt storage technology. The former has built a test system and installed it in a Spanish thermal power station with a capacity of 19.9 megawatts, and confirmed that it can use the stored heat to run the power station all night. The latter plans to build a solar thermal power plant in California using a molten salt system. (Wang Lin)