When electricity suppliers generate power from burning fossil fuels, they are able to adjust the rate of combustion, and they make it match the rate of demand for electricity. As we start to get our electricity from renewables, it's important to be able to warehouse electricity, because nobody can predict when renewables like wind turbines or solar panels will be most productive. Cities will need grid-scale batteries, and this project was about installing them somewhere without exploiting the city's most vulnerable people, which has been the system for storing fossil fuels.