|
Wind Energy
The wind is a by-product of uneven
heating of the Earth's atmosphere by the sun, and has a very complex distribution pattern. Though widely spread, winds are
most prevalent along coasts, at higher elevations and at higher latitudes.
Siting
The power in the wind is
proportional to the cube of its speed; twice the wind speed gives eight times the power.
Small differences in average windspeed cause large differences in available wind energy.
So, for optimum performance, it is important to find a site which offers the highest
overall windspeeds.
Avoid locations with
excessive gustiness or turbulence, since they will reduce the output from a wind turbine
and lead to undue wear and strain on component parts.
Siting should take account of
exposure to the prevailing winds. Factors such as surface roughness and obstructions are
important, eg. woodland or built up areas will create higher turbulence than open
grassland. Cliff tops are to be avoided and wind generators must be sited clear of
obstructions to the wind.
A useful rule is to place the
turbine at a distance from any obstacle (building etc) of at least ten times the height of
the obstacle; or on a tower that is at least twice that height.
 Wind speed can increase
dramatically with height, especially over rough surfaces, such as in wooded or hilly
areas. This means a significant increase in power production can often be obtained for a
given cost by using a smaller wind generator on a taller tower rather than simply using a
larger machine.
The ideal site for a wind
turbine is a smooth hill top, with a flat, clear fetch at least in the prevailing wind
direction.
Near the top of the hill the wind
speeds up significantly and the flow should be reasonably smooth. In practice, especially for small
machines, there is a compromise between choosing the best wind site and other
considerations.
Cabling
A voltage drop occurs along
wires - in low voltage battery based systems this can be significant, so output
cables must be sized appropriately to avoid undue power losses.
Normally underground armoured cable
is used and since heavy cable can be expensive this can be a factor in the siting of a
wind turbine. However, if higher windspeeds are
obtained by siting further away, the resultant increase in power production can compensate
for these power losses.
For grid connection of a larger
machine, proximity to 11kV power lines is normally required. Conversely this means that
good wind sites with existing high voltage supplies can have the potential for the
commercial exploitation of wind power.
up to the top |
