Wind Turbines - Wind Energy: Renewable Energy and the Environment - page 94

or a submersible pump, which is run at variable rpm. The advantages of such a system are higher
efficiency and higher volumes of water, enough for village water supply and low-volume irrigation.
Such systems are now commercially available.
5.10.2 M ECHANICAL E NERGY
The major use for windmills has been the pumping of water. The farm windmill is well designed to
pump small volumes of water at low wind speeds. Since the farm windmill has a large number of
blades (vanes), it will start under a load because it has a large torque. However, the large number of
blades means it takes a lot of material, and the unit is inefficient at high wind speeds. Power ratings
are around 0.5 kW for a 5 m diameter rotor.
The Brace Research Institute combined a modern three-bladed wind turbine, a transmission
from a truck, and a conventional centrifugal pump on a prototype project to pump irrigation water
on the Island of Barbados [17, 18]. The rotor was not self-starting, and the blades of fiberglass were
expensive. A person had to manually shift the transmission to match the load of the pump to the
output of the wind turbine at different wind speeds.
In 1976, AEI and USDA studied the feasibility of using wind turbines for pumping irrigation
water with positive displacement pumps and airlift pumps. There are problems in matching the
power output of the wind turbine with the power needed by the irrigation pump. Calculated maxi-
mum efficiencies were very low, on the order of 10%, for both types of pumps.
The airlift pump has the advantages of no moving parts in the well, and the wind turbine
does not have to be located at the well. Airlift pumps were in use at the turn of the century for
pumping water from mines, but were replaced by other types. Two companies in the United
States have manufactured a wind-powered airlift pump to compete with the farm windmill;
however, only Airlift Technologies has units for sale today. For maximum efficiency, the sub-
mergence, depth of pump below the water level, should be equal to the lift. Wells with little
water at large depths present a problem for airlift pumps. Also, there is the problem of load
matching between the wind turbine and the air compressor, a constant torque device, and the
inherent inefficiencies.
A wind turbine can be connected mechanically to another power source, a wind-assist system
for pumping water. The other power source could be an electrical motor or an internal combustion
engine. Both systems have been tested.
5.10.3 T HERMAL E NERGY
Thermal energy can be obtained directly by churning water or some fluid with viscosity. The load
matching between the wind turbine and the churn is very good. A prototype system for providing
heat to a dairy was tested by a research group at Cornell University [19-21]. Conversion of electri-
cal energy to thermal energy by resistance heating has been tested a few times [22]. At one time, a
company marketed such a wind system.
5.10.4 W IND H YBRID S YSTEMS
A large market exists for wind-assist to diesel-generated electricity for isolated communities, busi-
nesses, farms, and ranches [23]. There are around 2 billion people without electricity, and hybrid
systems consisting of wind, photovoltaic, hydro or diesel, battery storage, and an inverter are
now part of the planning process to provide alternating current (AC) electricity for villages with
an energy use of 20 to 200 kWh/day [24, 25]. Hybrid systems have also been installed in very
remote locations, such as remote military locations and telecommunication systems. For telecom-
munications the emphasis is on continuous power, so redundancy is important to achieve the high
reliability.