Project Malta – a new approach to thermal energy storage

A molten salt and low temperature liquid energy storage system is under development by Google’s parent Alphabet.
Published: Thu 03 Aug 2017

Storage comes in various forms of which batteries are the most advanced and with the fastest dropping prices, leaving others in its wake.

One of these with a range of technology options is thermal storage – and that is the one that Google, through its parent Alphabet Inc’s X labs, is putting its money on. Specifically, the proposal is to store electricity in tanks as heat in molten salt and as cold in low temperature liquid as a means of having dispatchable energy available on timescales from a few hours up to weeks or months.

The problem, according to an X statement, is that current solutions are expensive and are not capturing all of the energy produced by renewable energy sources. The goal is to develop an inexpensive system that takes full advantage of the renewable energy and that could be located just about anywhere.

For X, the aim of such so-called ‘moonshot’ projects is to utilise ‘breakthrough technology’ in a ‘radical solution’ towards a ‘huge problem’ that if solved, “could make the world ‘a radically better place.”

Other X moonshot projects have included self driving vehicles and Google Glass. Another, Project Foghorn, was aimed to develop a synthetic carbon-neutral fuel made from seawater but the cost made it unfeasible to scale and the project was terminated.

Another energy project, Makani, is looking into the concept of using energy kites with multiple rotors to generate wind energy from stronger and steadier winds at higher altitudes than traditional turbines – the aim being to generate more energy with less materials.

Project Loon is focused on the use of high altitude balloons to provide internet access in remote areas.

The storage process

Neither molten salt technology nor cryogenic energy storage is new but what appears to be new in Project Malta is their use in combination in a process which was developed by Nobel prize-winning Stanford physics professor Robert Laughlin (as illustrated below).

When such storage types are used individually an external process needs to be applied in the reconversion to electricity. In this case, it is the combination of the hot and cold that is used to drive a turbine to create the dispatchable electricity.

Project Malta energy storage process

According to the X statement, in his work, Professor Laughlin mapped out the overall system and proved the maths for how all the components should work together.

X’s participation is aimed to take the next step of designing the individual components and understanding the system overall well enough to evaluate whether it would work in the real world and at a competitive price point.

And after more than two years building CAD drawings, running extensive computer simulations and 3D printing of parts, X has detailed engineering designs that are nearly ready to be turned into real machinery.

Project Malta qualities

The X statement also says it has learned that the system has some important qualities that make it viable from both environmental and cost perspectives.

One of these is the use of inexpensive components. Although the turbines and heat exchangers need custom engineering, much of the system uses conventional technology such as steel tanks and air and cooling liquids that are all simple to procure. Salt is easily extracted from the earth.

The system also 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.

Further 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, the numbers of tanks of salt and cold liquid are simply increased, which keeps system costs low.

Next steps

According to the X statement Project Malta is moving quickly towards commercial viability testing and innovative industry partners are being sought to help bring the 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.

X is also looking for partners with the expertise to build, operate and connect a prototype to the grid.

Studies of the thermal storage market have led to estimates of a value of $1.8bn to $3.6bn by 2020.

Ultimately a utility’s storage options will depend on the use case(s) it needs to meet and the cost effectiveness with which it can do so. A key challenge with thermal storage has been the reversal of the stored energy into electricity and if this can be overcome, it will open the way for its wider use in grid applications.

With renewables on the increase the onus is on generators to maximise the capture and use of the energy generated. With the range of slower response and longer duration applications that require dispatchable energy these have the potential to bring thermal storage into its own.

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