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Forget solar panels, it's time for rooftop slime-tanks

And offshore 'artificial tree' forests. Apparently

By Lewis Page, 27 Aug 2009

The Institute of Mechanical Engineers has called for the UK to adopt a strategy of "geo-engineering" techniques to extract huge quantities of carbon dioxide from the atmosphere.

The headline ideas are these: CO2-capturing "artificial trees", growing of biofuel algae on rooftops, and the use of reflective building materials to send solar energy back out of the atmosphere before it can cause global warming.

The IMechE report is called Geo-Engineering – Giving us time to act? In the introduction, it states bluntly that plans to reduce carbon emissions aren't working fast enough. It says that this is because of three things. First, green technologies such as efficient solar power "are still a significant way from being ready". Second, there is a lack of technically qualified people in the UK to take plans forward - specifically, it seems there aren't enough nuclear power specialists to build new nuke stations. Thirdly "and maybe most significant, markets around the world are simply not interested. Green energy is expensive".

The IMechE authors suggest that the only way for humanity to gain some breathing space before a disastrous temperature increase is to consider geo-engineering, the use of engineering on a planetary scale to remove CO2 or heat from the atmosphere. They offer three techniques which they say are the most promising ones.

First up is "artificial trees", essentially building- or goalpost-sized structures through which the wind blows. As air passes through them, the "trees" extract CO2 from it for later sequestration.

According to the report:

A unit based on current technology, the size of a standard shipping container, would capture about one tonne of CO2 per day or 365 tonnes annually ... However, it is conceivable that with further research ... a single unit with a larger collector would be able to capture as much as ten times more [in which case] 100,000 units would be sufficient to capture the whole of the UK's current emissions from non-stationary and dispersed sources [eg, those which it wouldn't be practical to capture at the source].

Or in other words, existing technology would require a million "trees" covering at least 15,000 acres of accessible land (or sea) to do a meaningful job, at an estimated fabrication cost (for landbased jobs) of US$20bn - say £12bn. And the trees are only 20 per cent of the cost of this plan - getting the CO2 out of them uses a third or so of the energy generated by burning the fuel in the first place, and then it has to be transported to an old oil or gas field and stuffed into the ground. The IMechE authors suggest that the "trees" actually be planted offshore among windfarms in the North Sea, so having a ready source of clean power and lots of old fossil fields close to hand - but this would increase costs, just as placing windfarms offshore does.

Rip the solar panels down, we're going to put slime-tanks up there instead

The next brilliant plan is "algae on buildings", or "the large scale introduction of algae into the built environment".

The rough plan would be to fix sealed tanks of algae known as "photobioreactors" (PBRs) to "available vertical and horizontal surfaces" - ie walls and roofs. You need a sealed unit, apparently, as it "guards against infestations" - whether of or by the algae inside isn't clear.

The PBR-clad buildings would seemingly yield a rich crop of algal biofuel as well as "biochar" which is excellent fertiliser, while extracting CO2 from the atmosphere in fine style.

Bottom line, then? Would having our cities clad in bottled scum be better or worse than covering them in solar panels? Which would cost more? Is it, in fact, the time for slime?

At this juncture, this geo-engineering solution is very much at a conceptual stage [no shit] and has attracted little if any assessment of its technical feasibility [not even from us at the engineering institution] ... implementation on a large scale is a plausible outcome.

Oh really.

Finally, the report suggests that it could be a good notion to use more reflective materials to build - or at least cover - our cities. At present, there's a known "urban heat island" issue whereby roads, buildings etc. get hot on sunny days and further heat the air above them. If they reflected heat rather than absorbing it, this effect could be lessened.

But it seems that this idea isn't actually much use in a saving-the-planet context.

It is clear that ... urban albedo modification does not produce a large enough effect to contribute significantly to balancing global warming.

However, in hot places where air conditioning gets used a lot, like Los Angeles, shiny roofs might cut cooling demand by up 60 per cent. Again, you have to wonder if there might not be some argument from people wanting to put solar panels there instead, or maybe algae PBRs. The IMechE offers no comparison of the various plans.

To sum up, then. Option one is a £60bn plan for huge fields of roadside or offshore carbon-sequestering machines which would consume colossal amounts of energy on top of what we now use. Option two is a vague suggestion that it might be nice to cover our cities in biofuel slime tanks instead of solar panels. Option three is to cover them in infrared-reflective paint instead, though this last would apparently have very little effect.

Frankly, it seems difficult to see how the IMechE's original objections to more conventional green plans - that the tech isn't ready, that the skills don't exist, that the market isn't interested - don't apply with hugely increased force to these plans.

Even by the standards of summer news-drought barrelscrape notionry reports, this is poor stuff. Those interested can read the whole report here (warning - troublesome image pdf). ®

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