# Wind turbine questions **URL:** \ **Category:** Factual Questions\ **Created:** [December 1, 2014, 5:07am UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012 "2014-12-01T05:07:29Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Slypork](https://avatars.discourse-cdn.com/v4/letter/s/9fc29f/32.png) [@Slypork](https://boards.straightdope.com/u/Slypork)\ **Post date:** [December 1, 2014, 5:07am UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/1 "2014-12-01T05:07:29Z")
I have a couple quick questions about wind turbines used for generating energy and hope they can easily be answered. 1. I only see wind turbines in the 2 or 3 blade propeller design. It seems like a vertical axis turbine would be more efficient. It doesn’t have to turn into the wind and could probably be enclosed in some kind of screening to prevent birds from being killed. Is the standard bladed version better or is there a cost reason why the vertical one isn’t used? 2. Could wind turbines placed alongside highways generate enough electricity off the wind produced by passing cars to light streetlights? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [December 1, 2014, 7:54am UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/2 "2014-12-01T07:54:18Z")
1. They do make vertical axis wind turbines. As they get larger, the variations in torque on the blades throughout the turbine’s rotation get very significant. This requires much stronger materials than a conventional 3 blade turbine. Newer designs have a more helical shape which helps to reduce this, but you’ve still got the additional cost of stronger materials. They have also had problems in the past with variations in torque load on the blades causing them to eventually fail. 2. No. Cars and trucks produce “wakes” through air kinda like boats through water. The air moves back and forth a bit but they don’t really produce a constant “wind”. There’s not much energy there to harness. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [December 1, 2014, 8:11am UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/3 "2014-12-01T08:11:30Z")
I was going to page **engineer\_comp\_geek** , but he found the thread 😃 ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 1, 2014, 10:05am UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/4 "2014-12-01T10:05:07Z")
Think about it. Those guys back when they built windmills from stone and wood, found out, probably by experience, that the standard sails-facing-the-wind type gives you the most watts for your money. There were ‘vertical’ windmills in some countries, but they never caught on. I just thought - I bet those ‘vertical’ ones were more likely to blow down in a gale too. ---
**Author:** ![Ken001](https://avatars.discourse-cdn.com/v4/letter/k/43a26b/32.png) [@Ken001](https://boards.straightdope.com/u/Ken001)\ **Post date:** [December 1, 2014, 10:55am UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/5 "2014-12-01T10:55:47Z")
Think about it further. Blow a full breath of air at an unsuspecting friend. He’ll be surprised but he might not even notice. Now throw a glass of water at him. The impact is obvious. Water has magnitudes more energy than air. Wind turbines have their place but only where there is a constant reliable wind which translates to only a few places around the world. Solar energy has good possibilities now that more efficient panels are being made but only in sunny places and you better be up for the cost of batteries and inverters. The panels are the cheap bit. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [December 1, 2014, 12:40pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/6 "2014-12-01T12:40:32Z")
Also, the ‘screening to protect birds’ is both impractical & unnecessary. Its impractical because because it would cause too much air resistance, and unnecessary because the number of birds killed is negligible, ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [December 1, 2014, 12:44pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/7 "2014-12-01T12:44:25Z")
> [@bob\_2](#): > > Think about it. Those guys back when they built windmills from stone and wood, found out, probably by experience, that the standard sails-facing-the-wind type gives you the most watts for your money. They also had four blades, not the three we typically see. Just because they did something like use four blades back when doesn’t mean it’s the best approach given modern materials and design. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 1, 2014, 1:10pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/8 "2014-12-01T13:10:02Z")
> [@ZenBeam](#): > > They also had four blades, not the three we typically see. Just because they did something like use four blades back when doesn’t mean it’s the best approach given modern materials and design. Some had more but I think that this is a reflection of the relative inefficiency of the sails themselves and the limitations of available materials. The arch bridge was the best design for stone - the development of high tensile steel allows us to build suspension bridges. ---
**Author:** ![Slypork](https://avatars.discourse-cdn.com/v4/letter/s/9fc29f/32.png) [@Slypork](https://boards.straightdope.com/u/Slypork)\ **Post date:** [December 1, 2014, 2:09pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/9 "2014-12-01T14:09:43Z")
> [@engineer\_comp\_geek](#): > > 1. They do make vertical axis wind turbines. As they get larger, the variations in torque on the blades throughout the turbine’s rotation get very significant. This requires much stronger materials than a conventional 3 blade turbine. Newer designs have a more helical shape which helps to reduce this, but you’ve still got the additional cost of stronger materials. They have also had problems in the past with variations in torque load on the blades causing them to eventually fail. > > 2. No. Cars and trucks produce “wakes” through air kinda like boats through water. The air moves back and forth a bit but they don’t really produce a constant “wind”. There’s not much energy there to harness. Thanks for the info. I always wondered about them, thinking you could place more in the same footprint as the standard turbines and increase energy generation/area. I mentioned the bird strikes because I keep seeing that as a complaint as to why some people don’t want wind turbines to be built. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [December 1, 2014, 2:54pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/10 "2014-12-01T14:54:18Z")
> [@bob\_2](#): > > Some had more but I think that this is a reflection of the relative inefficiency of the sails themselves and the limitations of available materials. The arch bridge was the best design for stone - the development of high tensile steel allows us to build suspension bridges. Yes, just as the development of newer materials may make vertical windmills more feasible and more attractive. It may never happen that they become the best design, but you can’t just look at old-fashioned wood and stone windmills and say that that’s the case. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [December 1, 2014, 2:57pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/11 "2014-12-01T14:57:52Z")
> [@Hail\_Ants](#): > > Also, the ‘screening to protect birds’ is both impractical & unnecessary. Its impractical because because it would cause too much air resistance, and unnecessary because **the number of birds killed is negligible** That turned out not to be the case in Altamont Pass: > [@](#): > > The small turbines used at Altamont are dangerous to various raptors that hunt California Ground Squirrels in the area. 1300 raptors are killed annually, among them 70 golden eagles, which are federally protected; in total, 4700 birds are killed annually. Overall there has been an 80% decline in golden eagles in Northern California, with no golden eagles nesting near the facility, although it is a prime habitat. Considered largely obsolete, these numerous small turbines are being gradually replaced with much larger and more cost-effective units. The larger units turn more slowly and, being elevated higher, are claimed to be less hazardous to the local wildlife. This claim is supported by a report done for the Bonneville Power Administration. > > As of 2010, a settlement has been reached between the Audubon Society, Californians for Renewable Energy and NextEra Energy Resources (who operate some 5,000 turbines in the area). Nearly half of the smaller turbines will be replaced by newer, more bird-friendly models. The project is expected to be complete by 2015 and includes $2.5 million for raptor habitat restoration.[6] > **[Altamont Pass wind farm](https://en.wikipedia.org/wiki/Altamont_Pass_Wind_Farm)** > > The Altamont Pass wind farm is located in the Altamont Pass of the Diablo Range in Northern California. It is one of the earliest wind farms in the United States. The first wind turbines were placed on the Altamont in the early 1980s by Fayette Manufacturing Corporation, on land owned by cattle rancher Joe Jess. The wind farm is composed of 4,930 relatively small wind turbines of various types, making it at one time the largest wind farm in the world in terms of capacity. > Altamont Pass is stil... ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 1, 2014, 5:07pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/12 "2014-12-01T17:07:56Z")
Windmills are spaced the distance apart they are not because there’s no room to pack them any tighter, but because at their current spacing, they’re extracting as much energy from the wind as they can. If it takes more vertical-axis windmills to extract that amount of energy, then that’s a point against them, not in their favor. **Ken001** , you’re right that it’s a lot easier to extract energy from moving water than from moving air. That’s why we’ve already tapped all of the good sources of moving water. But there’s not enough moving water to meet all of our energy demand, so we have to turn to other sources as well, even though they’re not as good. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [December 1, 2014, 5:45pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/13 "2014-12-01T17:45:04Z")
when placed at low elevations and homemade or crude the vertical axis machines have value. you can use heavy material for the support, you could support both top and bottom. this style gets used where lower amounts of power is needed and only heavy materials is available or lower costs are required. it is used worldwide. height is important for higher yields of power. bladed machines do well if lighter weight high tech materials are available. ---
**Author:** ![UncleRojelio](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unclerojelio/32/3160_2.png) [@UncleRojelio](https://boards.straightdope.com/u/UncleRojelio)\ **Post date:** [December 1, 2014, 7:20pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/14 "2014-12-01T19:20:10Z")
There is an alternative energy firm here that has a bunch of its products arrayed on and around its building. One of the products is a rather large vertical wind turbine. Over a year ago one of the helical blades snapped off and the turbine has been motionless ever since. Apparently, even the prospect of the negative advertising generated by displaying a broken product in the front yard is not incentive enough to repair it. ---
**Author:** ![Deeg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/deeg/32/2955_2.png) [@Deeg](https://boards.straightdope.com/u/Deeg)\ **Post date:** [December 1, 2014, 9:26pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/15 "2014-12-01T21:26:59Z")
I have a question: why are fewer, longer blades better than shorter, wider blades? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 1, 2014, 9:55pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/16 "2014-12-01T21:55:46Z")
> [@Deeg](#): > > I have a question: why are fewer, longer blades better than shorter, wider blades? Turbine blades are basically wings. Wings with high aspect ratio (large span, small chord) are more efficient than wings with a short aspect ratio: > **[Aspect ratio (aeronautics)](https://en.wikipedia.org/wiki/Aspect_ratio_(wing))** > > In aeronautics, the aspect ratio of a wing is the ratio of its span to its mean chord. It is equal to the square of the wingspan divided by the wing area. Thus, a long, narrow wing has a high aspect ratio, whereas a short, wide wing has a low aspect ratio. > Aspect ratio and other features of the planform are often used to predict the aerodynamic efficiency of a wing because the lift-to-drag ratio increases with aspect ratio, improving the fuel economy in powered airplanes and the gliding angle of... [Wingtip vortices](http://en.wikipedia.org/wiki/Wingtip_vortices) (or [prop-tip vortices](http://en.wikipedia.org/wiki/File:DN-SD-06-03008.JPG), for a propeller/turbine)represent an inefficiency; if a wing or prop blade must have that tip vortex as a fixed waste value, then you maximize efficiency by making the wing/prop blade as long as possible. This is why gliders have long wings with a short chord. Commercial airliners aren’t too different from that idea (you need to be efficient to cover thousands of miles without refueling), but they make compromises for load-carrying ability and the aerodynamics of high-speed flight. Fighter aircraft need to tolerate the extremely high loads encountered during aerobatic maneuvers, so they pretty much have to go with low aspect ratio wings (small span, large chord), efficiency be damned. And so it is with wind turbines: longer turbine blades with shorter chords are more efficient. As to the # of blades, there’s a [theoretical upper limit](http://en.wikipedia.org/wiki/Betz%27_law) for how much kinetic energy can be harvested from a stream of moving fluid. Modern 3-bladed horizontal-axis wind turbines are already achieving around 80 percent of this limit; I suspect the economics don’t justify the addition of more blades to reach for just a thin slice of that final 20 percent. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 1, 2014, 10:05pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/17 "2014-12-01T22:05:09Z")
> [@ZenBeam](#): > > They also had four blades, not the three we typically see. Just because they did something like use four blades back when doesn’t mean it’s the best approach given modern materials and design. It’s interesting how many times the same thing gets re-invented. The last great heyday of wind generators was the 1970s, when every commune was rediscovering what the makers of Winchargers in the 1930s had already learned. I realize that things like computer modeling and engineering analysis can carry things further and perhaps more easily, but the basics are still old news - if any bright young UC researchers care to look. The optimal number and orientation of the blades haven’t changed, for example. The Albers did extensive experimentation to discover that three blades were optimal and caught as much wind as could be caught - more blades just dragged down efficiency and the vertical orientations were only suitable for small-scale because of the material strengths needed. They knew all this in the early 1930s. 🙂 Original Winchargers are still highly prized. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [December 1, 2014, 10:07pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/18 "2014-12-01T22:07:09Z")
> [@Deeg](#): > > I have a question: why are fewer, longer blades better than shorter, wider blades? It’s all about maximizing efficiency. You need at least two blades to create a balanced turbine. As you add more blades, you basically add in the cost of each blade, but the gain in performance you get decreases with each additional blade. In other words, if one blade costs X, then your minimal two blade system costs 2X just for the blades. Adding a third blade costs 3X and gives you a decent boost in performance, but adding a fourth blade costs 4X and does not give you anywhere near double the performance of the two blade system. Additionally, each blade disturbs the air for the blade that follows it. The more blades you have, the more you lose efficiency due to the turbulent air. These things push towards fewer and thinner blades. However, there are some design considerations that push things the other way as well. Fewer and longer blades may be more efficient, but you can’t just keep making longer and longer blades out of the same material or it will flex more and eventually break. Longer blades also require a longer mast so they don’t hit the ground (which again requires stronger materials or a different design), and if the blades are too long the tips can start to go supersonic, which adds drag and totally screws up your efficiency. So these considerations push for a larger number of shorter blades. The sweet spot that tends to give you the best efficiency for the least cost is the current three-blade design with fairly long and narrow blades. ---
**Author:** ![Deeg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/deeg/32/2955_2.png) [@Deeg](https://boards.straightdope.com/u/Deeg)\ **Post date:** [December 1, 2014, 10:29pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/19 "2014-12-01T22:29:29Z")
Interesting. Thanks Machine Elf! ETA: and ecg! ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [December 1, 2014, 10:54pm UTC](https://boards.straightdope.com/t/wind-turbine-questions/706012/20 "2014-12-01T22:54:30Z")
There are roughly a dozen pairs of nesting golden eagles in the Altamont pass area. The figure of 70 killed annually is bullshit, even when the windmills were the small very fast moving variety. That figure multiplies to total population by three and then assumes annual full extinction. I go bird watching on the pass the past 5 years on a monthly basis, and all the birds know how to handle the newer and larger windmills and even play and harass each other in their wakes. Goldens are _very_ territorial and their number limited by area. Propeller type windmills have a significant advantage over vertical windmills in that they can “feather” so that the blade may rotate on its axis to be more or less efficient in different wind conditions. [Next page](https://boards.straightdope.com/t/wind-turbine-questions/706012.md?page=2)