Storing energy is currently an endeavour that is bringing the attention of various research groups and companies. New technologies such as hydrogen fuel cells and graphene ultracapacitors are being developed but still not technically mature. Other companies such as Siemens are developing prototypes for decentralising energy storage. However, around 99% of bulk storage capacity in the world, equivalent to 130 GW, comes from pumped-storage due to its low cost and high energy conversion efficiency (70% to 80%).
Energy storage is used so that the excess electricity supply from intermittent technologies such as wind and solar can be consumed at a different time and expensive 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 used to rely 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 drink tea.
What people failed to realise, however, is 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. In the case of Loch Morar, the deepest loch in the UK with a depth of 310 metres, if a 280 metres and 1.8 km dam is built on the surrounding highlands, an upper reservoir with 300 metres can be created. As the water is drained from Loch Morar its altitude could reach as low as -300 metres. This would result on a height difference of 600 metres between the two reservoirs.
This pumped-storage site would have the capacity to store 1,800 GWh of energy, which is equivalent to 1.7 days of electricity consumed during the winter in the UK and 2.4 days of the electricity consumed during the summer in the UK. The generation capacity installed, however, would vary with the amount of wind turbines and nuclear power plants available. Perhaps, 15 GW storage capacity could be installed until 2020 and 30 GW until 2050.
A first cost estimate for this pumped-storage site with 15 GW of pumped-storage capacity is around £12B, which is cheap given the amount of energy it can store. This estimate, however, could considerably increase if there is the need to waterproof the upper reservoir to stop leaks and waterproof the lower reservoir to stop salty water getting into Loch Morar. In addition, the transmission costs required are very high and will considerably increase the project’s final cost.
The availability of cheap energy storage would bring a lot of investment to the UK energy sector, especially the wind industry. This site can store energy from wind turbines in the UK and Ireland or from the excess energy generated at night from nuclear energy, coal with CCS, and geothermal if a transmission line connecting Iceland and the UK is built.
This is a big and challenging project, but the technology is available and it would be a great asset for the UK to become a strategic country in the area of future energy generation.
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Authored by:
Julian Hunt
Julian Hunt submitted his D.Phil (PhD) thesis to the Department of Engineering Science at the University of Oxford in January 2013. During his D.Phil he developed a decision support system called the University of Oxford Tool for Decision Organisation (OUTDO) with the intent to standardise decision-making processes. This tool has been applied to find the recommended electricity generation ...
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