Tuesday, 14 April 2009

Sustainable energy - without the hot air

Inspired by the glowing review in the Economist, I've just been reading David MacKay's Sustainable Energy - without the hot air (available as a book through the usual sources, or as a free download under a Creative Commons licence). Like the Economist, I'd strongly recommend the book to anyone involved in sustainable energy, whether as technology developer, investor or policy-maker; and whether your main interest is in renewables, nuclear or clean(er) fossil fuels, or in energy efficiency.

MacKay might seem like an unlikely person to write such a book - a physics professor from Cambridge, he's primarily a specialist in information theory, with a sideline in international development. It's maybe that off-centre viewpoint that allows him to use some simple tools from physics and maths to address the most basic question - can renewable (or, at least, sustainable) sources replace fossil fuels for the UK?

Along the way, he demolishes some of the wilder, waftier claims of industry boosters and environmental campaigners, as well as many of the objections of the climate change deniers and do-nothings.

MacKay starts with a basic balance sheet for the UK, roughly adding up the net energy consumption - around 195 kilowatt-hours per day per person (195 kWh/d/p), including domestic heating, transport, consumables, etc - and potential renewable resources - 180 kWh/d/p, including on- and off-shore wind, biomass, solar heating and PV, wave and tidal, and all those other technologies that VCs love. (A brief chapter towards the end sketches out the equivalent numbers for Europe, America and the world.)

So, it's a pretty close thing. A bit more energy efficiency, and a bit of coal and nuclear generation, and we should be OK. Right?

As ever, the devil's in the detail. MacKay uses pretty basic considerations to derive estimates for each slice of the two pies, and leaves all other social, political, economic and environmental factors to hang.

For onshore wind power, for example, it's a simple question of finding average wind speeds for the UK, typical power per area of wind farms, and population density; guesstimating what portion of the country we could conceivably cover with windfarms; and doing the sum. If we cover the whole country with windfarms, we find that we could just about cover our current consumption. Slightly more realistically, if we put windfarms on just the windiest 10% of land, we could generate around 20 kWh/d/p, a bit less power than is consumed by domestic heating.

Somehow, that kind of datum doesn't crop up too often when wind developers talk about Britain's huge wind resources. Obviously, that's not to say that on-shore wind doesn't have a role to play in a sustainable energy mix, but if it's to be a significant role, we'll need to dedicate significant resources to it.

It's a similar story with the other renewable areas, as well as areas like 'clean coal', carbon scrubbing and nuclear, and the potential for importing our energy from overseas. The basic message is that the necessary reformation of our energy system requires major action. Perhaps most importantly, it also demands more realism in facing the challenges than is often encountered on any side of the debate.

There's little consideration of individual technologies - solar PV is just considered as working at 20% conversion efficiency, for example - but that's no bad thing given the uncertainties that remain. There's also little consideration of the affordability of various solutions (or, perhaps more importantly from the VC perspective, their potential profitability) but that's a whole other can of worms which MacKay deliberately skates over.

From a cleantech VC viewpoint, this all provides another valuable perspective on which broad categories of technologies genuinely do have the potential to make a substantial contribution to the energy mix, and which don't. Jatropha-based biofuels seem of very limited use, for example - MacKay calculates that covering the whole of Africa with jatropha plantations would only replace a third of today's global oil consumption.

Moving to a sustainable energy economy is (just about) possible, given the right political and industrial leadership. The most important things, MacKay concludes, are to electrify transport; electrify heating and cooling in buildings through heat pumps; and ramp up domestic renewable generation, perhaps alongside clean coal and nuclear. But the most important thing for the UK is likely to be large-scale solar generation in hot, less-populated countries:
As long as we can build peaceful international collaborations, solar power in other people’s deserts certainly has the technical potential to provide us, them, and everyone with 125 kWh per day per person.

In all, it's a remarkably provocative and eye-opening analysis. No less remarkably, it's also very accessible - clearly and entertainingly written with diagrams and doodles aplenty, but with exhaustive footnotes and references and the more technical bits rounded up at the end. Highly recommended - and, like I said at the top, available for free.


Alex said...

A quick point - the 20% solar effiency isn't pulled out of thin air, but a realistic figure which we are very unlikely to significantly exceed, due to the fundamental photophysics of Silicon. Look up the Shockley-Queisser limit - about 30% effiency is the absolute maximum for simgle-junction photovoltaics.

Tim Chapman said...

Absolutely right. The tech companies still like to boast about getting an extra percent when they can, though.