Storing energy is an endeavour that has come to the attention of various research groups and companies. New technologies such as the hydrogen fuel cell and graphene ultracapacitors are being developed but are not technically mature. Other companies such as Siemens are developing prototypes for decentralising energy storage which might work for small scale systems. However, around 99% of all bulk generation capacity based on storage schemes, equivalent to 130 GW, comes from pumped-storage due to its low cost and high energy conversion efficiency (70% to 80%).
Energy is stored so that the excess electricity supply from intermittent technologies such as wind and solar can be consumed at different times. Nuclear reactors can operate at full capacity at night when the demand for electricity is low as the energy is stored. For example, around 9% of Japan’s electricity generation capacity is pumped-storage as Japan once relied heavily on nuclear power.
Most people have assumed that the UK does not have enough feasible pumped-storage potential for a renewable energy revolution to take place. Wind energy in Scotland is abundant and given its high speed and frequency it is arguably one of the cheapest sources of energy in the world. However, the problem of intermittency is the biggest challenge for the wind power sector as electricity has to be generated when there is demand for it and, unfortunately, the wind can blow at dawn when there is low demand for electricity and stop blowing when people wake up to start the day.
It turns out that the lower reservoir of a pumped-storage site can be a drained lake and the drained water can be used to increase the height of a new upper reservoir. This is the case of Loch Morar, the deepest loch in the UK with a depth of 310 metres. If a 280 metres high and 1.8 km long dam is built on the surrounding highlands, an upper reservoir with a water level of 300 metres above sea level can be created. As the water is drained from Loch Morar its altitude could reach as low as -300 metres. This results in a height difference of 600 metres between the two reservoirs.