Heating water with a wind turbine

[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.

 

[SystemTheory]

abcrepair,

Prairy Turbines sells a DIY system for direct grid-tie with a 3-phase motor.

http://www.prairieturbines.com/theory.htm

http://www.prairieturbines.com/purchase.htm

Maybe there's some ideas here you could use.

 

[abcrepair]

I am making progress on testing this plan. I could use "engine block heaters" for the elements. I can get 200W to 1500w 120V or use the standard hot water heater elements. so the next thing is the generator this is maybe were you guys can help.
I am trying to find something I might have that would work. would a three phase electric motor turned by a hydraulic motor produce the same kind of power as a Synchronous permanent magnet generator. or a small gas powered generator ?
Thanks Ed

 

[sophiecentaur]

A three phase motor has no magnets in it so it would not generate any power. The principle of the three phase motor relies on a phase difference between the windings to turn a 'squirrel cage' or equivalent. The rotor has no electrical connections to it so you couldn't use it as a field winding.
I don't understand where the hydraulic motor comes from. Surely the place to put the alternator is right up there on the turbine and avoid any more transmission losses - other than the negligible resistance of the downlead.

 

[SystemTheory]

As I understand it, for heat production testing the plan is to run the electrical generator from a hydraulic motor on a test bench to simulate output prior to building the actual rig.

If you turn the squirrel cage with a drive torque it induces a magnetic field in the stator windings so the machine acts as a generator, according to the Prairy Turbines link. This is the best type of unit for the grid-tie system without using a traditional invertor (see reference links above).

(Edit: on second thought, some excitation winding may be necessary in the Prairy Turbines unit.)

But in this application I am not sure what type of generator would be most effective in all wind conditions. It could be a straight DC generator or 3-phase AC. The DC losses will be greater if there is a long wire run between the generator and the load. That much I know.

 

[sophiecentaur]

That does surprise me (the squirrel cage thing) but, if they are using one, it must work. I might suggest that it assumes that there is already a three phase supply connected, which is not usually the case for an isolated alternator.
I though you wanted something that 'just worked' and produced some free hot water for your heating system. What you are now suggesting is something much more sophisticated and serious Power Engineering (cooh!). I would not be happy to install anything like that for myself unless I did an awful lot of homework and got to know all about the control and safety aspects of such an installation. I should not imagine your electricity supplier would be happy with anything other than a really pukkah system to be connected to their three phase supply.

DC generators are not as good, in many respects - particularly for an application in which you don't actually require DC. A commutator and heavy rotor windings is a much more costly arrangement than a light rotor with slip rings. A straight alternator is bound to be the best solution - and you're more likely to get hold of one, I should imagine. Does anyone actually use DC Dynamos these days?
I don't think the 'long wire' would be a problem for such a small amount of current. 10 sqr mm would be more than adequate. Any energy loss which is actually inside the building would not matter in any case!

I think that a synchronous generator would not be particularly efficient because it would require a constant speed turbine. This would require you to vary the pitch of the blades to suit the wind speed (like the big jobs all around our coast). That is another layer of cost and sophistication.

Do you know, I think you ought to sit down and write down a specification of your minimum requirements. It would help you actually decide on something specific and you could eliminate a lot of unsuitable solutions. At the moment, you seem to be on a divergent design path? :-)

 

[abcrepair]

As I understand it, for heat production testing the plan is to run the electrical generator from a hydraulic motor on a test bench to simulate output prior to building the actual rig.

that is correct, my goal is to prove the theory. I want to raise the temp of water with a 3 phase generator. allso find the correct size elements for any given wind turbine.
so the only way this will work is to get a generator from a wind turbine.
I spoke to a supplier today and I have two choices the "off grid" version 0-60Vac or the "grid tie" at 0-400Vac
I would think the 60V unit would be better for "off the shelf" elements. but is the higher voltage better ?

 

[abcrepair]

Do you know, I think you ought to sit down and write down a specification of your minimum requirements. It would help you actually decide on something specific and you could eliminate a lot of unsuitable solutions. At the moment, you seem to be on a divergent design path? :-)

what I was trying to do is test this theory with something I had around here. but I have come to the conclusion that I must use a synchronous generator because what I want to prove is that at low generator speeds (low voltage) I can get the 3.41Btu to Watt thru a element that can take the max out put of the generator.
this started out to heat my shop with wind but now I am thinking if I could get a working system going I could share it with everyone. I have limited education, time and money to work with.
Thanks for your help Ed

 

[sophiecentaur]

You will never get a lot of power out of your turbine at low wind speeds - unless you make it so enormous that it will blow away in a high wind. If you try to take too much power at low wind speeds, you will just stall the blades (my little system does just that). There will be a specified (or a measured) power output from a turbine for a certain wind speed and no choice of generator can improve on it. Choose the setup appropriate to a certain peak output and put up with the power dropping off at other times. Feathering blades and regulators will make the costs soar.
Perhaps this has to be a two stage project. Get a low power system going (really basic with a lowish design power) and measure the average power you can get from it over the winter - say 200W. That figure should scale up to whatever you judge to be necessary for your full requirement - say 2kW. Then choose the appropriate piece of kit.
I think you are over optimistic in wanting to supply other people from a home built system without getting professional (=expensive) advice and equipment. It's a different ball park from DIY.
If, as you say, you have limited education you will find that, apart from on forums like this, you will pay and pay for what you need to know. Turnkey systems are V expensive and you could buy a pig in a poke if the wind statistics are not suitable.
Even a modest heat output from a cheap, home brewed would be worth having and it would establish your cred with future customers. You want to learn as cheaply as you can, I assume. The experience of a simple system would be the best value for you, I am sure. (You could always sell it on if it's a success)

 

[SystemTheory]

Ask the supplier if a wiring diagram is available online to evaluate for your needs. I am not sure if you'll need excitation in the synchro generator from an electrical source?

Here's a map of wind resource. I know a solar contractor who always puts up a tiny wind sensor on a tall pole to study wind resource before installing a generator in New York or North East residential systems:

http://www.awea.org/faq/usresource.html