Technology

Small Wind Technology

Small Wind Turbine and Controller Update (November 2009)

WIND ARROW is undergoing some new improvement that will be available in January. The latest version of the AFC controller board now has all of the improvements from the original model now built into the board instead of having a few discrete components added on during assembly. In addition there is provision for doubling the power with a second power output section so when we introduce the 2kW the same controller can be used for both.

The Yaw component has had it's tolerances tightened up a bit and it will have a new brush-holder that is more tolerant of moisture or condensation inside the lower section. We've seen cases of humidity build up under some climate conditions that reduce the efficiency of the brushes so this can now be eliminated. In addition the upper housing end caps have been redesign to use 8 larger external bolts rather than 8 thinner internal ones. Also, the lower housing end caps mount with an "o-ring" seal rather than silicone. This better sealing of the lower compartment so it can be easily inspected in the field without having to re-seal with silicone. . . The RED handles on the left image are just a quick release mechanism for testing.

Small Wind Turbine and Controller Update (December 2008 - August 2009)

There is always some new machine on the market offering a different small wind turbine that bolts to your roof or "starts in 3mph wind" or "Can run your whole house" and they all suffer from too much hype and not enough REALITY. Horizontal axis 3 blade turbines offer the most efficient solution for personal power. Even though vertical systems work fine they are inherently less efficient for the same cross-section because generally the air passes through or by the rotor twice and the second time as it exits the rotor is turbulent and so has little to no energy to transfer . . and is likely just adding resistance.For those claims of even 15-20% of an average home from a 6ft cross-section it would have to violate the laws of physics . . and suggesting that there is some value in collecting energy at 3mph is simply misguided since even if the machine could be 100% efficient there is less than 1WATT!! or energy per square meter to collect in 3 mph wind . . . it is simply wrong to suggest anything else from a machine with 2.6 sqm cross-section even at 100% efficiency. realistically at 10mph you could only expect it to extract 50-60 watts from such a cross-section.Blade technology is pretty simple and while an efficient airfoil shape is important for efficiency and low noise the real advances in blades today are in how they are built.

If they are very stiff and cannot flex then they will likely be quiet but if they are heavy the lift they collect from gust spreads is limited. Instead, the newest advances in small wind turbine will be in the area of control. The fewer the parts the better. The less they contact each other the less they can wear, so look for a turbine with the fewest mechanical mechanisms and this one should last the longest. Solar panels are kind of like that. . . no moving parts. As soon as someone figures out how to extract energy from the wind without moving parts we'll have a REAL breakthrough.Meanwhile, True North Power has been focusing on both blades and controller of its new 1kW turbine called the WIND ARROW. It uses a new PWM technology called the Active Flight Controller (AFC) because what it does is actively "fly" the turbine under normal wind conditions and then unlike other small turbines it continues to produce continuous power well above 30mph without any mechanical furling system. Turbines with mechanical furling systems suffer from excess weight and stress failures but more importantly the energy they produce above the furling speed is far less than their "power curve" would suggest because as soon as it hits a high gust it only produced its power for a brief moment before it furls and drops power to near ZERO.The advanced carbon fiber blades of the WIND ARROW weigh barely 450 grams each and can react instantly to gusts by transferring more energy than heavy high inertia blades and the AFC can extract this energy like no other known controller. Software changes and variable pitch settings for the blades allow many variations in power management. An electronic and automatic storm shutdown feature means you can leave it unattended for months at a time and not worry about overworking it.

Inside the AFC Controller

Many people are asking about the AFC controller and how it works. So, without getting too technical here's what happens. The AFC uses pulse width modulation (PWM) like other wind and solar controllers but the difference is that the AFC controls the Pulses with a very fast microprocessor using a logic strategy that can take advantage of every wind condition. It constantly monitors the power being produced by the turbine and decides when and how much power to extract to actively "fly" the turbine under control. It knows how much power is available from the blades at various wind speeds and rpm based on its knowledge of the optimum power profile from the alternator. It behaves kind of like MPPT control of solar panels ... (but not really . . since wind power production is far more dynamic than solar PV). It then takes just enough to slow the rotation but not too much that it stops the blades from "flying". For every blade size and cross-section there is only so much energy in the wind at any speed and so as the wind speed and power available increases, the controller gets more and more aggressive in stopping or holding back the blades and taking more power. Up to about 30mph it can reach about 1000-1200 Watts and at that point it will drop the rpm significantly . . kind of like shifting gears with software . . .to prevent the alternator from being overpowered by a stronger gust.

You may see the blades practically come to a halt for a second while AFC analyzes the current power conditions and it may then release the turbine to produce again if the wind's energy is not too high. It is designed to oscillate in and out of production this way quite safely during the transient 28-32mph area. What is very different from virtually all other small turbines is that, if the wind stays steady above 30mph it will still release the turbine to fly in a reduced power mode and continue to produce power at a lower, more controllable rpm. This mode is called "Soft-Stall Power Mode", and can produce up to 250-600W or more even in winds up to 60+mph. If you do not need the power or wish to save the turbine excess wear and tear then you can simply switch it off manually at any time . . even in winds above 60mph it will shut down easily and safely .. . and will not start again until you switch it back to "FLY" . . which you can do even if the winds exceed 60+mph. Not sure why you'd want to do that unless you were freezing in Antarctica and need some heat maybe but that's as far as we've tested yet. You can safely then turn it back on in 30-50+mph winds and it will go immediately into its "Soft-Stall Power" mode at about 1/3 to 1/2 of normal full power. AFC is a true breakthrough in small wind technology because the turbine no longer needs a mechanical furling system to remain under control yet still producing usable power in high winds.

Many other power profiles are possible with the the WIND ARROW because the pitch of the blades is adjustable in the hub. By increasing or decreasing pitch the AFC can be made to fly a more appropriate power curve for the local wind conditions from very low wind sites to extreme arctic or high altitude locations.

Solar Technology
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