This one is now the most frequently asked of our frequently asked questions!

The answer is — yes you can. Details follow.

• With an Islanding grid-tie system, you would simply wind your turbine’s stator for your system voltage (battery bank voltage).
• (An islanding grid-tie system is one that uses batteries for back up.)
  
• After your grid-tie system is inspected, permitted, approved and turned on by the power company, you would wire your turbine into the battery bank just like you would do in an off-grid system.
• The system would not have a diversion load controller running heating elements, though. Instead, your grid tie inverter gets rid of extra power by selling it to the utility.
• UL listing is not generally a problem–there are no UL standards for wind turbines anyway. Only your grid-tie inverter and it’s associated disconnects, wiring, etc. would need to be UL listed.

• With a non-islanding grid-tie system, (also called “direct grid tie”) you will run into all kinds of hassles and expenses, plus a bit of risk (more below)…
• (In a non-islanding system, there are no batteries, but if there is a grid blackout, you then have no power for your house even if the wind is blowing. Ouch! That must be a frustrating experience!)
• There are two inverter products out there for direct grid-tie of wind turbines: The SMA WindyBoy and the PowerOne Aurora. Since the authors both live off-grid, we have not tested either of them.
• You would need to wind your wind turbine’s stator for higher-voltage output; this is easy to calculate and scales up directly from turbines for islanding systems, and the information is available from the inverter manufacturer’s websites. For example, the SMA inverter needs 150 volts DC coming in before it will even turn on.
• Here’s the problem—both the SMA and the PowerOne need to be custom programmed at the factory to match the power curve of your wind turbine. Not a problem with big wind turbine manufacturers, as all the turbines that come out of their factories are identical. A big problem with home builders, since every turbine will be different.
• These large inverter companies are not willing to provide this service for each individual home builder, at least not at low cost. You would need to ship the actual alternator that you built to them, and pay a hefty fee….if they were willing to even touch the job.
• Here at our wind turbine shop, we produce quite a few turbines. It’s likely that we will pursue getting a custom firmware program for our machines in 2009….but that doesn’t help the home builder at all! If you used the (not yet existant) program for our machine and your machine performed even slightly differently than ours, the inverter program would be wrong, and your turbine, your tower, and your fancy new direct grid-tie inverter would be at risk. And you would likely not receive warranty service on the inverter.

Conclusion

So, in conclusion — Stick with an islanding grid-tie system and you’ll have no troubles at all. For direct grid tie — good luck, an be sure to factor in the cost of shipping and programming (if even available) to your initial investment and return on investment (payback time). And when it’s windy outside, your turbine is cranking out 1000 watts, and your house goes black because the grid went down and you have no battery backup………come over for a beer, because OUR lights will be on!

UPDATE 4-20-2009

Some of you have been following direct grid-tie discussion on the AWEA mailing list and other discussion boards. And have pointed out that Hugh Piggott successfully direct grid-tie a homebrew turbine in France. Here’s the scoop:

Homebrewers have now successfully done direct grid tie with no batteries using both the PowerOne (Magnetek) and SMA units. The factory can set a ‘generic’ wind turbine program for you based on your swept area, it will be very similar to programs for similar sized commercial turbines. Then, using your laptop, you can “tweak” the program to best match your performance. We would recommend starting with the alternator performing too ’stiff,’ stalling the blades, and then working back towards better performance.

Here’s the hitch — you will need to convince your SMA or Magnetek dealer that you know what you are doing. You may also NOT be successful in getting a warranty on the inverter, this seems to depend on how convincing you are about your skill level. AND, keep in mind that the responsibility of preventing an overvoltage condition is entirely yours….neither of these inverters warranties, if you can even get a warranty, will cover damage from overvoltage caused by a  homebrew turbine!

If anyone takes on this project, please do post your successes and failures here!

DAN F

We get bombarded here with questions about short towers:

• I built your turbine, but they won’t let me put it up on a tall tower, is it OK to put it up on a 20 foot tower in the garden behind the house?
• So and So’s website said that their wind turbine design works better than yours right on the ground!
• Such and Such wind turbine design “eats up turbulence for lunch,” it says so on their website and since it’s on the internet it must be true! And some of the text in their website blinks!
• “They” (or “everyone”) say that VAWTs (vertical axis wind turbines) work better on short towers and in turbulence than HAWTs (HAWTs are what we build in our book).
• “They” say that if I buy their turbine, I can put it on my roof because the wind speed increases going over the rooftop, just like an airfoil. Why doesn’t your turbine do this?
• There’s a very reputable big company that sells a grid tie wind turbine on a 30 foot fiberglass tilt up tower, and it’s only a 30 foot tower. They obviously know what they are doing, so I’m going to buy one and line my bird cage with pages from your book. Thanks for wasting my $39.95. (OK, we made that one up, but we are sure we’ll be getting emails like that soon).

It’s all Hokum! Hogwash! People are making this “data” up for good reason–most folks, when considering a wind turbine, do not want to or are not allowed to build tall towers. And that really puts a big crimp in wind turbine sales. There’s no guarantee from the manufacturer of energy output per month with any wind turbine, it depends on your wind regime. And once you sign on the dotted line, all you can do is scratch your head a year later and wonder why your turbine is putting out only a tenth the energy per month that the website and friendly sales rep said it would. Frankly, the authors spend as much time convincing folks that wind power is NOT right for them as we do helping folks with wind turbine questions.

The only published, scientific test results out there completely disprove all of this nonsense about rooftop turbines and short towers. Look at it this way — the earth’s surface causes “friction” to the wind. This has been extensively field tested and computer modeled for decades now. Friction slows the wind down. And the power available to you in the wind goes up by a factor of 8 when you double the wind speed!

Here are a few of those articles, from reputable wind power scientists:

Hugh Piggott’s measurement of urban wind speed over a roof top at Wind Speed Measurement in the City.

Comments by Hugh Piggott “Rooftop wind turbines are a load of nonsense”

Rooftop Turbines: Rooftop Mounting and Building Integration of Wind Turbines
By Paul Gipe

The case (or not) for Roof Mounted Wind Turbines by Nick Martin

Andy Mahoney’s Rooftop Mounting Failure at http://navitron.org.uk/forum/index.php?topic=942.0

Some test data from the authors:

Co-author Dan F and Otherpower.com Stator Specialist Rich C fly the exact same little wind turbine, the 7-footer that’s described in detail in Homebrew Wind Power. We both really enjoy this little machine.

We had no way to easily make this a scientific test…but we DID measure kilowatt-hours per month from identical turbines at sites only 1/2 mile away, during both high-wind and low-wind months of the year.

• RIch’s turbine was on a 50 foot tower, with hub height about 10 feet above the nearest tree within 300 feet. However, the hillside stretches up above his turbine, so there was turbulence caused by that. It was a ’so-so’ location by normal standards (which say your turbine must be 30 feet above anything within 300 feet in any direction) but far less obstructed than DanF’s, below.
• Dan F’s turbine was on a lattice tower, 40 feet in the air, right next to his house. The turbine is above the house roof peak by about 10 feet. There are numerous trees in the area taller than this within 100 feet. DanF broke all the tall tower rules he talked about in Homebrew Wind Power because he didn’t listen to his own advice wanted to prove a point about the importance of tall towers.

During the same period of 3 months, Rich’s identical 7-foot wind turbine made over 10 times the amount of energy per month (in kilowatt-hours, the only really important measurement) because of Rich’s fairly OK tower site, compared to DanF’s bad tower site.

Ten times the energy……

What were you THINKING, DanF?

(authors note — DanF was thinking that it would be cool to have an easily accessible tower top where he could test different small turbines and swap them out with little effort. But that’s not much use when the tower is not tall enough)

Well, at this time we have no errata whatsoever for the book!

Thanks to astute readers we are finding a few errata! Nothing critical.

Our Stator Master Rich C found a typo in the Glossary, but that’s about it so far.

If you are reading along and find a typo, please post here and let us know. We’ll fix it for the next printing. Dan F is keeping a master copy of the book with all typos and such noted for correction.

Click the comments balloon above for the list of errata as it gets longer, and to post your own.

Editors note: This really is coming in handy, thanks everyone for pointing out these errors!

OK, well, there is one “sleeper” in there. It was left in to make sure our editors were paying attention — It’s a photo of a common electrical part from the hardware store, but the part shown is not what is described in the caption. A free autographed copy of the book to the first reader that spots it and posts here.

We attribute the lack of major corrections and typos to the incredible skill and attention to detail incredible luck of the authors and copy editors. Thanks, everyone!

DAN F