Why Wind Turbine Capacity Factor Matters
My criticism yesterday of the Dorset Renewable Energy Strategy (DRES) focussed on the inflated Capacity Factor values used for wind turbines in a Dorset environment.
Why does this matter so much?
The standard Wind industry response to a criticism of a particular Capacity Factor (CF) is that you can increase the Capacity Factor by simply decreasing the size of the generator attached to the turbine. Like many of the wind industries statements this is, on a simplistic level, true. But they carefully avoid mentioning the affect this would have on the turbine output.
If you decreased the size of the generator on a given diameter turbine in a particular location then you could increase the Capacity Factor. Unfortunately though, you would also significantly decrease the amount of energy generated by the thing over a year. There is an ever worsening trade off where the energy generation falls away as the generator size is decreased to force up the capacity factor.
This is simply because the energy in the the wind obeys a cube law. 2 x wind speed -> 8 x energy. So by decreasing the size of the generator you reduce the opportunity to exploit infrequent short term high wind events that actually produce most of the electricity generated.
The sad fact about wind turbines is that for most (60%) of their operational life they are either producing no electricity or an amount that is well below their annual Capacity Factor. When they do produce large amounts of energy is is at random and unpredictable times and essentially in relatively short bursts.
However, wind turbine Capacity Factors do provide an effective method of comparing relative productivity between wind turbines in different locations. But that is all.
Wind power is unique in being the only major power generation method that when operational, has a typical output that is significantly below its Capacity Factor. Consequently wind turbine CF inflates the perceived ability of turbines to produce power when compared with other generation methods.
Comparing wind CF with any "on demand" CF ( like the DRES laughably does with your gas boiler) is totally absurd.
Let us come back to Dorset. Why has there not been a rush to build turbines here before now? Why have they been built mainly in Northern Ireland, Scotland and Northern England?
The simple reason is that the wind speed is lower down south. The capacity factor for a given turbine is consequently lower and the southern turbines are actually even more dependant on rare high wind events to big up their CF.
Take two identical turbines in England. One in Workington (2009 CF 32% - the best in England) and a one in Dorset where the CF is going to be around 21% at best. The energy produced by the Workington turbine is 1.5 times as much as that produced by a Dorset turbine. It is also double that of the infamous Reading turbine.
All create similar environmental damage and yet all make a profit.
A turbine with a low Capacity Factor is by definition less productive compared to its peers. However such is the largesse of the ROC subsidy that even a turbine with a capacity factor of 15%
will make a healthy profit.
If the ROC subsidy was cut, many turbines in the UK would become unviable overnight. Cut it out completey and at least 90% would be shut down.
Nothing is going to get better about this.
There is no magic fix to increase the wind speed. There is no wondrous widget being designed that will allow installed wind turbines to generate more electricity.
The turbines and their operators are wholly dependent on the ROC (in perpetuity) to make a profit. Without it, all but a few are doomed.
As they get older they will get more unreliable and their CF will actually fall. Eventually, one day, sanity will return and the governemnt will be forced to cut the ROC.
Then you will see wind farms being sold on - and on - and on. Until one day they will mysteriously cease to operate.
When the bailiffs turn up we will find the final owner is a company operating out of a post office box in Belise.
We the taxpayers, will end up paying to have them pulled down.