Residential Grid Tied Wind Turbine

IamSmooth, Sat Jun 20 2009, 07:34PM

I have not had an electric bill for two years due to the solar array I installed on my roof. I wanted to do more, so I figured a wind turbine would be a nice addition. However, I wanted to do it myself, and not purchase a pre-made system.

I initially started with a F&P system by re-enginneering the Fisher & Paykel washing motor with neo magnets. My tail boom was too thin, and it snapped in some high winds and it destroyed my first turbine blades and assembly. I followed through with an axial flux design.

The axial flux design has the magnetics on two spinning rotors. The flux is contained between each magnet pair and the iron disk that supports them. The stator is a three phase disc that rests between them.

I did everything myself, except build the inverter. I got some help on this board for building the shunt controller, and I am very thankful for it, especially for the time Neil gave me.

I kept a very detailed photo log on a website and the project can be viewed from start to finish here. Here you will find an index that can take you to various sections. I start with my Fisher&Paykel system. After its destruction, I continue with the axial system. The project consists of many parts and disciplines. They are:

Mechanical/construction: tower analysis & construction, winch design
Welding skills
Woodworking, Blade carving/shaping/balancing, airfoil analysis
Metalworking and lathe working
Electrical engineering: stator/rotor design to match power from blades
Electrical engineering: shunt controller design
Electrical engineering: working with MAINS, interfacing with GRID and Solar inverters
Electrical engineering: lightning protection

Basically, the project consists of building a tower that is easy to raise and lower; building the generator; carving the blades to match the generator; running the power to the grid with the appropriate disconnects and power diversion features. Most people charge batteries with wind energy. This requires a compromise in power output. This is because wind energy goes up with the cube of speed. Low winds have little energy and high winds have enormous energy. One has to determine if they want to harness more consistent lower energy winds, or capture infrequent high energy winds. This is because the stator and blades need to be matched. A stator that can handle high power levels in high winds will stall out the blades in lower winds. If the blades are too large for the stator they will run away in high winds and fry the stator, or cause the turbine to self destruct from high RPM. I chose to feed power to the grid, allowing the inverter to draw off the appropriate amount of power at various wind speeds.

I have the inverter programmed to expect 15% efficiency from the system. Losses are due to limits on wind-power extraction (theoretical maximum is 59%), friction, stator heating, power transmission, and inverter power conversion. I will experiment with various efficiency numbers and see how much power I can squeeze out of the turbine. I am hoping to get 1.5-2kw from 30mph winds. After this the turbine will start to furl out of the wind.

Below are some pictures of the project, but you can see the whole thing at here. The last page of the project is here


This is a 42' tower made from 3"ID steel pipe. The rotor is 10.5' in diameter. The whole assembly weighs close to 100 lbs. Three levels of guy wires hold the tower in place.




This is a close-up of the rotor and assembly. The blades were made from laminated pine that I carved with a chainsaw. After shaping they were coated with epoxy paint and spayed with acrylic clear coat enamel. The tail furls in high winds.




Here is a close-up of the steel assembly. I did all the welds myself. I did 95% of the cuts. The rotor discs and stator bracket were water-cut.




The anchors need to withstand a lot of force. They are buried almost 4'. High strength concrete is poured over 12" brake rotors. The rods are 5/8" galvanized steel.




Here is the winch assembly. The pad is 4' deep with rebar and 12" J-bolts for attaching the winch. The winch is rated for 2500 pounds. The 1/4" cable can hold 1400lbs. I also have a lateral support line wrapped around a tree. This is a safety line that takes most of the lateral shearing force. The 4 bolts holding the winch down are enough, though, even without this extra line.




After calculating the profile, I made a jig so I could use a chainsaw to carve the blades. Once the jig is made, I can bang out blade after blade, saving a lot of time carving.





The blades can rotate over 500 RPM so they need to be perfectly balanced.





The coils need to be wound tightly with exactly the same turns for the three phase stator.




The stator is 3 phase. Each phase has three coils of 110 turns #16 wire. It is cast in fiberglass resin filled with marble dust to help dissipate the heat. ATH was another option, which theoretically would be better, but I don't know if it will make a huge difference. The center of the coils is open to help disperse the heat.




Stator is cast in fiberglass resin, mixed with chopped glass and marble dust.



Magnetic rotor made from 1/4" steel discs and 42N 2"x1/2" neodymium magnets. Each magnet can pull 110 pounds. There are 24 of them.




The shunt controller will divert power to a dump load. This is important to protect the inverter if the grid (load) goes offline, or if the voltage becomes too high for the inverter.





This is part of the MAINS interface. There is an electronic brake that shorts the phases. This keeps the turbine from moving. There is a wind disconnect, inverter/filter box, and shunt controller. Not shown is the DC disconnect, inverter and AC disconnect subpanel.




The power curve for the turbine is programmed into the inverter. This allows maximum power extraction from the wind without stalling the blades by drawing too much power at a given wind speed. When the blades stall the wind no long flows laminarly over the blades. It pulls away and the lift is lost.





Programming setup is shown.