Heating Water with a Wind Genny

[Michael G]

  First I would like to say I have been one of the people lurking around on this site every day for the last year or two. It is very enjoyable to read what everyone is doing with RE.  (Yes you all can tell me to get a life!!)  

  Now to my pickle.  I want to heat water with wind power and not have to use my LP water heater so much.  I thought I had it all worked out then I read a reply to a post yesterday stating that heating water with a generator would require a 20 ft prop.  My plans were to build a 4 phase machine (actually 2 phase) with 16 overlapping coils and dual 11 inch rotors with 16 slightly skewed magnets.  I had intended on using a conventional 240V dual 5500W element water heater tying 2 of the 180 degree out of phase signals to either side of the elements (hence the 4 phase).  This design either doubles the voltage across the elements or drops the resistance of the element in half (depending on your point of view or so I think).  No diodes or common points.  I believe the elements measure 10 ohms.  

  I do have an electronics background but mostly aircraft radios and inverter power supplies so this flux and left hand rule stuff has a little magic to it.  Does anyone have any suggestions as to any changes or scrapping the design or wire size and number of turns? or maybe trying to match impedances?  Will the cogging be unbearable?  There is no such thing as bad advice.

[Countryboy]

I think it might help if you did a google search of the board for available power in the wind.

If it were me, I'd try to build a genny capable of producing 5 Kw to run the heating element.

You may also want to read zubbly's posts on his 7.5 HP conversions.  I believe he is planning on using that to power heating elements too.

[Dave B]

Michael,

  I have been experimenting with heating water with a 12' single phase set up. I drew this chart (please someone correct this if you see errors) which gave me a good idea what to expect. As you can see over time (and with a very well insulated tank) it is very possible to heat or pre-heat water with wind power and on a reasonable scale. The trick, as always, is to match the power output to the load. A search will bring up many threads on this subject and certain ways to help achieve this. You will find that direct heating is a different ballgame than as with most here who are charging batteries. My next one will most likely be 18' diameter shooting for 300 watts @ 10 mph and would like to keep things safe and reasonably slow at 2000 watts max. It is amazing how much heat even 300 watts is, keep your elements submerged or they will burn out. Keep us posted, Dave B.

[Flux]

Yes it was me that made that comment.

It largely depends on the wind you have and the quantity of water you want to heat (or warm).

Dave has given you the information on the water side of things. 40degF is not exactly hot water but gives you a basis to work on.

You can easily calculate the energy in the wind. Do you know wind speed and how long it blows at a certain speed. What you can do in gales bears little resemblance to the average day. If you have wind 24 hrs a day you will do much better, here wind comes by 10 am and is gone by 7 pm except in storms.

You like so many others have totally misunderstood the issue of cogging. I have tried several times to lay this one to rest, but so many don't get it that they keep throwing it in and others believe it.

Cogging is a term that describes the magnet attraction of iron causing a torque variation as the machine is turned. Without iron there is no cogging, it is only a concern to motor conversion people and those using F & P motors. even then it is only a concern for starting.

Torque pulsating on load is not cogging and messing about skewing magnets and all the other tricks to reduce cog will not change things, except for reducing the output if you go to extremes.

All single phase machines have a pulsating load, it is inherent from the fact that the power in a single phase load has a sinusoidal form and twice line frequency.

If power delivered has a cyclic variation so must the torque.

If you intend to use a single heater then the load is single phase and by spreading it among the 2 phases of a 2 phase alternator all you are doing is to widen the coil distribution and to a point where you are not gaining much. Adding 2 voltages at 90 deg gives you little gain for twice the resistance.

This vibration from a single phase load is one reason not to do it but not the main one. Single phase alternators are common up to about 10 kW and if constructed robustly they work without trouble, but on a windmill the vibration will make you have to strengthen everything else as it is all a resonator.

The single phase winding only uses about 2/3 of the copper effectively and you need a 50% bigger machine for the same job. Losses are also higher.

To solve these problems you need a polyphase load. Loading your 2 phases with 2 separate heaters will be far better, but it adds complexity to the control. I would go the whole way and use a 3 phase load, it is not much worse for the control and has several advantages over 2 phase in use of connecting wire and the vibration may be marginally less.

Check your wind speed and distribution, decide how much water you need at what temperature and you can see where to go. If you have built the machine, try it with 2 heaters as load ( properly matched) and learn for the next one. If you haven't built it, don't.

Flux

[Stonebrain]

Hi,Michael

Just one thing: electricity is a very expensive way to heat water.

Direct heating of water with solar is the way to go in most cases.

Electricity is a highquality energy (but expensive)that is necesary

for light,anything that has an electric motor(frig etc),and electronics

(computer etc).It should be used in priority for these purposes.

Using it for heating is like pearls for the swines.

heat is a lowquality energy(cheap) that only can be used for heating.

The cheapest way to have it is directly from sunlight.

Something to consider before constructing a huge windmill.

cheers,

stonebrain

[powerbuoy]

One thing though ... an electric heat element submerged is almost 100% efficient, if you have free electricity (wind) then there is actually no cheaper way of heating water ...right?

Powerbuoy

[scottsAI]

Hello powerbuoy,

As with most things around here, I would give that a YES, and NO, it all depends...!

At market prices, burned fuel is 2-3x cheaper per BTU than electric heating.

All depends how it's burned, efficiency plays a big role.

Use of geo-thermal heat pump can make the electric cheaper than burned fuel.

Like you said if free then no cheaper... True, but is it the best use? well maybe.

If the electric could be used to displace other electric cost it may not be the best payback. Which most of us are looking for.

If the heat is needed in a remote location, have to hand carry any fuel etc

You get the idea.

Then again as a hobby it does not have to be the best anything, just want to do it.

Have fun,

Scott.

[altosack]

It depends on how much water you want to heat and whether or not you want to have it on demand or not. A direct solar heating system cost a lot to start, but it will heat more Btus/$ than a wind generator if you need a lot of hot water.

But it's not this simple, either. If you are already planning a wind generator for electricity, you can increase the size somewhat for much cheaper than getting a separate solar hot water system, even if you need to heat a lot of water. The disadvantage to the wind system is that there will be longer times without wind than without sun, so if you want this to be your sole source (no fossil or other backup), you will need a large, very well-insulated storage, and you won't get that much in the summer in most of the US.

To put my money where my mouth is, I have installed several solar hot water (and solar PV systems) for me and for others and on my next system (not yet built, I'm in the process of leaving the US mainland) I plan to use wind only. Since I want electricity too, I will use a diversion system, not direct heating, and I will be eventually using a 15' diameter, whereas 8' would be sufficient for my electricity needs. The extra cost for the extra size and diversion capacity is less than a separate solar hot water system, even in a place where it doesn't ever freeze.

Dave

[Dave B]

The figures I wrote are to raise the temperature of 40 gallons of water 40 degrees F. Lets say your tank is in the basement at 60 degrees F, from the numbers shown this would increase this water temp to 100 degrees F. Also, there is no reason why you cannot rectify your AC and run your heating elements DC, this simplifies multi phase control. I use hot water maybe an average of 10-15 minutes a day, this leaves 23 hours 45 minutes each day for the wind to help me out and obviously more if I am not here. Protect your storage tank with high pressure / temp. release and have another saftey diversion load just in case you max. out the storage. If it's spinning it's heating, this is the most simple direct use of wind for me.  Dave B.

[Stonebrain]

Yea,you're right,powerboy

no cheaper than free.

Some can build a good windmill or solarheater from

junk.Then it's free.

For fair comparing though,you must compare at least cost of

materials/watt and wearing out of materials / watthour

There is nothing wrong with including some

economic considerations in your hobby.

cheers,

stonebrain

[elvin1949]

 And even free ain't free.Fuel to haul in the

scrounged material's.

later

elvin

[elvin1949]

 Forgot TIME invested in finding material's.

elvin

[lohearth]

   Although electric heating is the most efficient form of heating,( 100% energy goes into creating heat no waist) it would be the least cost effective way to go. Solar isn't as energy efficient but is by far the cheapest and much simpler way to go. If you need convenience, then I would look into fuel/heat exchanger style system. If you feel real ambitous, then shoot for a combo  of the three available.

[Michael G]

Thanks for all the input.  I should have stated that this project is for both fun and to reduce dependency on fossil fuels.  Not only that, here in Iowa I booked LP for $1.47 a gallon this season.  I was able to take my furnace use down to only about %10 of normal last year with the purchase of a corn stove.  Kept the house warmer too.  The stove did run up my electric bill some so any excess electricity from the genny could go to charging a couple batteries and then I could run the stove off them.

 So conventional 3 phase sounds like the best way to go. But would one really want diodes in series with the heating elements for the water heater?  I would think the highest voltage possible across the elements is what a person should strive for. But increased resistance in the stator is not good.  Have a good day all!

[DANO]

Hey, was doing some research and came accross your water heating issue...although I haven't tried it yet, I've seen 12 volt heater elements (25 or 50 amp)  available, also in 24 volt @25,30, or60 amp...to be used as a diversion load.  I would use it as an assist to the main heater...every degree raised for free is that much less gas used...they turn into the heating unit just like the big boys 4500 watts, etc.