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The unbearable lightness of wind

Feb 5, 2009 - The omens for wind power are very good, and there is cause to believe that the EU's 2020 targets in this area will be exceeded.

But as grows, it may be wind's impact on electricity prices that presents the most immediate problem.

Wind's intermittency cannot be wished away, even if it can be ameliorated, and the development of the infrastructure needed to deal with it is lagging the installation of wind power itself.

There are few renewable energy policies that do not depend heavily on wind power and wind is certainly at the heart of the most ambitious, the EU's binding target of sourcing 20% of final energy consumption from renewable resources by 2020.

As the EU's target for transport is half that for energy consumption as a whole, it follows that the power sector will be required to source a proportion of energy from renewables that is much higher than 20%.

According to the European Wind Energy Association (EWEA), the figure is 35%.

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Within that, wind will be the largest contributor, accounting for just over one-third of 'green' electricity, suggesting that between 11.6-14.3% of the EU's power will be supplied by wind by 2020, according to the EWEA.

This would mean the installation of 180 GW of wind power by 2020, up from 56.535 GW installed in the EU-27 at end-2007 , producing about 477 TWh of power. (See map: Cumulative wind power installed in Europe end-2007 (MW)).

The transport element of the EU plan is also dependent on future scientific advances, for example, that second generation biofuels become commercially available.

This uncertainty will put more pressure to achieve in areas that are already within technological reach.

But if these targets seem ambitious, it is also evident that wind capacity is being installed at much higher rates than previously forecast by bodies such as the International Energy Agency.

According to Stefan Gsänger, secretary-general of the World Wind Energy Association, worldwide wind capacity had risen to about 120,000 GW by end-2008, an increase of 30% on 2007.

According to Platts Power in Europe, wind additions in Europe for the first time in 2008 accounted for more new generation capacity than any other power source, including gas.

A study carried out by the Deutsches Windenergie-Institut in 2008 estimated that the annual worldwide installation capacity of the industry would have risen above 100 GW by 2017.

Experience in Europe shows that with the right policy framework, wind capacity can rise fast. And while the 'binding' nature of the EU's targets means little in practice, it is a serious statement of intent.

Renewable energy also promises new jobs, making it an attractive sector for policy makers on a counter-recessionary spending spree.

Wind would appear to tick all the right boxes in terms of energy, environmental and industrial policy, suggesting, as some non-governmental pressure groups do, that the EU's targets for wind are in fact not that ambitious and could well be exceeded.

The desirability of wind

But just because you can, doesn't mean you should.

Wind power has its critics and they feel that their reservations have been overridden by policy makers whose imaginations have been captured by a green agenda that downplays wind's limitations.

Wind's intermittency cannot be ignored just because it is the most readily available and domestically attractive technology to hand, they argue.

Any electricity system needs a mix of baseload generation power - which tends to be relatively inflexible in terms of switching on and off - and peaking plants, which are more flexible and, as their name suggests, designed to take advantage of high electricity prices at times of peak demand.

Wind falls into neither of these categories because it is essentially unreliable.

Proponents of wind power dislike the negative connotations of the word 'unreliable', pointing out that on average the amount of power supplied by a given capacity of wind turbines is reasonably predictable.

But, according to the EWEA, wind turbines produce no electricity at all between 15% and 30% of the time.

And, on average, the load factor for onshore turbines is about 30%.

This means that over 24 hours, 1 MW of wind capacity would provide about 7.2 MWh of power, but there's no knowing exactly how much or when until the last minute.

As wind provides neither baseload nor peaking plant it has no impact on reserve capacity.

There will always be the possibility that, at some point, no power will be produced at all.

This threat falls as more wind capacity is added; some analyses suggest 26 GW of back-up is needed for 100 GW of wind, others that back-up needs range from 60-95%, depending on the make-up and size of the system.

But wind's intermittency ultimately means that a system reserve must remain in place.

The system must be set up to accommodate wind, but also to work as if it did not exist.

But if wind turbines add little or no reserve capacity, they do produce power.

And the impact they have depends on a range of factors, including when the power is produced, the ability of the system to add and withdraw non-wind capacity and how power is priced.

Imagine two scenarios; peak and trough demand.

During lower demand periods, the system is at its least flexible, with power supplied by baseload plants.

A surge of wind power may simply result in surplus power production, sending prices towards zero.

In effect, it is as if the system has too much baseload generation plant that cannot be turned off quickly enough, either for technical or economic reasons.

The ability to export might provide a key safety valve, but would depend on; first, the physical infrastructure being in place; second, prices falling below the external system's baseload prices; and, third, the lack of a similar wind surge in the external market, either as a result of different weather patterns or of less wind capacity in that system.

At times of peak demand, the system is at its most flexible because the maximum amount of the most flexible power generation capacity is in use.

A wind surge would look as if the system had in effect much more flexible plant that it really does.

Prices would be shaved, but underpinned by a greater ability to withdraw peaking capacity.

So, in the low demand period, the impact on peaking plant is negligible - they are not producing power anyway.

The impact on baseload plant is principally in terms of price rather than generation displacement and therefore would not necessarily result in carbon emissions being avoided.

Prices react as the ability to withdraw capacity is low.

In the high demand period, baseload plants again suffer from lower prices when the wind blows.

Peaking plants experience either lower prices or generate for shorter periods.

This suggests that the principle result would be for wind to displace peaking plant, i.e. gas rather than more carbon-intensive coal or low-carbon nuclear.

The thorny issue of subsidies aside, adding an intermittent energy source would act to reduce prices overall as wind adds power but does not add reserve capacity. In so doing, it increases redundancy in peaking plant and reduces the profits of baseload generation; potentially good for consumers but bad for investment in non-intermittent sources of power, and presenting the risk of a decline in reserve capacity.

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'Back-up' capacity not required

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