Wind Power Reassessed: A review of the UK wind resource for electricity generation 

This study uses wind data extracted from airfield weather-observation reports to calculate the likely performance of wind fleets across Europe, but concentrating mostly on the UK. Airfield weather reports are in the public domain, use a standard reporting format, are taken at a standard observation height, and in many cases use instrumentation provided and operated by national meteorological offices. The study covers a span of 25 degrees of longitude, and ten of latitude and includes 43 ‘monitoring’ sites over a period of nine years; over 6.5 million wind-speed observations are included. The objective has been to explore the scale of onshore wind fleet output variability, and intermittency, the benefits of European interconnectors, the improvement possible with increased storage, and many other matters.

The following conclusions are demonstrated for a UK wind fleet of 10 GW nameplate capacity:

1. Power output changes continuously and commonly by as much as 300 MW over each half-hour period; output changes as high as 700 MW within a half- hour period are not uncommon. This variability can be compensated by fossil fuelled or pumped storage generators operating in response mode, but this will increase grid operating costs, and divert this valuable response capability away from more usual grid stabilisation duties.
2. The model wind fleet reveals many instances of high wind-speed power cutouts;
   this phenomenon does not appear to be a problem with the present wind fleet and may only occur with larger, higher hub height machines.
3. Claims that there is always somewhere in the UK where the wind is blowing are correct, but only sufficient to generate 2 % or less of full wind fleet output. The power output mode is approximately 800 MW, 8 % of nameplate capacity. The probability that the wind fleet will produce full output is vanishingly small.
4. The capacity credit for the model wind fleet is shown to be 2,300 MW. The sensitivity of this result to various model parameters is explored.
5. Power output for the model wind fleet can be characterised by the following statements:

   • Power exceeds 90 % of available power for only 17 hours per annum
   • Power exceeds 80 % of available power for 163 hours per annum
   • Power is below 20 % of available power for 3,448 hours (20 weeks) per annum
   • Power is below 10 % of available power for 1,519 hours (9 weeks) per annum
6. Of the 3,448 hours when the power output of the UK wind fleet is below 20 % of maximum, 2,653 hours (77 %) occur in events when that condition continues for 12 hours or more.
7. Of the 1,519 hours when the wind fleet power output is below 10 % of maximum, 1,178 hours (78 %) occur in events when that condition continues for 6 hours or more. Thus production gaps are commonplace in wind fleet operations. Many of these low power events occur during periods of prolonged, cold weather.
8. Slightly more of these low power events seem to occur in autumn, but are otherwise evenly spread amongst the seasons.
9. If this wind fleet were required to offer a guaranteed production output equal to the capacity credit during winter periods (when wind production is highest), this study shows it would require an energy storage facility holding perhaps 150 GWh, which is the equivalent to that held in 15 ‘Dinorwigs’.
10. Given these observations, the model wind fleet would require a conventional generation fleet of equal nameplate capacity to be built and operated alongside it to mitigate the wind fleet deficiencies.

Data for a model Irish wind fleet, based upon airport weather reports, reveals a wind fleet with slightly higher performance than that for the UK. A model of wind operation across the northern European plain and covering Belgium, Holland, Denmark and Germany shows much poorer performance. Both fleets suffer intermittency
and variability problems similar to those of the UK.

Unifying all three fleets by installation of European interconnectors does little or nothing to mitigate the intermittency of these wind fleets. For the combined system, which has an available power output of 48.8 GW:

• Power exceeds 90 % of available power for 4 hours per annum,
• Power exceeds 80 % of available power for 65 hours per annum,
• Power is below 20 % of available power for 4,596 hours (27 weeks) per annum,
• Power is below 10 % of available power for 2,164 hours (13 weeks) per annum.

European interconnectors may have other uses for grid management, but they will have little impact upon the mitigation of wind fleet intermittency and variability.

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