Wind turbine furling
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Wind Turbine Furling
You worked hard building your DIY wind turbine and now you look forward to days when the wind blows hard. The power output increases as a CUBE of the increase in wind velocity - a 3 fold increase in wind speed means a 9 fold increase in power output.
Problem is, your DIY wind turbine won't survive very many of those "extreme" wind days. You need a way to protect your wind turbine from high wind damage, while allowing it to still produce power at the top end of it's output curve. You need to FURL your wind turbine in high winds.
Furling is one method of preventing a wind turbine from spinning too quickly, simply by turning the blades away from the direction of the wind, either horizontally or vertically.
Wind Turbine Furling Methods
Large wind turbines use very accurate, but complex systems to turn the blades away from the direction of the wind. We will look at a couple of passive systems used on DIY sized wind turbines. The simplest way of furling a wind turbine is a passive system in which the turbine is yawed sideways away from the wind as maximum power is reached. You can also move the
I'm not a fan of spring loaded hinges. We'll cover some methods of furling which use spring loaded hinges and you can decide for yourself which system would work best for you.
On the wind turbine to the right, a spring loaded hinge is placed below the alternator in the pole, with a weight out the front. The spring and weight keep the blades sitting upright, in lower speed wind. If the wind gets strong enough, the top is forced back against the weight and hinge, pulling the blades up out of the wind and slowing them down.
To set the spring strength, in no wind, tip the blade back by hand as far as it can go and ensure it returns to the upright position when you let go. Setting the correct weight is harder. You need several trial and error sessions, adding and subtracting weight until you find the spot where it tips at the correct wind speed. As I already mentioned, I'm not a fan of spring loaded hinges. In a strong wind, there could be considerable sideways stress on this hinge. Yet, you can find this type of furling, on small commercial wind turbines.
In the picture to the right, a spring loaded hinge is added to the point where the wind turbine alternator meets the mast. The alternator is mounted slightly to one side of the tower. When the wind is very strong, it will blow over the turbine pushing it sideways, out of the wind. By adjusting the strength of the spring, you can fine tune the exact furling wind speed your require. This requires several "trial & error" applications before you'll find the perfect wind speed.
This video shows furling in rough wind:
This one is a little harder to understand but works in the same way. The blades are centered a bit off the center of the tower (say 5cm) where the whole system pivots. Since they are off center, when the wind pushes on the blades, the turbine naturally wants to swing to the side. In order to balance that out we place the tail on the other side of the tower, keeping the blades facing the wind.
This video shows the blades & tail, offset from the tower:
Note: Quite a few very small wind turbines use the generator or alternator as a brake. You can place a load on them (eg. turn on a heater) to make them do more work or simply short the two power leads together via a switch. This usually does a good job of slowing down your blades. However, if your alternator is too small or the wind gusts are too strong, this can just burn out your alternator leaving nothing to slow it down and you needing to buy a new alternator. I prefer a passive furling system.
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