Too often when reporting on renewable energy news, we bloggers can sometimes project the feeling that everything is going to be alright, look at all the pretty technology we’re rolling out and saying it will power this many homes and take this many cars off the road and so on.

In an effort to get some perspective on these numbers I want to take as an example a story doing the rounds of the internet this very day.

The story is entitled – Government: Off-Shore Wind Could Power Every UK Home by 2020

and it says:

A recently completed study from the Department of Energy and Climate Change has concluded that off-shore wind power may be the key to the UK’s energy future. According to the study, 5,000-7,000 new turbines could be built off the coast by 2020. The turbines could generate 25GW of power— the equivalent of 25 large coal-fired plants. 8GW of additional offshore wind power are already planned. There’s just one problem— many of the current UK off-shore projects may not even be completed. Emily Highmore, a spokeswoman for the London Array project, warned, “Off-shore wind has always, and will always be, very expensive. We can’t be confident it will go ahead, but we believe it’s a cracking project and very important to helping the government meet its renewables targets.” However, if current and future projects come to fruition, up to 70,000 new jobs could be created and UK carbon dioxide emissions could be cut by up to 14%.

So it’s great that they have cautioned about the fact that the wind turbines may not be built at all, but let’s assume they were all built and more.

The UK’s own DTI, (Department of Trade and Industry) estimates the potential offshore wind generation resource is 4.6 kWh per day per person, from both shallow and deep waters. The UK government announced on 10th December 2007 that it would permit the creation of 33 GW (13 GW more than is being claimed here) of offshore capacity (which would deliver on average 4.4 kWh/d per person).

To obtain this average power requires roughly 10 000 ‘3 MW’ wind turbines (They’re called ‘3 MW’ but on

average they deliver 1 MW.)

What would this 10 GW of power cost to build?

Well, the 32 MW Kentish Flats farm cost £105 million, so 10 GW would cost about £33 billion. This statement violates my rules of comprehensibility – who has got a good feeling for what a billion means? But “ 3 million per MW” or “3 billion per GW” is something we might compare with nuclear power. Nuclear power stations cost about 1.25 billion per GW to build. So at present prices the capital cost of offshore wind is greater than the capital cost of nuclear power. However, we’re not really comparing like with like here. The 1 GW delivered by a typical nuclear power station is always on; the power delivered by wind farms is erratic and would need a large amount of baseload generation to back it up. Nuclear power and wind power have different clean-up costs and different risks, but I would think that if anything they would actually compliment each other quite well. I haven’t talked about maintenance because I don’t know the costs of that. If any readers of this site would be kind enough to supply that information, or comment on it I would be very happy to see it.

Special construction requirements.

Another bottleneck constraining the planting of wind turbines is the special ships required. If Britain were to erect 10,000 wind turbines over a period of 5 years then roughly 100 jack-up barges would be required.

These cost £60 million each, so an extra capital investment of £6 billion would be required. Not a deal-breaker compared with the £33b price tag we already quoted, but the need for jack-up barges is certainly a detail that requires some forward planning.

A second way of expressing the £33 billion cost of offshore wind delivering 4 kWh/d per person is to share it among the UK population; that comes out to £550 per person. Not too bad, and certainly less than the cost of recent bank bailouts.

So those are the possible costs, now let’s look at the power generated. Remember that figure of 4 kWh per day per person, let’s take that see what that kind of power can really achieve:

If If you have the kettle on for 20 minutes per day, that’s an average power consumption of 1 kWh per day.

One ring on an electric cooker has the same power as a toaster: 1 kW. If you use two rings of the cooker on full power for half an hour per day, that corresponds to 1 kWh per day.

A microwave oven usually has its cooking power marked on the front: mine says 900 W, which is nearly a kilowatt; but it actually consumes about 1.4 kW. If you use the microwave for 20 minutes per day, that’s 0.5 kWh per day.

A regular oven guzzles more: about 6 kW (when on full). If you use the oven for two hours every six days, that’s 2 kWh per day.

So by the time you’ve made a few cups of tea, and done some cooking you’ve used up all the power generated by those offshore wind turbines.

I don’t want to imply any criticism of the websites, or authors involved, in fact they are one of the reasons I think we have a decent chance of transitioning to a better culture. As I said before I am just seeking to make a point about the truly vast challenges that await us all, as we strive to make the transition from a fossil fuel to a renewable energy civilization.

Image is of Offshore Wind Park in the Baltic Sea near Samsø, Denmark by m.prinke on flickr under the Creative Commons license