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Molten Salts Might Provide Half-Price Grid Energy Storage

A startup, Halotechnics, is building a pilot electricity storage system that will use molten salt.
February 27, 2014

A small startup based in Emeryville, California, will build a pilot-scale energy storage system that could provide a cheaper, more practical way of storing large amounts of electricity and help enable the power grid accommodate large amounts of renewable energy.

Halotechnics has announced a deal with a partner to construct a one-megawatt plant that will store energy in molten salts—a technique previously used to store energy at some large solar thermal plants. The company says it will cost half as much as battery storage, and could compete with the cheapest way of storing large amounts of electricity—pumping water up a hill and using it to drive a turbine as gravity brings it back down.

Molten salt storage is less efficient than battery storage—only about 70 percent of the energy used to heat up the salts becomes electricity again, whereas batteries can be over 90 percent efficient. So Halotechnics will need to offset that inefficiency with low costs. The company’s energy storage technology is made possible using molten salts discovered using a high-throughput screening system built to discover new materials. Energy storage is becoming ever more important as the share of variable sources of energy like solar and wind power increases. The technology is one of several large-scale energy storage technologies being showcased this week at the Advanced Research Projects Agency for Energy Summit (see “ARPA-E’s Strategy for Survival”) in Washington, D.C.

Cheaper energy storage could also make the power grid more resilient and efficient by giving utilities more flexibility in how they produce and distribute power. Experts in grid energy at the ARPA-E summit say that storage will be central to restructuring the grid in coming decades, but current approaches, such as water storage, only work in certain situations and take up too much space.

Various types of salts are good at storing heat; they can be heated until they melt, and then stored in insulated containers. When the energy is needed, the molten salts can be pumped out to release their heat through a heat exchange system. Molten salts are being employed at solar thermal power plants to store heat from the sun during the day and then generate electricity at night.

Halotechnics is developing a new kind of system that uses a new molten salt chemistry to store energy from any source of electricity. It uses electricity to drive a heat pump, which can take low temperature heat. Halotechnics’s innovation is developing molten salts with the properties that allow them to store heat from off-the-shelf heat pumps. Developing the salts involved the use of a robotic system that combines many different types of salts and tests the properties of the resulting mixture, allowing it to quickly develop mixtures that have different properties.

Halotechnics had previously been focused on developing new energy storage materials for solar thermal technology (see “Cheap Solar Power at Night”). It has a $3.3 million grant from ARPA-E to develop materials that could store heat at temperatures of 1,200 °C, which would make it possible to shrink the number of mirrors used at solar thermal plants to generate electricity. It’s still developing these materials, but solar thermal technology is facing difficult times now that its competitor, photovoltaic solar panels, has fallen in price. Halotechnics’s new plan to store electricity from any source could be easier to bring to market. The company will be announcing the name of its new industrial partner in the coming months.

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