Figure 1: Batteries can function in electric grids to store up energy from (e.g. from solar power in yellow) when supply exceeds demand (the solid green). This can then be used later when additional energy is needed, such as when the sun is no longer shining. Base load power is shown in purple, and is provided by plants that are on constantly. Electricity demands beyond this base load are met by a combination of renewables and additional “peaking” power plants.