Small wind turbines have been installed in urban and turbulent locations with surprisingly poor performance and this has been backed up by data from a trial at the Dublin Institute of Technology. In order to develop the small wind turbine industry, a careful examination of assessment methods for the wind resource is required. Small wind turbines are connected in parallel with the grid use inverters. As the wind turbine is not always at max output, a Weighted Average Efficiency for wind inverters is proposed. Pitfalls associated with developing an accurate weighted average efficiency for an inverter are identified and this will enable a more accurate sizing of the inverter for the turbine. The methodology for determining the performance of inverters and small wind turbines can be applied to any location.