Pumped-storage hydroelectricity facilities account for 2.5 percent of global installed capacity and 99 percent of the total capacity of energy storage facilities. It is the most competitive and reliable way of storing electricity, enabling both the efficient use of surplus energy and the returning of a significant amount of energy back on the grid.
The advantages of the technology were confirmed in a recent study conducted by Stanford University, which analysed the financial benefits of a range of energy storage technologies and found that pumped-storage hydroelectricity was one of the most efficient, as over its life cycle a plant can store 210 times more energy than was needed to build it.
Enel is one of the most experienced European utilities in pumped-storage hydroelectricity, with 28 plants in Italy, Slovakia and Spain that have a total capacity of 9,598 megawatts, including four large facilities in Italy each with a capacity exceeding one gigawatt.
A pumped-storage plant uses excess electricity produced at night or when there is less demand to fill a hydroelectric reservoir that can provide electricity when required. Performance averages out at about 70 percent or slightly higher, meaning that for every 10 kilowatt-hours used storing, 7kWh are produced during generation.
This makes these plants important for grid management, because they can be put into service in a very short time and tackle the grid's load variations, are extremely reliable and are not impacted from outside, as they mostly work in closed cycles.