What Happens When There Is Too Much Wind?

By Paul Homewood




The problem of intermittency with wind power is well known. Normally however it is only seen as a problem when not enough power is being produced, thus necessitating the need for back up capacity.

There is another problem though. There are times when too much power is produced, though currently with the small amount of capacity in the UK this only exhibits itself on very windy days, and tends to be due to the limited transmission capacity from Scotland.

However, as more and more wind capacity is built, there will be times when there is too much power for the Grid to handle on a regular basis. The Committee on Climate Change neatly showed this in their Fifth Carbon Budget working papers.


This was the situation in 2014; demand always exceeded wind, solar and nuclear output:


However, with the higher deployment of low carbon needed in 2030 to meet decarbonisation targets, combined output will often exceed demand.


I have done some number crunching, based on the “High Renewables” scenario used by the CCC, (this is the most realistic one, but all scenarios tend to the same conclusion).

Figure 4.4. Capacity for scenarios that reach around 100 g/kWh in 2030 GW

High nuclear High renewables High CCS
Nuclear 11 6 8
Onshore wind 20 22 20
Offshore wind 20 25 20
Carbon capture & Storage 4 4 7
Solar 20 40 20
Tidal 1 1 1
Biomass 3 3 3
Hydro 2 2 2
Total 81 103 81

Wind capacity, as at Q3 last year, was 19 GW. Taking account of the greater proportion of offshore forecast, and therefore the higher loading, average output should be about four times greater in 2030, averaging 14.7 GW.

I have downloaded the whole of last year’s Half-Hour generation data from BMR, and projected the wind output at half hourly intervals, based on the 2030 capacity. It varies from between 0.6 GW to 38.6 GW. However, after counting nuclear, tidal, biomass and hydro, demand to fill with wind can be as little as 9.5 GW.

I have, by the way assumed that nuclear and the others fulfil demand first, before wind power. This seems logical, as they can all sell baseload power on a forward basis. Also, given the CfD that Hinkley Point has, it can sell to the market at as low a price as it wants in order to secure the business, in the knowledge it will still be paid its guaranteed price.

If, for some reason, wind power is given priority on the grid, the problem of surplus power becomes Hinkley’s problem. But it is a problem nevertheless.

For simplicity’s sake, I have also left solar out of the equation. The CCC project 34 TWh of solar in 2030, which is similar to the increase in total generation needed by then, so the two tend to cancel out. Most solar power is, in any event, embedded, and consequently does not appear in the BMR data, and instead is reflected in reduced demand. Again, if wind takes priority over solar, it would simply mean that the problem was also passed to solar farms.

Either way, when you add all of the low carbon sources together, there is massive overcapacity at various times of the year.

If, as I have assumed, this all impacts wind power, my calculations show that it would reduce demand for wind power by about 10%. In other words, about 12 TWh a year of wind generation would be surplus to requirements.

Of course, there has always been spare capacity in the system, necessary for managing fluctuations in demand and to provide essential reserves. But two things make this a problem now:

1) With the advent of renewables, there is much more generating capacity in the system.

As we can see above, the CCC project 100 GW of low carbon alone. On top of must be added 50 GW of proper generation, making about twice as much as we used to have.

2) The capital and fixed costs of nuclear, wind and solar are much higher as a proportion of total costs than gas and coal power plants.

This means that the former are extremely vulnerable to reduced activity levels. In contrast, for instance, a CCGT plant would expect to be viable working at maybe only 50% of capacity. This is because variable and fuel costs account for most of the overall cost per MWh.

Using wind as an example, if 10% of generation is left unsold, the cost effectively rises by 10%. Wind farm projects currently know they can sell all of the output and base their costings accordingly. But if they need £100/MWh to be viable now, they may find themselves needing £110/MWh in future.

Which all leaves the question, who will pay for these losses?

Will wind farms be expected to stand the loss themselves, or will they receive constraint payments not to sell, as happens now? If it is the latter, electricity users will be left holding a very expensive baby.

Or maybe the surplus will be sold to Europe, no doubt at a huge loss, which again users will have to pay for.

And as the share of low carbon energy increases beyond 2030, the problem becomes even bigger.



March 14, 2018 at 01:48PM

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