While Roger and the west coast of Mexico had rather too much wind recently, the UK has just enjoyed a superb spell of weather with high pressure in charge for several weeks. I’m not sure how unusual these conditions are and one reason for this post is to benchmark the effect of flat calm conditions on wind output for future reference.

On 4th October, in the early hours of the morning, 9136 MW of wind turbines were producing 66 MW of electricity. The load factor dropped to 0.7%. I find this astonishing from a meteorological perspective since about half the metered turbines are offshore and many of the rest are on Scottish hillsides. The wind momentarily dropped effectively to zero across the whole of the UK. As an aside, on the same day South Carolina and the South of France were hit by severe flooding.

Figure 1 Roughly 7 weeks of data shows clearly the spells of high pressure centred on the UK separated by brief spells when fronts moved through. On 3rd and 4th October the wind dropped completely across the whole of the UK. I’m unsure how rare an event like this is. X-axis marks at 24 hour intervals. Click all charts for large readable versions. Data from BM via Gridwatch.

Installed and Metered Wind Capacity

Balancing Mechanism (BM) reports wind production in two different ways. Large wind farms are connected to the high voltage grid and are metered but small wind farms and individual turbines are not. The latter are connected to the low voltage grid and are seen by BM as negative demand. The same applies to roof top solar PV. Clive Best looked into this a few months ago and concluded that only 68.5% of UK wind was metered. The remainder shows up as reduced demand. Clive now grosses up metered wind reported by BM by a factor of 1.46. If you check his and Leo’s wind figures using the links on the right side bar you’ll see the difference. The factor of 1.46 is of course not constant, and will require revision in future as the wind fleet evolves.

Figure 2 shows “demand” from BM reports compared with metered wind. One observation is that the demand curve looks a bit ragged and I believe that is because unmetered wind and solar are included in it. I think it is also likely that the “V” shaped notches in the middle of the demand peak will be filled with solar supply (seen as negative demand).

Figure 2 UK demand (less embedded wind and solar) compared with metered wind, 1 Sep to 22 Oct 2015. Note that I downloaded the data during day time of 22 October. The load statistics are calculated only for full days ending on 21 October.

Renewables UK (RUK) and The Renewable Energy Foundation (REF) both report up to date figures for installed wind capacity as follows:

RUK onshore 8258 MW

RUK offshore 5054 MW

RUK total 13339 MW

REF onshore 8414 MW

REF offshore 5031 MW

REF total 13445 MW

Using Clive’s factor of 1.46, I am estimating that metered capacity for September / October was 9136 MW. From 1 Sep to 21 Oct, metered wind produced 2018 GWh out of a possible total of 8990 GWh yielding a load factor of 22.5% for this quiescent period. This compares with an average load factor of 31%.

Total metered demand was 38884 GWh, hence metered wind produced 5.2% of metered demand. Total wind would have produced 7.6% of the total.

Figure 3 illustrates the distribution of capacity factors. Over the 51 day period, wind output was below 10% of capacity for the equivalent of 15 days, i.e. for 29% of the time

Figure 3 BM reports data with 5 minute resolution producing 14890 lines of data for the period in question. The data were sorted according to wind output and capacity factor calculated on the sorted data to produce this chart. The x-axis marks with 288 spacing represent 24 hour periods. The chart shows that for the equivalent of 15 days, capacity was below 10%.

Concluding Thoughts

It is possible for wind across the whole of the UK to fall effectively to zero. It will never be possible to assume that wind can offset dispatchable capacity. No number of inter-connectors internal to the UK can solve this problem.

Embedded wind and solar is seen by the Balancing Mechanism as negative demand. This needs to be taken into account in any analysis of actual UK power demand and consumption.

Future analysis may include Ireland, Denmark and Germany for the same period.