Energy Systems and Technologies for the Coming Century ...

engaged in wind energy assessment, and methods develop rapidly. Furthermore thedegree to which wind assessment data is open and freely available, as well as the extentto which the methodology is transparent and subject to scrutiny by the wind resourceassessment community, is also disparate.Because of the incomplete assessment of wind resource over the world, policy makersand energy planners have been forced into using coarse resolution global reanalysis datato estimate wind resources. This has a very serious drawback in that the coarse resolutionleads to an erroneous negative bias in the wind resource. Consequently the role of windenergy in the future energy mix may be downplayed, with grave implications formodelling approaches to climate mitigation.Making a complete global wind atlas using a single unified method available in thepublic domain provides the solution to the needs of the policy makers, energy planners,and Integrated Assessment Modelling (IAM) community. The Global Wind Atlasmethodology will be transparent, and presented to wind resource assessment communitythrough conferences and peer reviewed journal publications.The term wind resource assessment covers a very broad range of methods and manykinds of data. For example, the assessment can be based on in situ measurements and assuch pertain to the measurement location and height only, unless some kind treatment ofthe measured winds is carried out. At the other end of the range, the assessment may bebased on modelling, giving wind resource in 3 dimensions. However, the value of suchmodel derived assessment is limited without some kind of verification againstmeasurements.Therefore the most valued wind resource assessment will feature a combination ofmeasurement and modelling. For example the European Wind Atlas (Troen andPetersen, 1989) developed a pioneering method to analyse in situ measurements in sucha way that the information obtained from the measurements can be applied away fromthe measurement location. The analysis is done by modelling the effects due to localchanges in terrain elevation, local surface roughness changes, and obstacles, each ofwhich impacts the measured winds. The result of the analysis is a generalized windclimate. To predict the wind resource at a new site requires the application of the sameaforementioned models (calculating effects due to local changes in terrain elevation,local surface roughness changes, and obstacles) on a generalized wind climate. Thismethod comprises the workings of the WAsP (www.wasp.dk) software developed byRisø DTU and now used by over 10000 users worldwide.Wind resource assessment of the kind outlined above required a dense network of highquality and long term measurements. This is because a generalized wind climate is onlyvalid for a limited area. Where measurement data is missing, which is more often thecase, numerical wind atlas methodologies are used. The conventional numerical windatlas uses long term, but coarse resolution, atmospheric datasets (e.g. reanalysis fromNCEP/NCAR, Kalnay et al, 1996) to force mesoscale models, capable of modelling theatmospheric flow at scales ranging approximately from 100 km to 5 km. This comprisesa so-called downscaling technique. From the mesoscale model simulations, maps ofwind resource can be created. In the method developed at Risø DTU, post-processing ofthe simulations results in a grid of generalized wind climates which can be used inWAsP. The huge advantage of creating the generalized wind climates is that these can becompared to generalized wind climates derived from measurements in the region ofinterest. Even if there is a limit to the number of high quality measurements, thiscomparison of model and measurement derived climate allows for a verification ofmodel results. A proper verification adds tremendous value to a wind resourceassessment.So far the Risø DTU methods outlined above have been used in numerous locationsaround the world; most recently in India, north-eastern China, and South Africa.However up to this point no single unified wind resource assessment has been performedfor the whole world, and it important to note the objective is not to perform a globalversion of these country-specific studies. A new method is required to generate theRisø International Energy Conference 2011 Proceedings Page 216