Electricity storage can smooth out fluctuations in supply and can overcome mismatches between supply and demand of electricity. On the transmission grid level, this is overwhelmingly achieved with large pumped hydropower units. The need to integrate a growing share of intermittent renewable energy sources in the electricity mix has created a new interest in storage, although there are challenges as well as opportunities. With recent breakthroughs in technology, electricity storage can provide services in parts of the power system value chain previously not considered.
Centralised storage is most useful for the generation and (to a lesser degree) the transmission segments of the value chain and accounts for about 95% of current energy storage for electricity. Decentralised storage – like batteries linked to small-scale and domestic solar installations – could play an increasing role for the distribution, retail and end-use segments.
Storage technologies can also be differentiated according to the time for which the energy is stored: from less than an hour, for example to cope with sudden fluctuations in demand or system failures, to daily (e.g. to store solar power for use at night) and even seasonal storage, to be able to meet increased demand in winter.