Presentation by Professor John Merrill of the University of Rhode Island for the Renewable Energy Siting Partnership.

1. Meteorological Observations for Energy Siting
John Merrill,
URI GSO
November 3, 2011

2. In the wind resource assessment portion of the project we are
funded to acquire and use instrumented towers and acoustic wind
profilers to gather data on winds. Data above the surface are
scarce, as a general rule. We will also prepare an archive of
observations, both at and above the surface, and make them
available in user-friendly form through the Web interface discussed
earlier.
Towers are usually utilized to acquire longer-term records, while
acoustic profilers are often used for brief deployments at multiple
sites.

3. Instrumented Towers - characteristics and sites
Two instrumented towers are to be installed in this project. A site
has been identified adjacent to the Bay Campus of URI. Our
intention is to continue operation of this site into the indefinite
future; it will serve as a baseline and point of comparison. A
vertically-resolved wind and stability record extending over multiple
years will be valuable.
The second tower site is to be in Westerly, adjacent to the Town
Transfer Station (near the capped landfill site). We are working
with the WCRPC on this site.
The pictures that follow are from a site in Tiverton, where
equipment similar to what we have in mind is currently in use.

4. • Modern towers are
actually masts. 60 m is
just below the FAA limit.
• Anemometers, vanes and
T/RH instruments are
used at 40, 50, 60 m.
• Wind and stability profiles
fit through the data can
be extrapolated with
adequate accuracy.
• Paired booms allow
anemometers to be
upwind of the tower no
matter the direction.

5. The two towers we will deploy supplement towers already in
place. An instrumented tower is in use at a site in Ninigret Park, in
Charlestown. Another is in use at a town-owned site in Tiverton.
In each case, vertically-resolved wind data are available, at heights
up to 50 or 60 m.
Together, data from these four towers will provide a transect
across the state of Rhode Island, in the area near the coast where
prior work suggests the available wind resource may be interesting.
There will be an overlap of the period of these observations. It
would be desirable to extend the time frame of the observations so
that a year or more of observations would be available at the four
sites, but it is not clear that this is feasible.

6. • Acoustic profilers sample
wind, volume-averaged,
from 40 - 200 meters in
20 m increments.
• They are much easier to
deploy, requiring only
limited cleared area and
having few impacts.
• Their easy deployment
will be enhanced by
placing the instrument on
a utility trailer.
• Our intention is to
continue using sodars
after this project ends.

7. Questions are often asked about comparison of sodar-observed
winds and winds measured on towers. The agreement is excellent
as long as you take into account the fact that these instruments
measure different things. Anemometers and vanes yield estimates
of the wind, speed and direction, at a particular height. Sodars, in
contrast, estimate the wind, speed and direction, in a volume
about as high as the vertical resolution of the data.
The greater height to which sodar data extend must be balanced
against the fact that the fraction of time over which acceptable
wind estimates are available decreases with height. Turbulence
characteristics also sensed by acoustic profilers are not as useful in
vertical extrapolation as are static stability data.

8. Our project will utilize two sodars. In their initial use they will be
deployed near instrumented towers. The aim is to “anchor” the
sodar profiles to the in situ anemometer data, and to extend the
range of available wind estimates above the top of the towers. The
colocated observations will be carried out for between a few weeks
and three months.
Later, the sodars will be moved to a series of sites, at which
profiles will be observed for a period of months at each location.

9. • These curves illustrate the
distribution of wind vs.
height.
• The marked asymmetry
nearer the surface gives
way to a more nearly
normal curve.
• Despite reduced data
return, the wind estimates
above 120 m are
statistically sound.

10. • The mean and variability of winds vs. time can be shown in a
box and whisker plot.
• Here near-surface winds at the state airport are shown in this
form.

11. • Especially when looking at winds above the surface, the
distribution is more informative.
• The preference is for time-resolved data; hourly averages are
preferred over even daily averages.

12. ⇒ finis ⇐