Feasibility of smaller turbines/higher wind speed

Arqane
Arqane Solar Expert Posts: 31 ✭✭
Obviously most generators are used for standard outdoor conditions, so maximizing their potential at 15-25mph will get the most bang for your buck.

I'm fairly new to the wind generation scene. At least seriously looking into it (and it's my first post, so hi :D). So I was wondering if anyone is knowledgeable about whether the science limits higher sustained speeds (35-75mph), or if that is more a factor of the materials being used.

Since I'm looking more at very small size generators, using heftier materials won't make as big a difference as it would on a 100ft. blade. I also read up on the new wind belt technology (http://www.humdingerwind.com/), which may be promising... but a cheap version you can make yourself would only apparently get 1 Watt per square meter or so. I'm not sure what their advances will get.

As for turbine technology, do you think it's possible to get 1kW+ at a sustained 50mph from a 3-5 foot diameter?
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    There are real limits to how much energy you can get from wind--Betz Law.

    Realistically, from 6 m/s wind, you will get from a good quality turbine around 42 kWH per month per square meter...

    Link you have will generate around 7.2 kWH per month per square meter... Only about 1/6th the amount from an equivalent turbine.
    • 7,200 WH per month / (30 days * 24 hours) = 10 watts at 6 m/s (or ~13.4 MPH)
    A standard windy open field at 10 meter elevation with average wind speed of 4.4 m/s (windy season) assuming wind energy cube of speed:
    • 7.2 kWH per month * (4.4/6)^3 = ~ 2.8 kWH per month at 4.4 m/s (9.8 MPH)
    • 10 watts * (4.4/6)^3 = ~ 3.9 watts at 4.4 m/s (9.8 MPH)
    Energy from wind goes with the cube of the speed... So, 50 MPH:
    • 10 watts * (50/13.4)^3 = ~ 520 watts per square meter (~10.76 sqft)
    My questions would be:
    • Where do you get 50 MPH winds?
    • Where do you get 6 m/s (13.4 MPH) winds on 10 meter towers?
    • Windy open field in Netherlands averages around 3.4 to 4.4 m/s
    • Humdinger shows fixed arrays mounted on buildings--no tracking to wind, heavy turbulence from building would seem to significantly limit and already very poor power output.
    • Ability to handle high wind conditions (gust of 60-100+ MPH)?
    • They talk about no audible noise--But the smallest version (~6" vane?) appears to vibrate at 70Hz--The 1 meter version would flutter at a much lower frequency--Does this cause the the mounting/building/etc to resonate sub-sonically?
    • Water/Ice/Weather/Sun resistance?
    A 1 meter square solar panel would output, roughly:
    • 1 meter * 0.15 eff * 1,000 WH per sq.meter = 150 watts (4-6 hours per day)
    • 150 watt * 4 hours per day average sun * 30 days = 7,098 = 7.1 kWH per month per square meter
    Interesting--Very roughly, the output of an "average solar panel" with "average sun" produces 2-3 times as much power per square meter as this "wind panel" would produce in "average windy month" weather conditions in windiest coastal region in Holland.

    Many regions have 5-6+ hours of sun during the summer (even more power from solar).

    And, for most people, the amount of sunlight is much more predictable and less seasonal variation vs wind.

    No wind expert (and I am, personally, not a fan of small wind)--The above are my back of the envelope calculations.

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    I suggest the OP visit some place that has an anemometer and research average wind speeds to start.

    Any location with 50 mph average wind speeds will have zero inhabitants - unless it is a research station at the South Pole. or similar.

    The wind belt is a neat science project and nothing more.
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, this application is not for your standard atmospheric conditions (your standard tall wind turbine in the middle of a field). I'm well aware that 50mph is ludicrous under those conditions.

    The reason I homed in on the windbelt was because of the space requirements. Really I'm looking for 1 square meter. Building a turbine that small may be hard because of the parts involved. Or so I read.

    From your calculations, you say a turbine could potentially put out 3kW per square meter as long as the wind is blowing at 50mph? But if a turbine is rated at 6 m/s, it would likely not perform well at higher speeds. Still, 1-2kW would be promising.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    Potentially--But more horizontal axis wind turbines seem to max out around 25-30 MPH and may even shut down at 50 MPH.

    3kW is over 4 HP... That is a heck of a lot of energy from a small turbine.

    Note my guestimates where just back of the envelope calculations--there may be other aerodynamic effects that are affected by scaling. I am not a turbine designer.

    If you have a specific application, you would probably need to design for it (ducted fan, water turbine, etc.)...

    For the most part, I cannot really think of an application where there is 50 MPH "free wind" available short of in a major storm... And if you design for optimum output at 50 MPH--it probably would have close to zero output 98% of the time in "standard" weather conditions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, as the idea isn't new, I was considering wind power for electric cars. Since they don't need a fuel/air mixture (though they do need some cooling), the air is essentially free.

    I'm aware that they would cause drag, which would take from the power produced. And I've heard the standard response of the law of thermodynamics, that you can't get any more power than you put into the system. Of course, the question is if the 'free air' is actually part of the system, or simply influenced by it.

    So for those of you here who have obviously worked with turbines first-hand, would the drag necessarily be as powerful as the gained energy?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    Look at sail boats--The get "free power" from the wind--but they do not have to follow lanes and traffic laws (at least rules of the road--there are rules of the water that have to be obeyed).

    The Laws of Thermodynamics are very well understood and have worked well in every application to date... Sort of some sort of major discovery in physics (zero point energy, dark matter energy, etc.)--We are left with what we have today.
    The four principles, or laws, of thermodynamics are:[1][2][3][4][5][6]

    In the end, what you are describing, in real life, is a perpetual motion machine. It takes more power from the drag of the turbine/wind band/etc. that you can get from the devices...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, though it is getting a bit off topic, I compared it to a chemical reaction. Bear with me for a moment, if nothing else... it makes for a funny anecdote.

    Imagine that you were in a boat with a gasoline engine, and 1 gallon of gas in that engine. Let's say it gets 10 miles per gallon in a freshwater lake. So you could go 10 miles before you ran out of fuel and the boat was simply floating. If the lake instead was the consistency of molasses, you would get much less than 10 miles because of the added friction. Now imagine the lake was filled with gasoline instead of water. How far could you travel? A long, long, long, long way... assuming you had a scoop hooked up to the engine that could fill the engine. It's essentially a perpetual motion machine, at least until you run out of the lake :roll:.

    Now as I understand it, the chemical reaction (providing heat and expansion to gas) is what adds to the power of the system. So if I'm right, using material that is outside of a particular system can add power to the system, as long as you have a method of extracting the power. So my question is, what makes the energy transfer different between a turbine and a combustion engine?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    Interestingly, viscosity is not the major factor in efficiency of motion through a medium (i.e., water vs some sort of agar/gelatin mixture).

    The difference is that a fuel powered engine is using stored energy to provide the energy to move forward.

    A turbine/sail/wing/etc. is using the differential speed and vectors of relative motion to extract energy from the air and use it for moving forward.

    For example a sail boat can tack and move up wind (at an angle to the wind). However, that same sail boat cannot move directly into the wind, either using a sail or a turbine.

    We had a related discussion here (I don't know that we convinced everyone that the original article, as written, is not possible):

    Wind-Powered Car Actually Moves Faster Than Wind Speed

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    It would be nice if something like this would work, but it just defies known laws of nature. Wind turbines are known to be relatively inefficient - converting a small percentage of the energy available in the wind to electrical power. That inefficiency combined with the large increase in aerodynamic drag (especially as speeds increase) makes a bad combination for this idea.

    Too bad we live in a world full of losses (and inefficiencies)!

    Edward
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    The drag from the turbine added to a car would be greater than any gain - simply adding inefficiency to inefficiency.

    This idea floats around green sites every six months or so and people comment - Oh! How wonderful! What a great idea!

    Betzs law describes the amount of power in wind nicely - done and published by a German scientist about a century back.

    If you try to exceed the allowable limit according to Betz the wind backs up and bypasses the turbine.

    All sorts of shrouding have been tried with virtually zero success.

    Russ
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, at least we still get free air from it. Just have to find another way to extract the energy from it, I guess. And until we figure out that whole fusion thing...
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    OK, so I'm back with the same old crazy idea.... sort of. Mostly I just want to make sure I understand the physics of it correctly. But there is a possibility for at least some regeneration.

    Drag is caused by the surface area covering the main direction of the wind. The more surface area on the leading edge, the more drag. Cars try and get a fairly low profile in that respect to minimize the drag. Turbines generally work with the opposite concept. They want to cover more surface area to generate more power.

    Theoretically, if that surface area on the car was made to catch the wind, then as long as the surface area remained the same, the drag should remain the same. Currently it's not being used, simply lost. Standard turbines would obviously have some problems, due to size, lack of space for the volume of air behind, and small moving parts. But if you find a way to utilize that same surface area, shouldn't you be able to recover 30-60% of the force lost potentially?
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Shrouded turbines are designed by some to do just what you are talking about.

    There have been a number of spectacular failures and no (zero) positive outcomes that I have read of.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    I hate to turn every question about wind into a copy of our Wind FAQ... But, we do have some pretty good wind links to read through from many source:

    Wind Power Links
    www.otherpower.com (good forum for DIY Wind Power)
    Hugh Piggott - Scoraig Wind Electric site for tons of info (from mike90045)
    www.greenpowertalk.org (added from "russ"--Like here but more wind/less solar)
    Small windpower a scam ? Survey says SO
    Truth About Skystream & SWWP
    Windmax HY-2000 2kW Wind Turbine (apparently, some vendors don't sell spare parts--just new turbines)

    And a general DIY Solar Builder site:

    www.builditsolar.com

    Some commentary about Ducted Wind Turbines. More Ducted Turbines. And more. More. Abandoned from the 1970's...

    And, think of drag as a drain of energy from the moving object (or moving airflow).

    I can have a flat disc or a 1/2 round ball, or even a tear drop shape. And each will exhibit a vastly different amount of drag eventhough the have the same "forward facing" surface area.

    From a Wiki Drag coefficient article article:

    200px-14ilf1l.svg.png
    A modern car may have a drag coefficient of 0.34 and a parachute 1.41 or so.

    A wind turbine is designed to pull as much energy as possible from the moving air stream. So, you can bet that it will have a pretty poor coefficient of drag.

    For an airplane, if you have a propeller aircraft, there is big difference in drag for a "gliding aircraft" with the motor turned off and the propeller spinning vs gliding and the propeller stopped.

    In the end, there is never "free energy"--There is always a cost and conversion of energy always ends up being quite a bit less than 100% efficient for each conversion (frequently, 50% efficiency seems to be a common cost of conversion).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, from what I read, and sort of expected about automotive aerodynamics was the following:

    "The air that rams into the engine bay, is used for cooling, combustion, and for passengers, then reaccelerated by a nozzle and then ejected under the floor. For mid and rear engines air is decelerated and pressurized in a diffuser, loses some pressure as it passes the engine bay, and fills the slipstream. These cars need a seal between the low pressure region around the wheels and the high pressure around the gearbox. They all have a closed engine bay floor."

    Straight from good ol' Wikipedia. I know, not the perfect source. As for frontal engines, you wouldn't need the air for combustion in an electric. Air for passengers doesn't need to be pressurized, and cooling can be done by other methods. For rear engines, the air is already decelerated. There's your loss right there. The only problem that I can see from those examples is the lack of enough area on the other side. Otherwise if you need to decelerate the air, why not use a turbine to do it, or something else that turns the maximum possible kinetic loss back into electricity?

    EDIT: Simply editing because the previous post showed up before I finished.

    As for the free energy, that's why I'm considering a regenerator, not a generator by itself. I'm looking for mitigating losses, not adding power to the overall system. An object (such as a wall) can have the exact same drag as a turbine, yet get no electricity from it. And as for the first article that was mentioned, they actually said that they augmented the flow to add power, even though it was very small.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed
    Arqane wrote: »
    Well, from what I read, and sort of expected about automotive aerodynamics was the following:

    I think this is the Wiki Link for the following:
    "The air that rams into the engine bay, is used for cooling, combustion, and for passengers, then reaccelerated by a nozzle and then ejected under the floor. For mid and rear engines air is decelerated and pressurized in a diffuser, loses some pressure as it passes the engine bay, and fills the slipstream. These cars need a seal between the low pressure region around the wheels and the high pressure around the gearbox. They all have a closed engine bay floor."
    There can be an interesting effect here--If I understand your point.

    It is possible to have a "ram scoop" that brings air into a chamber, then heat is added, and then there is a constriction at the exit for the air to exhaust and this creates thrust.

    This is exactly how the radiator works on a P-51 Mustang.
    The other was a new radiator design that exploited the "Meredith Effect", in which heated air exited the radiator as a form of jet thrust.
    The Meredith Effect is a term for the use of the hot air from a radiator to provide thrust in aircraft engines.[1][2] The concept was devised by Fredrick Meredith at the Royal Aircraft Establishment (RAE), Farnborough, prior to World War II, and incorporated into a radiator-duct design that produced thrust, helping to offset the drag produced by the radiator.
    One of the first aircraft to incorporate a radiator designed to make the use of the effect was the Supermarine Spitfire.
    But this thrust is not "free"--It is waste thermal energy (pulled from the engine cooling system) and introduced into a ducted radiator to turn what, used to be, wasted energy drag from the radiator, into useful thrust.

    So--we still have not suspended the laws of thermal dynamics--Instead they took a waste product "heat" and turned it into useful energy (to move the plane forward).

    If, instead, you placed a ducted fan there in place of the radiator, you will have increased drag instead... No way around it. And the energy needed to turn the fan (and alternator, etc.) would be greater than the energy collected from the ducted fan assembly to provide useful work.

    Things like ducted fans are not uncommon in the aviation industry... Obviously a modern High-Bypass aircraft turbine is really just a big ducted fan driven by a smaller fuel burning turbine. The ducted fan being more fuel efficient than the low-bypass turbines engines of decades ago.

    Hmm... Somebody has a sense of humor:

    Ram Air Turbine (RAT):
    A ram air turbine (RAT) is a small airflow driven engine that supplies emergency electrical or hydraulic power to aircraft or, in the case of crop dusters, powers ancillary equipment. These turbines are stowed away behind closed panels during normal flight and are generally only deployed in the case of total loss of power due to multiple engine failures. RATs are standard parts of the redundancy backup systems on larger commercial, military, and many crop dusting aircraft. The average ram air turbine on a passenger aircraft can generate over 50 kilowatts (kW) of power and have a propeller several feet in diameter. Older RAT designs featured twin bladed propellers although newer examples generally have multi-bladed, ducted fans.
    ...
    The RATs on commercial aircraft are obviously far larger with the Airbus A380 ram air turbine measuring five and a quarter feet (1.63 m) across. The average RAT is a little smaller, at approximately 2.6 feet (80 cm) in diameter.
    These large commercial ram air turbines are capable of delivering between 25 and 70 kW of peak power to the aircraft systems. This will reduce when the aircraft's speed drops and is a factor which pilots have to contend with during emergency procedures. Older RATs had standard two or four bladed propellers similar in design to those used to drive propeller aircraft. Modern variants have multiblade propellers with shorter, duct enclosed blades which greatly increase efficiency.
    Note that a engineer could have designed a "RAT" to operate 100% of the time if it was more efficient... Instead these are devices of last resort... Engines have failed, APU's (auxiliary power units) have failed, and the "RAT" is deployed to take the only energy available (aircraft altitude and speed)and convert into enough energy to operate the aircraft control surfaces, landing gear, brakes, avionics, etc.--Until the plane is on the ground (or has restarted the engines).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, one way to test the theory would be to attach a turbine (or a windbelt might be easier) to a car with a low drag coefficient so that it equals the drag of a car with a higher coefficient. With turbines, you should be able to furl (I think that was the term) the blades so that you limit power, but get a set amount of drag at certain speeds. The windbelt takes up surface area... and I suppose it would add more surface area at higher speeds for more drag.

    Obviously the exercise seems simple. As long as the coefficients end up the same, with the same weight, they should draw the same amount of power. Reminds me of the Mythbusters episode where the flipped the car around, and the drag went from .34 to .37 or so.

    But why would you add drag when you lose power in the process? They already have to add some, as I understand, mainly to add downforce for traction. If some wind power generating equipment could cause downforce, so that you could get traction for braking/accelerating then you could potentially get your 50% efficiency back for the same drag coefficient.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Since you mention the Mythbuster's episode I'll point out one of the flaws in the reasoning they had. Jamie said that the shape of a drop of water falling is the least resistant to the air flow. This isn't so. Water would normally form a ball, other forces not acting on it. When the ball falls through the air it distorts into the drop shape. The least resistant shape is a parabola. Hence the design of a bullet; made to slice through air above, below, and on the sides.

    One of the "slipperiest" cars ever built (in its time) was the Citroen DS19. Looks a bit like a frog. But for air-flow purposes the shape was a relative parabola. I recall its drag coefficient being a very low 0.29 (but my memory tends to be faulty).

    So you could equip an electric car with "free running" turbines that would add to the drag under normal use and then activate upon the need for braking and put that braking power in to the batteries. But would it be efficient? Probably not as efficient as the usual regenerative braking, which does not add to the drag because it's "enclosed in the envelope". Both will add to weight, which is another factor.

    Straight forward turbines of any type are not very efficient in converting the available mechanical force into electrical power. Especially not over varying speeds, as the best design for 5 mph is not the same as for 50 (other factors being equal, which they never are). And remember that in the example Bill cited power is actually being added to the wind stream by the heat it picks up.

    Some things work only on a given scale, too. You can't grow a 50 foot ant and you can't make a 1 inch sun. And when it comes down to it, how practical would it be in terms of cost and over-all efficiency? Since you can't really use turbines to add power while the vehicle is moving, how much time would you spend braking?

    I have to admit I love looking in to this sort of thing, though! :D
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, I think they mentioned a drop of water forming the best shape because it takes the path of least resistance, and is malleable enough to change shape to make that happen.

    I'm just saying if you could get some power out of an added drag coefficient of .05 (the difference between your example, and say a Prius), then it is quite likely that you can design a car to regenerate power due to wind with all the features that you want from the drag. Downforce, cargo space, and wheels all necessitate some drag.

    But weight as you mentioned wouldn't necessarily be a problem. If you could draw 50% efficiency, you could actually remove about half the batteries (by far the majority of the weight) for the same range. If you had a 200 mile range, swapping the weight with a regenerative device at 50% efficiency, cutting out half the batteries would give you 100+50+25... =~200 miles. Since the method of extracting the air might not weigh as much as the batteries, you would actually get further due to less overall weight (say 75%).

    I've got a few engineers in my family, so the old joke about engineers never getting to their destination because they can only go half of the way each time pops up a lot. If you could actually get 50% of all power lost regenerated, then even a fairly weak generator like solar cells added could give you extreme range.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    No... Adding a wind turbine (drag) to a car is a lost cause... Otherwise I would have put a wind turbine on my old airplane. You probably would loose 80% of the energy by adding that drag. Spending 5 units of energy to get 1 unit of useful energy is a lost cause.

    Using regenerative braking on a car is not a huge gain. ~30% of a car's energy is loss in braking (assuming city traffic? freeway traffic is a lot less). Assuming 50% of energy is recovered and reused (that is on a good day)--That would give you ~15% increase in fuel economy.

    If you live in a hilly area--it is not impossible that long down grades will produce more energy than the battery has the ability to store--so then you get 0% from regenerative braking in these cases).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    As to the issue of efficiency, a typical solar panel is only about 18% efficient which is rather dreadful. I'm not sure a turbine can even meet that level.

    If you think about it, a turbine blade is an incline plain. Air moving over it is force to change direction when it hits the surface. If it were fixed, the air would retain most of its energy except that converted to heat by the redirection (partly absorbed in deflection, partly radiated). Since it can move, it takes whatever force is applied to it (again, a small amount of what hits it - depending on blade size et cetera) and turns it into a leverage force against the axle, which acts as a fulcrum (the resistance or load being the theoretical interface between the two magnetic fields). More loss as the mechanical force distorts the lever; more heat. Further resistance on the axle bearings and such turns more of the energy into heat. By the time you actually get to producing any electricity, most of the energy from the moving air is gone.

    Efficiency is the bugabear of all energy systems.
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    All power to a car is generated by an ICE (except electrics) that is not efficient.

    Attaching another inefficient item (wind turbine) to the car simply makes the ICE work harder.

    This is trying to have your cake and eat it too. Talk to one of the engineers in your family. They should be able to explain that what you want is impossible.

    Russ
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Well, the gist I'm getting from you guys is that any kind of inefficiency shouldn't be put into a car. But really, if everyone thought this way, they wouldn't have regenerative braking. Even though the weight of the system is almost negligible (like the weight of circuit boards), you're losing something before you're gaining it back. The newer hydraulic regenerative brakes they're coming up with most certainly have added weight, but they still give a net gain of overall range.

    The main trick, especially with the current regenerative brakes is that they're mostly utilizing a feature that's already there (in electric/hybrid cars). So instead of adding systems, they're mainly replacing them to keep the weight/drag the same. Ultimately the wind resistance is a transfer of energy, and if you can find the right method, you could extract some from the exchange.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    You have to remember that inefficiency isn't just "anything that detracts". Every aspect of design has some negative value, such as the extra weight of the regenerative braking you mention. The efficiency is determined by whether or not the benefit from the addition is greater than the cost (not just monetary). The thing about adding turbines is that they would only usefully produce while braking, whereas they would drag all the time. Vehicles spend most of their time moving, not stopping (except in Vancouver traffic :p ) so the standard regenerative braking adds more than it takes away but the turbines wouldn't.

    Whenever you explore a fresh, new idea you've had it's a good idea to research for previous attempts at the same thing. Almost always you'll find someone has tried it before, at least in theory. From there you can determine why it wasn't adopted. Once you know why something doesn't work, you can determine whether you're wasting your time exploring that avenue or if there's some way to make it work. A lot of the technology we have today didn't exist even 50 years ago, so it may be a matter of applying some of those new developments to make an old idea feasible.
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    As Marc pointed out - regenerative breaking is totally different - only in use at the appropriate times.

    Now if you can make a 'pop up' wind turbine the deploys during braking situations and retracts into it's aerodynamic holder during normal driving you might have something. Would add a new excitement level to cornering!

    Take the blinders off - you are on a one track road toward the cliff. There are plenty of other opportunities to develop something.

    The green sites love things like this - all the little boys and girls say, 'Oh Gee!'. I have seen the concept discussed a hundred times.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Feasibility of smaller turbines/higher wind speed
    russ wrote: »
    Take the blinders off - you are on a one track road toward the cliff. There are plenty of other opportunities to develop something.
    .
    Well said Russ. Some of you guys have far more patience than I.
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Resurrecting a YEARS old thread... obviously a big no-no on the internet. But it's the only time I've ever done it, so don't hurt me :). And don't worry, I don't expect a perpetual motion machine.

    The first idea I had on this obviously assumed more benefit than is possible. But the final 2 posts I never responded to were what I was trying to allude to. If you did use the system like regenerative braking, there should be some energy there. Whether you could effectively harness it, and how much it would give you is the question. Say you had a lightweight, plastic turbine embedded in the car with a door that would open to allow air in during braking, and close to an aerodynamic state while driving. Especially if you've already got a battery/inverter in the car (fully electric or just for regen. braking), it could add minimal weight. It would also add a LOT of drag, similar to a parachute on a drag car. But as I see it, if you've already got the heavy batteries and other electrical components, you may as well try and utilize it as much as possible.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    The regenerative braking used in some electric cars is much simpler than that; a mere change in the wiring and the driving motor becomes a generator to recharge the batteries. Same principle as engine braking on an ICE vehicle, and far fewer parts than having opening vents and extra turbines.

    Keeping designs simple is not only key to improving efficiency, but also to longevity and practicality.

    For a great lesson in "how not to do it" go look at an old combine harvester from the '60's. Old idea predating the 20th century with every bit of "modern" tacked on resulting in a complicated mess of machinery that broke down a lot and was difficult to service.
  • Arqane
    Arqane Solar Expert Posts: 31 ✭✭
    Re: Feasibility of smaller turbines/higher wind speed

    Definitely, the fewer moving parts, the better. A simple corkscrew-shaped turbine made out of plastic connected to a motor isn't much more complicated than the multi-wheel motors they're using now. And the brake line would have one more connection as well, to open the door. If something that simple could return another 5% efficiency on top of regenerative braking (the initial 50+mph wind *is* a lot of power), it would be worth it.

    It's basically the same idea as an efficient home system. If you've already got a battery bank, inverter, and solar collectors... why not add a wind turbine if the conditions are decent in your area?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Feasibility of smaller turbines/higher wind speed

    Thanks to Marc/Cariboocoot, I can now post this on the correct thread:

    What is the horsepower generated by a car braking... Figure it is at least 1/2 of the HP rating of the engine (there are whole bunch of issues with brake HP, SAE HP, Dyno HP at the wheels, etc...).

    In any case, look at the diameter of a wind turbine that is generating around 3,000 Watts in a 25 MPH wind. If you wanted even ~4 HP braking (~3kWatts), for speeds over ~25-30 MPH (typical wind turbine rating), you would be looking at a 12+ foot diameter turbine (Skystream, one of the more efficient turbines out there: Skystream 3.7 has a rotor diameter of 3.7 m (12 feet). At the rated wind speed of 29 mph, the turbine generates 2.4 kW of electric power).

    Just no practical way to do effective braking with a wind turbine.

    I had a ~1,000 lb airplane with 6 foot prop and 65 HP motor--It had rather "leisurely" acceleration with that combination.

    Believe me, you would not want a 6 foot prop spinning at ~2,600 RPM as you pull up to a cross walk or drive into an accident.

    -Bill "tofu for brains" B. :p:blush:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset