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THE 1982 WIND/DIESEL SCHEME
The Fair Isle community went "live" with
the world's first commercial wind/diesel electricity generating system, with
wind as the dominant generator, in June 1982. (1) This scheme consisted of a
50kW stall regulated, fixed pitch wind turbine of 14.6m diameter, equipped
with a brushless three-phase alternator and having a load control system
with a "Dump Load" resistance bank, to govern the turbine's speed. This was
arranged to operate in conjunction with the existing diesels. The control
centre was equipped with load sensors to compare the service demand with the
output of the wind turbine, in order that the wind turbine could be switched
to the network when able to meet the load, and the diesel would then be shut
down. When the diesel was not running, the turbine output was compared to an
adjustable pre-set reference signal and could provide a service outside
"guaranteed service hours".
In discussion with the island community at
the beginning of this project, it was suggested that the dump load was
wasting energy that could be used beneficially for heating, and a
distributed form of load control was devised. The original cables providing
diesel service distribution were not adequate to carry the additional
heating load and, instead of replacing them, new cables were run just to
cant' the heating load. This dual distribution network made it possible to
distribute wind energy to heating, even when it was not able to meet service
demand. This also meant that heat could be distributed during times when the
diesel was providing the service demand.
The block schematic of this scheme is
shown in Fig. 1. The diesel in use is selected manually, according to season
or availability. The run time of the selected diesel is controlled by a
time clock, except when the turbine is already providing both service and
heating power. The logic of the block schematic is simple, when it is
understood that the contactors D, E & F are interlocked so that no more than
two may be energised at any one
time. It follows that the wind turbine was never asked to operate in
parallel with the selected diesel generator. In winter, when there was no
wind, it was possible for the 50kW
diesel to provide service and some heating load by adjusting the governor
upwards slightly. This allowed the larger' diesel to operate at a higher
load factor and yield a higher fuel efficiency.
During the 'planning of the project the
extensive records held by the island's resident meteorologist were examined,
and the data for many years applied to the predicted power performance curve
for the proposed wind turbine. This analysis is set out in Table 1., and
produced an anticipated energy capture of 195,490 kWh per annum. This was
nearly four times greater than the existing island use.
At the request of the island community,
provision was made to feed selected loads directly, and only, from the wind
turbine, shown as "reserve". The concern was that the domestic heating load
would be insufficient to absorb the wind energy generated in excess of the
service demand. The utilisation was, in fact, very high and the reserve load
facility was never used. |
