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.


Anonymous said...

Without ROCs, there would be no clean, renewable energy and we would be committed to paying escalating gas prices.
BTW, gas added approx. £120 to the household energy bill last year whilst onshore wind cost less than a fiver! (http://www.businessgreen.com/bg/news/2159407/onshore-wind-farms-add-gbp5-household-bills)

As we know nuclear also needs subsidies to survive, why do you never mention that?

BilloTheWisp said...

Dear Anonymous,
You are right about wind-power. No ROC - no turbines. At the end of the day, wind turbine operators get paid at least twice the going rate for the electricity they produce. Without the ROC, only about 5% of the turbine fleet would be potentially viable - that is the percentage actually that make it to a 30% CF. Even then these few turbines would hardly likely to appeal to the greed factor we see so eloquently expressed by the wind industry cartel.

Nothing is going to get better about this.

Turbines dependent on the ROC are dependent on it forever.

It looks like you suffer from the infinite resources illusion. i.e. cost does not matter. You assume that as long as any amount of carbon is offset, irrespective of how pitifully small, then any excess, any level of grotesque profiteering is acceptable.

You forget that money squandered on lining the pockets of wind farm operators means even massively effective technology (such as boring old insulation) goes without.

I once (twice actually) compared wind turbines to trying to bail out a water-logged dinghy with silver spoons. Lots of noise, action and cost, but not much gain. The posts are in the windpower section if you want to read them.

Remember when you compare costs: Wind provided just 3% of electricity. Even then, it did this intermittently and unreliably, requiring backup from those same gas fired CCGT's you malign.

As to gas prices rising - in the USA they have now been just about halved. For the first time in history, gas and oil prices in the USA have significantly diverged.

This potential for a huge fall in gas prices is actually one of the reasons new nuclear may require price protection (NOT subsidies like the ROC).

In order to encourage the large capital expenditure on nuclear plant rather than a smaller spend on CCGT plant (with its falling fuel price), the governemnt may have to offer a guarantee of market share. But this is not a subsidy, let alone one as profligate as the ROC.

But if we want effective carbon free electrical generation rather than expensive and ineffective fashion statements, then we are going to have to live with that.

Dr. R. Stott said...

Bill, you believe that a guaranteed market share is not a form of subsidy.

Of course a *guaranteed* market share which enables an energy source to charge what it needs to be profitable is a form of subsidy. Any energy source could exist if it was the beneficiary of that distortion of the market. It's nonsense to deny this is a form of subsidy.

You also seem to see no benefit in renewable energy - it only has cost in your 'analyses'. This is a deeply flawed way of assessing the viability of renewable energy today. You must look at both side of the ledger.

Bill, you seem to have started with beliefs - "I love nuclear and I hate wind energy" - and worked back from there, cherry-picking data to suit pre-conceived beliefs and prejudices. This is not scepticism and informed analysis, it's advocacy based on personal biases and is unpersuasive as such.


BilloTheWisp said...

Dear Dr Stott,

Thanks for the comment.

I can see where you are coming from, but even a guaranteed market share does mean that the operator still has to participate in the NETA trading mechanism - and without further advantage.

There is a significant difference between ensuring a market share and providing a false trading mechanism like the ROC, which is simply a huge rolling semi-obscured subsidy.

Don't forget, not only do turbines have the ROC they also have a right to sell in to the market irrespective of the current demand or need for electricity.

I would, be quite happy to see a market share guarantee given to to wind generators, as long as they participated properly in the current NETA trading mechanism with other generators.

The current arrangements which guarantee the turbine operator somewhere between 2 and 3 times the market value of the generation without any penalties for non generation essentially ensure turbines are built in wholly inappropriate locations where they can never possibly hope to break even without the crutch of the ROC.

The whole thing, instead of being a measured step forward with effective turbines (there are a few) and with a properly thought through backup policy has become a Klondike style gold rush instead.