Wind Energy Resource Atlas of the Philippines - NREL

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Wind Energy Resource
Atlas of the Philippines
such as Maasin on Leyte Island, have no more than 2,000 observations in any year and sometimes
less than 500 observations.
The data records for each of these stations were processed to produce monthly and annual
averages of wind speed and power. The summarized data are presented in Table 5-4, and copies
of the processed files are presented in Appendix B for selected stations. These data are useful for
evaluating the inter-annual, monthly, and diurnal variability of wind speed and power, and the
joint frequency of wind speed and wind direction.
Visual inspection of the plots of the various wind characteristics data for each station sometimes
revealed trends and peculiarities, particularly in the inter-annual variability. For example, the
long-term average wind speed and power density at Cuyo Island from 1973 to 1996 was 3.5 m/s
and 123 W/m 2 , respectively. However, an inspection of the yearly wind speeds and power
densities from 1973 to 1996 reveals that the average wind speeds were about 5 m/s in the 1970s
and had decreased to about 2 m/s by the mid-1990s. The wind power was in the range of 200 to
300 W/m 2 in the 1970s and decreased to less than 20 W/m 2 by the mid-1990s. A long-term
downward trend in wind speed and power at a station frequently indicates that either the site is
becoming less exposed to the prevailing wind because of an increase in obstructions around the
site or there is a degradation of the anemometer. Similar types of trends and peculiarities were
found at many other stations in the Philippines.
Although the average wind speeds and power densities are presented in Table 5-4 for each
station, these data may not be a reliable indicator of the area’s wind resource because of problems
with the data. Unfortunately, information on exposure of the wind measurement equipment and
maintenance of the equipment is not available for meteorological stations in the Philippines, (nor
most countries of the world, for that matter). With the various inherent problems in the reliability
of the surface data from meteorological stations, using the appropriate upper-air data and ocean
satellite data to characterize the ambient wind-flow characteristics and to develop the
meteorological inputs for the wind mapping system becomes even more important. Nevertheless,
screening the available surface data helps identify the most reliable data for evaluating the wind
characteristics and helps validate the resource estimates generated by the mapping system.
5.3 Upper-Air Data
The upper-air data, consisting of wind speed and direction profiles, are an important component
in the development of the wind resource projections. These data are available in either the ADP
database or the Global Upper Air Climatic Atlas (GUACA).
The upper-air database consists of information obtained from surface-launched meteorological
instrument packages. These packages are usually launched once or twice daily, at 0000 GMT and
1200 GMT, via balloon, and are managed under WMO guidance and procedures. There are 11
locations in the Philippine archipelago where upper-air wind data are available from the ADP
Database: Basco, Laoag, Baguio, Crow Valley, Clark AFB, Olongapo, Legaspi, Cebu, Puerto
Princesa, Davao, and Zamboanga. These locations are shown in Figure 5-8.
The GUACA data consist of monthly means and standard deviations of upper-air parameters for
the mandatory pressure levels on a 2.5-degree global grid. The mandatory levels of interest
include surface, 850 millibar (mb), 700 mb, and 500 mb.