Windy Jenny
Our wind generator is a new addition to our off-grid power system. Long ago I did the calculations and showed that it is not really economically sensible to invest in a wind generator. Yet now we have one.
Why Wind in West Wyalong?
Given that the average wind speed in West Wyalong is around 12m/s putting up a wind generator may see a little pointless. However there are a couple of other factors.
- My Wife and I like to watch and listen to the wind generators
- They make some power at night and in overcast days that may mean less noise from fossil fuel generators
The results
As I have made clear, you will never make a large impact on your power generation with a wind generator in West Wyalong, however this winter we have used it about a dozen times where it stopped us from having the petrol generator going. Most days it does nothing, but some windy, rainy overcast days it puts in about 300W with some days averaging higher or lower than others. So far my peak is 1250W. Not too bad from a generator rated at 600W.
The Generator
The generator is a 5 blade chinese made unit that used to be sold by Jaycar electronics. It is a PMA alternator with slip rings and about 4.5m^2 of swept area. It uses a pivot tail furling system.
The Tower
I did a fair amount of research before designing, building and erecting my wind generator tower. Most reliable sites such as www.fieldlines.com gave advice to build a tower at least 20m in the air. It really depends upon the trees and other obstacles around you how high you go. Higher is always better, it is just a initial cost vs lifespan power calculation. One interesting fact was the ground shear effect. This means that for every doubling of height, the wind speed increases by about 10%. This means the power output increases by about 34% for each doubling of height.
I looked at a couple of designs, but found it a little hard to find a step by step enginering on wind towers. I decided on a 4 rope, guyed pole system. This will mean a single person can winch the tower up and down easily by themselves. Good for maintenance and realitively cheap to make. The calculations ended up being realitivly simple. The most strain will be with tower down in the horizontal usually. Use the weight of the generator and poles. It is suspended on both ends, one half the weight will be on the guy. Then use trigonometry to vectorise the forces accordign to the gin pole lenght. Check the forces for the rated wind velocity over the swept area to make sure the WLL of the guy wires aren't exceeded when it is in the air. I used a distance of about 1/3 the height of the tower for the distance to the guy wires.
The first night I had it up I was out of town and we had some 70km/hr winds and it was all good. We have since had some pretty gusty winds come through even providing peaks of 1250W and it is still standing strong.
The Controller
The controller is still a work in progress. Currently using the one that came with it. It simply shorts out the input once the outputs reach 30v. I have also attached a voltage doubler to the output from the generator. This does a nice job of increase the output in light breezes from nothing to around 50w. In the future my powerhouse controller will operate the shutdown of the generator based on current flowing, battery voltage and weather reports via the home automation system.
