Environmental Engineering Reference
In-Depth Information
Stand-Alone Turbines for Remote Homesteads and
Telecommunication Sites
The initial capital cost of a wind power system has been a major deterrent to homeown-
ers but less of a concern to operators of remote telecommunications installations where reli-
able power is a necessity. Commercial wind turbines have been developed specifically for
these remote applications since the late 970s and have performed satisfactorily in harsh
environments. Because of the need for storing excess energy to compensate for extended
periods of low winds, nearly all stand-alone wind systems are designed to charge batteries.
However, few turbines available today generate DC directly. Most drive alternators and
rectify the AC output to DC.
In the developing world the market for small-scale turbines used in remote applications
has been primarily for telecommunications, both commercial and military. Manufacturers
who design products for the remote market have modified their turbines in response to cus-
tomer needs, particularly their need for high reliability with minimal maintenance. In devel-
oping world communities, demand continues to grow for small wind systems of modest out-
put that are used to power essential appliances, like refrigeration units in medical facilities.
Operational Issues on Small Grids and Isolated Applications
Because the generation of electricity from the wind varies with wind speed, other energy
sources or storage are needed in applications requiring continuous electric power. Currently,
wind turbines are designed to operate with some other generator setting the line voltage and
frequency. In most small or isolated grids, wind generation is used as a fuel saver, reducing
the need for diesel fuel, water impounded behind a dam, or some other controllable but in-
termittent source. Weather changes affect wind speed seasonally, hour-to-hour, and minute-
to-minute, but these fluctuations are easily compensated by output from other sources. Wind
power can be considered as backup for a hydroelectric plant during droughts and vice versa,
as backup for diesels during fuel shortages.
Blending the outputs from wind, hydropower, and fuel cells will be an increasingly at-
tractive and synergistic option in the future. In arctic regions the windiest season is typically
in winter months when hydro resources are sequestered in ice and snow. Spring and summer
melting and runoff are often the low wind periods. This inherent seasonal energy synergism
could be enhanced with storage systems, either in diesel fuel today or in fuel cells in the fu-
ture. The cost of fuel cells is declining and this quiet, clean energy source could be used to
make hydrogen from excess wind or water power that could be stored for later use.
Penetration
There are a variety of operational issues involved in integrating wind turbines with other
energy sources. One of these is
penetration
, a term which refers to the ratio of wind power
to the utility's total power at any instant of time. If the amount of wind-generated power is
small in relation to the total capacity of the utility, no
power curtailment
controls on the wind
turbines (
i.e.
, methods for reducing maximum power) are needed. Recent wind power station
experience indicates that wind turbines can contribute 50 percent or more of the grid power
without upsetting power quality. Wind penetration in some areas of the Hawaiian Islands is
already reaching this level during the night, when demand for electricity is low. When wind
power generation is a large fraction of the load, the control system of the turbines must play
an active part in regulating power characteristics. This control can be achieved by reducing
power, dumping energy, or storing excess energy.
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