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July 25, 2007

Renewable Energy Calculations

Fascinating stuff about the relative efficiencies of the various forms of renewable energy.

Large-scale renewable energy projects will cause widespread environmental damage by industrialising vast swaths of countryside, a leading scientist claims today. The warning follows an analysis of the amount of land that renewable energy resources, including wind farms, biofuel crops and photovoltaic solar cells, require to produce substantial amounts of power.

By looking at the amount of land required to produce energy....or rather, calculating the amount of energy produced by each sq m of land using different technologies, we can see how much land we'd have to use to power civilisation.

The analysis showed that damming rivers to make use of hydroelectric power was among the most harmful to the landscape, producing around 0.1 watts of power per square metre.
Biofuel crops and wind energy fared better in the study, with both generating around 1.2w to a square metre. Leading the renewable energy sources were photovoltaic solar cells, which use sunlight to create electricity, at around six to seven watts to a square metre.

While this is interesting, even amusing (Another calculation revealed that to meet US energy demands for 2005 with wind power would require constant winds blowing onto wind farms covering more than 780,000 square kilometres of land, the area of Texas and Louisiana combined.) it's not quite the slam dunk some will claim it to be.

For we do also have to look at whatever the alternative uses for the land might be. The hugeseries of hydroelectric plants in Northern Quebec, for example, may only be producing at that 0.1 watt per m2, but there's not a lot else anyone is going to do with that land. Smelting, as is done, a significant protion of the world's aluminium there might indeed make sense.

Biofuels, almost by definition though, are going to be on higher quality land: not necessarily prime farmland, but reasonable stuff all the same. That solar result might be the most interesting though. 6 or 7 watts a m2: the average US suburban house has what, 80, 90 m2 of roof space? Is 480 watts enough to run a household? (No, I have no idea. I get terribly confused about power, generation, consumption, per hour etc etc)

Wouldn't it be an interesting result if single family housing, essentially, suburbia, were in fact the most environmentally sustainable form?

July 25, 2007 in Climate Change | Permalink


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That 480W is for the daytime, therein lies the problem, as more electricity is needed during the night, for lighting and heating, once you figure in energy storage it drops from 7W/m2.

For domestic use, a lot of energy is used to heat water or provide heat directly, this can be done without the PV cells but using solar directly on the water used for cleaning and heating. This is not so much power generation but power saving, and is difficult to calculate.

Solar has come a long way, and as you state, we could be looking at decentralised power generation. But if we do choose to go down a domestic energy generation route rather than centralised, we could start with self-contained combined heat and power (CHP) for using excess heat, we could move towards domestic incinerators and composters to extract energy from waste, we could even look at compact nuclear units (cue popping noises from nearby environmentalist head explosions).

Regarding biofuels; what this really needs is a genetically engineered plant that can increase crop yield and density and improve fuel oil production, as well as reduce costs and lessen environmental impact. Try suggesting to an environmentalist that GM food is desireable, and just like with discussions on "emission free" nuclear power, you'll find that the natural aversion kicks in.

Posted by: IanCroydon | Jul 25, 2007 9:12:29 AM

I don't really see how a single family house could be more 'environmentally friendly' (on these criteria) than a semi-detached or terraced one. Not to say they are preferable, as obviously there are other considerations.

Posted by: Matthew | Jul 25, 2007 10:05:01 AM

I did this calculation for the UK in May this year.


Posted by: mark Brinkley | Jul 25, 2007 11:06:04 AM

Mark, Rock on mate .. though you could have saved yourself the trouble of actually running the numbers with the simple expedient that if the greenies are for it then it is bound to be pants.

I doubt you would get an EPR for just one billion quid, though perhaps less than two billion.

Some of your interblogutors (I made that word up!) point out that costs of microgen stuff might come down, but there is always the cost of maintenance to also consider and we havent even considered availability.

30 EPRs I say, and soon, and then some more.

Posted by: johnnybonk | Jul 25, 2007 1:52:59 PM

"what this really needs is a genetically engineered plant that can increase crop yield and density and improve fuel oil production" - spot on, and even better if it could walk to the bio-fuel refinery. Triffids, in short.

Posted by: dearieme | Jul 25, 2007 3:00:50 PM

By comparison (total hand-waving figures here), the Drax power station occupies about 1 km^2 (1 million sq m) and produces 4 GW, for an areal power density of 4000 W/m^2. Of course there's all the contributory technologies to be considered—coalmines, railways etc., but it still shows the gulf between 'green' power generation and traditional installations.

Posted by: David Gillies | Jul 25, 2007 3:46:18 PM

Just to answer Tim's question; my electricity bill suggests my average power usage, over 24 hours, is a bit over 2 kw - four or five times his figure. Worse, peak demand is likely to run to at least 5 kw. Allowing for short winter days we'd need photocollectors about 15 times more efficient than at present, plus some very efficient storage means to handle peaks and night time demand. Not inconceivable, but a long way from off the shelf right now.

Posted by: John Davis | Jul 25, 2007 4:21:49 PM