# Cost of pumped hydro storage

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Apart from hydropower, virtually all of the new renewable energy technologies suffer from one serious problem. A problem that, to my knowledge, there is no solution in sight.

We simply do not have an efficient, low cost technology for storing large quantities of electrical energy for periods of hours, days and months. Until this is invented, no intermittent renewable energy technology can be used on other than a relatively small scale.

The only available technology for storing large amounts of electrical energy is hydropower pumped storage. A pumped storage station costs in excess of US\$1000/kW and the overall losses are about 25%. Most pumped storage stations store sufficient water for 6-10 hours of operation. The ideal operating head is between 500 and 700 m (1500-2200 ft). To build a pumped storage station you need to find, in one place, a source of water, a hill at least 400 metres high and topography suitable for building a large pond at the top of the hill and another large pond at the bottom of the hill.

As an example let us examine a pumped storage scheme associated with a 1100 MW solar power installation. The solar power station would have a capacity factor of 20% or less. Most power systems have a capacity factor close to 60% . If we assume 90% efficiency for pumping losses, the 1100 MW solar power station plus pumped storage would be equivalent to a 330 MW conventional power station (1100 × 0.9 × 0.2/0.6 = 330). The pumped storage station would have a capacity of about 900 MW (so that it could absorb the surplus solar power when the sun was shining brightly and the system load was at its average value of about 200 MW). It would have to be able to store electricity for at least a week to allow for cloudy periods or for 5-6 months to be able to use surplus summer electricity during peak demand periods in the winter.

If the solar power station cost \$1000 per kW (a ridiculously low figure at the moment) and the pumped storage station costs \$1500/kW (because it needs to have additional storage) then the total cost would be \$2.45 billion. As the effective output at 60% load factor is 330 MW (1750 GWh pa), this works out at \$7400 per kW.

A nuclear power station – which is also clean and produces no carbon dioxide – would cost about \$4000/kW. If it operates at 60% capacity factor, a 240 MW nuclear station plus a 100 MW pumped storage station would do the same job (330 MW and 1750 GWh pa) as the 1100 MW solar power scheme and would cost \$1.1 billion. So, even if the solar power installation cost a ridiculously low \$1000/kW the delivered power is 2.2 times the cost of nuclear. If the solar installation cost a more realistic \$3000/kW then cost of the solar scheme is \$5.8 billion and the cost of the delivered power is 5.3 times the cost of nuclear.

For wind energy instead of solar the only difference is the the cost is now about \$2000/kW and the capacity factor is about 25%. So we need 1000 MW of wind power plus 600 MW of pumped storage, costing \$2.9 billion. 2.2 times the cost of nuclear!

The answer is clear: until the cost of these renewable technologies reduces by a very large amount and a low cost efficient method of storing large amounts of electricity is invented, solar and wind power and other intermittent renewables cannot compete with conventional power generation. It is crazy to spend money on new renewable technologies while ignoring the need for large scale, low cost storage. Alternatively, it is crazy to squander large amounts of money on subsidizing wind, solar and marine power rather than spending money on improving existing technologies such as High Temperature Gas Reactors and research on fusion power.

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