The electricity we use today is, for the most part, generated by power plants connected to our homes and offices through a network of transmission and distribution lines. In order to ensure that the lights always come on when we turn the switch, well functioning power grids have to be designed to ensure that, regardless of fluctuations in supply and demand, we always have electricity when we need it.
One way to ensure this would have been to build energy storage facilities that operate as a buffer, storing excess energy so that it could be released when supply is unable to meet demand. However, instead of creating these buffers, our modern grid was crudely designed to simply ensure that the electricity generated always exceeds the total demand for power.
Apart from its obvious inefficiency (evidenced by the load shedding and blackouts we still have to endure every summer), this lack of storage is proving to be a serious impediment to our plans to transition away from fossil fuels. While renewable energy is practically infinite, it is also notoriously fickle. When the sky is overcast, it is next to impossible to be able to generate sufficient solar energy, just as it is impossible to get wind turbines to move on a still day.
If renewable energy is ever going to be as reliable as conventional energy, we will need to find a way to store energy when we can get it so we can use it during periods that we can’t.