How we store that energy is a constant work in progress, and while plenty of scientists are making important but incremental advances with inventive new materials and electrolytes, others are out to entirely reinvent what we think of as a battery. Here are five examples from 2018 that might open up new doorways in energy storage, and are thought-provoking concepts that came from thinking outside the square.

Consider a regular spring. If you coil that spring with your finger, you are packing it with potential energy. If you then allow it to uncoil, you are letting that energy free. Now imagine that principle applied to a tower of stackable concrete blocks, with a six-armed crane acting as the finger. 

This is the vision of Swiss startup Energy Vault, which is developing a new kind of battery, if you can call it that, designed to store energy from renewables like wind and solar in skyscraper-sized concrete towers. To charge it, the crane lifts blocks off the ground and stacks them to create a tower. To discharge it, the crane lets gravity lower the blocks to the ground and converts the kinetic energy generated during the descent into electricity. 

This is a similar premise to pumped hydro plants, which are commonplace and also rely on gravity. These pump water up to into a reservoir during periods of low grid demand, and then capture the power generated as it is released to rush downhill through turbines. Energy Vault says its solution could hold a capacity of up to 35 MWh and 4 MW peak power and offer a roundtrip efficiency of 90 percent. It is deploying its first system in India in 2019.