Wind-Electric History & Home-Scale System Design: Page 2 of 5

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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.

With the expansion of the electricity grid and the low cost of fossil fuels, wind energy development proceeded in fits and starts. Plenty of variants were discovered and rediscovered, including the vertical-axis type. In 1924, a Finnish inventor, Sigurd Johannes Savonius, popularized a variant with two offset half cylinders. Very slow and inefficient, its main appeal is its simplicity.

In 1931, a French engineer, Georges Jean Marie Darrieus, patented a high-speed vertical-axis turbine with slender blades that has been the darling of university engineers ever since. It has many inherent challenges they can try to deal with. It is not self-starting, nor is there any simple way to control its speed when running. Vertical-axis designs remain popular in spite of failing to achieve commercial success over a long period. It often appears that enthusiasts are unable or unwilling to learn from past failures of the genre.

From time to time, the “ducted” turbine is hailed as a new discovery, intended to funnel the wind into an aperture where it can be processed by a turbine. These projects fail to produce cost-effective turbines because the wind simply makes its way around the structure. Unlike water, it is impractical to trap the wind and concentrate its energy. Another folly is the building-integrated turbine, which is installed on a rooftop or built into a hole in a wall. Winds around buildings are generally inadequate in speed, and are turbulent. If the turbine actually does run, it generates considerable noise and vibration within the building.

The search continues for an improved wind-energy converter, but the most important thing to know about using wind turbines is that they need wind. Just as you would not mount a solar-electric array in the shade, a small wind turbine cannot be viable unless it is prominently exposed to the wind resources, on a site that has few to no obstructions.

Larger Collectors

The rotor blades of a wind turbine are the engine. The wind is the fuel. The amount of energy it can capture depends directly on the rotor’s diameter. Increasing the diameter makes a big difference, because the energy captured is determined by the area of the circle inscribed, and this is figured by the radius, squared. Doubling the area is a sure way to double the turbine’s energy capture. (See the AEO table in the “Wind Reality Check” sidebar.)

The number of blades is less important. If three blades can produce 1 kilowatt, it does not follow that six blades can produce 2 kilowatts. A properly designed turbine will capture almost all the power that can realistically be captured. Wind turbine blades rotate several times faster than the wind speed. If there are fewer blades, they simply need to move faster to cover the ground. The higher airspeed generates more lift force per blade, which compensates for having fewer blades.

For example, two-bladed turbines run at higher rpm than three-bladed ones—an advantage for electricity production as it allows for a lighter-weight, less-expensive generator. Some downsides are that the blades will be slightly noisier, and the tips may become eroded over time.  And the two blades switch rapidly between horizontal and vertical alignment, causing a jerky motion when the turbine yaws to face a changing wind direction. This can shake the machine and tower, leading to extra wear. Many observers also agree that a three-bladed turbine is easier on the eye. More than three blades is less common, as they add to the cost and weight without any particular benefit.

Governing

If a site has enough wind to produce useful wind energy, the wind will sometimes gust at much higher speeds, which challenge the turbine’s survival. Turbines must include an automatic protective governing system to limit blade speed and power. Otherwise, the generator will be overloaded and burn out, or the blades will overspeed and possibly break. Coping with high winds is just as important as working well in useful wind speeds, or the wind turbine won’t last long.

The “furling tail” is a simple, popular governing system. When the wind is below the speed for maximum power, the tail steers the machine to face the wind directly. In higher wind speeds, the tail folds partially or completely, allowing the turbine’s rotor to yaw sideways and present a smaller profile to the wind, catching a smaller proportion of the increasingly strong wind. The system uses few moving parts and there’s little to go wrong—but the drawback is that the yawing motion is slow, so the governing action is delayed and imprecise. In high winds, a good furling system needs to keep the turbine safe, protecting it against sudden gusts, resulting in an average output that is often quite low. This is of less concern in an off-grid situation, as the battery is likely to be already fully charged at this time, but it can represent a missed energy-harvesting opportunity for grid-tied systems.

A more precise method of controlling turbine speed and power automatically adjusts the pitch of the blades to fine-tune the lift force. Pitch-controlled turbines have a steadier speed and output than tail-furling turbines, but this comes at the cost of a more expensive and complex governor, with moving parts and springs that can wear or break.

Some modern wind turbines rely instead on stalling the blades. The generator acts as a dynamic brake, using an electrical load to limit the blades’ speed. The blades perform less well when turning slowly in relation to the wind speed, so this method limits the power without extra mechanical parts. Sometimes, a backup braking system is needed for safety in stormy conditions, when the wind is fast enough to overcome the electrical load.

A machine’s “power curve” is a good representation of how well it governs in high winds. Wind energy continues to increase cubically as wind speed increases, and a method of protecting the turbine in powerful and damaging winds needs to be available.

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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