There’s one major drawback to most proposed renewable-energy sources: their variability. The sun doesn’t shine at night, the wind doesn’t always blow, and tides, waves and currents fluctuate. Even in conventional systems sometimes load vary, sometimes there will be a peak load, sometimes load on the grid will be less. A large battery storage can save fuel . But there is no such a storage system for electricity on large scale. That’s why many researchers have been pursuing ways of storing the power generated by the sources(non-convetional and conventional) so that it can be used when it’s needed.