DNV KEMA, in collaboration with developers and consultants, has developed a new framework document for wind energy assessments.
Various entities in the Renewable UK Wind Resource Working Group have come together to propose that the wind energy industry adopt a common framework for discussing both energy losses and uncertainties around energy assessments. According to DNV KEMA, the new framework document will lead to more transparency and advancements in the quantification of project losses and uncertainties.
‘The loss and uncertainty framework will aid the consultants when performing due diligence on energy assessments completed by other leading consultants,’ explains Ruben Menezes, project manager for the framework and consultant at DNV KEMA renewable energy services in London. "All participants agree to report on their energy assessments in accordance to this framework."
Menezes says a typical wind resource and energy yield assessment derives gross generation from a site's wind speed frequency distribution and a turbine's power curve. Technical loss factors are then applied to derive expected net energy generation. Example loss factors include equipment availability, wake losses, icing losses and electrical line losses.
An uncertainty analysis is then conducted to determine the probability distribution of net energy production. Example uncertainty categories include those associated with wind speed measurement, wind shear extrapolation, modeling, and loss assumptions.
"However, without standard definitions for such loss factors and uncertainty categories, it is difficult to compare studies prepared by different consultants," Menezes says. "Standardized definitions will not only facilitate direct comparison of energy estimates among different consulting studies; it will lead to more productive dialog and, ultimately, improved understanding of technical losses and uncertainties."
According to Menezes, it is not uncommon for more than one energy assessment to be prepared for a proposed wind power facility.
"Often, the results of the assessments will have material differences, and these differences typically include different assumptions regarding technical losses used to derive net energy generation from gross energy generation," he says. "However, when both the definition of a loss and the value of the loss differ, direct comparisons are difficult to make.
"Compounding this challenge is the use of different uncertainty categories and their definitions, making it difficult to interpret and compare the results of different reports at the various probability levels," Menezes continues. "Developers, investors and the consultants that support them will be able to focus on actual differences between assessments if assessments use a common set of loss and uncertainty definitions."
The framework document was developed in collaboration with the following participants: Arcus, Dulas, Natural Power, Oldbaum, Prevailing Wind Farm Analysis, Sgurr Energy, SKM, Vattenfall and Wind Prospect.