Page 150 - Fluid Power Engineering

W ind Resource Assessment 125

These sites are expanding rapidly to provide wind data for
a large number of countries. The wind data is available for
multiple grid sizes and heights.

These maps provide annual average wind speed categories or wind
speed ranges over large areas. Most online maps are based on 2.5 km ×
2.5 km grid while others are based on a coarser grid. These maps
normally display wind speed at 50-m height. As expected, these maps
display large-scale patterns with no temporal variation. The maps do
not provide information about wind direction and shear. Therefore,
the maps should be used as a tool to identify regions with good wind
resources, and not for serious viability of a wind project.

Preliminary Analysis of Data from Neighboring Airports
and Other Met-Towers
If the wind resource maps show promise, then the next task is to
find neighboring airports within 100-km radius that have topog-
raphy that is similar to the site under consideration. The simplest
form of preliminary airport data analysis is available in RetScreen
(www.RetScreen.net), a free MS-Excel based application. It contains a
database of monthly average wind speed data from major airports at
an elevation of 10 m above the ground level. Information about wind
direction and shear is not available from this data source. The user
has to input wind shear and input wind speed at the proposed site
based on the airport data. That is, the user estimates wind speed at
the proposed site based on a subjective assessment of how different the
wind speed is at the proposed site compared to the airport. The user
can select a turbine or create a turbine and its power curve. With this
information, RetScreen computes average annual energy production.
It also has a financial model that take as input capital costs, recurring
costs, recurring revenue, debt/equity ratio, interest rates, and other
parameters to compute payback period and other financial metrics.
It produces pro forma income statement and cash flow statement.
Although RetScreen has significant limitations, it is a good starting
point for prospecting for developers that do not have access to more
sophisticated tools.

Detailed Analysis of Wind Data from Neighboring Airports
and Other Met-Towers
The WAsP methodology provides a more sophisticated level of
prospecting analysis with a model for translating wind speed data
from onelocationtoanother. Italsotakesas inputelevationandrough-
ness to estimate shear. Applications like WindPRO, WindFarmer, or