What supply chain must meet rare periods of peak demand with no inventory, and operates in an environment where demand equals supply? The answer is the electricity grid, and a new design for an old concept, the battery, could change the way this supply chain operates.
Don Sadoway, John F. Elliot Professor of Materials Chemistry, MIT, described the battery at MIT CTL’s Crossroads 2015 conference, March 24, 2015. Sadoway and his team invented the new battery, which is due to start field trials in Cape Cod, MA, next year.
The reason why a device that is usually perceived as 19th century technology could revolutionize the way electricity is generated and delivered can be summed up in a single word: storage. It’s the missing piece of the energy puzzle, according to Sadoway.
The grid is designed to meet peak loads, which is typically about 40% greater than the average load and occurs around 1% of the time. As Sadoway points out, an airline based on that business model would have 40% of its planes sitting on the ground except for perhaps five days of the year when the whole fleet would fly to handle peak passenger numbers on special holidays.
Renewable energy sources are not viable as a major contributor to the grid because much of their output varies according to the availability of wind, sun, and tidal power. There is no storage to buffer these fluctuations. “Imagine if every time you took a shower it had to be raining because there is no such thing as a water tank,” says Sadoway. “Without storage they don’t contribute to base load, and if they don’t contribute to base load they are not a solution, they are a headache,” he says.
But even the long established grid powered by traditional energy sources is in desperate need of storage solutions, maintains Sadoway. For example in Manhattan energy demand keeps rising. There is enough generating capacity in the New York region, but transmission lines are needed to bring the electricity to Manhattan. Sadoway estimates that Manhattan’s transmission line capacity will be exhausted in 2016/17, and since they cost billions of dollars apiece and permits to build them are very difficult to obtain, it’s unlikely that a new line will be available any time soon. “That means rolling brownouts and blackouts,” he says.
One solution is the liquid metal battery that Sadoway’s new company, Ambri, has pioneered. It consists of three liquid layers: a light metal on the top, molten salt in the middle that acts as the electrolyte, and a dense metal on the bottom. The substances have different densities so do not mix.
The battery goes against convention. Instead of running cold it runs hot, and the units are large not small; a block of 10 is about the size of a shipping container. It is safe because if the shell is punctured the contents immediately become solid. The device has no moving parts, and retains charge much longer than conventional batteries. Sadoway says that a lithium-ion battery retains about 80% of its charge for some two years, whereas the liquid metal battery can maintain this performance for around 305 years!
Moreover, the battery is constructed of abundant materials, which means that production can be scaled up economically, and the device can be built locally with local materials.
When operated in conjunction with renewable energy generators or conventional power plants, the battery provides the storage capacity that both sources of electricity need. Despite much skepticism in the wider energy community, Sadoway believes that his invention is a game changer. “With enough ingenuity the impossible becomes inevitable,” he says.