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Limitations to Wind Penetration  

Author:  | California, Denmark, Germany, Ontario, Texas

A great deal is made by wind proponents about how much of any country’s, state’s or province’s electricity is now, or can in the future, be provided by wind power. The best measure of this is the amount of wind electricity actually produced for consumption as a per cent of the total. When the experiences of aggressive early adopters of wind power are examined, a pattern emerges, which shows roughly that:

  • Between 2-4 percent, the problems of wind’s unreliability and variability start to become apparent. Sudden drops in wind output require some users to accept their electricity being cut off, often by pre-arrangement, or rolling blackouts may result. This has occurred in Texas. During periods of high demand and low wind output, wind is not available to do its share, as in California during peak summer periods. Sudden surges in wind output require that wind output be curtailed, or shut down to some degree. This has occurred in the US Pacific northwest. In Alberta, Canada, the cap on wind implementations was removed after the Alberta Electric System Operator was allowed to impose curtailment on wind plant output, among other measures.
  • Between 4-6 per cent, the conditions described above occur. Spain has had to cut off selected customers. Electricity systems failures have occurred, affecting multiple countries. This happened in Europe on November 4, 2006, as a result of the presence wind power in Germany. Further, curtailment is widely used by German utilities. In Denmark’s case, high wind output is dumped (exported at low prices) to its much larger neighbours, Norway, Sweden and Germany.

Figure 1 shows where the aggressive, early adopters of wind power are in their implementations relative to Ontario’s plans.

Figure 1 – Experience of Early Adopters Compared to Ontario’s Plans

Comments on Figure 1 are:

  1. Germany has steadily grown to the point at which it has reached the maximum. There are indications (not publically wide-spread yet) that there is some concern about this. I predict that it will de-commit from its aggressive future wind implementation plans (largely offshore) after the 2009 federal elections.
  2. Denmark reached this point earlier and since then, as indicated above, it has had to export (dump) excess production to Norway, Sweden and Germany (upper line). Domestic use at 6 per cent will fluctuate to some degree, and the straight line shown (lower line) is therefore representational. A more extensive treatment is provided below for those who want more details, with the final conclusion that what is shown here is reasonable enough. It is obvious how the misconception that Denmark gets 20 per cent of its electricity from wind (with the assumption that it is consumed within Denmark) has grown.
  3. In California, implementations have slowed down as it has approached the 2 per cent area. Interestingly, California is in discussions with British Columbia for it to assist as California’s source of wind power.
  4. Texas has rapidly reached the same point of penetration as California and has surpassed it in installed wind capacity. They have become aware of problems, and a recent report by the Texas Public Policy Foundation is cautionary.
  5. Ontario started later but will catch up quickly approaching 5 per cent by 2015 and will progress to over 6 per cent by 2020 according to OPA projections. Assuming a more conservative capacity factor of 20 per cent versus the OPA assumption of 28 per cent will keep it under 5 per cent. In any case Ontario will have reached the maximum amount of wind energy that the electricity system can withstand. There is no room left for additional wind capacity, including offshore. Ontario will not escape the problems experienced elsewhere.

Limits for the UK

In case there is some question about these conclusions, I refer you to an article in the November 2005 issue of Civil Engineering, “Why UK wind power should not exceed 10 GW” written by Hugh Sharman, the principal of a Danish energy consulting company, Incoteco (Denmark) ApS. Table 1 provides the related statistics for electricity generation in the UK, which contains about 1 GW of wind capacity today. The percentage of electricity produced is consistent with the findings presented here.

Table 1 – UK Electricity System Information


Electricity Produced

Total System Today

75 GW

400 TWh

Proposed Wind Upper Limit

10 GW

18 TWh
(at 25% cap factor)

Percentage of Wind to Total



There are a number of factors leading to Sharman’s conclusions. The reality is that each country’s, state’s or province’s electricity system should be looked at individually, because each may have unique characteristics. For example Norway and Sweden combined obtain 75% of their electricity production from hydro.

More Detailed Analysis of Denmark’s Domestic Use of Wind Electricity

Table 2 shows the exports and imports of electricity for Denmark for four years based on the latest available information from the Danish Energy Association.

Table 2 – Electricity Exports and Imports for Denmark (TWh)















Net Exports





Immediately obvious is the fact that, although net exports can vary substantially, the exports remain at a fairly steady and high level. In Denmark’s case, the exports represent 25-33 per cent of the total electricity produced, which is very large compared to a few per cent for most other countries. The EU directive for calculating the share, of say, wind energy contribution to domestic use is to take the gross amount of wind and divide it by the total electricity production less net exports, that is, domestic supply. In almost every other country the inaccuracies introduced are not significant. Denmark dutifully follows this, which produces misleading results.

An “expert” study of Denmark’s use of wind electricity domestically for 2005 concludes the result to be 13 per cent. One of the underlying assumptions is that when Denmark is a net importer of electricity, all the produced wind power is used domestically. Think about that one!

Table 3 shows the results of my more detailed look for 2003-2007, taking exports and imports into account separately, and assuming 60-80 percent of the wind energy is exported. The basis for this assumption is: an article by the Utilities Journal in July 2004, which claims that 84 per cent is exported in 2003; and the very strong co relationship between wind production and exports in a timely manner. The 2003 wind production was the lowest of the years 2003-2007, and the actual installed capacity was level throughout this period. It is reasonable to assume that the internal consumption will not vary significantly from the 2003 level. The percentages are based on domestic supply.

Table 3 – Domestic Use of Total Wind Electricity Produced

Assumed % of
Wind Exported

Domestic Use as a %
of Domestic Supply







My previous (and preliminary) analysis was based on four year averages using net exports. It showed 6 per cent, and also assumed that domestic use would not necessarily vary depending upon wind production, but by the ability of the Danish electricity system to absorb it. Given the results in Table 3, I have left Figure 1 as is, which is probably conservative.


This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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