In a previous posts I have raised the real issue of how to balance renewable electricity from different renewable resources. One way of doing this, perhaps the best way, is to store electricity. The ways of doing this directly are very limited (capacitors?). There are a number of chemical (batteries/hydrogen) and mechanical methods (flywheels/compressed air). The remaining method is the oldest-that is pumped storage.
This means of “storing” electricity involves pumping water up hill to a reservoir and releasing it when required. It is then used to generate electricity by means of a hydroelectric turbine. Strictly speaking this is not renewable energy, or is only as renewable as the electricity used to pump it up hill. Typically these systems are used during the day and use cheap electricity to replenish their higher reservoir capacity during the night-time when power demand is low. These pumped storage systems have been traditionally used to balance high demand for example in the mornings when everyone gets up to have breakfast, or the evenings when people get home from work (the highest regular demand period in the UK for electricity).
Recently we were on holiday in Wales and went to visit what is still one of the largest such schemes in the world (as well as the fastest to swing into action when demand rises) at Dinorwig. What is so impressive about this scheme is that you would hardly know it was there. Due to its location in Snowdonia the power station was built in the middle of a mountain and its entrance is where a slate quarry was. In addition the transmission lines are buried underground for around 6 miles as cables. A huge man-made cavern contains the six turbines rated at 300MW each (which act as pumps when required to reverse the flow) and the generating sets. Whilst these turbines are large they are surprisingly small considering their power output – being only a few metres in diameter. The weights on the valves used to stop flow to the turbines are also very impressive. All in all well worth a visit-its a superb piece of British Engineering.
The problem is we don’t have enough of these systems (very few countries do apart from perhaps the Japanese and Norwegians). Whilst these systems have been used to balance out short term demand on the grid their focus will change to balancing out renewable production with demand. I understand there was a similar scheme proposed for under Dartmoor which was cancelled. Maybe its time to resurrect it and convert some existing hydro schemes to pumped storage? Of course it would help if we could find ways to use less electricity…
Of the other types of types of energy storage mentioned above we think the chemical methods will run into resource issues and the mechanical methods are largely untested (with the exception of compressed air in Germany and a small flywheel in the US). In principle though mechanical methods and pumped storage are the solution.
A couple of final thoughts- it takes more energy to pump water up hill than you get when it flows back down again and as the share of renewable electricity rises the pumped storage systems are getting more renewable.