4. The problem of intermittency and need for backup

 

What 'they' say

 

“What happens when the wind stops blowing?

 

When the wind stops blowing, electricity continues to be provided by other forms of generation, such as gas etc. Our electricity system is mostly made up of large power stations, and the system has to be able to cope if one of these large plants goes out of action. It is possible to have up to 10% of the country's needs met by intermittent energy sources such as wind energy, without having to make any significant changes to the way the system operates.” (BWEA FAQs)

 

A likely story.

 

In 2003 the BBC 2 programme If….. The Lights Go Out' (10 March) included a contribution from Dr Dieter Helm, Energy Economist and Fellow in Economics, New College, Oxford. Dr Helm has been on the DTI Energy Advisory Panel since 1993.

 

He commented on wind power: -

 

“What we know, is the wind blows sufficient for these windmills to be producing about 35%, perhaps 40% of the time. So the paradox of building windmills is that you have to build a lot of ordinary power stations to back them up and those are going to be almost certainly gas in the short to medium term and that’s what’s required. If you ask the question who’s making sure that there’s enough gas stations out there to back up the windmills the answer is nobody.”

 

This was one of the first official acknowledgments of a point which Country Guardian and many campaigners had made for years. Because of the unpredictable intermittency of wind, and the very long time required to bring 'cold' generating capacity into production, it is necessary to keep a substantial reserve of spinning backup. This is usually arranged by keeping turbo-alternators at less than peak output so that an instant increase of generation is possible. This causes a significant amount of extra CO₂ emission from such plant.

 

E.ON Netz (2004) admitted that every megawatt of installed wind power required 0.8 MW of backup from ‘shadow power stations’, thus, even when not generating, wind turbines are still causing some CO₂ emission. The following year E.ON Netz (2005) went further: -

 

"... Dependence on the prevailing wind conditions means that wind power has a limited load factor even when technically available. It is not possible to guarantee its use for the continual cover of electricity consumption. Consequently, traditional power stations with capacities equal to 90% of the installed wind power capacity must be permanently online in order to guarantee power supply at all times."

 

In the words of ESB, the Irish National Grid (2004): -

 

“As wind contribution increases, the effectiveness of adding additional wind to reduce emissions diminishes [and] the cost will be very substantial because of the back up need”. 

 

Using wind power to reduce CO₂ emission seems akin to emptying the Atlantic with a teaspoon! The wind power industry and the DTI seem very disconcerted by the widespread revelation of just how serious this problem will be.

 

A very recent report, commissioned by the DTI, edited by Graham Sinden (Oxford Environmental Change Institute, 2005) purported to demolish this argument by claiming that the wind always blows somewhere in the UK and led Energy Minister, Malcolm Wicks to say "This new research is a nail in the coffin of some of the exaggerated myths peddled by opponents of wind power." (Independent November 14 2005).

 

 One could retort "So what? - 200 turbines generating feebly on Stornoway and the rest of the country’s wind fleet becalmed". However it is worse. Sinden simply compared the incidence of 'no generation' versus 'some generation' but this is not the point. Had Sinden’s group compared incidence of generation above a sensible threshold (say 20%) with incidence of maximum generation it would have been apparent that in anticyclonic weather there are many occasions per year when the whole UK wind fleet would be contributing very little.

 

This was indeed realised by the House of Lords Science and Technology Committee in Feb 2004 when Baroness Platt of Writtle questioned Mr Sinden on his research. He replied: -

 

 “There will be times when you have quite low speeds and consequently you have low electricity output from it. The analysis that I ran was of wind speeds being so low that electricity would not be generated, that was the criteria for it. As I said, the single worse case in the last 21 years was 11 hours over summer when that did happen. If you raise the bar higher and say "We want 20 per cent output or 30 per cent output" then it may look a little bit different but we have not carried out that analysis.” (House of Lords Science and Technology - Minutes of Evidence Session 2003-04)

 

This weakness in the argument is such an Achilles heel that it has led the DTI and wind industry to clutch at the straws of electricity storage and/or hydrogen generation by electrolysis. These are expensive technologies to prop up a wind power industry whose electricity is already over twice the price of 'conventional' generation!

 

A recent report from UKERC (2006) seems to be directed at downplaying the problem of intermittency but it fails to convince. One of its conclusions is that: -

 

 "Wind generation does mean that the output of fossil fuel-plant needs to be adjusted more frequently, to cope with fluctuations in output. Some power stations will be operated below their maximum output to facilitate this, and extra system balancing reserves will be needed. Efficiency may be reduced as a result."

 

UKERC suggests that this will happen only with substantial wind penetration but the document also reports “that a study of the "... transmission network-constrained Swedish system concludes that energy spill levels would reach 16.7% at an 11% penetration level" “

 

Energy spill” is a euphemism for shutting down turbines as a consequence of over-generation.

 

The UK is, like Sweden, constrained by a transmission problem. We have only one interconnector to Europe, the 2.0 GW cross-Channel link so our system is effectively islanded. We cannot export or import significant over- or under-production of electricity and are thus faced with the problem reported to the Royal Society of Edinburgh (2005): -

 

“As a retired grid control engineer my instincts react against all thought of unpredictable renewable power on the scale proposed, sloshing around the system... Wind resource does not provide any governor response to assist the automatic correction of system frequency deviations. Its exploitation on any scale would deter the introduction of new replacement capacity by soaking up available demand, the basis of payment within a market driven structure. At minimum levels of system demand with fixed base load operation of nuclear plant, in turbulent conditions, the control of system frequency would become a nightmare.”

 

Thus wind-power must call upon conventional reserve generation to smooth its short term vagaries and it is dishonest of the wind power industry and DTI (2005) to claim "The reserves needed to guard against loss of a large power station will readily cope with the small perturbations due to the wind". This may be true at the moment, with wind power providing less than one percent of average generation from an installed capacity of just 1500 MW but if the contribution of wind power should rise to (say) 10% of average generation i.e. 4,500 MW we would need a wind installed capacity of up to 18,000 MW to provide it (load factor 25%).

 

Thus within a period of just a few hours, wind output could swing by a substantial fraction of 18,000 MW, balanced against the Grid’s peak load ‘insurance’ of  c. 20% (which represents about 11,000 MW – see notes on ‘Reserve capacity’). It can't be done. We shall in due course need a bigger insurance policy and as Dr Helm said, for the DTI (above) "the paradox of building windmills is that you have to build a lot of ordinary power stations to back them up..."

 

It is my view that the BWEA and the DTI are misleading us over this matter. There is certainly no consensus that intermittent wind power can be fed into our electricity network in large quantities without action being taken soon to ensure stability. Such action will add cost to an already very expensive technology which needs a 100% ‘subsidy’ to survive and will substantially