You are probably familiar with various types of batteries based on their chemistry: lead-acid, carbon-zinc, nickel-cadmium, lithium-ion and air batteries, to name a few. But have you heard of the gravity battery? It could be the next big enabling technology for the electrical grid to expand the use of renewable sources such as solar and wind power. 

The obvious problem with solar and wind is that the sun doesn’t always shine, and the wind doesn’t always blow. Generally speaking, this has limited these sources to a supplementary role, with more traditional sources, such as coal, natural gas, nuclear and hydroelectric plants, making up the majority of electrical generation. To become more reliable, wind and solar facilities need a way to store excess energy when they are producing, and tap the stored energy at night or on calm days. Batteries are clearly one choice for this task. 

Of course, batteries to store significant amounts of energy are large, expensive and already in high demand for electric vehicles. On the plus side, the latest generation of lithium-ion batteries are over 90% efficient, so relatively little energy would be wasted by this method. 

The gravity battery, however, stores energy in the gravitational potential of large weights. Energy is expended to raise the weight and recovered as the weight falls (in a controlled fashion, of course). This is how clocks were, and still are, powered, from small cuckoo clocks to giant bell tower clocks, such as Big Ben in London. The key enabler for gravity batteries comes from the electric vehicle, specifically, regenerative braking. 

Regenerative braking uses the momentum of the vehicle to essentially run the motor in reverse, functioning as a generator and routing electrical power back to the battery. The ability to use a single motor-generator, and rapidly switch between these modes of operation, makes the gravity battery economically viable. Modern regenerative braking systems are over 70% efficient, and in the case of stationary, largescale applications, such as gravity batteries, could be even more efficient. Combined with lower cost, the gravity battery is an economically viable alternative to chemical batteries for extending the utility of wind and solar plants. 

These devices can be placed in high-rise structures designed to blend in with the surrounding architecture, making them acceptable in both urban and rural environments. Another possibility being actively explored is to use existing mine shafts, so the weights would be underground.

Is the term “battery” really appropriate for this type of energy storage? While contemporary usage of the term implies “chemical battery,” in fact, “battery” originally referred to a collection of military weapons, such as artillery, mortars and rocked launches. It was Benjamin Franklin who first used the term for storage of electrical energy, when he linked together a series of capacitors and called it a “battery.” So really, to be a gravity “battery” there just needs to be two or more of them in one location!