Heating water with a wind turbine

[abcrepair]

Hello,
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 without 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

 

[Jobrag]

What is the maximum power that the turbine can develop?

 

[sophiecentaur]

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. . . . .

 

[abcrepair]

What is the maximum power that the turbine can develop?

The maximum power would be 4,394 watts @ 28 MPH wind. I must say that I have done a lot 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.

 

[abcrepair]

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. . . . .

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 until 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.

 

[sophiecentaur]

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)

 

[abcrepair]

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. let's 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 let's 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

 

[sophiecentaur]

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.

 

[mabs239]

Answering:

1- would the heater element make any heat at let's 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.

 

[abcrepair]

Answering:

1- would the heater element make any heat at let's 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.

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

 

[SystemTheory]

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.

 

[mabs239]

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 ?
NO

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.

 

[Jobrag]

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?

 

[Jobrag]

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.

 

[abcrepair]

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

 

[sophiecentaur]

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.

 

[abcrepair]

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.

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"

 

[SystemTheory]

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."

 

[abcrepair]

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 !

 

[russ_watters]

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.

 

[sophiecentaur]

abcrepair
You're my kinda guy.
Just get going and stick that turbine into the air. The mast and the supports will take a bit of ingenuity and all you'll want to do will be to get something out of it. Whilst everyone else on this forum is busy doing sums, you'll have free hot water.
You could lose a lot of sleep wondering how optimal your load is and what resistance you really ought to be presenting to the generator but, if you have a few hundred Watts available, the water will still warm up. Once it's up and running you could measure the source impedance of the generator at different speeds and you may be able to switch different resistors in and out, depending on the speed. But, nothing is more convenient than an of the shelf water heating element and they don't make them in many different resistances.
Good value.
Good luck.
You can DO it!

 

[abcrepair]

Russ,
I would agree with you if I was looking to make "domestic" hot water. my goal is to store the heat in the concrete floor. or hook it to any hot water heating system. it would be simple to turn on the curclutator pump when the water tank got up to 120 deg. my thinking is use this as a addition to the normal fuel used to heat in my case it would be waste oil. if you had several windy days I suppose you could over heat the system. I never heard anybody complain it was too hot on a cold snowy night.

 

[SystemTheory]

Not to discourage or encourage anyone, I offer a couple links to inform of current trends in energy efficiency. Generally the biggest gain in efficiency comes from using the heat load to also generate some electricity from the fuel (CHP, combined heat and power). In Europe and American cities CHP plays a large role in the utility scale model, and new technology will integrate CHP into microgenerator applications.

Freewatt home cogen:

http://www.hondapowerequipment.com/products/homeenergy/freewatt.aspx

Tecogen embedded microgrid cogen:

http://www.tecogen.com/cogen.htm

On details of your project, if three commercial electric water heaters were to be hooked up as the load, do you have a guess and a specification as to which models might work? Did you locate a spec on a three phase water heater to serve as a reference?

My dad used to do plumbing. He said radiant heat (pipes in a concrete floor) is the best, but it can become too hot. I don't know how storing energy in the floor gives you much of a regulated comfort in the building?

 

[russ_watters]

Russ,
I would agree with you if I was looking to make "domestic" hot water. my goal is to store the heat in the concrete floor. or hook it to any hot water heating system. it would be simple to turn on the curclutator pump when the water tank got up to 120 deg. my thinking is use this as a addition to the normal fuel used to heat in my case it would be waste oil. if you had several windy days I suppose you could over heat the system. I never heard anybody complain it was too hot on a cold snowy night.

Oh, ok -- any reason why you want the water so cool?

 

[abcrepair]

Russ, when I built my shop I ran 1200 ft of 1/2" "pecks" tubing in the concrete floor, 4 runs at 300 Ft each. the part that has heat in it is 32' x 40' and 6" thick. the concrete will crack if you get the water too hot. I run the boiler at 110 deg. the good thing is that once it is warm it stays warm for a long time, it is well insulated. years ago when i was trying to get a reliable waste oil burner working i could go for two or three days with below freezing weather out side and stay warm in the shop. so I look at the wind power as "storing" the heat in the floor for when the wind isn't blowing.
System Theory, I was thinking 3 120V 1500 watt elements, I think I could go as low as 1000 watts but the turbine can produce 4000 watts so I would be afraid of burning out the elements. all the 3 phase heaters i could find were well over 10,000 watts.
I don't think that I could heat the shop on wind alone, whatever heat I could get from the wind would be that much less fuel I would have to burn. I am allso looking at this to create or invent a new kind of system for wind power. right now you have two choices off grid with batteries and a load dump or a grid tie system with "net metering". with the off grid you have to deal with batteries and the grid tie system shuts down when the grid power is down. you could have a grid tie with battery back up but you are talking big money. with the system I am trying to make you don't need any of that, it reduces the cost of a system as much as 40%.
I know that i could buy a lot of fuel for the money that a turbine would cost. but I just get a kick out of making something from the wind.

 

[abcrepair]

You guys have got me really thinking ! I could throw together a hydraulic test stand together real easy. I would just need some type of generator that matches the wind turbine. then I could simulate wind speed with different hydraulic flows and try different elements.
I am still not sure on the math of this whole idea. a hot water heater element is just a wire with something non conductive around it. so a heater element that was rated to produce 1500 watts at a given voltage would have a smaller wire than a element rated 4500 watts at the same voltage. more energy can fit thru the bigger wire. I am I think right ? if so if we put a lower voltage thru the any element will it still produce the 3.41 BTU per W.
this is the big question in my mind. if that conversion stays constant then the rest can be worked out

 

[SystemTheory]

From what I see here, the wind velocity probably has a v-squared impact on RPM, and the voltage is a linear function of RPM. The power output is a velocity cubed relationship.

http://www.windstuffnow.com/main/wind.htm

To rate the heater element begin with drawing a three phase source/load schematic. Your hydraulic rig could possibly confirm the rpm/voltage relationship but not the wind speed rpm relationship, as I see it.

 

[abcrepair]

From what I see here, the wind velocity probably has a v-squared impact on RPM, and the voltage is a linear function of RPM. The power output is a velocity cubed relationship.

http://www.windstuffnow.com/main/wind.htm

To rate the heater element begin with drawing a three phase source/load schematic. Your hydraulic rig could possibly confirm the rpm/voltage relationship but not the wind speed rpm relationship, as I see it.

That was a good link for building a wind turbine. I agree the test stand will only give voltage to RPM, the wind turbine will determin the amount of power at a given wind speed. I have all the flow charts and power curves for the turbine at different wind speeds. I know I can make power with wind. but there is still that big question, will I have 3.41 BTU per watt at different voltages thru the same heater element. I don't see how it can.
Thanks Ed

 

[SystemTheory]

Go to google and type "btu per watt hour". Result: 1 watt hour = 3.41214163 btu.

This is just a unit conversion factor. It always holds. Your problem would be maximum rating of the heater element (high wind, high voltage, high current) and some estimate of the average watt hours (time integral of wind speed and duration) for btu conversion. You may want to derate the heater core elements if you purchase units, i.e., use a 240V element at lower voltage for more durability.

Also the thermostat on the boiler provides temperature regulation in cold weather, since you are using the wind as a preheat source. Warm weather is another matter ...

 

[abcrepair]

Go to google and type "btu per watt hour". Result: 1 watt hour = 3.41214163 btu.

This is just a unit conversion factor. It always holds. Your problem would be maximum rating of the heater element (high wind, high voltage, high current) and some estimate of the average watt hours to btu conversion. You may want to derate the heater core elements if you purchase units, i.e., use a 240V element at lower voltage for more durability.

I am sitting here thinking how could this be. someone needs to come on here and say this won't work. so what you are saying is, If we put a given amount of voltage in a heater element made for 120V we would get the same amount of btu's if we put it thru a 240V element ?

 

[SystemTheory]

In the moving air, a watt is proportional to the air density times velocity cubed. It hits the wind turbine and generates watts as torque times angular velocity, with some loss. It jumps the air gap in the alternator and converts watts to volts times amperes. So if you work backwards the volts are proprtional to wind speed squared (most likely approximation) and the amps will adjust to the resistance in the load (each heater element is mostly resistive).

My derating comment needs further thought, so don't get distracted by that. The machine will make so many watts, on average, per hour at the heater elements, and that should convert to 3.42 btu if it converts 100% to heat stored in the water/concrete floor. I read a post by a mechanical contractor. When the 120V heater elements burn out, he recommends replacing with a 240V element having a similar power rating, and says those cores will never burn out. That is what I meant by derating the component (using a superior quality core to get the same power output but perhaps longer service life).

 

[YellowTaxi]

The most efficient way to heat water from a wind turbine is just allow it to churn the water. No electricity required, you just use the friction of the churning water itself to heat it up.

 

[SystemTheory]

Doing work directly on the water may be more efficient if the mechanical transmission is more efficient than the electrical transmission. The classic demonstration of the equivalence of work and heat is Joule's experiment of doing shaft work on a fluid inside a thermally insulated container. This is called paddle wheel work and it equals the heat gained by the fluid if the process is adiabatic (no heat lost from the thermos container).

 

[sophiecentaur]

Interesting that the name of Joule came up at this point.
He was a good theoretician and a good experimenter, so I believe. However, there is a story that he went to climb a mountain whilst on holiday in Switzerland and calculated that a sandwich would get him to the top - on the basis of Energy needed for Work done in getting his mass to the top. He forgot the need to keep warm and found that he'd nothing like enough food for the climb. Perhaps his practical sense was not in proportion to his other abilities.

Have either of the two previous posters any idea how inconvenient it is to transfer mechanical energy over a (unspecified) route and then to provide just the right amount of braking / friction to make effective use of it - reliably?
If God (a figure of speech, so please don't pick me up on it) had intended us to use paddles to heat water with, he wouldn't have given us electrons!

 

[SystemTheory]

I'm a firm believer that, in the future, green energy will be clean and widely distributed the way nature does it with chemical reactions powered by high energy electrons. Some have called this philosophy "the electron economy." I think the mechanical transformer (driveline) would be difficult to optimize and very likely yield no gain in efficiency, since few such machines exist, and machine designers are very innovative.