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Sebastin Sancho Dobles Lahmeyer International GmbH

San Jos, Costa Rica - 1971 E-Mail: ge_265@lif.deStudy program in Germany: Oldenburg PPRE 96/97 Internet: www.lif.de

German cooperation partners:

Recommended practices in wind speed measurements

Nowadays whit the increasing amount of wind energy developments, mostly in Europe and some

other industrialised countries, arises a strong demand for bankable wind measurement campaigns

by independent expert companies.

Projecting a wind park involves several constrains such as: environmental, administrative,

bureaucracy, economical and technical. Out of these constraints the economic parameters will bethose which will define whether a wind project as feasible or not.

However, there are procedures to select a promising wind site. Concentrating in the technicalaspects, a project developer should look firstly for sites where the wind conditions are promising

e.g. yearly wind speeds above 6 m/s and sites free of restricted areas. Nevertheless, just the fact to

meet these requirements does not mean that the wind project will be environmentally and

economically meaningful.

Wind energy developments are subject of financial risk. The financial risk is, as well, a

consequence of the uncertainties in the wind resource assessment which later will be amplified inthe energy prediction due to the non linear connection between wind turbine output and wind

speed. The combination of the uncertainties gives the total uncertainty in energy production

which in some cases could vary between 3 and 30% or even more.

In order to avoid financial disadvantages in a wind park development, the uncertainties must be

minimised and risks carefully analysed. Technical uncertainties depend on the following subjects:

Wind resource assessment Power curve performance Wind turbine availabilityCommonly the wind resource assessment is carried out by the project developers wind expert,

whereas the last two are responsibility of the wind turbine manufacturer or the wind farm

operator.

Wind resource assessment

The process to assess the wind resource can be summarised in the following steps:

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Wind measurement campaign

Wind data validation and generation of wind statisticsTerrain and roughness modelling

Wind flow model calculation (Micro-siting)

Measure-correlate Predict procedure (MCP)Yield estimation (WT power curve and wake model)

A minimisation of the financial risk already starts in the early stages of planning by performing

high quality wind measurements. Thus, in order to perform such measurements the following

practices must be strictly followed:

1. Anemometers calibrated according to international standards2. Mounting according to the best recommended practices (IEA)3. Choice of measuring site. Representative of the wind farm.4. Measurement as close as possible to hub height5. Measurement period at least 12 months6. Data check and validation (Minimum acceptable data recovery 90%)7. MCP8. Wind flow model calculation (Micro-siting)By minimising the uncertainties in points 1 to 8, one can achieve lower financial risk. The

uncertainty in the energy production level will be a determinant parameter for risk management

in wind farm planning.

It must be kept in mind that in complex terrain the uncertainties must be increased and therefore

on site wind measurements will be reliable within short distances around the measurement.

Hence, the costs associated with high quality on site measurements (roughly 0,1% the investment

costs) are rather low compared with the reduction in the financial risk. The energy yieldestimation processes the results obtained during the measurement campaign (wind statistics)

together with further input information like terrain model and wind turbine power curve.

Since the wind measurement is the basis of any wind energy development, any uncertainty in themeasurement will be amplified to the energy calculation level, therefore it must be noted that a

high quality measurement will reduce the risk in the energy prognosis.