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Most of us recognise that the Earth is warming and that — despite our planet’s temperatures having dramatically risen and fallen before — we humans must accept some measure of responsibility for the current changes.

Already consuming at least 1.1-1.5% of global power, and only forecast to grow ever-more rapacious, the data centres that power our information economy are surely one area in which we can, should, and must find ways to reduce consumption. And, although by no means perfect, data centre builders, operators and suppliers are paying attention. Individual servers are becoming more efficient. Buildings are being cooled by the wind and by toilets. Waste heat is warming homes. Newer facilities are being sited to save the planet (and money) by drawing power from hydro-electric schemes rather than coal, oil, gas, or the once-again-unpopular-and-scary Nuclear.

And then there’s solar. On the face of it, the ultimate renewable. The sun shines. It does so every day. It will continue to do so every day for millions of years to come. Every watt diverted to a data centre has absolutely no effect whatsoever upon the sunlight that the rest of us receive today, or that we shall receive tomorrow. There’s certainly a location trade-off to be made, as the sunshine rarely reaches the ground for much of the day in locations where the air is cool and damp enough for all that fresh air cooling to work, but there should certainly be a case to be made for both. If you’re in Iceland or Ireland or Oregon, sunlight is not something to rely upon for meeting your ravenous appetite for energy. But if you’re in sunnier climes, surely it’s a no-brainer?

Apple, for one, is constructing a 171 acre (69 hectare) solar farm next to its North Carolina data centre. That’s big. It’s apparently the biggest commercial deployment in the United States and — with some help from WolframAlpha — it’s also equivalent to 1.6 Vatican Cities or 13 Great Pyramids.

More tellingly, it’s also a lot of fields and trees.  If all those mirrors reduce the impact of Apple’s data centre on the environment, then maybe — just maybe — the loss of forest and farmland and open space is a cost worth paying. But Amazon’s James Hamilton does some maths, which he shares in a recent blog post, and he reckons that all the mirrors in that 69 hectares contribute around 3.2 MW to the data centre’s power requirements; requirements that Hamilton calculates to be around 78 MW. That’s 4%, which really is not that much at all. It’s worth noting that the figures for the solar array’s power output and the data centre’s consumption are only Hamilton’s estimates, but he tends to know what’s he’s talking about. In the absence of solid numbers from Apple, you can do a lot worse than believe the maths of someone like Hamilton.

So… why the enthusiasm for solar? Are data centre operators taking reductions where they can get them, and calculating that a 4% contribution to the fuel bill is worth 69 hectares? They might be right. Maybe. Or are they being more callous and calculating than that? Are the ‘savings’ on energy bills and greenhouse emissions essentially negligible, and are trees and fields being turned over to big mirrors simply so that companies can look good? They get a tick in the “green” box. They get a mention from Greenpeace. Customers, consumers and law makers think they care. Whilst actually, they don’t care at all.