I have been thinking a lot about renewable energy sources lately and I have come to a surprising conclusion: Even in the not-so-sunny, rather-windy UK, solar photovoltaic panels generate more power per square metre than wind turbines. Of course this is not what determines the economics of a technology, but it is an interesting statistic nonetheless.
Below I have calculated rough figures for 5 power generation technologies: three renewable: Solar PV, Wind, Geothermal; and two non-renewable: gas and nuclear. And for each technology I have calculated two statistics:
- the power density – the amount of power available for each square metre of Earth used.
- the cost per installed watt – the current price to install one watt of generating capacity using that technology.
Solar PV: Here I take my data from my colleague John Gallop’s south facing roof installation 9 m2 generating on average through the year 3.5 kWh/day, an average of 140 W. The cost several years ago was around £9000 and I don’t think this kind of cost has changed much over the years. So the statistics are power density: 16 W/m2 and capital cost cost per average watt: £70/W.
Wind: Here I take my data Renewable Energy without the Hot Air (strongly recommended) which suggest that a fair figure for wind is around 2 W/m2 – 8 times less than a solar PV installation in the south of England. The capital cost cost per average watt is difficult to estimate but is much lower: something close to £0.30/W or less – 200 times cheaper than solar PV.
Geothermal: I was reminded of geothermal energy by an e-mail today from my colleague Richard Gilham referring to a company selling ground sourced heat pumps – not able to generate electricity, but a still a source of renewable power. As I have mentioned previously, the actually renewable gethermal heat source is tiny in the UK – on average 0.038 W/m2 . Now systems can be built which heat the Earth in summer (cooling your house) and then use the heat in winter. This is a smart thing to do, but it is really energy storage rather renewable energy generation. So the power density fron geothermal is still a paltry 0.038 W/m2 . The cost per installed watt appears to be around £2.50/W.
Gas: Here my guesstimates are based on a very rough figure of £1 billion for a 1 GW plant which can be built on land occupying 1 km2 . So the power density from gas is an impressive 1000 W/m2 and the cost per installed watt appears to be around £1.00 /W.
Nuclear: Here my guesstimates are based on a rough figures of £10 billion for a 1 GW plant which can be built on land occupying 10 km2 – nobody wants to live a near a nuclear power station. So the power density from is an impressive 100 W/m2 and the cost per installed watt appears to be around £10.00 /W.
And so my conclusions are…
- That it is is the installed cost per watt of generating power that drives investment – coupled with assessment of technological risk.
- As my previous musings had led me to surmise – wind energy is a very diffuse resource – requiring large areas to generate significant power. But the capital cost of the generating capacity (someone else pays for transmission and storage) is accessible.
- Solar PV makes good sense from an ecological view, but is still currently too expensive to compete with wind – subsidies excepted.
My caveats are that all these figures are very approximate, and I have ignored the effect of subsidies because (a) I don’t know what they are and (b) they change from year to year.