Alphabet’s Project Malta to Use Salt for Large-Scale Energy Storage

August 01, 2017 by Paul Shepard

Wind and solar power are abundant, clean, increasingly inexpensive energy sources, and already contribute significantly to efforts to decarbonize the electricity grid. But since the sun shines only part of the day and wind is unpredictable or strongest late at night, these energy sources are not consistent.

If there's more energy produced than the electric grid needs, the capacity of wind and solar farms is simply wasted. Worse, if electricity demand spikes during periods of low renewable energy generation, utilities will often fire up so-called "peaker plants" which emit large amounts of CO2 relative to ordinary power plants. With no clean, cost-effective technology for storing renewable energy to serve these peaks, the amount of renewable energy the grid can handle could be capped, and the growth of renewable energy over the next decade could stagnate.

Technologies do exist to help the grid cope with quick demand spikes and to store energy for several months. But current solutions are expensive and are not capturing all of the energy produced by renewable energy sources. What if we could take full advantage of renewable energy with an inexpensive system that could be located just about anywhere and store energy for a few hours or even up to several weeks?

Nobel prize-winning Stanford physics professor Robert Laughlin designed a theoretical system that stores electricity as heat (in high temperature molten salt) and cold (in a low temperature liquid similar to the antifreeze you have in your car). The energy stored in salt can be kept for days or even weeks, until it's needed.

In Alphabet's Malta's system, energy is stored as thermal energy - both heat and cold. The thermodynamics behind Malta's storage technology is shown here:

In his work, Professor Laughlin mapped out the overall system and proved the math for how all the components should work together. X decided to start a small team to take the next step: designing the individual components and understanding the system overall well enough to evaluate whether this would work in the real world - and at a competitive price point.

After more than 2 years building CAD drawings, running extensive computer simulations, and 3D printing lots of parts, the team at X has detailed engineering designs that are nearly ready to be turned into real machinery - down to the exact angle of each blade in a turbine and the strength and thickness of the material used.

(Left) Siyuan adjusts CAD drawings of technology that facilitates the cooling process. (Right) To build a highly efficient system, the team needs to design from every angle. Here, Sebastian, Adrienne, and Siyuan look at a 3D prototype to discuss blade height.

The team has also learned that this system has some important qualities that make it viable from both an environmental and cost perspective:

  • Inexpensive components. Although the turbines and heat exchangers need custom engineering, much of the system uses conventional technology - steel tanks, air and cooling liquids are all simple to procure. Salt is easily extracted from the earth and can be used over and over again to store heat without degrading or emitting toxic byproducts.
  • Flexible siting. This system isn't dependent on particular weather or specific locations. It can be close to the renewable energy source, or near where there's high demand on the electric grid.
  • Long-lasting and easy to expand. The salt tanks can be charged and re-charged many thousands of times, for possibly up to 40 years - three or more times longer than other current storage options. To add more storage capability, you just add more tanks of salt and tanks of cold liquid, which keeps system costs low.

Malta is moving quickly to test commercial viability and is looking for cutting edge, innovative industry partners to help us bring this system to life.

The next step is to build a megawatt-scale prototype plant which would be large enough to prove the technology at commercial scale. Malta is looking for partners with the expertise to build, operate and connect a prototype to the grid. Also, X is interested in talking to customers of grid-scale energy storage, energy system manufacturers, and energy system construction companies.