On Monday afternoon I was driving south towards Seville on the motorway when I saw two bright lights just above the hazy horizon of the Guadalquivir plain to my right. I’ve a poor snapshot to prove it (at the end). They were reflections from the collectors of the two solar power towers at SanlÃºcar la Mayor: twelve miles away. Wow.
The anecdote has no bearing on the rational case for solar thermal technology. Power towers may or may not be a better choice than parabolic trough, linear Fresnel, or Stirling-dish designs; and solar thermal may itself be bypassed by some breakthrough in photovoltaics. But it does speak to the irrational component of attitudes to technology. Some of the objection to renewable green energy is from machismo: rooftop windmills and solar-powered lights are small, intermittent, toylike, in short girly. Real technology is big, strong, reliable machinery at high temperatures and pressures. It’s easy, as I’m doing. to poke fun at the engineering romanticism of men – I think it’s always men – who yield to temptation in hardware stores and buy 50-piece socket wrench sets. (I have one gathering cobwebs in my cellar too.) But the boy’s romance with good tools is surely important to many scientists, engineers and skilled workers, and it’s connected with their pride in doing a good job. Kipling’s Scots ship’s engineer McAndrew gives this a religious turn:
From coupler-flange to spindle-guide I see Thy Hand, O God –
Predestination in the stride o’ yon connectin’-rod.
John Calvin might ha’ forged the same – enorrmous, certain, slow –
Ay, wrought it in the furnace-flame – my “Institutio.”
There’s a grain of truth in Shelley’s boast that “poets are the unacknowledged legislators of the world”, and the lives of scientists and engineers are in part the fulfilment of childhood dreams.
In this powerful romantic aesthetic, the ideal energy technology is fusion: temperatures of half a billion degrees, superstrong magnets or lasers, an exotic (but not incomprehensible) scientific basis, and a bit of danger. But it’s nowhere near a workable energy supply. Solar power towers are not bad runners-up, and we can have them tomorrow. A research solar furnace can routinely create temperatures up to 3,500Â°C in a pan-sized target, enough to melt pretty much every elemental material but diamond. For a power tower, you want a lower temperature over a much bigger area. The SanlÃºcar power towers use a conservative design of collector, 14 metres wide, to generate steam at 250Â°C and 40 bar.Â This is quite enough to drive a standard steam turbine. The next step up has so far been taken in small demonstration setups: to heat air to 1000Â°C or so in a ceramic exchanger to drive a gas turbine directly. The beauty here is that you can combine the solar generator with fossil gas at night. And the technology (in whatever version) lends itself to grandiose plans to cover the Sahara with solar generators and ship the electricity to Europe.
Source: DESERTEC, via Wikipedia
The holy grail here isn’t really power generation – we know this works, it’s a matter of settling on the best technology and bringing costs down – but cement: 1.8 billion tonnes a year of it, made in kilns at 1450Â°C. The process generates a startling 5% of the world’s carbon emissions, comparable to those of steelmaking. Why not use the sun to calcine the limestone? This has been demonstrated on the kilogramme scale, and in a continuous process, by Bonaldi and Meier in a Swiss laboratory linked to Einstein’s ETH. I couldn’t find any evidence ofÂ a bigger pilot plant.
If I had money to spend on long-term, high-risk, high-payoff green research, I’d put a lot into solar cementmaking. For real men, and the boys inside them. You could build huge solar cement works in the remaining expanses of the Sahara and ship the powder out in bulk carriers drawn by giant kites …