Wind Resource - Wind Energy: Renewable Energy and the Environment - page 52

wind speeds are only for 1 year; however, it was considered representative of the 5-year period
1998-2002.
Wind Atlases of the World [4] shows another wind map for the world, which includes values
of mean wind speeds at 10 m height for the period 1976-1995. Again, the global westerlies in the
southern hemisphere are prominent.
A project for renewable energy resource assessment, REmapping the World, will provide infor-
mation for potential users, from individuals to governments. The interactive map provides global
wind data at heights of 20, 50, and 80 m, with a 15 km resolution for a single year. It estimates that
40% of the world's land mass has wind speeds of 6 m/s or more. The global wind map can be viewed
at firstlook.3tiergroup.com.
As more data have been collected specifically for wind power potential for nations, states, and
regions, digital wind maps are available with better resolution than the older maps, and the values
are more accurate, as data above 10 m have become available. However, the data collected by
private wind farm developers are not available to the public, so data at 20-50 m heights are still
being collected to provide regional data bases. Anemometer loan programs are available for private
individuals in some states in the United States, and after some period of time, the data generally
become public.
Computer tools for modeling the wind resource have been developed by a number of groups:
NWTC NREL, RISO in Denmark (WAsP), other government labs, and private industry. Information
from AWS True Wind about the Northwest Wind Mapping Project describes the process.
The advanced MesoMap™ mesoscale modeling system simulates complex meteorological
phenomena not adequately represented in standard wind flow models. It models sea breezes,
offshore winds, mountain/valley winds, low-level nighttime jets, temperature inversions,
surface roughness effects, flow separations in steep terrain, and channeling through moun-
tain passes. This model utilizes historical upper air and surface meteorological data, thereby
providing a consistent long-term, three-dimensional wind resource record. This record can
later be used as a substitute for long-term surface wind measurements in the correlate-mea-
sure-predict (CMP) method, which adjusts short-term site measurements to the long-term
climatological norm. The modeling results can help identify where limited wind measure-
ment resources should be applied. Based on prior model validations, the expected range of
discrepancy between measured and predicted winds in complex terrain is 3 to 7%.
Now remember what a 5% error in wind speed does to the error in wind power. Therefore, siting
for wind farms is still important, and on-site data are imperative for financing a project.
4.1 UNITED STATES
A number of wind power and wind energy maps have been prepared for the United States; how-
ever, the earlier maps did not take into account the height differences of the anemometers. As part
of the overall evaluation of wind energy, two major contracts were awarded to General Electric
and Lockheed in 1975. Their estimates of the wind energy potential for a height of 50 m indicated
that most of the United States has a fairly large potential. The problem is that most of these values
were estimated from data taken at a height of 6 to 10 m, with the value at 50 m being double that
at 10 m.
Pacific Northwest Laboratory oversaw a comprehensive assessment of the wind energy poten-
tial. The Wind Energy Resource Atlas covers the United States and its territories [5]. Wind power
potential by year and season were also estimated for each state and region. The wind power classes
(Table 4.1 ) were estimated for a grid of 20 min longitude by 15 min latitude (27 by 25 km, 16 by 15
miles). This atlas and the wind maps were updated in 1985 [6]. The different wind power maps are
similar in gross features. Regions of better wind power are in the Great Plains, along the coasts,
Hawaii, and selected sites, such as ridges, mesas, and mountain passes.