Wind Turbine

The 225 kW wind turbine has a hub height of 36m and a rotor diameter of 29m and is a Vestas V29 model previously in operation in the Netherlands. The turbine is connected to the buildings’ electrical distribution network and to the national grid. It is expected to generate 250MWh annually, which is greater than the anticipated building consumption, and excess power (equivalent to the needs of around 40 homes) will be exported to the grid.

Biomass

The buildings’ heating needs will primarily be met by a biomass boiler fuelled by the energy crop: Miscanthus or ‘Elephant Grass’, 5 hectares of which have been planted on the site. The crop is harvested annually in the late winter with conventional harvesting equipment and stored as bales until needed. The bales are shredded before being fed into the biomass boiler. The field is expected to yield 60 oven-dried-tonnes per year with a calorific value of 17GJ/tonne. The 100kW biomass boiler is provided by Talbott’s Heating.

It is 80 to 85% efficient and can modulate down to 25% of full load. The shredded bales are fed into the boiler by a mechanical screw auger. Biomass is carbon neutral as the CO2 emitted during combustion is balanced by the CO2 absorbed by the crop, which is coppiced on short rotation. The emissions from the boiler comply with the Clean Air Act. The boiler is expected to be installed and operating in 2004-2005.

Ground Water Cooling

Ground water is used to cool the buildings during the summer. Water is extracted from the local aquifer at 12°C via a 75m deep borehole. First it is used to cool and dehumidify the incoming air to the buildings in the Air Handling Units. The water is then circulated at 15°C through chilled beams (finned tubes) at high level in the offices. Finally, the water is used to irrigate the energy crop.

PVT Array

The 170m2 solar array comprises 54m2 of PVT panels and 116m2 of solar thermal panels. The PVT panels consist of a photovoltaic module, which converts light into electricity, and a copper heat exchanger on the back to capture the remaining solar energy. The panels have been developed by ECN in the Netherlands, incorporating Shell Solar PV elements and Zen Solar thermal elements. They produce electricity and hot water. The solar thermal panels are identical to the PVT panels, but without the photovoltaic element.