Author: Alicia Webb
Contributors: Chris Blanksby, Natalie Lukies
Once you have a year or more of data, you need to give it to a consultant, who will write an energy yield analysis report (or energy resource assessment report). This report plays an important part in development and negotiations for any wind farm.
The energy yield analysis helps you make financial predictions about the commercial viability of your project, and helps turbine suppliers choose the turbine model most suited to the site. It will also provide an independent energy output baseline, which you can use to compare the various energy yield assessments of turbine suppliers. It's in the interest of turbine suppliers to be conservative when predicting energy yield as they'll eventually sign a production guarantee and don’t want to risk producing less energy than promised. Energy yield predictions:
- feed into discussions with the electrical grid operator
- define how much energy the wind farm is likely to produce
- inform technical concerns, such as the need to augment the grid near the wind farm.
What the consultant needs
To do the energy yield analysis, a consultant needs:
- the wind data
- the tower installation report
- a description of the proposed wind farm, including the number, locations, and type of turbine planned
- a description of the wind farm area, including site photos
- elevation contour data for the site area which extends at least five kilometres beyond the site boundaries
- long term reference wind data, usually from a nearby Bureau of Meteorology site.
The proposed wind farm layout
To do an accurate energy yield prediction, a consultant will ask about the turbine model and location. It doesn't matter if some details are still being finalised, as a consultant can also help you design the layout and choose your turbine. At this stage in the project, you may have narrowed down some details based upon other constraints. For example, the number of turbines you're considering, or the boundaries of the site. Providing these constraints to the consultant will help them price and scope the analysis.
Wind consultants can do calculations for several different turbine types, and several different layouts. They can also run calculations which identify locations for the highest energy output at the site. If you have energy calculations for several types of turbine, this can help you choose your model and negotiate prices with turbine suppliers.
Designing a wind farm and running energy yield analysis reports for different turbines can get expensive. So it’s best to outline clearly whatever constrains exist at this stage. If you haven't yet narrowed down a turbine model, it can be cheaper to ask the consultant to perform the analysis based upon a ‘generic 2 MW wind turbine’ or similar, rather than on six different types. You can always update your calculations when you choose your model.
Each turbine supplier you negotiate with will re-run the energy yield analysis anyway. But you can use the independent consultant report to benchmark their calculations.
What the report will say
An energy resource assessment or energy yield analysis report essentially tells you how much energy a wind farm in your chosen location should produce.
Using the information detailed above, the consultant report will go through a few standard discussions and calculations. You can expect the report to discuss:
- the monitoring site, mast and the quality of data it produces
- data (including any cleaning of the data), the measured wind direction rose and the average wind speed
- long-term reference site data quality and validity
- the correlation between the monitored data and the reference data
- adjustment of the on-site data to represent a long-term wind speed prediction
- adjustment of the data to represent hub height wind speed
- wind speed modeling for the wind farm area
- the turbine model, its power curve and any adjustments which make it specific to air density at your site
- proposed layout for the wind farm
- energy yield predictions at the location(s) you specify
- losses in the calculation, including electrical and wake losses
- any mathematical uncertainty in the calculations.