Storing renewable energy in molten salt

Renewable energy is abundant, clean, and increasingly inexpensive, however it’s not always available when the demand is greatest

If wind and solar farms are producing more energy than the electric grid needs, the energy goes to waste. In California, up to 30% of solar energy cannot be used when it’s produced (Source: California ISO). Worse, if electricity demand spikes during periods when the sun isn’t shining or the wind isn’t blowing, utilities will often fire up “peaker plants” to bring extra power online quickly. These are usually powered by fossil fuels and emit large amounts of CO2 relative to ordinary power plants.

Malta is building a grid-scale energy storage technology that stores electricity from renewable energy sources as heat inside large tanks of high temperature molten salt and as cold in large tanks of chilled liquid. The system can discharge electricity back to the grid when energy demand is high - effectively “time shifting” energy from when it’s produced to when it’s most needed.

A 3D-printed prototype of Malta's energy storage system

Building a next-generation energy storage system

The Malta system has some important qualities that address this challenge – making it viable from both an environmental and cost perspective. The components and raw materials are inexpensive because much of the system uses conventional and easy-to-procure technology like steel tanks, air, and cooling liquids. Salt is easily extracted from the earth and can store heat with minimal degradation or toxic byproducts. The salt tanks can also be re-charged many thousands of times, for possibly up to 40 years – at least three times longer than other current storage options.

While at X, the team incubated the electro-thermal storage technology and developed detailed engineering designs for each component. They also worked with experts in the utilities, grid, and power industries, to ensure that Malta could meet the energy needs of the future grid.

The Malta team inspecting a scale model of Malta's electro-thermal storage technology

The process of electro-thermal storage

Malta is built on research conducted by a Nobel Prize-winning physics professor, who came up with a theoretical system that stores electricity as heat in high temperature molten salt and cold in a low temperature liquid similar to the antifreeze in cars. The energy stored in the system can be kept for days or even weeks, until it’s needed.

Renewable energy is gathered from wind or solar farms on the grid as electrical energy and sent to Malta’s energy storage system.
The electricity drives a heat pump, which converts electrical energy into thermal energy by creating a temperature difference.
The heat is then stored in molten salt, while the cold is stored in chilled liquid.
The temperature difference is converted back to electrical energy by a heat engine.
Electricity is sent back to the grid when it is needed.

Bringing Malta to the real world

Malta Inc. is now an independent company. It plans to build and sell industrial-grade, grid-scale energy storage solutions that can be located anywhere in the world. These storage solutions will collect and store large quantities of energy to dispatch quickly as electricity on demand. The team will develop a megawatt-scale pilot plant to prove the technology at commercial scale, and are working with partners that have the expertise to help them build, operate and connect a pilot to the grid.