There is considerable uncertainty about the role that small and medium wind turbines may play in the production of sustainable electricity. In the present work, we identify the main factors affecting the economic viability of small and medium wind turbines (herafter SMWTs). We then propose a framework for more efficient and reliable predictions of the annual energy production of SMWTs.
We demonstrate that these turbines are indeed profitable, provided that an appropriate turbine is selected and that the annual energy production is estimated carefully. These seemingly simple tasks are non-trivial and current practices too often lead to unreliable assessments.
We first assemble a database of wind turbines with a rated power up to 100 kW. Such a database is a necessary tool when assessing the feasibility of a project involving SMWTs, since the market is very immature, with a wide variation in quality between different turbines.
We then calculate the annual energy production (AEP) for a number of measurement sites in Belgium and The Netherlands and for different independently-tested SMWTs. Based on these data and on first principles, we show what the best methods are to select an appropriate turbine and what the expected accuracy is of the AEP estimate. We have found that a particular statistical error has been overlooked in the current methods to estimate the annual energy production. This error is the possible mismatch of the averaging times with which wind speeds and turbine power outputs are sampled. Using wind speed and power measurements, we show how this error can be minimised.
Our findings have an immediate practical importance. We therefore apply our methods in a number of case studies, and give recommendations for future SMWT projects.