Copyright © Encraft 2009 Page 1
EXECUTIVE SUMMARY
This report summarises the full findings from the Encraft Warwick Wind Trials Project covering 168950
hours of operation of 26 building mounted wind turbines from five manufacturers across the UK during
2007-2008. These turbines were mounted on sites ranging from theoretically poor (single storey urban
buildings) through to theoretically excellent (45m tall exposed flats in isolated settings on hilltops).
The objectives in setting up the trial were to see how grid connected microwind turbines perform on a
variety of building types and to see if any patterns emerged that could provide a helpful guide to potential
purchasers and also help manufacturers and installers direct their sales and marketing efforts
appropriately.
Important caveat
Non-technical readers should be aware that the findings of this report apply only to currently available
models of building-mounted wind turbines, designed for connection to the national grid. As anyone
who knows anything about wind power will attest, urban environments and building mounting is
probably the most challenging context in which to try to make wind power work, and the findings of
this study cannot be generalised to larger-scale wind, nor to freestanding wind of any size mounted on
poles or masts well away from obstructions. All the evidence (and theory) is that wind power is an
excellent and highly effective choice for such conditions, which exist widely across the UK away from
buildings and towns.
Trial results
The average energy generated per turbine per day across the sample set has been 214 Wh (including
times when turbines were switched off for maintenance or due to failures). This is equivalent to an
average of 78 kWh of energy produced per site per year and an average capacity factor of 0.85%. (This
compares to typical capacity factors of between 10% and 30% for larger turbines on free standing sites in
good areas).
If the results are adjusted to exclude data from periods when turbines were switched off or broken the
average energy generated per turbine per day rises to 628 Wh (230kWh per year equivalent) and an
average capacity factor of 4.15%.
Of particular note is that turbines on our high rise sites, Eden, Ashton and Southorn Court were able
generate as much energy in one month as other turbines in the trial did in one year. It is unfortunate that
these high performing turbines had to remain switched off for the majority of the trial following
complaints about noise from the building residents.
The best performing turbine in the trial generated an average of 2.382 kWh per day when in operation,
equivalent to 869 kWh in a full year. The poorest site generated an average of 41Wh per day when in
operation or 15 kWh per year, which is less than the energy it consumed to run the turbine’s electronics.
Energy consumption averages 80Wh per day per turbine (29kWh per year) which is significant on some
sites.

Copyright © Encraft 2009 Page 2
Wind speed and power curve data available to predict performance is not very accurate and requires
significant adjustment to generate predictions that fall within error ranges of +/-25%. Using unmodified
wind speed data by postcode from the national NOABL model and manufacturer power curves for
turbines can lead to overestimating likely energy output by factors of between 15 and 17. Buyers should
beware.
Overall the trial has painted a picture of an industry and technology that is still at development stage and
is likely to make a tangible contribution to energy and carbon saving only on the most exposed sites and
tallest buildings. The combination of this reality, aggressive and over-optimistic marketing by some
suppliers, and the enthusiasm and credulity of the market (and regulators) has potentially led to an
unfortunate outcome where the wind industry as a whole is in danger of suffering from a setback in
credibility.
The evidence form this trial is that such potential setbacks can be avoided in future by greater openness
by the industry as a whole, and more effort to educate the market and opinion formers about the
fundamental science and challenges of new technologies earlier. Micro-technologies need not fear
customer resistance, because there are plenty of early adopters out there willing to give things a go.
Sustainable technologies and a sustainable future require customers who are properly informed and able
to take individual decisions that are both economically optimal and environmentally sustainable. Without
open data this is impossible.



Acknowledgements
This project would not have been possible without the support of the individual customers who
volunteered their turbines for the trial, and we are very grateful to all of them.
Particular thanks to Pilkington Energy Efficiency Trust and BRE Trust who have provided funding to enable
the trials to maintain their independence, and to Warwick District Council, in whose planning area eleven
of the turbines are located.
BWEA, the Micropower Council and DTI all offered support in kind initially which helped the trials get off the ground,
and the Energy Saving Trust has more recently provided financial support to the Warwick Wind Trial to fund the
inclusion of additional sites and extend the period of data collection.