1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Heating water with a wind turbine

  1. Dec 3, 2009 #1
    I am new to this forum, I thought you guys could send me in the right direction. what I am trying to do is heat water with a wind turbine. the turbine produces 3 phase wild AC with voltage of 0 to 270V. related to wind speed. I am aware of the general practices with wind turbines- charging batteries and grid tie systems. what I am trying to figure out is the physics of the energy produced by the turbine and the best way to convert that energy into heat with out the batteries and converters.
    Is there some kind of resitive heating element that could handle the changing voltage ?
    any help would be great ! if you think I am crazy then let me know.
    Thanks Ed
  2. jcsd
  3. Dec 4, 2009 #2
    What is the maximum power that the turbine can develop?
  4. Dec 4, 2009 #3


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Actually, if you are not charging batteries, you can use a simple system, involving just a resistor. Along as the turbine is turning, you will get 'some' power out - which is better than when you are using a battery because you ned a certain minimum output voltage to start any current flowing into the battery. If you expect a maximum of, say 1kW from your turbine then the resistor (heating element) must be beefy enough to handle a kW, even is it will not get that hot, most of the time.

    The down side of wind power is that the average power you get from a wind turbine is not a lot, particularly when you want Heating from it. Electical energy appears 'go a lot further' when you use it for working electronics, motors and lights than when you want to heat things up. I know that a kWh is a kWh is a kWh but. . . . .
  5. Dec 4, 2009 #4
    The maximum power would be 4,394 watts @ 28 MPH wind. I must say that I have done alot of searching for any information on this and there is nothing out there. so it makes me think that it is not a good idea. but it would seem to me that in a cold climate something like this would be usefull.
  6. Dec 4, 2009 #5
    what would the conversion be from KWH to BTU ? the other problem is by have heating element sized to handle the maximum output of the turbine that would load the turbine and it would not turn untill the wind speeds were high. the ideal set up would be a "stepped up resistor" or some type of controler that could get the maximum energy for slow wind speed than could handle the higher current from high wind speeds.
  7. Dec 4, 2009 #6


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    A single resistor is all you need and, preferably, a very basic alternator with no diodes up there. You won't get any more actual power by switching resistors. Some protection may be needed to cope with excessive wind speeds but the last thing you need is a regulator. That would just cost you money and would dissipate 'extra' power needlessly when the resistor could do just as well and for free. You don't care what volts you get - just the more the better.

    I don't see anything wrong with your idea, in principle, as long as your house is well insulated enough for a peak of 4.5kW (and a mean value could be less than 1kW). A 4kW system would not be cheap and even in cold climates (away from the arctic circle) you can get plenty of thermal energy (several kW), even on a dull day, with one of the better solar collecting systems (a black polythene box wouldn't be good enough). That could be a better way to spend your £5k+. But if you live in Antarctica, things would be different in the winter and your wind system could be very good value -'cos it's always blowin a gale down there.

    btw, 1 kilowatt-hour (kWh) = 3413 British Thermal Units (Btu)
  8. Dec 4, 2009 #7
    I agree that solar collector systems are cheaper. what i am working on is becomming a wind turbine installer. the "off grid' and "grid tie systems" are costly with all the controlers and batteries. but they are proven to work. I am just looking for a different angle, If I could set up a system like this it would be a good addition to a solar heating system. IE when it is storming the solar is not making heat but the wind is blowing.
    I own and operate a machinery repair shop now. I heat my 1500sq ft shop now with a waste oil boiler with pipes in the shop floor. it would very simple to put a heater inline and use the heat energy
    my idea is to take a "off the shelf" tank water heater. lets say a 20 gal 120V 1700 watt unit and hook the turbine directly to the heater. some of the question that I have :
    1- would the heater element make any heat at lets say 60 V and 500 watts ?
    2- how could I use or hook up the 3 phase power ?
    3- at what point would the 120V element burn out from over voltage?
    Thanks for all your help Ed
  9. Dec 4, 2009 #8


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    V sensible to consider both wind and solar systems.
    It seems that you may be able to get hold of an old / cheap turbine (?). Good value if you can, once you have done some installing and replacing.

    Answers, 'off the cuff':
    1. Half volts will just give you 1/4 power. If that's enough for your it's enough 'cos you can't do better. I have a small wind turbine on my Yacht and most of the time it is supplying much less than half peak current to my batteries so you'd have to know or experience the actual statistics of wind in your area. (Many small scale systems which have been planned / installed in the UK are little more than useless, based on very over-optimistic predictions for wind in city areas).

    2. 'Hook-up'? To the mains? Not a chance without very sophisticated gear which you'd have to buy in. Even used locally, the speed of your unregulated turbine and the AC frequency would be very variable and not much good for anything but heating. Don't go there unless you are going to do it on a big scale and pay for the know how.
    3. The burn out voltage depends entirely on the actual design. If this wild, unregulated turbine could give 100% over-volts then you'd need European heaters or US ones in series / parallel. (Four: two series pairs in parallel would have the same resistance as a single heater, produce the same output power and stand 100% over voltage) . A suitable fuse would protect the element. tho' - but the turbine would still need help to stop it shaking itself to death in a really high wind.
    If it were me, I'd put up a turbine with the simplest arrangement and see how well it actually works with a single heater. You could always step up the tech if it works well.
  10. Dec 4, 2009 #9

    1- would the heater element make any heat at lets say 60 V and 500 watts ?
    Yes! depending upon its rating.

    2- how could I use or hook up the 3 phase power ?
    Is the turbine output three phase? you need three heater elements and then can join them in two possible configurations, Y and Delta. In Y, all three elements are tied at one point, remaining three terminals of each are connected to each phase.

    3- at what point would the 120V element burn out from over voltage?
    For short durations it might survive large voltage. Anyway it is more a question of the quality of the material and its working life.
  11. Dec 4, 2009 #10
    Wow! Everyone has been so helpful thanks.
    so here is what i am thinking: the turbine I will be using puts out 270V three phase at rated wind speed (28 MPH). I would need the turbine and a wind control unit to regulate the turbine speed or "over speed".
    then take 3 standard "off the shelf" 120V 1500 watt elements hook them in a Y pattern to the turbine.install them in tank of water.
    I am sure that you would have to play with element sizes to get the peak performance out of the system. but I am just trying figure the "physics" or the basic principle of this plan. Some questions that come to mind :
    1- Can I assume that the Watt to BTU will be constant with a given resitor regardless of voltage?
    2- If the wind was blowing at 14MPH, the turbine would be putting out 1000 watts at "135V?" or 45V per leg. will a 120V 1500w element make heat and be efficient at that voltage?
    3- if my turbine out put is 270V can I assume that each leg will produce 90V ?
    4- if the answers for all three are yes, why hasn't anyone thought of this ?
    Thanks Ed
  12. Dec 4, 2009 #11
    The project is interesting and may have merit. As to why others have not thought of this? I offer some comments which you may or may not know.

    Generally a building, on grid or off, has an electrical load and a heat load. Efficiency improves by matching the load with a source. In a conventional building I understand that electric heat has the highest cost and lowest quality. This despite the fact that electricity is ultimately derived from some other fuel source. I am not sure the economies change for an off-grid design.

    You could calculate the cost of fuel versus investment in electrical alternative over some time frame, and estimate the payback on converting wind to heat. Chances are it is a better payback to convert wind to battery energy, but maybe not, if you have a good thermal capacitor design.

    On a tangent path, the CERTS microgrid initiative seeks to integrate wind and solar generators as "negative loads" on a stable small grid. Each microgrid would be stable on its own but plug into the grid for power sharing under normal circumstances. These grids might also support "off-grid" local grid communities in the near future.
  13. Dec 4, 2009 #12
    1- Can I assume that the Watt to BTU will be constant with a given resitor regardless of voltage?
    > No, power(measured in watts) depends upon voltage squared. Double voltage would produce four times power, also said in a previous post. BTU is equal to the product of Watts and the time for which these watts are used. 1 electric unit or 1000Watt for 1 Hour is 3413BTU.

    2- If the wind was blowing at 14MPH, the turbine would be putting out 1000 watts at "135V?" or 45V per leg. will a 120V 1500w element make heat and be efficient at that voltage?
    > No, per leg voltage are essentially equal for their RMS value (measured with voltmeter). Just they have different phases. Instataneous voltage of a phase depend upon the position of the rotator with respect to the three coils that produce voltage.

    3- if my turbine out put is 270V can I assume that each leg will produce 90V ?

    4- if the answers for all three are yes, why hasn't anyone thought of this ?
    My guesses: Electricity is far more convenient form of energy then the Heat. Heat can not be stored and retrieved as efficiently. Electricity could be stored in batteries. It could be used to drive thousands of other devices besides producing heat.
  14. Dec 4, 2009 #13
    I would think about using 6 domestic elements arranged in star (Y) with two elements in series in each leg this would keep the voltage drop across each element to something close to the design value, better still might be to get some UK 240 V AC elements.
    BTW abcrepair when you quote voltages what are you quoting line to neutral or phase to phase?
  15. Dec 4, 2009 #14
    We've all been blinkered by our obsession with electricity, if the windmill is close enough to the shop why not just hook a pump up to the windmill, and pipe it into the tank, make sure that the pipework outside the building is well lagged and there you go.
  16. Dec 5, 2009 #15
    Well, I didn't think this was going to be so easy, or someone would have done it by now.
    I was a service manager in a standby generator company for a few years, but that was completely different. the voltage was always constant (with regulation) and the KW was relative to engine HP. with "wind power" the voltage is relative to the wind speed. so with the voltage squared = power at low wind speeds we will not make the energy needed to make this work. so we are left with the normal way that wind turbines are used now. IE rectify the wild AC to constant DCV then invert it to AC at a constant voltage. so this puts me back to "square one" my goal in this was to produce useable energy from wind without the $3000 to $5000 of batteries and controlers.
    I am not ready to give up on this idea but I just don't have enough information. I don't have a wind turbine working now to use so I am working off a spec sheet for the turbine.
    I am comming to the conclusion that this project is "over my head" I still think that the basic idea is sound but to make it work is a different story.
    Thanks Ed
  17. Dec 5, 2009 #16


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Don't bother to go for a 'smart' solution. Just connect three standard 110V heaters in a star, if there's an Earth on your alternator and watch the water get hot!
    Anything else will be a matter of diminishing returns and you'll basically have to PAY(omigod) someone for their knowhow and for special equipment.
    This is Scrapheap Challenge - go for it.
    You will, presumably, have thermostats on your heaters.
    Good luck.
  18. Dec 5, 2009 #17
    It is funny you said that, I have been thinking the same way all morning. the wind turbine is a Synchronous permanent magnetic generator 3-phase 16 poles. I have all kinds of alternators from tractors and a 6000 watt gasoline powered generator to play with but I don't think I could make the same kind of power as the turbine. I could try and remove the bridge rectifier on the tractor alt and use the engine on the tractor to regulate the speed and use some type of small resitors. but I am just not sure if that would be the same.
    this is why I am going for the "smart" solution.
    I should be working in the shop taking this tractor engine apart and making money instead of working on my "ideas"
  19. Dec 5, 2009 #18
    I've been doing some multidomain simulations in the free version of DYNAST shell. The software has a learning curve, but provides a 3-phase source model that could probably be programmed to respond to wind speed. The loads are most likely simple resistors in a star or delta configuration, but there may be a temperature-dependent feedback parameter from the thermal system in a realistic model (the resistors may have linear or non-linear temperature curve).

    The tricky part of the simulation is creating a thermal model that converts power dissipation in each resistor to useful heat stored in the heat capacitor (water tank). I would look into instant hot water heaters and/or electric hot water heaters to study some heat exchanger designs (personally having no experience with heat transfer). If I were trying to design a system on the cheap, I'd build confidence with some simple simulator models just to get on the "right track."
  20. Dec 5, 2009 #19
    I have looked into some different types of water heaters. the instant water heaters or hot water on demand are huge energy users infact most times a normal household doesn't have enough power to run one. IE 200 amp service.
    I have also looked at a 3 phase hot water heater but they are all too large for this application.
    I can say that the system that i have in mind for the hot water requires a max 110 deg water. and the return water would be around 60 deg. unlike a domestic hot water heater that takes 45 deg water and makes it 160 deg.
    that simulator sounds interesting but I don't think I am smart enough to make it work
    Thanks for your help Ed
    PS I have the oil pan off the engine !
  21. Dec 5, 2009 #20


    User Avatar

    Staff: Mentor

    Since hot water is a momentary load and wind is a more continuous (but somewhat unreliable) power source, you'll want a tank to store and heat the hot water. But since your usage won't necessarily match your heat input, you'll want to connect the wind powered water heater to a secondary water heater that will provide a regulated, consistent water temperature. The wind powered water heater can probably be a normal water heater (though I'm not sure about the heating element itself).

    You'll want to calculate your monthly hot water usage and the energy it takes to warm that water. Depending on how much energy you can generate and how much you will use, you will want one or more of the following features:

    1. You must utilize a high-limit switch on the water heater - you can probably use the one that comes with it. It has a limit of 150F, I think.

    2. Depending on your usage, you may want to add a tempering valve to mix cold water with hot water to drop it from 150F to 110F before getting to your secondary water heater.

    Running some quick sample numbers:
    The incoming water temp can vary from 45-70F.
    Using your max of 110F... (seems low, but ok)
    100 gal/day hot water usage
    200w wind turbine

    In summer, your system looks like this:
    ((200W/3.41btu/h/w) * 24h ) / (100 gal * 8.3 lb/gal) = 20 F dT
    Since you need a 40F dT in summer, you can use a 50 gal tank and be sure you won't overheat your water.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Heating water with a wind turbine