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Keener to be greener

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The first step in making Great Notley a 'sustainable' school (aj 16.10.97 and 5.2.98) was using materials in a way that minimised the use of energy and non-renewable resources, and co2 emissions.

But true sustainability means more than this, and the environmental consultant Atelier Ten, in association with the other team members, carried out an appraisal of the options for taking sustainability further. Its report argues: 'The notion of 'sustainable' development however suggests that the conservation measures so far proposed should be supplemented by an element of renewable energy generation in order to demonstrate fully both sides of the energy efficiency story.'

Hidden in the report is the very important point that the aspirations expressed at the Kyoto Earth Summit in 1997 to reduce co2 emissions by 10 per cent in the next 10 years have major implications for new buildings. Given that we are likely only to replace about 10 per cent of our building stock within that period, and that we will probably expand our built area by a further 2-3 per cent, the onus on the new buildings we do construct will be severe.

With this as its background, Atelier Ten analysed the potential for the application of four established technologies to Great Notley:

wind power

photovoltaic solar power

thermal solar power

heating by biomass.

With wind power, the report considers three options:

A size of turbine and batteries to meet the winter load. This would require a 25m-high mast and a 10m rotor diameter, with significant planning implications. A 19m2 building would also be needed to house the battery and controls. This solution would provide about 70 per cent of the school's annual demand, for a capital cost of approximately £60,000. But the report finds the battery requirement to be unfeasibly large.

A size of turbine and batteries to meet a specific circuit load. For example, it could meet the requirements of the lighting circuit with a 6kW machine with a 5.5m-diameter rotor and either a 9m or a 16m mast. Cost would be about £17,000 per unit installed, and the report suggests that if the less-obtrusive, 9m mast were chosen, then two units could be installed.

A demonstration machine. The least expensive option would be to install a small demonstration turbine with a rotor diameter of 2.4 - 3.6m on a 10m mast. This would cost £1000-4000 for the turbine and a further £4000- 6000 for ancillaries. At 1000-2000kWh per year, it would only generate three to six per cent of the total energy requirement of the building, but would be valuable for demonstration and research purposes.

With photovoltaics, says the report, the mathematics are such that the module area is generally driven by capital cost limits or by the space available, rather than by a real intention to generate 100 per cent of the electrical demand for the building. With this in mind the team has proposed three options:

An area of pv panel to match the peak solar-hour output with the peak summer demand. This would require a pv area of 70m2 inclined at an angle between 20degrees and 30degrees to fulfil the 7kW peak load. This could be achieved by locating a 35 x 2m panel array on the upstand to the main classroom roof. Total cost of the system would be about £66,500.

Reducing the area of pv panel to a 1 x 35m strip along the rooflight. Fundamental costs would halve, but the installation costs would rise, making the total cost £34,500.

A nominal array. This could power, say, the corridor lighting with an array of about 10m2 directly linked to luminaires. Cost would be about £10,000.

Ignoring the possibility of selling excess production into the grid, which is not feasible at present, the terrifyingly long payback periods for these three options are, respectively, 211, 217 and 222 years. The rationale is of course in the co2 savings made (5400, 2700 and 770kg a year) and in the potential for different funding arrangements in the future.

For solar water heating, the rooflight over the main hall offers a suitable location at an optimum inclination for an array of flat-plate solar collectors which would offer the least expensive method of generating hot water. An array of about 20m2 would meet the demand pattern. Capital cost would be £3800 with a simple payback of 30 years.

Biomass - using renewable or sustainable materials for fuel - was not pursued as an option. As well as there being no readily available source, although one possibility would have been to grow and harvest willow on the site, the major drawback was that biomass is very maintenance-intensive, requiring daily attendance, and the school decided this could not be justified. With an annual heating bill of less than £800 per year, the cost of employing a boilerman, even for an hour or two a day, would far outweigh any savings.

Having looked at the option for each kind of saving in non-renewable energy, the report then goes on to combine them in two ways:

An extreme option, with the larger wind turbine, a 70m2 array of pv panels and solar water heating

A median option, with a single smaller turbine, 35m2 of pv panels and solar water heating.

Reductions in grid-supplied electricity and hence in co2 emissions are significant, particularly for the extreme option (see graphs) but, as the report points out, even with the extreme option the school is still far from truly sustainable: 'Even though the loads in the school have been minimised by integrated design and passive control features, it is still very difficult, even with a further large investment in equipment of this type, to meet 100 per cent of the building's demands by renewable means.'

And of course there is the cost. There is no money in the school budget to pay for these options which, with their long payback periods, are not strictly financially viable. The report suggests potential sources of additional funding, either by sponsorship from suppliers or from eu and uk grant-giving bodies. Achieving sustainability is hard work.

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