Agenda: Herald 26 May 2014 – by David Watson
THE announcement of a possible doubling in the capacity of the Cruachan
hydro-electric scheme in Argyll has stimulated public debate around the
perception of pumped storage as a means of storing the energy randomly and
inconsistently generated by “renewables” such as wind turbines.
Pumped storage involves the pumping of water, generally during periods of
lighter energy use on the grid, from a low-level reservoir to a high-level
When there are short-term energy demand peaks, the water in the high-level
reservoir can be drained back to the lower one, driving electricity
generators. This very quickly releases more energy into the grid and it is
very useful to the generating companies.
Pumped storage, however, consumes energy because it takes up to 25 per cent
more energy to pump the water up than it generates.
The schemes we have in the UK were built long before large-scale wind farm
development, which has brought very different electricity network
challenges that are increasing as we increase wind generation.
Wind turbines experience lulls both from loss of wind and from wind-speeds
too high for operation. Their outputs are variable between these limits. UK
weather records document low wind lulls lasting two or three days several
times a year affecting the whole of the UK. Lulls of five consecutive days
are not unusual.
On average, each day the UK consumes around 1000GWh (gigawatt hours) of
electricity. When wind is generating 33 per cent of our needs then 1000GWh of pumped storage will accommodate a lull of just three days. The UK’s
existing total pumped storage capacity from its four stations is 30GWh;
only 3 per cent of our typical daily demand.
To achieve a storage system of 1000GWh using as an example Cruachan, which
is the UK’s largest energy storage at 10GWh, we would need to create 97 new
Cruachans. Topographically, geologically and geographically there are
insufficient sites around the UK.
Likely costs, were it achievable (based upon the recently mooted £1bn to
double Cruachan’s capacity where considerable infrastructure already
exists) can be reasonably assumed to exceed £1.5bn x 97, or £145bn. Power
companies are mostly not investing capital in pumped storage, so how are
they combining to control the supply frequency within the statutory limits
of plus or minus 1 per cent as generation changes with wind variations?
Contracts are placed for very expensive additional fast-standby capacity
and UK industry is charged punitive rates during highest demand periods
(the Triad Demand system).
The National Grid (a private company) employs short-term operating reserve
(Stor) and fast-response contracts. Private companies can bid to make
available standby generating plants from a tiny 3MW (megawatts) upwards.
This has led to a growing number of private capital organisations setting
up diesel generating sets around the country, increasingly in car parks and
These schemes are not cheap: generator manufacturers are advertising
available payments of 300 times the normal energy rates of £50 per MWh
(megawatt hour): £15,000 per MWh plus additional availability payments of
up to £47,000 per MW of capacity and so on.
For the longer windfarm lulls, too, we are going to have to live with
increasing standby generation, not pumped storage, to offset most of the
renewables intermittency. Standby generation that is relying on diesel
generators, gas turbines or coal-fired steam generators (some constantly running “warm”) delivers reduced or no load but also delivers heightened
exhaust gases (up to 80 per cent more with some equipment) while operating
at inefficient outputs.
We have a topical reminder too that the UK imports 40 per cent of its
diesel, mostly from Russia, and four out of the eight UK refineries are up
The reality is that these problems need to be avoided or minimised by
increasing base-load generation instead of indiscriminately adding more
windfarms, whose targets need to be re-examined. The starting point should
be a full UK system grid analysis.
If industry finds UK energy expensive or unreliable, it will up sticks and
leave. The sooner we curtail political sophistry and face up to the real
problems we have created the better.
What this failed to address is the fact that pumped storage needs cheap energy from fossil or nuclear power, normally night time coal. Spare capacity that they get for pennies. Without that the sums don’t add up and even if they used night time wind the subsidy or strike price makes the exercise totally unviable. This says that it requires 25% more to pump water back up than the energy it produces. From figures that I have previously seen that seems an underestimation unless they are working on values. As the demand led pumped hydro energy is very expensive but fulfils a justifiable need and replenishment power cheap, 25% more in cost is credible.