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The great green gimmick
Last updated at 08:48am on 8th December 2006

Forget David Cameron's Wind Turbine. The Big Clunking Chancellor has unveiled his own environmental gimmick, the zero carbon home. He doesn't intend to live in one himself - 10 Downing Street will never be carbon neutral - but he wants all new homes to be zero carbon by 2016.

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• So what exactly is a 'zero-carbon' home?

A zero carbon house is one which - by making much of its own energy through wind turbines and the like - returns to the National Grid every year the same amount of electricity as it uses, and doesn't burn fossil fuels.

It's a nice idea, and one which has been tried in South London, by the Peabody Trust housing association, which built a small estate of 82 supposedly carbon-neutral homes there a few years ago.

The Treasury, if you ask them about Gordon's idea, helpfully send you details about BedZed (Beddington Zero Energy Development), the company that built these homes.

They were built with super-insulating walls, south-facing to take advantage of natural light, sealed against drafts with a heat exchanging ventilation system, water harvesting systems, solar panels and, of course, wind turbines. They were to be the houses of the future.

Unfortunately, four years on, there have been problems. Electricity and hot water for the site were supposed to have been supplied by a wood-burning combined heat and power generator which, it was promised, would provide all the electricity and hot water that residents would need. It soon became clear that there wasn't enough hot water, and gas boilers had to be installed.

last year, the CHP generator THEN, stopped working completely, and BedZed has had to buy electricity from the National Grid. A new CHP generator is now being installed. BedZed also installed an state of the art eco-sewage system, which would clean waste water by running it through a reed bed.

Very green, but unfortunately this happened to falter as well, something the site's founder, architect Bill Dunster, blames on 'management problems', and promises that it is about to get going again.

There are also arguments between the architect and the environmental consultants about just how much carbon has been saved by all this effort.

There are other difficulties, like the hidden environmental costs in the construction of all this kit, but that's another thing the eco-warriors would rather not discuss.

To be fair to BedZed, it is a pioneering exercise, and you wouldn't necessarily expect it all to work first time. A more serious problem is cost. The Government recently published a helpful table of basic green technologies for the home, showing how much they cost, and how long it would take to pay them back.

Solar water heating, which costs on average £2,625, and saves you just £48 a year, would take 97 years to recoup its costs.

Photovoltaic electricity, from the sun, costs £9,844 on average and would save you £212 a year, so you've paid off the loan in 54 years. A wind turbine apparently pays for itself in ten years.

But even these figures make assumptions about the price of electricity, and also about the price that you can sell extra electricity back to the power company at, when you generate more than you need.

In Britain, this is unregulated, so companies can and do pay widely varying rates, some of which are ridiculously low. There is also a substantial cost implication involved in building a super-insulated house in the first place, which is why there aren't many of them around. BedZed was essentially subsidised by the Peabody Trust, and by the local council, which sold the land at a cut-price rate.

Even the architects who built BedZed believe that zero carbon homes are only currently commercially viable with help from the local planning authority.

If the planners will allow eco-friendly houses to be built closer together, allowing a developer to build more on a piece of land, then that might offset the extra building costs.

They suggest that the building costs - before profit, and all the extras include wind turbines, plumbing, boiler, electrics, etc - would be between £120,000 and £140,000 for relatively small houses compared to, say, £85,000 for a conventional structure.

And that's before you've even factored in the cost of the land, the most expensive single item on this crowded island. They'd have to be substantially subsidised to be a realistic proposition.

But that's not what Gordon Brown is suggesting. He's offered to let buyers off stamp duty, but that won't begin to meet the increased cost.

His initiative is also missing the point. Carbon-free homes may be a wonderful dream for the future, but most of us live in existing houses, and at the current rate of replacement, 70 per cent of the existing housing stock will still be around in 2050.

So we'd be better off trying to make existing houses more eco-friendly, with dull but sensible initiatives like cavity wall insulation, hot water lagging, loft insulation, draught proofing, and improved heating controls.

The Government does have a grant scheme to help with these. This year it contained the princely sum of £6.5million, and ran out half way through the year. Pathetic.

So the Chancellor's zero-carbon homes are, for the foreseeable future, nothing but a giant green photo-opportunity - a gimmick which will have virtually no environmental impact at all.

PHOTOVOLTAIC ELECTRICITY: Cells on the roof converting sunlight to electricity, provide power to the eco-house. Any surplus may be sold to the national grid.
WINDOWS: Triple-glazed, floor to ceiling and best when south-facing. Source: Zed Factory
WOOD PELLET BURNER: Highly efficient and carbon neutral. One large unit could provide heating for up to 40 houses.
RAIN WATER: Water is collected and filtered. Better for use in the washing machine, or toilets than for drinking.
WIND TURBINE: A small 'David Cameron' wind turbine on the roof can provide 20 per cent of your electricity.
SOLAR THERMAL PANELS: Can provide up to 60 per cent of the hot water.
REED BED SEWAGE SYSTEM: Human wastes are filtered slowly through a reed bed, which cleans the water organically. The solid wastes can be removed every ten years and used as fertiliser.
WIND COWL VENTILATION: Air is drawn into the house through a large metal hood on the roof, which also expels used air. An exchanger transfers heat from the internal air to the new air coming into the house.
SEDUM ROOF: Sedum is a hardy plant with thick leaves and stems. When grown on the roof it adds an extra layer of insulation.
CONSTRUCTION: Timber frame, wrapped in a draught-excluding membrane. Super-insulated walls retain heat in winter, and keep house cool in summer. Ideally central heating would not be needed at all.
GEOTHERMAL HEATING SYSTEM: Extracts heat from the ground and pipes hot water into the house.

Actually, I think photovoltaics have a rosy future. The trick is an acceptance of "Diminishing returns" combined with true mass production. They are only expensive (In both cash and energy terms) because they are only manufactured in relativly small quantitys and the manufactureres obsess about getting every last % point of efficiency!

Photovoltaic electricity, from the sun, costs £9,844 on average and would save you £212 a year, so you've paid off the loan in 54 years.