Damning Report on Urban Wind Turbine Performance March 9, 2009

The results of the Encraft Warwick Wind Trials Project have been released and the news generally isn’t good for urban-based microwind turbines.

The report, dealing with typical building-mounted wind turbine installations in built-up areas, has found massive discrepancies between the performances of turbines depending on their location. While it is to be expected that turbines situated at high-rise sites would out-perform those in less optimum conditions, the results show a massive variation in yearly energy yields. In fact, the worst performing turbines produced so little electricity that it did not cover the turbines electronics requirement. In other words, they were actually net electricity importers!

However, the main criticism isn’t levied at the wind turbines or the technology, instead it is the methodology used to estimate turbine energy outputs.

Typically, the current procedure for site assessment is based on a speed database produced by NOABL. From this database, an average predicted wind speed can be obtained for any location within the UK and then, using manufacturer’s turbine data, an estimated annual electricity yield can be predicted. However, this approach doesn’t take into account the nature of the site, in particular, other buildings or obstructions that disturbs the wind flow.

In London, the London Plan requires an even simpler approach that doesn’t rely on particular turbine types, with each expected wind speed having a corresponding predicted electricity output. From the graph below, it can be seen that the variation between the Warwick Wind Trials Project and the London Plan’s predicted turbine output is large. The measured outputs are between 17 and 26 times less than expected using the London Plan methodology.

Comparison of measured output and predicted output as calculated using the London Plan

The conclusion must be that, if we are to make efficient use of wind resources in the urban environment, more detailed analysis should be considered before specifying turbines. The one-size fits all approach, like that used in the current London Plan, results in an inefficient use of wind resources. Instead of relying on predicted wind speeds, the feasibility of individual sites, whether through experience or modelling, should be favoured.