Breakthrough grid-scale renewable energy storage in a battery made from... gravel?!
Is this the breakthrough we need?Renewable energy production is going up rapidly - worldwide solar power capacity is up 53X in the past 9 years - but to reach the finish line, the world will also need a lot of cheap energy storage. That's because wind and solar power are intermittent, and sometimes they produce more than we need and sometimes not enough; if we can store energy when there's a surplus, we can then use it when there's a deficit and smooth things out.
But getting large-scale storage has been a challenge so far. Almost all of the world's current large-scale energy storage is pumped hydro, which is great in many ways, but expensive and not easy to deploy everywhere (having mountains and water really helps).
There are many other approaches that will probably move from the lab and small-scale deployments to the real world in the next few years. One is to use the same type of batteries that are used in electric cars, but in much larger quantities. Elon Musk is planning to build a battery Gigafactory to lower costs, and a good chunk of the production from that factory has already been earmarked for stationary storage (see the image above).
Another way to do it would be with relatively inexpensive liquid-metal batteries (pictured above). They are still in development, but if they can be scaled up and mass-produced, they could revolutionize the whole energy industry...
But all this is pretty high-tech; advanced lithium-ion batteries, molten metals... What about make large-scale energy storage dirt cheap by literally using dirt?
This is what Isentropic, a young company from the UK, is trying to do. They are working on a heat pump system that uses gravel (or more precisely, the thermal mass of small rocks) to store thermal energy and then extract it back when required. This would mean that when renewables are producing a surplus, that energy could be used to run this system one way, and when there's a deficit, the system is reversed and turned into an energy source. Check out the video below to see how it works:
The beauty of such a system is that it doesn't require a specific type of terrain, like pumped hydro. And it's more efficient too: Isentropic claims that its system has a "round-trip" efficiency of between 72 and 80%, which compares favorably with about 74% for pumped hydro. Costs amortized over 25 years are estimated to be about $50 per megawatt-hour, while pumped hydro is about $65 per megawatt-hour.
And it doesn't use any dangerous chemicals, so that's a plus too!
The real question is, will this be competitive with liquid metal batteries? Time will tell. After all, gravel is pretty cheap, so that might be an advantage, but Dr. Sodoway's liquid metal batteries have also been designed to use cheap materials, and maybe they can store energy more densely because they reach much higher temperatures... Whoever wins, we'll all benefit from a cleaner power grid that can handle more renewable energy!