By 2020, when wind could be providing 15% of Europe's electricity, the additional cost incurred by this variability is about €1/MWh and may be more. Yet, if the European electricity system can be managed as a single entity, then these balancing costs can be reduced by over 30%.
Increasing the number of transmission connections where they are inadequate will lower the additional costs to consumers by smoothing the wind variations and enabling states to draw on reserves from their neighbours or export surplus electricity when the wind power production exceeds national demand.
With the recent allocation by the European Commission of over €903 million to electricity interconnection projects, this looks increasingly likely. Additional transmission may also be needed to bring wind power from regions with plentiful resources, such as northern Germany, to the urban and industrial centres where there is a high demand for power.
While the variation in wind is an issue when increasing its share on the network, it is precisely because of the variation that it should be integrated into the European electricity system rather than be run on a separate wind-only grid. Economies of scale will help to reduce the balancing costs, and most of the hardware and software needed to manage wind variability is already in existence.
All electricity networks need to manage unpredictable fluctuations in consumer demand and plant breakdowns. They do this by looking at the performance of the system as a whole, rather than by focusing on any one type of plant. Because thermal plant outputs, such as nuclear, coal and gas-fired power generators can break down without warning when components fail, they are truly intermittent.
This can pose a greater threat to the stability of the electricity networks than the relatively benign fluctuations of power output from wind installations. Short-term operational reserve (see Integrating the variable, below right) ensures that backup production is available to cope with unexpected power fluctuations in the short term, and the plant margin - the excess of installed capacity over and above the expected peak demand, as backup - ensures that there is always adequate power available to meet consumer demands.
Wind is variable, not intermittent
When considering the introduction of variable renewables sources, such as wind, it is important to preserve the economies of scale from an integrated electricity network, as that minimises the additional costs to consumers.
The UK's National Grid, having researched the incidence and variations of wind speeds, stated that it does not expect wind to pose a major problem for stability and that it can be adequately managed, adding that an integrated electricity network can diversify and average out the individual fluctuations in output across the whole system.
Just as diversity smooths demand fluctuations, so it also smooths wind power variations. While the output from a single wind farm can change from zero to its maximum within an hour, over the whole of western Denmark's 2.4GW of wind the maximum hourly change observed is about 480MW, or 20% of the rated capacity. For half of the time, the change in output fluctuates by only 2% of the rated capacity, demonstrating a degree of predictability.
Coping with fluctuations
The effects of operating an electricity network with wind are often discussed without any reference to the fluctuations in demand that already need to be managed. Adding wind is not a straightforward process, but as electricity systems already have provision for dealing with unexpected mismatches between supply and demand, no special additional measures are needed to integrate wind energy in modest amounts of up to around 25%.
Beyond that, a little wind may need to be curtailed on a few occasions (see Integrating the variable, below), but grid operators do not foresee a technical limit. Wind fluctuations are managed by scheduling additional short-term operating reserves, usually in the form of part-loaded thermal or hydro plants, and which are readily available. Additional costs incurred are modest, generally adding less than 1% to domestic bills with 20% wind on the grid (the average EU consumer price is about €14/MWh, and 20% wind adds about €1.3/MWh).
There are various ways of mitigating the extra costs of the variability of wind, mostly with concepts that already exist or are under active development (see left). Many aim to cut the extra costs of operating electricity systems with high renewables input, rather than focusing exclusively on the wind itself.
Others, such as electric cars, electric space- and water-heating, and the hydrogen economy, may come to fruition for reasons quite separate from wind. The most obvious wind concepts, better wind forecasting and high offshore productivity, reduce costs specifically for wind. Demand-side management, storage and more international connections reduce costs to the electricity system as a whole.
Overall effects of mitigation measures
Precise estimates for savings from the mitigating measures noted overleaf cannot easily be made, but it is possible that the various measures will reduce the extra costs by 30% or more. The prospects for improved wind forecasting are very good and the most significant savings would be at the higher levels of wind energy penetration. And the economic justification of additional international connections should also consider the overall benefits to the complete system, the need to strengthen links in the existing European network and also to transport power efficiently from the new generation of offshore wind farms.