Electricity conversion: pretty darn efficient.
Conveying the heat from a brake to a building: not so much.
Conveying the heat from a brake to a building: not so much.
A windmill with a generator inside it that is hooked to a wire that drives an electric heating element inside your house will be more efficient then a water break inside an insulated chamber that pushes hot water through tubes into your home.
If we already have electric generation and conveyance in the picture, then the pump and tube system is additional.
Electric generation and conveyance is "low tech": we've had it for over a hundred years now. It has few moving parts.
Pipes can leak. The fluid needs to be drained and replaced. the system needs to be bled. Pumps break; seals wear out, and such.
Electronics can get phenomenally complicated, but electricity itself can be pretty fantastically simple. There's no such thing as electrons leaking out of a poorly sealed wire onto your floor, for example, and you'll never accumulate sediment and corrosion inside your wires...
Electrons leaking out of a poorly sealed wire onto your floor is otherwise known as an arc fault. Sediment in your wires is the degradation of the electrical insulator by heat, radiation, chemical solvent, or biological factors such as rodents or insects, followed by moisture infiltration and oxidation in the current-carrying elements.
A junction of aluminum and copper wiring without dielectric protection may eventually burn down the building. That doesn't happen when your plumbing goes from copper to PVC, or PVC to PEX.
If you have a closed-loop circulating-water heating system, with the thermal energy produced by a windmill, its pipes are unlikely to freeze, unless the place gets really cold, without wind. The supply and return lines would probably be buried as deeply as is feasible, too.
But yes, hanging an outdoor-rated NM cable between windmill and building, and placing a resistive element inside it, would be cheaper, quieter, and more reliable, even accounting for squirrel mishaps. If you can spare the expense, mineral-insulated cable is a very durable, bio-resistant way to move power.
There are interesting Phase Change Materials (PCM) out there that take advantage of a material's latent heat properties that get you a bit closer.
How so?
Typically you have an AC alternator (because DC generators have too high a loss in the brushes). How do you control the excitation voltage, you'd want high enough voltages to allow reasonable sized wiring but not enough to damage the insulation? How do you control the speed of the blades (under and overspeed) etc?
I can see how these things could be easily managed using direct water to heat. Simple spring loaded governors etc.
The difference is that a watermill would have a lot of extra heat lose from the very long prop shaft/belt drive to reach the top of the tower to the bottom, as well as heat that would bleed out of the chamber via the drive shaft, as well as heat lost in the tubing going both to and from the house.
Assuming the gearing and insulated piping carry high costs anyway, you could put that money instead into low gauge wire to lower resistance getting to the house heater element.
What kind of voltages are we talking about? I know that to get 12v from an alternator in a van to a leasure battery in the back with a modest voltage drop you need cables sized like welding cables. Is it possible to generate voltages nearer 240v directly from an alternator or do you need an invertor somewhere? How does the load on a heating element vary in low wind conditions? Presumably the voltage and / or frequency would be lower in that case.
With water you have the fact that it'll boil naturally regulating itself (so long as you let it escape). You could raise or lower the water level in the stirring chamber and possibly take advantage of convection to pump it back to a reservoir when it gets to a good temperature.
This is because the voltage is low, so the current has to be high for a given wattage (V x A). High current requires thick gauge wire.
> 240v directly from an alternator.
is it possible to generate voltages nearer 240v directly from an alternator or do you need an invertor somewhere
Yes, and since what comes from an alternator is AC, you don't need an inverter, but a simple transformer to step the voltage up or down. (However, you can't store AC, let alone high voltage AC.)
Motorists use inverters to get AC because the car's system is DC, as such. The car's alternator, however, "natively" puts out AC; this gets rectified to DC. (I think, alternators in fact put out three-phase AC.)
Car alternators are specially designed to output 12V; there is no such limitation in generators as such. In fact car alternators use voltage regulation to stay at around 12: when the system voltage rises above the target voltage (e.g. due to higher RPMs), the "field current" to the alternator is trimmed, which acts to reduce its output voltage.
I probably should have said AC-to-AC convertor rather than inverter.
My problem with that is if your using a permanent magnet generator then the voltage generated is proportional to the speed and then how do you know how to size your wiring and your transformer? It's probably not that big a deal and the answer is probably somewhere along the lines of 'leaving plenty of room for error'.
In short though, I don't think it's quite as simple as just connect a generator and some wires to heat the water.
You can use the windmill to also drive a pump that pumps the water through, say, 20 meters of well-insulated pipe and from there through your floor heating system.
Also, https://en.wikipedia.org/wiki/District_heating is at least somewhat competitive with other methods, so scaling up may be possible, too.
https://www.lowtechmagazine.com/2013/03/the-mechanical-trans...
It sounds like air-to-water pumps may offer a new alternative, but it's still more expensive than gas in many scenarios.
However air to water heat pumps are also applicable in cold climates. If you're interested here is an example datasheet[1] of an air to water heat pump (2018) (using Celsius here):
Mitsubishi PUHZ-SHW112YAA Guaranteed operating range (outdoor): Heating: -28 to +21 Domestic hot water: -28 to +35
On page 108 you can find the actual co-efficient of performance (COP) for different outside temperatures and inside water heating temperatures. As an example: at -10 and an water temperature for heating at 25 you still get a COP of 3+. That means that 100% electricity moves 300% of heat into your house.
[1]: https://www.mitsubishi-les.info/database/servicemanual/files...
Effective? A watt is a watt. A heater putting out 2000 watts of heating intensity is exactly as effective whether it runs on electricity, nuclear fusion, or burning dried unicorn poop.
Some electric heaters (like baseboard units) don't circulate air very well. They sometimes get installed under windows and basically just move hot air toward a cold window. If we take that to represent all manner of electric space heating, that is a strawman.
As another poster mentioned, it’s different in a place with unlimited hydropower like Quebec. Places like Boston or NY are about 3x more expensive for electricity... so gas is a no brainer and will be for a long time.
For example - Prague is (partly) heated by waste heat from Mělník power plant.