Hornsea One is a Round 3 wind farm which began construction in 2018, with completion in January 2021.
It has a capacity of 1,218MW, and was the largest wind farm in the world on completion.
Its website tells us that it is "Powering well over one million homes with green electricity".
Where does that number come from, and how true is it?
One million homes?
There are various ways that people use to calculate how many homes can be powered by a specific wind turbine/farm. I have tried a few, but in the interests of fairness I have used the one published by RenewableUK, a wind industry trade body in the UK. As they point out, this calculation is updated annually, and I'm using the December 2021 edition here.
1,218MW for 24 hours a day and 365 days a year means that Hornsea One would produce 10,670GWh of electricity in a year if it operated at its installed (nameplate) capacity. Applying the "all wind" capacity factor of 0.3164 that RenewableUK use estimates that Hornsea One's actual annual generation would be 3,376GWh.
Now, using the value for annual household electricity consumption that RenewableUK use of 3,748kWh that means that Hornsea One would generate energy that is the equivalent of the requirement of just over 900,000 homes.
Where does the operator Ørsted get the figure of over 1 million from?
Could somebody from Ørsted provide a link to their calculation?
In the absence of a resolution of the above issue at present, let's take the number of homes as 1 million.
The statement "Powering well over one million homes with green electricity" could be taken at face value, and perhaps people who are not familiar with the variability of wind power might think that over 1 million homes could rely on Hornsea One.
So, how often has Hornsea One generated enough power for a day to meet the requirements of 1 million homes for that day?
To generate enough electricity for 1 million homes for 1 day requires on average 10,268MWh.
Using the Elexon website and its BMRS official data reporting, on how many days from 1 July 2021 to 30 Jun 2022 did Hornsea One produce at least 10,268MWh?
The answer is 219 days. Which means that on 146 days those million homes would not have all been fully powered by Hornsea One.
This shows the fundamentally misleading nature of the claim "Powering well over one million homes with green electricity"
Should it really say "Powering well over one million homes with green electricity sometimes" or "providing the equivalent of the electricity needs of 1 million homes"?
So, how did their lights stay on?
For those 1 million homes the lights will have stayed on somehow (notwithstanding any specific power cuts there may have been due to other circumstances). So how did the lights stay on if Hornsea One couldn't do it?
The answer is that fossil fuels - primarily gas - will have kept the lights on.
When power from variable sources can't do the job, GB reverts to using fossil fuels. That is still what we are doing, and our reduction in the use of fossil fuels has pretty much ground to a halt for this reason.
To enable the termination of the use of fossil fuels we need to provide clean electricity to meet demand.
Doing this needs to be a combination of clever provision of clean electricity and clever reduction in demand.
How low does Hornsea One go?
On how many days from 1 July 2021 to 30 June 2022 would Hornsea One have produced less than half of the electricity needs of those 1 million homes? 83 days
On how many days from 1 July 2021 to 30 June 2022 would Hornsea One have produced less than 10% of the electricity needs of those 1 million homes? 24 days
Were there any days from 1 July 2021 to 30 June 2022 when Hornsea One produced no electricity (other than due to maintenance or breakdown)? There was 1 day, and it was 24 March...
...and on that day Hornsea One achieved something that would have left those 1 million homes even more under-supplied ...
... its own electricity needs meant that it took more from the grid than it put in.
Don't believe me?
Here's the sequence:
1. Go to the Trading Data page
2. Choose a Settlement Date of "2022-03-24" and Period of "*"
3. Click More Filters
4. Enter Trading Unit Name of "T_HOWAO-1" and press the View button
5. You'll see that Phase 1 was importing from the grid all day.
6. Repeat for the other two phases: T_HOWAO-2 and T_HOWAO-3.
Do other wind farms do this sometimes? Yes, they do.
Is Hornsea One a particularly bad example? No, it's one of the newer wind farms with more and larger turbines.
Should wind farm operators have to make more accurate claims about the performance of their wind farms? Yes, they should.
At the moment such claims make it sound as though wind is a predictable and reliable source of electricity. It isn't.