Wind-Electric History & Home-Scale System Design: Page 3 of 5

Intermediate

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The world’s first automatically operated wind turbine was built in 1888 by Charles F. Brush. It was 60 feet tall with a diameter of 56 feet, weighed 80,000 pounds, and had a 12 kW generator.
Two wrongs don’t make a right. Here, a Savonius rotor is placed at the center of a Darrieus to make it self-starting. But Darrieus turbines are inefficient and structurally flawed.
For overspeed protection, Bergey’s Excel 10 kW turbine features a pivoting tail and flexible blades, which twist to allow furling under excessive wind load.
A 41% increase in radius/diameter results in a doubling of swept area, and thus twice as much energy potential.
This Renewtech turbine is a tailless upwind turbine that uses electronics to yaw. Larger turbines are often better at obtaining both efficiency and durability, but that can challenge the budget of a homeowner.
This Pika Energy turbine is a classic three-bladed, tail-yawing, upwind turbine.
The Kingspan Environmental KW6, 6 kW turbine is a downwind turbine. Speed control is provided by a unique pitch-control system that relies on a string and two hinges at the blade root.
Wind power may seem like an easy solution, but adopters need to be ready for the logistics, infrastructure, and costs of both installation and maintenance.

Alternator & Controls

Most small wind turbines use permanent-magnet (PM) alternators to produce an AC output that varies with rotational speed. Very powerful magnets are used, and sophisticated power electronics are needed to deal with the wild AC that they produce. Compared with conventional generators that need to feed current to rotating coils to create a magnetic field, the efficiency is higher, and there are fewer moving parts to fail.

 The “wild AC” from a PM alternator is rectified into DC. Turbine voltage and speed are determined by what it is connected to. The simplest electrical configuration is to hook this DC output directly to a battery. The battery acts like an anchor to the rising voltage by drawing current that matches what the wind has to offer. Unlike PV modules, which can be safely disconnected when the battery has had sufficient charge, a wind turbine must be kept connected to a load all the time or it will overspeed and produce excessive voltage. Surplus energy must be diverted into a suitable heater (also known as a diversion load or dump load). A diversion controller must be used to regulate the battery’s voltage. However, this is not a fail-safe strategy—the National Electrical Code requires a “second independent means” of diversion as a backup to keep the battery from overcharging.

Some small wind turbines can be connected to the grid without batteries. A batteryless grid-tied inverter converts DC from the turbine’s rectifier to standard AC power—and this can be fed back into the grid. In the past, the power was generated by induction motors “backfeeding” power, but this restricted the blades to a fixed rpm. Modern PV inverters have opened the door to using DC rectified from the wild AC from turbines instead, but at several hundred volts DC rather than at battery voltage. The higher voltage means considerable cost savings on long wire runs. Just as with maximum power point tracking (MPPT) of PV arrays, it’s advantageous to tweak a wind turbine’s operating voltage to optimize blade speeds for different wind speeds. The MPPT algorithm in a batteryless grid-tied PV inverter will not work to optimize a wind turbine, because the wind changes too rapidly, and the turbine also has inertia. So inverter software has to be modified to produce a “wind inverter” that’s programmed with a “curve” that tells it the best DC operating voltage for that turbine at any particular level of power output.

A wind inverter also needs to be protected against overvoltage from the wind turbine. When running unloaded, the “open-circuit” voltage rises much higher than in a PV system. Overvoltage protection devices from inverter suppliers or from wind turbine manufacturers are essentially diversion-load controllers that dump excess wind energy into resistance heaters when the grid-tied inverter cannot use it, such as during a utility outage.

Even stand-alone battery systems (with no grid connection) can benefit from using higher-voltage turbines and MPPT controllers adapted for wind-electric systems. Another popular configuration for larger systems is to use AC-coupling. This means using a grid-tied wind inverter to connect your turbine to the AC service panel (which is also connected to a battery-based inverter). If the turbine produces more energy than is required by the loads, the battery inverter can use the surplus to charge the battery.

Comments (8)

mberdan's picture

Brandon, thanks for the insight, I hope I understand you correctly, when you say small, you are right this is a relative term. I hope my analogy is correct when I remember what my parents taught me. Save a penny every day, it may not look like much now, but 20 years from now it can be allot.
I am not really aware of any dedicated sites to what you may consider small wind. To me small wind is under 10kw, but others have posted under 100kw is considered small wind.
Other than what is available thru search engines and standard sites, such as SWCC, AWEA, CANWEA and European market or those companies selling small wind technology. It is hard to find, good data.
This is true for both Vertical and horizontal turbines.
Our process was many years of research collecting documents from hundreds of different university publications and then putting them together. Once we had that, the rest was developing a structure to be
structurally strong and support the loads as well as have redundancy.
Then years of testing and refining.
Many people who are working on this technology, tend to keep it to themselves. Why? many reasons I assume. I know we too kept our project in the dark for many years. Maybe it is my background in R&D
for Aerospace projects. Or just staying away from the negativity in bringing new technology to the market, especially if it can be disruptive. If you are very interested in Vertical systems. I believe in transparency and sharing where it can do the best for all. I have years of university data from many of the top research labs working on small wind. I would be happy to point you in that direction.
you can contact me thru our website.
Not sure if this answers your question.
Thanks Mike Berdan

Brandon2's picture

First-time poster here (I think!), and not nearly knowledgeable enough to offer much to the discussion. But I do have an observation that I hope others find useful, and a related question.

Every time I read about smallish-scale wind, vertical-axis, etc., it seems that it is said to not be viable. I get that. BUT, this conclusion always seems to be followed/backed-up by "large-scale" reasoning, such that there ends up being a disconnect between the topic itself ("small") and the reasoning that follows ("big").

It's as if, every time I "tune in" to learn real information and experience about someone using *small* scale wind to consistently/reliably do *small* things (charge a tablet for an hour's worth of use, charge a non-smart phone for a couple days of use) and live *small* for those days/weeks when the sun isn't shining...it's only a few sentences before the discussion diverges hopelessly into *big* ideas about *broad* viability and the *bigger* picture, etc.

A possible, sad irony here is that the heavy focus on the *grand* scheme and the vacuum of discussion it creates regarding truly small-scale, actionable / applicable light uses may actually in turn have a self-defeating effect on the *big* picture itself. It's as if the old adage has been flipped: we can't see the trees through the forest.

What I mean to say is, experts and experienced people seem to start by talking about "small scale" and, as I listen attentively, within only a few words begin talking about "big" concepts such as viability on a national scale, 10/20 year ROIs, carbon/energy input/output ratio efficiency, and getting a pole 500 ft in the air.

I'm interested in small scale wind, and vertical-axis. So, let's say this is my hobby. That is, I'm not so concerned about those aforementioned things as I am the joy of learning, exploring, and producing my own energy (a cell phone for a few days, maybe) without the utility company and in a manner that won't drive my neighbors next door to declare war between our households (noise in an urban-ish environment). I'm interested in sharing my *small* bit of what I learn with others, perhaps the kids around that might be inspired to later become part of a team that helps solve things on a *big* scale (but wouldn't have happened if we didn't value the *small*).

This isn't a criticism I suppose, but an observation. I value the various perspectives, especially those of experts and people with lots of experience. Perhaps it has to do, in part, with different opinion of how small is small.

It would be great to get more interviews and more real, in depth discussions and examples of truly *small* wind applications as I mentioned. Which leads to my question: is there a source I can turn to for good, consistent, accessible, in-depth and analytical-but-not-too-big-picturey information about truly small-scale wind?

mberdan's picture

Thanks to everyone for the response. I understand your opinions and agree in many ways. But as an engineer, the words spoken in the early 60's from JFK still linger in my mind.
"We chose to do this not because they are easy, but because they are hard" thanks Mike Berdan.

mansberger's picture

Great quote Mike!

mberdan's picture

Todd thanks for the reply. nonsense, I do not think so. I just witnessed
a university competition from AWEA last summer. 10 universities who are all testing new ideas, blade design, performance enhancements in both Vertical and horizontal. top winner Vertical axis turbine.
Yes as I mentioned there is a long way to go and improvements are moving forward. Materials and technology are letting the new breed of engineers explore both sides. I am not against Horizontal, as I agree they are the main standard and work well. Lets look at some aspects.
horizontal systems work well, they must be placed high off the ground to capture strong winds. RPM's tend to be higher , fatigue is greater at higher RPM, tip speed higher , noise level higher , so they tend to be placed further away from source, longer cable runs, bigger foundations. Great if you are a farmer or rancher. what about the Urban environment, people want to go green there as well. solar has made it's way in the Urban because of that. Vertical systems are a way to give alternative or hybrid solution in a more Urban environment.
As you have seen , yes there is still a ways to go to make Vertical systems work efficiently and produce power as defined. But it is those challenges that will eventually give us a break thru. We are all part of making this world a little greener, so lets work together before we just Bash ideas with out supporting the technology. I have been working on our technology for 10 years, testing , redesigning, testing , looking for new products and ways to improve performance. From this we developed the system we currently have. Our systems are in the market and working for many years. yes power production is not fully there but some of that is the Inverter / controller side. Try and find a high tech wind inverter, good luck. We have a dual Vertical system, which we try to combine the 3phase AC to DC output for the inverter to convert back to single phase AC. Solar has expanded to micro inverters and more advanced controllers. wind needs the same, but yet not available, so most wind companies have to develop and sell their own. we try to use off the shelf technology. so in short, Yes we have a ways to go, but we should not push the Vertical technology aside. As I still say, it has far more consumer growth options than Horizontal.

Todd Cory_2's picture
Todd Cory_2 (not verified)

"The vertical systems have allot more promise than the horizontal and the major down falls of horizontal systems that exist are lending the way to Vertical systems."

you might want to reconsider that nonsense:

http://scoraigwind.co.uk/2016/12/wh...

mberdan's picture

I remember many years ago when hybrid and electric cars where just a twinkle and everyone said that it will never take off. small wind has been developed mostly by individuals and hobbyist. but those who seek to bring new technology to small wind, are on the up-rise. New technology and computer aided design with CFD capabilities are moving into the small wind industry. and Vertical axis systems are tacking hold.
Yes we still have allot of work to do, but the discussion of horizontal being the safe decision maker is irrelevant. The vertical systems have allot more promise than the horizontal and the major down falls of horizontal systems that exist are lending the way to Vertical systems.
my opinion anyway.

Michael Welch's picture
I don't think anyone with any knowledge said that about EVs. It's always been clear that we needed a better battery, and that those batteries were on the horizon -- but even with old battery technologies EVs made sense for a lot of us.

Much different with VAWT wind generators. As far as I can see, the only promise VAWTs hold is with **marketers** who eye the problems with horizontal axis turbines (viewed as cost, tower, birds, need for strong wind, and hassle); and want to be able to sell a machine because, after all, it is attractive for all the right marketing reasons. That's what marketers do -- create need to make sales, regardless of viability.

And engineers new to the industry jump on board because that's what engineers do: they believe they can find a technical fix for any problem. Even if there isn't one, it's their job to try and to make it seem possible. And, as long as there's a paycheck, to keep trying, no matter how fruitless the same efforts have been in the past.

VAWTs are not taking hold. They just haven't worked out, none of them. They sure look interesting, though.
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