Saturday, October 27, 2007

Double good: building without cement

Cement factory in Derbyshire, UK, by Roger B.Cement is a problem
Did you know that cement manufacture creates 5% of all industrial carbon dioxide emissions? That matches the pollution output of the world's aviation industry. What's more, both are set to increase, particularly in China. Construction inevitably means cement for mortar and concrete -- or does it? Certainly for the likes of high-rise city blocks, nuclear power stations and large dams, there's no alternative. But what about ordinary housing? How much concrete needs to be used in that?

Wood: a partial solution with a big bonus
A large building in Texas, all made out of timber. By Fatty Tuna (flickr)
Building houses out of wood is nothing new in timber-rich regions like Scandinavia and North America. Wood has many advantages over bricks, mortar, steel and concrete. For one thing, it's very easy to use so buildings can be completed in just weeks rather than months. When I 'built' my first house in western Canada back in 1971, it took 3 weeks to get the entire structure completed and watertight, ready for services to be installed. When I built my house in Spain in 1989, it took more like 6 months. Why? Because there was no wood used in my Spanish house at all, that being the local style of building. Prestressed concrete beams, which are used in large numbers, are incredibly heavy to manhandle into position or cast. So are blocks, bags of cement and making and carrying endless buckets of mortar. I worked on this house throughout the construction, so I know!

The hidden bonus of wood is that it is almost pure carbon. The growing tree grabs CO2 out of the air and converts it into sugars and, ultimately, to cellulose and lignin which is what we call wood. Everyone knows that trees sequester carbon and that they are one of several natural ecosystem services -- in this case, carbon sinks -- which counter climate change caused by humans burning fossil fuels. This is the rationale behing the burgeoning offsetting business. Plant a few trees and you can pollute as much as you want. That's what people seem to assume when guilt over squandering energy overcomes them a little.

The big issue: seeing the wood for the trees
Even if it were true that you can assuage your travel/consumer/heating/airconditioning energy use by offsets, there is one problem which seems not to enter general thinking. Natural forests are carbon neutral. As fast as young growing trees grab carbon, dead and decaying trees (and forest fires) release it again: the carbon cycle. To make sequestering carbon in trees really work to reduce atmospheric CO2, the mature trees need to be harvested and stored in such a way that they don't decompose and release all their carbon again. Carbon storage is what happened on a massive scale over hundreds of millions of years, as coal formed from dead but not decayed trees. The carbon has become safely locked away from oxidation into the atmosphere... until humans came along (and you know the rest). Yet when you think about it, we are storing carbon all the time -- in the form of timber-framed housing construction and, to a lesser extent, as books in the world's libraries.

So that's my point: countries which traditionally use cement in the form of concrete and mortar to build houses should change their construction practice and build from timber instead. This change of direction has several advantages:

  • timber construction locks away carbon
  • it's quicker and easier
  • self-build is much easier and in some countries, you can buy housing kits to do this
  • it is essentially non-polluting unlike cement-based constructions which cause massive CO2 releases into the air, principally from cement quarrying and manufacture
  • if real environmental costs are taken into account, wood is far cheaper
  • greater demand for timber would stimulate more forestry development with yet more sequestration of carbon as a bonus. At the same time, cement manufacture would decline as demand slackened off, so reducing carbon pollution
  • timber can be re-used
  • timber-framed buildings are intrinsically warmer than stone, brick, block and concrete. In addition, it is simple to incorporate insulation in the timber frame
  • wood is a pleasant material to work with and beautiful to look at. Concrete is messy and heavy to move around

Yes I know concrete is essential for many purposes, including the foundations (footings) of timber-framed housing. My point is simply that we could use a lot less of it -- a lot less -- if we wanted to.

Tuesday, October 09, 2007

The Future of Nuclear Power

Sizewell nuclear power station: a large footprint (and what about rising sea-levels?) by Rob.Stoke
Today is the final day for anyone to make their views known about future nuclear power in the UK. I've done this on the British Government's Future of Nuclear Power website. Just to put you in the picture, I have argued for some time that, if we are to have new nuclear power stations, they should be built underground.

Here are my responses to the Government's consultation questions:

1. Safety and security of nuclear power

Siting all future nuclear plants underground is something that should be taken very seriously. This does not even seem to have been considered. Yet it has three major advantages:

  1. immune to military attack from the air

  2. containment unbreachable (given proper choice of ground conditions, hydrogeology and rock types) and so immune to attack from, say, a suicide bomber. Even major LOCAs would be better contained than anything above ground

  3. no need ever to remove irradiated fuel assemblies. When the reactor reaches the end of its operating lifetime, the whole facility could be sealed, complete with its spent fuel. Monitoring would be needed but because nothing is above ground, access would only be minimal. Decommissioning surface plants is turning out to be formidably expensive and all radioactive materials end up having to be sealed underground anyway in all viable scenarios

2. Transport of nuclear materials: No reprocessing is the right route, but by siting each nuclear plant underground, there would be no need for the spent fuel ever to leave the facility. It would be stored there in a facility built at the same time as the reactor containment cavern. When the reactor's life is over, both it and the spent fuel stored close by would be made safe, sealed and remotely monitored. No radioactive materials, highly active or otherwise, need ever be transported on the surface.

3. Waste and decommissioning: Locating new reactors underground would avoid many of the serious problems of waste and dceommissioning. At the end of the reactor's life, all its fuel remains in the store which would have been constructed during the initial cavern excavations and the whole underground site becomes a remotely-monitored facility with little further need for maintenance. Such an arrangement is inherently safer than a surface reactor which will need to be guarded and monitored through at least three human generations before it can be finally removed: not a good legacy for future generations.

4. Environmental impacts of nuclear power: If the nuclear facility was largely located underground, the surface footprint of a site would be markedly less than at present, quite apart from the safety aspect which I've already dealt with. There would be no need for a secondary containment structure since this would be provided by suitably geo-engineered natural rock in the excavated cavern. Surface buildings could all be part of the non-radioactive secondary circuits. So the heat exchangers containing the pipework for the primary circulating coolant would be underground but the high pressure steam circuit for the turbo-generators could be ducted to the surface which is where generators, transformers, cooling and other facilities would be located.

Regarding the space occupied by a nuclear facility versus that occupied by a windfarm, I have two comments:

  1. most future windfarms should anyway be located offshore, so space and NIMBYism is largely irrelevant

  2. any space occupied by a windfarm remains relatively pristine. If needed, turbines and supports can be completely removed within months, leaving the site uncontaminated and as it was before. The same cannot be said of surface nuclear build because of the massive largely concrete bioshielding infrastructure required and the problem of the 'hot' reactor core which cannot be removed for over 100 years, or requires prohibitively expensive and hazardous remote-controlled decommissioning and transport of large quantities of medium level radioactive waste to a repository as yet not in existence. These 'inconvenient truths' are a prime reason why nuclear build should in future be underground.

5. Reprocessing of spent fuel: I agree that reprocessing should not be carried out. Storage for spent fuel assemblies should be 'built in' in the underground location scenario I envisage. This eliminates the need for surface transport of highly active fuel rods.

Obviously these remarks apply to any new nuclear build anywhere on the planet, not just the UK! At the very least, I think the onus should be on governments and the energy industry to explain why siting nuclear plants underground is NOT a good idea (if it isn't!). But I expect it will be ignored... ho hum!

Sunday, October 07, 2007

The Way the Wind Blows

How it all works, from Treehugger

How could we store surplus wind power? There is a solution right under our feet.

No wind: As I was travelling on the train along the North Wales coast last Friday, I had a fine view out to the North Hoyle Offshore Wind Farm. It's a great sight all these turbines, each rated at 2 megawatts, like rows of white statues far out in Liverpool Bay. But there was a problem: it was a fine sunny day and no wind at all. The sea was like a millpond and the turbines were indeed like statues for they were motionless. Electrical output zero.

Achilles Heel: And that is wind power's big problem. It only works when the wind blows so if we relied upon wind power, on fine calm days, there'd be no power at all. This is unacceptable, of course, in our modern, energy-hungry world. But now, there's a solution and its name is CAES: compressed air energy storage. Put simply, when the wind blows during the night, wind turbines generate power which is not needed since most people are asleep. If you use that power to pump air at high pressure deep into the ground, that high pressure air can be stored and later released when power is needed, driving modified gas turbines and generators.

It works too! If you think this is unlikely to work, it already does, and much more is underway. The first CAES plant came on stream in 1978 in Huntorf, Germany and a second much larger one was commissioned in 1991 in Alabama, USA. It stores its compressed air in a mined-out salt dome 80 metres across and 300 metres tall, lying 450 metres below ground, and can use the air to supply a turbine generating 110 megawatts of electrical power continuously for some 26 hours.

Giant battery: So just like hydroelectric pumped storage, wind powered compressed air storage could act like a giant battery, evening out fluctuations in demand by topping up the grid when needed. There are plenty of geologically-suitable locations all over the world so maybe we should push politicians and utilities to get moving on CAES. To find out more, read this New Scientist article and this Treehugger piece.