Page 136 - Fluid Power Engineering

W ind Resource Assessment 113

The output of the WRA is input to the financial analysis step, in
which the financial viability of the project is assessed.

Source of Wind Data
There are three primary sources of wind data: Onsite measurement,
network of weather stations, and numerical weather models. Onsite
measurement is described in detail in Chapter 6. It forms the core
input to the resource estimation and subsequent micrositing of wind
projects.
Thesecondsourceisthenetworkofweatherstationsallaroundthe
world that provide wind speed and direction data. Various organiza-
tions collect and provide this data. Among them is the USA’s National
Climatic Data Center (NCDC) of National Oceanic and Atmospheric
Administration (NOAA). It provides standardized quality-controlled
wind speed data at a height of 10 m for almost all airports worldwide.
The data is available from http://www.ncdc.noaa.gov/oa/mpp/,
item DS3505. The dataset covers about 10,000 locations. For most US
and European airports, hourly wind speed data is available for a fee.
An annual subscription service is also available from NCDC that pro-
vides monthly downloadable wind speed data for about 1,000 US
airports. Although this is valuable data, there are several significant
issues with this dataset:

Wind speed data is available at only one height, 10 m above

the ground. Dataset includes, hourly average wind speed and
wind direction; it does not contain standard deviation.
The age, quality, height, precise location, and surrounding en-

vironment of the wind measurement instruments at each air-
port location are not known with certainty. Without this meta-
data pertaining to the instruments, the quality of raw data and
the roughness surrounding the instruments cannot be deter-
mined. Common problems include height of anemometer is
low; anemometer mast is surrounded by obstacles like build-
ings, trees, radar, and others; and roughness and contour are
different at the airport compared to site of interest. Therefore,
the uncertainty of calculations based on this dataset is high.

The third source of wind data is the long-term reanalysis data. Ac-
1
cording to Kalnay, et al., “The National Centers for Environmental
Prediction (NCEP) and National Center for Atmospheric Research
(NCAR) have cooperated in a project (denoted “reanalysis”) to pro-
duce a retroactive record of more than 50 years of global analyses of
atmospheric fields in support of the needs of the research and climate-
monitoringcommunities.Thiseffortinvolvedtherecoveryoflandsur-
face, ship, rawinsonde, pibal, aircraft, satellite, and other data. These