Wind Power - 'Variable' or 'Intermittent'? - A Problem Whatever the Word

A RESEARCH INTO THE ACHILLES´ HEEL OF THE WIND INDUSTRY. With a wealth of examples and references, Dr. Etherington enlightens us on the principal weakness of wind farms: their erratic, unpredictable production of electricity. A modern economy cannot afford blackouts, so wind power production must be backed up 24 hours a day by conventional power, which substantially reduces the C02 savings.

by Dr. John Etherington

A car engine will run without its battery. But stop the engine and you are electrically dead - the engine cannot be started again and if it is dark you have no lights. That is the problem of intermittency, and despite squirming and turning by government, it is the problem of wind power - when the "wind engine" stops, there is no power.

For a few days in a year there is no significant electricity at all from wind turbines in Britain. For the majority of the days in the year they produce far less than half of their potential maximum. This is why the average yield (load factor) of wind power in the United Kingdom (UK) was just 25.4% for the last two reported years (2003-4).
 
At present there is no economically viable way of storing electricity in quantities sufficient to smooth wind power generation through periods of low generation and for that reason wind stations must be coupled to the conventional electricity system, which provides the necessary backup.
 
The argument that has raged around this requirement concerns need for dedicated backup, stability of electrical supply and the claims for saving of CO2 emission by displacement of fossil fuelled generation.
 
"Intermittency is a problem"

Twelve years ago I wrote of wind "farms" - "(Because) they fail to generate in windless periods cannot even replace the conventional stations...".
 
The British Wind Energy Association (BWEA) has long known this to be the case: - In answer to its FAQ “What happens when the wind stops blowing?" the reply is "... 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.”
 
A recent report by the UK Energy Research Council was aimed at answering claims that intermittency is a problem. Despite this, the report admits 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."
 
The Department of Trade and Industry (DTI) has been warned of the intermittency problem. In a 2003 BBC 2 documentary, Dr Dieter Helm, Energy Economist and Fellow in Economics, New College, Oxford, 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.”
 
Dr. Helm has been on the DTI Energy Advisory Panel since 1993 (I think even the industry would now agree Dr. Helm’s upper limit of 40% was over-optimistic and the lower limit would be nearer 20%).
 
The most recent and positive statement that there is a problem is in a 2006 report to the Scottish Executive which inter alia concludes: -
 
"Nevertheless there will be many hours in a year when renewable output from wind, waves and tidal currents falls below demand targets and balancing plants would be needed."
 
Reports from the wind power generating companies are even more damning. The German company E.ON Netz is operator of the largest assemblage of wind turbines in the world. In 2004 it admitted that every megawatt (MW) of installed wind capacity required 0.8 MW of backup from ‘shadow power stations’, and in 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."
 
The E.ON area is well away from the Atlantic coast and suggestions have been made that its large requirement for backup is consequent on lower wind speeds and load factor than prevail in the UK. However the Irish National Grid (ESB) has reported similar problems in a windier climate than mainland UK: - “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.”
 
 "Intermittency is not a problem"

The DTI denies this problem. Its web page, Wind Power: 10 myths explained tells us that:
 
"Back-up generation is already in place to cover shut-downs of other forms of generation; little further back-up will be needed up to 2010 to cover periods when wind and other renewables generation is low."
 
Rather more vehement in denial is a recent report, commissioned by the DTI from the Oxford Environmental Change Institute, purporting to demolish the argument for a backup requirement by claiming that the wind always blows somewhere in the UK. This caused 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). However the Oxford report simply compared the incidence of wind speed permitting "no generation" versus wind speed allowing "some generation", however little. Had it 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 realized by the House of Lords Science and Technology Committee in Feb 2004 when Baroness Platt of Writtle questioned Mr. Sinden, the lead author of the report. He replied: -
 
“The analysis that I ran was of wind speeds being so low that electricity would not be generated... 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.”
 
Is there a consensus?

Reading the above account no one could be blamed for concluding that this was one of those childhood exchanges - "tis... tisn´t... tis... tisn´t..." and so on forever.

That this is happening and that the British Wind Energy Association and UK government are devoting so

much effort to disproving the obvious, seems proof enough to me. The EON report was written by working wind power engineers - so was the ESB report. These reports say intermittency is a serious problem on the Atlantic seaboard and further away in Germany on the fringes of continental Europe. It will be a problem here in the UK, whatever the DTI wishes us to believe.
 
I discount the Oxford report, which accidentally (or deliberately) used a zero generation as a baseline and thus concluded that there would always be "some" generation - so what if a few turbines on an outer Scottish island may be lazily turning?
 
Several of the reports I have quoted also suggest there is no real problem up to the 2010 target of 10% of electricity from all renewables - of which 75% to 80% will have to be wind. The reason given is that there is already back-up in place.
 
BWEA´s FAQ for example claims: - "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."
 
The UKERC 2006 report similarly claims "... there may already be more than sufficient reserve capacity on the system to deal with intermittency – particularly if the amount of intermittent generation is a small proportion of total supply."
 
It is quite correct that reserve capacity is provided for the conventional generating system. The National Grid plc aims for a system margin of about 20% over peak demand thus insuring against generating plant or transmission failure. Some of this spare capacity would be on ‘hot standby’, i.e. connected to the network and operating at part load to ensure a stability of connection as in the case of steam plant, or available for instant start-up and connection as is the case for hydro and gas-turbine plant.

It is this "instant start-up" component which wind-power calls upon to smooth its short term vagaries and it is dishonest of the wind power industry and DTI 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 (at a load factor of 25%).
 
Thus within a period of just a few hours, wind output could swing by a substantial fraction of 18,000 MW, balanced against that peak load insurance of 20% (which represents about 11,000 MW). It can’t be done. We shall in due course need a bigger insurance policy and as Dr. Helm said, for the DTI, "the paradox of building windmills is that you have to build a lot of ordinary power stations to back them up..."
 
This problem has already arisen in other countries. On March 1, 2005 the Spanish grid operator, Red Electrica Española, advised 300 heavy electricity users it was going to avail itself of the interruption clause in their contract. Then, their electricity supply was cut off. The reason for this was made clear by a Radio España´s Radio Litoral news bulletin, which explained the "brownout", saying the wind had dropped and reduced the electricity production of 11,000 windmills to 700 MW. Spain was unprecedentedly cold at the time, demand for electricity was high, gas reserves were low, and 5,000 MW of reserve capacity were out of commission, so the loss of wind power created a risk of blackout. Hence the decision to pre-empt by reducing demand in a controlled sector. It is not fortuitous that almost 6.9 GW of new gas-fired CCGT plant has been installed in Spain since 2002, and a further 6.8 GW is under construction!
 
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.
 
The consequences of intermittency

It is not a serious failing in itself that wind power is unpredictably intermittent in yield. The corn miller charged sufficient in producing his flour to compensate for his enforced idleness when the wind did not blow - and the trade became proverbially dishonest!
 
Rainfall, likewise, is intermittent and yet all life depends upon it. However water can be stored, but electricity cannot, at least not economically in huge quantities. So - it is not that wind generation is "inefficient" (an unfortunate and inappropriate word) but the fact that every kilowatt hour of electricity from these machines must be used instantaneously or "spilled" (another unfortunate weasel word meaning, in truth, that wind turbines have to be shut-down).
 
The problem is most easily solved if the wind electricity is fed directly into a nationwide grid system in which other flexible sources can be "switched-on" or "off" at very short notice. Such sources are conventional fossil-fuelled generators and using them to balance wind and other renewables imposes limitations and unavoidable expense.
 
Security of supply and need for backup

There is no argument about the need for some form of backup to compensate for the vagary of wind power. This is indeed accepted by the industry and it is dishonest to suggest that we can continue progressively to compromise the existing backup insurance as the DTI has suggested. Wind power is already twice as expensive as conventional generation, a fact camouflaged by the covert subsidy of the Renewables Obligation. The main reason that the wind power industry is attempting to deflect discussion of the looming need for dedicated backup is that it will further increase prices, as well is negating some of the saving of CO2 emission.
 
CO2 emission and fossil fuel consumption