Electricity storage systems are the set of methods and technologies used to store electricity. The need for electricity storage is due to an imbalance in supply and demand on the electrical grid due primarily to an increase in renewable energy generation. These supply and demand discrepancies occur because renewables are intermittent, meaning electricity isn't produced when the Sun isn’t shining or the wind isn't blowing, even though consumers still require electricity in these renewable downtimes. Currently, grids distribute electricity in real time, meaning electricity is being consistently produced to meet consumer demand. Electricity storage gives grid operators the flexibility to use electricity that otherwise would be wasted. This grid flexibility is highly sought after and has the potential to transform how we produce and consume electricity and is therefore being widely researched and tested. There are many different forms of electricity storage. The most common being: battery, pumped hydro, compressed air, and flywheel. Currently, the largest challenges in implementing electricity storage at the grid scale are the cost and the infancy of the technology that's electricity storage.