/* Written 5:18 am Sep 7, 1993 by tgray@igc.apc.org in igc:en.energy */
UCS REVIEWS PROGRESS
OF SMALL TURBINES
The Union of Concerned Scientists (UCS), a leading
environmental organization, recently published a major study,
Powering the Midwest: Renewable Electricity for the Economy and the
Environment, which concluded that wind energy is among renewable
energy technologies holding great promise for the region. This is
one of a series of articles reprinting excerpts from the report, by
permission of UCS.
DISTRIBUTED GENERATION: SMALL WIND TURBINES
Current Technology and Markets
Many of the same developments that have made intermediate-size
wind turbines a viable option for central generation have affected
the small wind turbine industry as well. Materials and designs
have improved, and manufacturers and operators have gained valuable
experience with the machines under a variety of conditions.
The improvements have grown out of lessons learned through
thousands of operating hours on older machines and improvements in
aerodynamics, mechanics, and electronics. Improvements in
structural and dynamic braking systems have made the machines more
rugged under extreme weather conditions, and improved blade and
generator subsystems have increased reliability and efficiency.
Advances in control-system logic and electronics have improved
energy production and refined start-up and shut-down performance.
Thanks to these improvements--and despite the near-death of
the small-wind industry in the mid-1980s with the decline of fossil
fuel prices and the elimination of renewable energy tax credits--
the machines have found a small but growing niche in global energy
markets serving electricity needs at isolated villages and farms.
Wind turbine suppliers offer machines generating direct
current (DC) power rated at a few hundred watts for communications
facilities in remote areas and larger DC machines rated at a few
kilowatts, which serve the needs of farms, residences, remote
villages, and rural health centers.
In windy locations isolated from central utility service, a
wind turbine/battery combination is often the most economical
choice among options that include gas or diesel fuel powered
generators. Some vendors offer specialized machines for
integration with electric water-pumping systems. Wind turbines
generating grid-compatible alternating current (AC) power and rates
from a few kilowatts to 50 kW or 60 kW supplement the energy
supplied by electric utilities to rural customers.
Small wind turbines could be used on a much wider scale,
however, if utilities recognized their value for reducing
transmission and distribution loads in rural areas. The
determining factors in such an evaluation are the quality of local
wind resources, the cost and performance of the wind turbines, and
the match of their output with local utility loads . . .
Like intermediate-sized wind turbines, the small machines will
perform better in stronger winds, but with some important
qualifications. For one thing, they are usually mounted on shorter
towers, 20 meters to 30 meters in height, as opposed to the 30
meters to 45 meters expected of larger machines. Since wind speed
increases and wind turbulence decreases with height above the
ground, small wind turbines are likely to capture less energy per
unit of rotor area at a given site than a larger machine. Shorter
towers also make small machines more susceptible to wind flow
obstructions on the ground.
Despite the progress of the last several years, there is
considerable room for technological improvements in small wind
turbines. In particular, they will benefit from improvements and
cost reductions in the power electronics used in system controls,
power conditioners, and inverters.
The systems will also become more sophisticated, offering, for
example, load management features under the control of the customer
or utility. Load management of this type would coordinate the
energy production from the wind system with off-peak battery
storage or controllable loads like electric water heaters or air
conditioners to reduce customer demands during utility peak
periods. Such capabilities will enhance the value of small wind
turbines in a distributed utility setting.
Substantial cost reductions for small wind turbines are
inevitable if the industry grows enough to support advanced
manufacturing techniques and large production runs. At present,
most small wind system manufacturers are relatively small
businesses assembling systems in small production runs. Sustained
increases in demand for such systems would allow manufacturers to
expand and further automate production, and purchase and assemble
subsystems and components in larger, more economical lots.
[Copies of Powering the Midwest are available for $15 members, $20
non-members from AWEA. For more information or to order by
VISA/Master Card, please call (202) 408-8988; FAX (202) 408-8536.]
===============================
The American Wind Energy Association (AWEA) has authorized me to offer
an electronic edition of its newsletter, _Wind Energy Weekly_, from
which the above article is excerpted, at no cost.
For those of you who have not previously seen excerpts from back issues
on Usenet or Bitnet, the _Weekly_ reports on the outlook for renewable
energy, energy-related environmental issues, and renewable energy
legislation in addition to wind industry trade news. The electronic
edition normally runs about 10kb in length.
If you would like a free electronic subscription, send me an e-mail
request. Please include information on your position, organization,
and reason for interest in the publication.
If the _Weekly_ is not quite for you, please pass this message on to
someone else you think might be interested. Thanks.
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Tom Gray EcoNet/PeaceNet: tgray@igc
Internet/Bitnet: tgray@igc.apc.org UUCP: uunet!cdp!tgray