Electrical Experiment


Nova Scotia
Just a question out of curiosity... Thinking about installing a 400W windmill set up with a controller and battery to feed an element on my hot water tank which includes supply to hydronic floor heating. I could use a 12V battery and element and I would have to be able to set up some logic so the tank wouldn't overheat and the windmill wouldn't run away on me with no load. Is this a crazy idea? Any advice?

Also, I am wondering if it is better to use a 120Vac element or a 12Vdc element. I have an old inverter that I could use but I am thinking this is another point for losses/failures and these two elements have the same amperage rating.


Senior Member
Durham, NC
A couple of things you should consider, that maybe enough energy to run a circulation system off of the water tank IE constant
Hot water.
What your missing is the Watts to Btu conversion to heat your water with a single element, which should take a lot of energy.
A 20 G tank is 2000 watts. 6,824.2823 BTUs per Hour. Your 400 watts only you 1365 BTU.

Another thing is that the average wind mill is not considered efficient or even consider worthy till about 14 MPH, to even create
workable power granted it a curved ratio of MPH of wind Verse desired efficiency to power your element.

I understand blade design has changed over the years to get better lower MPH output to create Watts.

One has to look at all the numbers involved to understand the values that they will present.


Staff member
Placerville, CA, USA
Retired PV System Designer
The other problem is that the fixed resistance of your heater element will make it difficult to match the voltage current characteristic at all points on the wind speed curve. This pretty much requires you to use an MPPT controller between the windmill and the battery. At that point, you might as well go with the 12V element. But you will end up switching it on and off based on battery drain rather than tank temperature.
You will need a separate controller element to protect against overspeed through loading, unless your windmill has a reliable furling mechanism.