Science in Society Archive

Taking to the Wind

Peter Bunyard looks at the realities of wind power and answers its detractors

Peter Bunyard will be speaking at Sustainable World Conference, 14-15 July 2005.

Wind power working

Ian Fells, professor of Energy Conversion at Newcastle University, told BBC’s Radio 4 Today programme back in December 2002 that if we wanted electricity on tap, while simultaneously meeting our Kyoto Protocol commitments to reduce carbon dioxide emissions, we would fail abysmally unless we replaced and even added to our nuclear power capacity (25 per cent of UK electricity generation in 2005). Renewable energy sources, such as wind-power, he insisted, would be marginal to needs and barely worth the cost of developing [1].

Ian Fells’ remarks contrasted with the experience of one of Denmark’s energy experts who, during the same December 2002 Radio 4 programme, pointed out how successful his country’s strategy had been in developing an electricity supply industry (in which wind-power provides nearly 20 per cent of the total in 2005). It had been good for jobs, good for exports and good for Denmark’s energy needs, with the industry employing 16 000 and annual sales of wind turbines reaching more than 2 GW, equal to two large nuclear power plants.

Peter Edwards, ex-chairman of the British Wind Energy Society developed the first British wind-farm at Delabole in Cornwall 14 years ago in response to the threat of a nuclear power station being built nearby. Initially the economics did not look good, at least in the context of the UK, and Edwards all but abandoned the idea. But then, in 1991, the government simultaneously introduced the fossil fuel levy on fossil fuel generating plants and the non-fossil fuel obligation (NFFO) to support at least 20 per cent electricity production from non-fossil fuel sources.

At the time, nuclear power was generating 20 per cent of the Central Electricity Generating Board’s production, and with privatisation in the offing, the NFFO was little more than a straight subsidy to sweeten up the City in time for a sale. Nonetheless, the subsidy did open up the possibility of investing in the alternatives, such as wind. In 1990, the fossil fuel levy amounted to £900 million, much of which went into the pockets of the nuclear industry.

As Edwards told me in 2001, ten years on from establishing his ten-turbine wind-farm, performance has been better than predicted. “We now have 10 years of records carefully analysed by ETSU (Energy Technology Study Unit) at Harwell, as well as by the DTI, and have discovered benefits from wind generation that we barely suspected. People are quick to say that the wind is fickle and that it fails just when you most need it, but such critics have also failed to understand that when we most need the energy, that’s when the wind blows. In our part of the UK, 60 percent of annual generation is between October and March. Consequently, wind generation and demand go together; in winter when the wind blows, the chill factor goes up and so does the need for electricity; in summer just when everyone is returning home for their tea in the early evening that’s when the onshore winds obligingly come into play.”

It took just a few months to get the Vesta 400 kilowatt turbines up and running. Moreover, each of the machines had been sited in hedgerows across the farm, with minimal loss of land, and since they were all plugged into the local Delabole 11 000 volt substation, they instantly provided power to the neighbourhood and hence avoided the substantial distribution losses that go with distantly connected power stations.

“Such embedded generation immediately improves the quality of supply,” Peter Edwards said, “evening out those fluctuations that have been a curse of electricity supply throughout Cornwall, not least because the bulk of our electricity comes from the Hinkley Point nuclear power station, more than 150 miles away. It’s rather like a blood transfusion into an extremity where bleeding is occurring: you balance out the loss and consequently the local voltage is now much more stable. Cornwall now has six wind-farms, enough to supply some 27 000 households, and whether locals know it or not, the quality of their electricity has gone up substantially.”

In much of Western Europe, wind-power has really taken off, for instance in Germany, Spain, Denmark [2]. In Britain, largely because of the cost of planning applications and public resistance, development has been slower. However, by the beginning of 2003, the UK had a total of 552 megawatts of installed capacity in place from 78 different projects and another 17 to be constructed over the coming two years. By January 2005, another 340 MW of wind farms were up and running, hence the equivalent in capacity terms of a small nuclear power plant, all constructed within a matter of months of the work commencing. Some of the new wind farms involve relatively large machines of 2 and 2.5 MW, and several are offshore. Britain intends to have 20 per cent of its electricity generated from renewable sources by 2020, Denmark intends to go a good step further with 50 per cent being provided from such sources [3].

The detractors

Wind as a source of energy for generating electricity has many detractors. The arguments range from “unsightliness and a blot on the landscape”, to noisiness and perhaps the most damming of all, to its ineffectiveness and inefficiency, particularly the intermittent and unpredictable nature of the wind. Here again, some myths need dispelling; first, that they are inefficient as measured by the percentage of electricity generated compared to the size and capacity of the wind turbine. Basically, critics refer to the 30 per cent or so of production compared to capacity. They neglect that the capacity of a nuclear power station tends to be measured in electricity capacity (MWe) rather than in the thermal units required to generate that electricity which can be more three times greater.

Godfrey Boyle of the Energy Environment Research Unit at the Open University points out in a personal email to me (March 2005) that the size of turbines has been increasing spectacularly in recent years and the largest machines in operation today can have a capacity as high as 4.5 MW. Most of the machines now being built in Britain, whether onshore or offshore, are rated at about 2 MW.

How much land would be required were such wind-machines to provide 20 per cent of UK requirements? In 2003, total UK electricity was a little short of 400 TWh (terawatt hours=1012 watt-hours) so 20 per cent would amount to 80 TWh. Denmark, which manufactures many of the turbines used here and has considerable experience of siting such machines, suggests that each individual turbine should have a downwind spacing of 7 to 9 diameters and a crosswind spacing of 3 to 5 diameters, with resultant array losses of around 5 per cent.

Therefore, each turbine of 2 MW at best would require a minimal area of 16.5 hectares, although it must be appreciated that the land is still open and can be used for recreational and agricultural purposes right up to the turbine tower. Including array losses of 5 per cent, the average annual output per turbine would be 5 GWh (gigawatt hours=109 watt-hours) and the output per hectare of 300 MWh/ha. To produce 80 TWh would therefore require 267 000 hectares, which is just over 1 per cent of the total UK land area [4].

In principle, the UK could meet up to 20 per cent of its current electricity needs from the use of land-based wind-turbines. Add to that offshore wind-turbines and the proportion could go up significantly and certainly surpass nuclear power’s current contribution of 25 per cent of all electricity generated in the UK.

Critics of wind power in particular and the renewables in general make much of their intermittency; the fact that they do not deliver a steady source of electricity hour by hour throughout the year. In a conventional electricity supply system attached to a central grid, the notion is to have base load electricity generated by plants that do best as steady work horses, such as coal-fired plants or indeed nuclear power. In fact, the economics of nuclear power stations demands that the high up-front construction costs are mitigated by constant operation with an optimum power output. Spurts in demand, or peak loads, add to the generating requirements and need to be met with other power plants, such as hydro- or gas turbines, which can be brought on stream rapidly and shut down equally rapidly. Response to such spurts in demand, or to unexpected breakdowns, is met by keeping some power plants in the electricity supply system as ‘spinning’ reserve whereby the turbines are kept rotating, even when their power output is not required. To meet peak demand is inevitably more expensive in terms of unit costs and therefore in relative greenhouse gas emissions, than providing for a steady base-load.

The renewables, such as wind, do not fit neatly into the category of providing base-load electricity nor can they be brought on at will to supply peak demand. As the engineer Andrew Ferguson points out [5]: “There is no way that we can order wind turbines to follow demand,”  and on the basis that the wind supplies 30 per cent of the ‘block’ of electricity determined by the peak demand, and the flexible back-up system provides 70 per cent then, according to Ferguson, the 70 per cent is likely to be supplied inefficiently at 35 per cent because of operating ‘in harness’ instead of 60 per cent as can be obtained in a combined cycle gas turbine (CCGT).

“Hence, the gas needed will be 0.70/0.35 = 2 units, whereas were there to be no wind turbines, 100 per cent of electricity would be supplied by CCGTs operating efficiently (60 per cent), and the gas needed would be 1/0.60 = 1.67 units.  Thus using wind turbines increases gas consumption by (2/1.67) -1 = 20 per cent.”

Ferguson’s pessimistic view is not held by others in the industry. Lewis Dale, a member of the DTI/Ofgem Technical Steering Group, together with David Milborrow, Richard Slark and Goran Strbac, all professionals in the field, have looked at the costs for introducing different proportions of wind power into the generating system [6]. They take into account the impact of wind on the need to establish and maintain other generating capacity; and network costs, which arise through reconciling the input from wind with the other inputs into the grid.

They then compare two scenarios for the year 2020 in which electricity demand has increased by 17 per cent with total electricity sales of 400 terawatt-hours and a peak demand of 70 GW. In the first scenario electricity is provided through using coal and gas, with progressive improvements in efficiency, and ever-greater incursions of combined heat and power. In the second scenario wind power has increased to the extent of providing 20 per cent of electricity sales derived from 26 GW of capacity with an average 35 percent load factor (a measure of efficiency given by the ratio of energy produced during a given period of time over the energy that would have been produced had the wind farm been running continually at maximum output) and a typical wind speed of 8.3 metres per second. For the sake of the analysis 60 per cent of the wind capacity is located offshore, connected directly to the central grid and the remainder is located onshore, connected to the 132 kV distribution network or even lower.

In effect, if 26 GW of wind power with a 35 per cent load factor were installed, some 5 GW of conventional capacity would no longer be needed, given that replacement electricity has to be generated to make for shortfalls as a result of intermittency. The authors do not deny that, “technical costs arise as reserve plant is part-loaded and, in consequence operates at lower efficiency...”

Most importantly for 20 per cent of the generating mix coming from wind energy, some 19 per cent of fossil fuel combustion is avoided. That includes a 1 per cent reduction in the savings because of using less efficient generators as part of the reserve. That conclusion presents a markedly different picture from the pessimistic one of Andrew Ferguson.

In general, the economics of wind power are based on the amount of fuel saved plus the amount of generating capacity not required minus the costs associated with intermittency. As the Carbon Trust and the Department of Trade and Industry conclude in a recent report: “10 per cent wind penetration would displace about 3 300 MW of capacity and 20 per cent about 5 000 MW. As far as generating costs the additional balancing costs would add between 1.6 and 2.4p per kilowatt-hour for 10 percent penetration and between 1.9 and 2.8p for 20 percent.”

Timur Gül and Till Stenzel, reporting for the International Energy Agency, conclude that windpower as well as other renewable energy sources, including photovoltaics, backed up by electricity generation from biomass, will make a good contribution to overall electricity supply. [9]

Ferguson, like the Carbon Trust/DTI, is hooked into a conventional way to supply and distribute electricity that entails a central grid system supplied by large thermal power plants, whether fossil-fuel fired or nuclear. But, what about an innovative look at an electricity supply system that does rely considerably on renewable sources, whether intermittent or not, and yet is energy-conserving and therefore efficient?

Embedded local power supply for maximum efficiency

To start let us look back to what is happening in France where the bulk of electricity comes from nuclear power plants (“Deconstructing nuclear power myths”, this series). The French consumer prefers to use natural gas for central heating, cooking and heating water, thus making heavy inroads into the supply of electricity from nuclear power, in much the same way that Ferguson has indicated happens with the intermittent supply from wind turbines. The difference is that the gas heating system switches on with demand rather than being prey to the wind, as is the case with wind turbines, while simultaneously being an efficient producer of end-use energy.

Judiciously sited in a housing complex or block of flats, the overall efficiencies of gas-fired combined heat and power systems, which provide useful heat and electricity, can amount to nearly 90 per cent. If biogas is used then the net carbon emissions are extremely low (and much better than using current nuclear power), moreover the system can be powered down when the wind is blowing strong and brought up to full power when needed.

With such a system, the wind would make a substantial difference to the amount of fuel required, simply because of the embedded nature of the flexible power supply system. That is not to say that the central grid should be dismantled but, acting in the manner of a back-up system for local embedded power production.

If so, at one stroke, the UK could reduce demand for electricity by 25 per cent or more, simply by balancing out the difference between base load and peak load requirements. Systems that do just that have been in operation for at least 30 years and were part and parcel of small-scale generating systems used in isolated dwellings and communities. The inspiration for such a system came from a West-country based engineer, Rupert Armstrong-Evans, who wanted to extract as much power from a system, such as mini-hydro plant, that it could possibly deliver [7].

Even though the electricity fluctuated on a daily or hourly basis, it could be manipulated electronically to provide superb quality power for delicate appliances such as computers, TVs, and the like. A black box between the end-use consumer and the supply took any excess power, over and above that being used for lights and appliances, and dumped it in a buffer heating circuit. Hence storage heaters, immersion coils in boilers and even storage heater cooking stoves benefited whenever excess electricity was available, such as during the night when the household was asleep, or indeed during the day if the occupants were out working.

Clearly, in such a localised embedded system, there are limits to the amount of electricity that can be provided at any one moment. Armstrong-Evans therefore devised his black box to warn the household that it was approaching the limits when demand for quality electricity was near to exceeding supply. Then all that the consumer had to do was to switch off some appliance that could be dispensed with, at least at that moment. In effect, the consumer was made responsible for judicious and constrained use of electricity without losing the comforts and conveniences of the modern home.

Imagine the use of such black boxes throughout the UK: they could be set to allow in a fixed amount of electrical capacity. When the household was asleep and using minimal appliance power, the electricity entering the building would pass automatically through to heating circuits, possibly including heat-storage cookers. In effect each household would have its base-load requirements that could be regulated from month to month, season to season. Were the demand to go above the set amount, then the consumer would pay heavily for the marginal costs of bringing in more electricity. It would then be up to the consumer to limit the intake into the household by switching items on and off as required, rather than leaving them on without regard for the impact on the total generating capacity required.

Once the levels of electricity supplied by an intermittent source, such as from wind turbines, fell below a critical point, then the back up Combined Heat & Power system would automatically come on stream, levelling off the power produced as the wind came back and then switching off were the wind to be back in full strength. The management of such a system could be left to electronic controls combined with self-responsibility.

Just by leaving appliances on stand-by in the home, gadgets such as TVs, washing machines, dish-washers, DVD players as well lights, we in the UK are responsible for emitting an extra one million tonnes of carbon-based greenhouse gas into the atmosphere  [8]. That is enough energy, says DEFRA, the Department for Environment, Food and Rural Affairs, which commissioned the report, to power the needs of 400 000 homes; and turning the appliances off could reduce electricity requirements by the equivalent to at least one large-sized generation plant [9].

The UK government is now suggesting that manufacturers should sell appliances that automatically switch themselves off when not in use. In essence, energy conservation in the home, at work, in factories and in transport, is by far the cheapest and most effective way of reducing greenhouse gas emissions — certainly an order of magnitude cheaper than building a new nuclear power station per kilowatt saved and immeasurably safer.

Whatever we do, we must avoid falling into the trap that Tony Blair and others are setting for us in making us believe that we have no options available to us other than resorting to nuclear power. And we must certainly give the lie to the notion that nuclear power is greenhouse gas emission free or indeed can provide us with bounteous energy for as long as we can see into the future. Renewable energy sources are there for the taking and we must learn to use them efficiently and wisely. It is time to take the wind out of nuclear power.   

Article first published 12/07/05



Bibliography

Fell Associates. Consultants in energy and the environment. http://www.fellsassociates.com/

Danish Wind Industry Association. Wind Maps of Europe 1 June 2003 http://www.windpower.org/en/tour/wres/euromap.htm

British Wind Energy Association, http://www.britishwindenergy.co.uk/map/list.html

Godfrey Boyle, personal communication

Andrew Ferguson. The Fundamental Problem with Intermittent Wind Supplies. Optimum Population, Document 6, 26/02/05.

Lewis Dale, David Milborrow, Richard Slark and Goran Strbac. The costs for introducing different proportions of wind power into the generating system. Power UK, issue 109, March 2003.

Timur Gül and Till Stenzel. Variability of Wind Power and Other Renewables: Management Option and Strategies. IEA, 2005. http://www.iea.org/Textbase/Papers/2005/variability.pdf.

 “Standby Britain” Ben Russell The Independent, Thursday, 23June 2005,

Sustainable Development Commission Report, 19th May 2005. http://www.sd-commission.org.uk/pages/media/list/wind.html.

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