While electricity is a form of energy that is easy to transport, its storage is much less straightforward.
The way the electricity grid works relies on a balance between production and consumption. Balancing is quite simple when production is based on controllable sources (hydroelectric, gas, nuclear to some extent), because production can be adapted to match consumer demand and avoid excessive wastage of energy.
Nowadays, with the advent of renewable sources (wind, solar), the storage of electricity is a challenge that is gaining in importance. Indeed, these production methods depend on natural elements which are not constant: sunshine and the wind. That means production will be high at some times of the day or year, but will not necessarily coincide with peaks in consumption. As this type of electricity plays an increasing role in the energy mix, the more necessary it becomes to find efficient ways of storing it, to secure supplies and avoid power losses.
A number of electricity storage methods exist (batteries, pumped hydro energy storage etc.), but most only provide short-term storage. Power-to-Gas, where electricity is transformed into hydrogen is, for now, the most promising long-term electricity storage process.