Wind resource and energy production assessments

The purpose of wind resource and energy production assessments is to determine the mean wind resource of sites and the long term mean annual energy production of wind farms that are planned, under construction or in operation. These assessments are the basis for the negotiations between project initiators, developers, investors, financing parties and turbine manufacturers.

On the market, the wind resource and energy production assessments elaborated by aj are considered as particularly reliable and well explained. Banks welcome our reports particularly.

In Germany, the standard approach is to derive the wind resource from the energy production of existing wind turbines in the surroundings, whilst site specific wind measurements are used as a basis in other countries (but also increasingly in Germany). The production data respectively the wind data used in these cases must be scaled to long term mean situations and then transferred from the positions of the existing turbines respectively the wind measurement to the planned turbine positions and their hub heights.

aj is particularly experienced in the in-depth check of available production and wind data on plausibility, disturbances, technical faults and erroneous information. Any available information is used (e.g. not only from the top anemometer of the mast but from all anemometers), in order to obtain the most complete picture of the wind flow. This approach, which is pursued on all levels and matters, is the most relevant particularity of aj on the market and allows us to achieve lower than common uncertainties.

To scale the existing data to the long term, data and procedures developed in house are used as well as data sets which are readily available on the market, as appropriate. Standard software tools are used for the extrapolation in space and for the production calculations. Detailed plausibility checks are considered highly important in this context. If experience or general considerations suggest that the most realistic results differ from those obtained with the calculation programs, corrections are applied in order to get closest possible to reality and to minimise the uncertainty.

When scaling data to the long term, a number of reference data sources are used in parallel, often even about 10 sources across three or four fundamentally different kinds. For Germany, own production indices are elaborated and permanently updated which are based on the operational data of long term operational wind turbines. These indices allow for verifying the common BDB indices independently. Wind speed data are extrapolated to the long term using an own, very detailed procedure. The results of long term extrapolations of aj have changed less over the years than those of many other companies. Changes in particular reference data sources usually affect our results only to little extent.

The wind flow modelling is preferably based on on-site wind data or on SCADA data of wind turbines in the region, since this leads to more realistic results than met station data.

The Technical Guideline no. 6 of the Fördergesellschaft Windenergie und andere Dezentrale Energien is followed by aj as far as this is sensible and feasible.