Molten salt might cut solar power costs
Solar power accounts for about 2% of U.S. electricity, but it could become more widespread if it were cheaper to generate this electricity and make it readily available on cloudy days and at nighttime.
To lower those costs, Purdue University engineers are developing ways to improve how facilities called concentrated solar power plants produce electricity. These plants provide power at off-peak times by storing heat captured from sunlight that is focused by thousands of mirrors onto a small area.
Developments in this research are important steps for putting solar heat-to-electricity generation in direct cost competition with fossil fuels, which generate more than 60% of electricity in the U.S.
Solar panel systems installed on farms and on rooftops are commonly used to generate electricity from the sun and already store energy for later use using batteries, but concentrated solar power plants can offer large-scale energy storage at a lower cost.
“Since storing solar energy as heat is already cheaper than storing energy via batteries, the next step is reducing the cost of generating electricity from the sun’s heat,” said Kenneth Sandhage, Purdue’s Reilly Professor of Materials Engineering.
There are only 11 concentrated solar power plants in the U.S., but the cost of producing electricity using these plants has dropped by more than 50% since 2010. Purdue researchers are working to reduce concentrated solar power costs even further to compete with fossil fuels.
Seeking solutions from seawater
To make it cheaper for concentrated solar power plants to produce electricity, the turbines of these plants need to operate at much higher temperatures. Turbines currently operate at a peak temperature of about 1,022-degree F.
By operating the turbines at 1,382-degree F or higher, a concentrated solar power plant could convert heat energy to electricity more efficiently. This also calls for enabling low-cost storage of solar heat at higher temperatures so that the plants can produce electricity 24 hours a day and respond quickly to surges in electrical demand.
Concentrated solar power plants can store energy from the sun by heating molten salts, but currently used molten nitrate salts would degrade at 1,382-degree F. Sandhage and other researchers in the field have been turning to seawater for chloride-based salts that can stay stable enough at higher temperatures.
But seawater-derived molten chlorides, such as magnesium chloride-potassium chloride-bearing salts that researchers have examined so far, degrade by oxidation in ambient air at 1,382-degree F.
In a study published in Materials Today, Sandhage’s research group predicted and demonstrated that a different sea-water-derived molten salt, a calcium chloride-sodium chloride composition, is highly resistant to oxidation in ambient air at 1,382-degree F.
Sandhage’s research group also developed a way to make nickel corrosion-resistant so that it can better contain a molten salt such as the calcium chloride-sodium chloride composition.
“We have identified and demonstrated a salt that is stable and plentiful, and we have a containment strategy for holding the salt for extended times to store the energy for use when the sun isn’t shining,” Sandhage said.