Pumped Storage

Originally posted on the RetroMat website a few years' ago, but is better placed here.

An often-heard criticism of reliance upon sources of renewable energy - specifically solar and wind power - is that they're no use when the sun isn't shining or the wind isn't blowing. This is not a trivial point - here in the UK, we do get such days nationwide, particularly in the winter.

Pumped storage schemes, whereby water is pumped from a lower reservoir to a higher one during periods of low demand and then released to flow back down and generate energy during periods of high demand, may look like a possible, if partial, solution. One such scheme is the Dinorwig power station in North Wales. (Another, 3 times the size, at Coire Glas in Scotland was proposed in 2013 and as at Feb 2026, is still proposed rather than under construction). The classic scenario for which it was intended is at the end of or during the commercial breaks of popular TV programmes when there is a rush to put electric kettles on to make cups of tea or coffee, i.e. to meet short bursts of high demand. However, it  can hold around 9 GWh of energy, enough for the daily requirements of about 1 million households, so can also be used for short-term storage. 

I read a while ago about a proposal to install such a system on a small scale in a high rise tower and this led me to wonder - briefly -  if it might be a practical solution for use in (2-storey) homes here in the UK, where traditionally we have had cold water storage tanks in the loft. There's been a move away from these in recent years with tanks being removed when combi boilers are installed. What if these were left in place and adapted for pumped storage instead? Could they be of use, even if drawn on for brief periods only?

Let's assume such a tank can hold 200 litres of water and is 5 metres above ground level. The potential energy stored in the tank is the weight of the water (200 kg)  times the acceleration due to gravity (~ 10 metres/second/second) times the height of the water (5 m), i.e. 10k Joules. That's 1 kW for 10 seconds, so 1/360 kWh, barely enough to power a low energy bedside light for 40 minutes! By contrast, batteries provided with domestic solar power systems typically store several kWhs. 

Not surprisingly, it's a fraction of the energy needed to boil water for a cup or two of tea, say a half litre of water. To boil this amount from room temperature (perhaps 20 degrees C ) requires the mass of the water, 0.5 kg, times the Specific Heat Capacity of water, 4200 J/kg/degree C, times 80 degrees, i.e. 168k Joules. That's only around one 1/20 kWh, but is still about 17 times the potential energy stored in the cold water tank!

So, it's a non-starter for our 2-storey home.  What about high-rise accommodation? Let's consider that water tank 100 metres up. In this case, it would store 20 times the potential energy, 200k Joules, enough to power that light for a little over half a day, and also now to boil that kettle! To provide that energy for all the households in the building, there would need to be a lot of water stored at the top, however.  Just think of the extra weight and the need to support it. Even if feasible,  managing peak demand through pricing would surely be a more effective solution. 

And anyone thinking that the problem of balancing supply and demand could be solved by simply building more pumped storage schemes should consider this:  in the UK we would need the equivalent of around 30 Dinorwig  power stations to store just 1 day's worth of electrical energy for domestic consumption alone and that's before considering any losses due to conversion, transmission and plant outages.

Back to those batteries used with domestic solar power:  those could keep an average home going for just a few hours - very useful in times of occasional power cuts of short duration, but much less so during a prolonged shortage of energy-generating capacity. EV batteries on the other hand can store 10s of kWhs of energy, enough for a household for several days of outages. It's an interesting idea to use these to back up domestic supply, even if it does mean people not being able to use their cars as a result. 

However, EVs are still very expensive to buy (even if much less so to run than petrol or diesel ones) and if we want to keep the lights on for everyone, then for the foreseeable future we'll continue to need to have substantial backup generating capacity in the form of gas turbines which can be switched on and off readily (unlike nuclear power stations). 

And here's a video on YouTube from someone who seems to know what he's talking about who's of a similar opinion, although I tend to think of wishful thinking/delusion/over optimism rather than hoax here. 

Unfortunately, there is a disastrous lack of critical thinking going on with energy policy when the climate zealots are in charge, as they are here in the UK. In particular, the "exporting" of our manufacturing industry sector and of our carbon footprint in the drive to so-called "net-zero", an accounting sleight-of-hand that will have no impact globally and a very damaging one here.