I get rather frequent traffic to a piece I once wrote called “How many wind turbines would it take to power the UK?”
There are multiple varients of the google search that have led people to reading the piece. Most strange are those who interested in finding out how big a wind farm would need to be to power a fun fair. Don’t ask.
Others are clearly searching google to find the answers to a question asked by a high school teacher. The sudden influx of almost identically worded google referrals is the giveaway.
But one question that people appear to want to know the answer to is of genuine interest, and the answer is very uninformative of the deep challenges we would face if we attempted to transition to a be a predominantly wind powered society.
How many wind turbines would it take to power London? Or perhaps more revealing: how big would a wind farm need to be to power London? When I mean I power here, I use the word colloquially, meaning electricity, and not scientifically. Enough people seem to want to know that it would be worth doing the basic calculations.
So, here goes. Roughly eight million people in Greater London, which covers an area of around 1.5 thousand square kilometres, or 600 square miles if you prefer long defunct units of measure.
According to DECC, annual electricity consumption in Greater London is just under 40, 000 GWh. This is, on average, 4.5 gigawatts.
This could be supplied by a couple of big coal or nuclear power plants. A typical nuclear power plant is made up of two 1.3 or so GW units, which have capacity factors of around 90%. So, London could be supplied by a couple of regular sized nuclear power plants.
But what about wind farms? Here we have the problem of low power density. Supplying London’s electricity with a nuclear or coal power plant requires you to build a big centralised unit that can be seen by more or less no one, except travellers on the occasional mainline railway. They just need a few square kilometres of land and can be tucked out of sight.
Not so with wind farms, which take up vast amounts of land. Powering London with a wind farm would require more land than London itself. The numbers are quite clear, and they are best understood by thinking in terms of power density.
Power density is a much under-discussed issue. Put simply, power density is a measure of the spatial requirements of a source of energy. We measure this in watts per square. It is rather like the way we measure crop yields. “Bushels per acre” or “tonnes per square kilometre” or whatever takes your taste. When it comes to coal, oil, natural gas or nuclear power, we don’t think to much about these things. They don’t take up too much space. Not so with some renewables.
What is the power density of London’s electricity consumption? On average it is just under 3 watts per square metre. It will, of course, vary a bit during the year. But that is a detail?
Wind farms however supply less than this throughout Britain. Using data for wind farms throughout Britain David Mackay has calculated that the power density of the average British wind farm is 2.5 watts per square metre.
In other words, per unit of land, London consumes more electricity than can be provided by wind farms; providing all of London’s electricity with wind farms will require an area greater than London itself to be covered in wind turbines.
This is the true reality of so-called “community renewables” in Britain. An essentially urban society cannot be powered by local, community energy. It is hard physical reality, and no amount of wishful thinking can result in the laws of physics being cast aside.
And we must ask what kind of society the various promoters of community renewables think we live in. A Google image search of “community renewables” is revealing. Pictures of wind turbines and flowing green fields. Everyone is white, happy and appearing to live a traditional British life. One must ask why, if these images are accurate, Ukip dislike wind farms so much.
And I have news for these people. We stopped living in villages more than a century ago, and there are no signs we are going to start moving back. The city is here to stay and it is time to make that work. London, Manchester, Glasgow, Birmingham, Leeds, Liverpool; these are the communities we now live in, not the villages of community renewables enthusiasts imaginations.
Powering humanity, then, means powering cities. This will require big scale things. Big wind farms, big nuclear power plants, big carbon capture and storage facilities. Big scale things may be out of fashion, but necessity and fashion are separate things.
And this stuff has already begun. The London Array wind farm covers 100 square kilometres of sea in the English Channel. 100 square kilometres. This seems a lot, yet it only provides the equivalent of 6% of London’s electricity demand.
So, next time you hear someone getting enthusiastic about community renewables, think about the communities we actually live in, and how big a wind farm would need to be to power one of them.