On a typical spring day in California, electricity demand starts to rise around 6 AM and again around 6 PM. Wind power often picks up at night and solar panels kick into gear around 7 AM, generating electricity until the sun sets around 7 PM. However, these renewable sources of energy can’t meet the peak demands of the day, so power companies rely on fossil fuels like natural gas to make up for the gap. Storing renewable energy is difficult, but companies like Energy Vault are using gravity to store renewable energy without the need for water or mountains. They use renewable energy to lift heavy blocks of concrete up into the air, where they become potential energy. When energy is needed, the blocks are released, spinning a turbine to convert the potential energy back into electricity. Energy Vault calls this technique “gravity energy storage” and claims it could be more than 80% efficient. Quidnet is working on a different version of the same principle, called “geomechanical pumped storage”, which uses renewable energy to pump water underground into a pressurized hole and store it as potential energy. Both techniques are betting on potential energy as an efficient way to store renewable energy for the grid. Other companies are also exploring different solutions, such as super heating salt and storing energy as thermal energy, or utilizing the chemical reaction that creates rust to store and discharge energy. These ideas are all in various stages of development and investors are taking notice, as the grid of the future will likely require a patchwork solution of different storage methods.