New Dawn Fades?

Before K. Eric Drexler devised and proselytised for his particular, visionary, version of nanotechnology, he was an enthusiast for space colonisation, closely associated with another, older, visionary for a that hypothetical technology – the Princeton physicist Gerard O’Neill. A recent book by historian Patrick McCray – The Visioneers: How a Group of Elite Scientists Pursued Space Colonies, Nanotechnologies, and a Limitless Future – follows this story, setting its origins in the context of its times, and argues that O’Neill and Drexler are archetypes of a distinctive type of actor at the interface between science and public policy – the “Visioneers” of the title. McCray’s visioneers are scientifically credentialed and frame their arguments in technical terms, but they stand at some distance from the science and engineering mainstream, and attract widespread, enthusiastic – and sometimes adulatory – support from broader mass movements, which sometimes take their ideas in directions that the visioneers themselves may not always endorse or welcome.

It’s an attractive and sympathetic book, with many insights about the driving forces which led people to construct these optimistic visions of the future. Continue reading “New Dawn Fades?”

What’s the best way of harvesting the energy of the sun?

This is another post inspired by my current first year physics course, The Physics of Sustainable Energy (PHY123). Calculations are all rough, order of magnitude estimates – if you don’t believe them, try doing them for yourself.

We could get all the energy we need from the sun, in principle. Even from our cloudy UK skies an average of 100 W arrives at the surface per square meter. Each person in the UK uses energy at an average rate of 3.4 kW, so if we each could harvest the sun from a mere 34 square meters with 100% efficiency, that would do the job. For all 63 million of us, that’s just a bit more than 2,000 square kilometres out of the UK’s total area of 242,900 km2 – less than 1%. What would it take to turn that “in principle” into “in practise”? Here are the problems we have to overcome, in some combination: we need higher efficiencies (to reduce the land area needed), lower costs, the ability to deploy at scale and the ability to store the energy for when the sun isn’t shining.

There are at least four different technological approaches we could use. The most traditional is to use the ability of plants to convert the sun’s energy into fuel molecules; this is cheap, deployable at scale, and provides the energy in easily storable form, but it’s not very efficient and so needs a lot of land. The most technologically sophisticated is the solar cell. These achieve high efficiencies (though still not generally more than about 20-25%), but they cost too much, they are only available at scales that are still orders of magnitude too small, and produce energy in the hard-to-store form of electricity. Other methods include concentrating the sun’s rays to the extent that they can be used to heat up a working fluid directly, a technology already in use in sunny places like California and Spain, while in the future, the prospect of copying nature by using sunshine to synthesise fuel molecules directly – solar fuels – is attractive. How do these technologies compare and what are their future prospects?

We can get a useful baseline by thinking about the most traditional of these technologies – growing firewood. Continue reading “What’s the best way of harvesting the energy of the sun?”