BRE FB18 PDF

INTRODUCTION

One of the Government's targets is to increase the amount of electricity generated from renewable energy to 10% by 2010. Initiatives to achieve this target include Government-sponsored programmes, such as the Low Carbon Building Programme, that offer grants for the installation of micro-generation systems, including small wind turbines. These grant programmes, together with media interest in a new generation of micro-wind turbines specifically designed to be attached to buildings, mean that the uptake of domestic wind turbine installations is increasing.

There have been a number of studies and reviews concerning the effectiveness of wind generation which have focussed on larger scale wind generation schemes. However, it is uncertain how applicable these studies are with regard to micro-wind generation installations and in particular those intended to be installed on a typical house, which are generally rated at 1.5 kW or less.

Clearly, the output from wind turbines is dependent on the local wind conditions. The BRE Trust report, Microwind turbines in urban environments^[1], gives the results of a BRE study of the factors that influence the power that can be generated by micro-wind turbines in urban areas. The power in the wind is due to its kinetic energy and is proportional to the cube of the wind speed. Hence, fairly small reductions in wind speed have a magnified effect on the available power (eg halving the wind speed reduces the available power by eight times). The BRE Trust report[1] concludes that this is especially significant for small-scale domestic installations in built-up environments where surrounding buildings can dramatically reduce the prevailing wind speeds. The presence of buildings in close proximity also increases the turbulence of the flow, which further reduces the turbine output. Additional reductions in wind speed occur due to the proximity of the building on which it is mounted: if a turbine is sited in the wrong location on a house roof, it is possible for the power output to be close to zero for significant periods of time, even when the wind is blowing strongly.

Therefore, to assess the potential for wind energy generation from roof-mounted micro-wind generators, quantitative information is required concerning:

• the expected wind speeds around house roofs, and

• the effect of terrain and nearby surrounding buildings.

This report describes a model scale wind tunnel study intended to provide, for the first time, quantitative measurements of wind speeds over house roofs to inform the siting of wind turbines.