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Heat Your House with a Water Brake Windmill (lowtechmagazine.com)
328 points by nyc111 on Feb 27, 2019 | hide | past | favorite | 172 comments

The article doesn't show a single non-demo installation.

This thing looks like a giant mechanical kludge. If you put the brake (the paddles in water part) at the top of the tower, you have to pump water up the tower. If you put it at the bottom of the tower, you need a top gearbox with a right-angle bevel drive, a bearing ring supporting the gearbox so it can face the wind, long shafting, and bearings. Some early power turbines were built that way, but nobody does that any more.

Vertical axis turbines like the Savonius turbine and Darrieus rotor can be used, but they're not very efficient, so you need a big one. They also are hard to shut down in an overspeed condition; they can't change direction, change blade pitch, or tilt upward, so you need a strong emergency brake system. Which is why they're rarely seen any more.

All this outdoor hot water plumbing needs to be well insulated, or you lose most of the heat. So a field of wind turbines, or one unit some distance from where the heat is wanted, is a problem. Moving energy around over wires is so much simpler.

Driving a heat pump mechanically might work better, but that's because heat pumps are far more efficient than heaters. (Moving heat is much cheaper than making it. See [1]). An electric windmill driving a heat pump is probably less hassle.

[1] https://dothemath.ucsd.edu/2012/06/heat-pumps-work-miracles/

> If you put the brake (the paddles in water part) at the top of the tower, you have to pump water up the tower.

You have a windmill, so you have a source of energy to do that. Much of the mechanical energy that goes into the pumping becomes gravitational potential energy, which will become heat when the water goes back down the tower. A lot of the rest will be lost as heat during pumping. Either way, it's ending up as heat, which is what you want.

Heaters are the only type of machine which are naturally efficient!

> Heaters are the only type of machine which are naturally efficient!

I had a big argument with my physics teacher about this back in highschool. He was so stuck on the "no machine is 100% efficient" dogma that he couldn't look past it to the definition of "efficiency" for a heater in a closed room.

Energy is conserved (under normal conditions) so everything is 100% efficient if you want to include waste heat.

However, "efficiency" is actually a value judgement. You probably want to heat something specific, so you're going to lose some fractional efficiency by accidentally heating something else. Resistance in the wires leading to your heater will accidentally heat the outside of your house.

It's also not a terribly useful definition of efficiency environmentally: if you multiply the efficiency of burning fuel to produce the electricity by the efficiency of your electric heater, you get a worse result than burning fuel in your home. And it's not a terribly useful definition as a consumer either, since that electrical heater is only producing about 50% the heat that a heat pump could do with that electricity.

And for that matter, heat pumps can be more than 100% "efficient", since they move more thermal energy than they consume.


They're not a conversion system so you don't measure them in terms efficiency, rather you use coefficient of performance, you can never have efficiencies above 100%.

In power terms it is above 100% efficient because the watts in is lower than the watts out.

No, the heat moved is greater than the watts in. The machine itself has considerable parasitic losses, and a simple electric baseboard heater is more “efficient”, using the strict definition of the term.

The difference is that most people don’t care about “efficiency”; they care about heat moved per watt. But it matters a great deal more when you try to use a heat pump in a really cold environment, as the heat-transfer ratio of the machine plummets (which is why, in the real world, heat pumps fall back to gas or electric in cold weather).

It also matters in a scenario where you’re comparing two different machines that are powered by something small and intermittent, like a windmill.

I'd assume that some tiny fraction of the energy is directly converted to radiation that escapes the room instead of kinetic energy. Some of the energy should be transferred to particles outside of the room directly by electromagnetic forces (they fall off to near zero quickly, but never fall off to zero). Etc.

Probably 99.many_9s efficient, but I don't think it could be 100%.

(We'll assume you're talking about a resistive heater, fire, or so on. Not a heat pump where you can play games with the meaning of 100% efficient)

"The article doesn't show a single non-demo installation".

It does. The Calorius windmill was commercially produced for about a decade, 40 of them were sold. Seventeen of these windmills were still operating in 2012.

It's all in the article. Also your points about the savonius are addressed.

Your article is interesting, but it makes a number of incorrect or misleading claims, the chief one being that heating via electricity produced by wind or PV is inefficient.

On the contrary, it is cheap, uncomplicated and very efficient in the modern context - by using the electric power to run a reverse cycle AC unit (in most cases, existing) you will get around 10 times the heat that a water brake system might deliver, with lower cost and much higher reliability.

My article shows that heating without electricity is cheaper and more efficient than heating with electricity. It also has references to back up these claims. What you write is simply untrue.

The math kind of backs it up the efficiency of solar power backed electrical heating over wind.

Sunlight has a power of ~2kw/m^2 in visible spectrum (solar panels cannot capture all of this). At a strong breeze (10m/s) wind has a power of ~1kw/m^2 (windmills cannot capture all of this). So the mechanical heat generation would have to be more than twice as efficient to electrical generation to be worthwhile. But the "complications" mentioned are really what kill wind.

You want to capture sunlight: solar panels on the roof. No real obstruction.

You want to capture wind: massive windmills on your roof, need to disable the fan blade if the wind exceeds a certain value. Moving parts wear out.

I am not going to install a 2m radius windmill on my roof. Two 1m radius windmills have 1/2 of the area and are still an eye sore. Four 1/2m radius windmills, 1/4 of the area of the 2m radius blade.

> Sunlight has a power of ~2kw/m^2 in visible spectrum

FYI, solar radiation is more like 1050 W/m^2 on earth's surface, of which about 40% is in the visible spectrum.


10 times compared to what? Installation cost? I can't make your post to make sense. Also, if it were generally true, why would solar heat systems be so popular? I am thinking of vacuum tubes, the kind of installation which looks pretty much like a PV roof but it's only heat and water.

Speaking of heat pumps, I installed one 2 months ago, and dropped my electricity bill for heating water from $85/mo to around $25/mo. This saved me around 69%!

Reference: https://russell.ballestrini.net/hybrid-hot-water-heater-save...

Nice, here in Sweden there are even more efficient systems that recovers the heat from your house ventilation system and uses it to heat water for heating and bathing.

The house we bought a year ago has an electric water heater, and it's a wishlist item of mine to upgrade it to a heat pump. Our electric bill is way higher here than where we lived previously, and the only thing significantly different is that we have electric hot water here. My in-laws have one and it seems to work pretty well. Plus you get a bit of A/C out of it in the summer.

What’s your payback period?

It's in his article - 1 year due to rebates, 2 years without.

Maybe, but two things to consider.

The drag force in the fluid brake is proportional to the velocity squared. So you get harder and harder braking. (The air blades still need to not blow off though.)

Insulation requirements decrease with the size of the reservoir. (Since volume increases faster than area.) Besides, the reservoir could be placed inside the house as well.

Totally agree with regards to it being a kludge; power electronics have come such a long way since the '70s...

For the mechanical+pump permutation, the plumbing needs to provide a way to prime the pump, and the pump cannot be more than 20-something feet up without the whole system being pressurised [1]. So, if you go that route, a pump near ground level will more-or-less be required.

[1] http://processengineering.co.uk/article/2019233/maximum-suct...

Afaik the savonius turbine is known to be good for torque, bad for speed. And because it's vertical, you don't need a sjaft or gear box at the top.

Dunno how to stop it at strong winds though.

Those very water brakes seem ideal to prevent runaway turbine blades. Their braking power goes up very quickly as a function of impeller speed (ever use a rowing machine?).

I worked on a wind turbine related project for some time and while I overall love renewable energy wind does have a few factors which can limit its effectiveness. This applies for heat as well as electric generation.

- As noted in the article, wind can be highly variable in most areas. Optimizing a wind turbine for the average low speed (like here in the US Midwest) means that at super high speed winds can damage your turbine and it may need to be shut off. If you optimize for the high speeds you can get a ton of energy at those speeds but your turbine will mostly be still. Regions with a nice steady wind profile work better for power generation.

- Wind turbines with variable pitch blades do exist but add cost and mechanical complexity.

- Turbines often are installed at remote locations and maintence is difficult. One crazy story is a friend of a coworker was a tech for the giant wind turbines and fell INTO those giant fiberglass blades and almost died wedged in there before he could be rescued!

- "Urban" wind turbines was an idea here in Cleveland a few years ago, but wind turbines generate a lot of vibration which isn't good for buildings. Plus the turbines don't always spin all the time which is bad PR!

All this said I think wind power can be a part of a good energy portfolio but like with anything in engineering it boils down to a big "but if.."!!

> As noted in the article, wind can be highly variable in most areas. Optimizing a wind turbine for the average low speed (like here in the US Midwest) means that at super high speed winds can damage your turbine and it may need to be shut off. If you optimize for the high speeds you can get a ton of energy at those speeds but your turbine will mostly be still. Regions with a nice steady wind profile work better for power generation.

This problem is solved centuries ago. Just cover only part of the blade with cloth.

> Wind turbines with variable pitch blades do exist but add cost and mechanical complexity.

I was about to suggest the idea of using gears like from a vehicle's transmission (i.e. first gear is easy to turn, will shift to larger when certain condition achieved), but it sounds like these ideas have been hashed out already.

Just a random shot in the dark but I imagine that you need variable pitch blades (in addition to or instead of gears) because gears would only regulate the speed of the turbine, but not the force exerted by the wind on the blade.

Put it into a high gear in a high wind, it may not rotate fast and fly off due to angular momentum, but it might just snap off.

Generally speaking a stopped turbine's blades are mostly stalled and under much lower stress than when rotating (albeit in different direction). The angle of attack of the blades is designed for moving blades.

The surprising result of this is that the brake force needed to keep the turbine stopped is much smaller than the one needed to stop it, despite the relatively low mass of the blades.

Yes, I'm curious about this, and a FAQ on the technical limitations which lead to the situation that GP mentions. I'd have thought that you could have a mechanical / electrical brake on the blades to keep velocities reasonable, or gears as uyou mention, or maybe it's other mechanical stresses.

The thing that's not obvious to most people is that the power contained in moving air is proportional to the cube of the airspeed.

If you're local "average wind speed" is 5m/s (~12mph, a "Gentle Breeze" and #3 on the Beaufort scale), and you size your wind turbine to generate useful power (say, 1000W, for example) at that speed, you have two consequences due to that speed-cubed term.

1) When there's only light wind - say half your design average speed, you're only gonna get 1/8th of your 1000W target, so only 125W which isn't very useful if you've got a 1000W requirement.

2) The _bigger_ problem is when the wind blows faster than average. If you get twice average speeds, your turbine is going to generate 8kW which you'll need to safely deal with. But twice isn't your problem - in the real world it's not uncommon for 3 or 4 times average windspeed (what we'd normally just call "a windy day" and 7 or 8 on the Beaufort scale), at which stage you're going to need to safely dump 64kW of power - if your turbine hasn't been braked/parks appropriately (or torn itself to pieces.) If you're still spinning in hurricane conditions, you've got another doubling of windspeed, and another eightfold increase in power, so now your "1000W generator" is unleashing half a megawatt into your wiring and control electronics (or the plasma in the smoke where your wiring used to be...)

Beaufort scale with speeds and descriptions: https://en.wikipedia.org/wiki/Beaufort_scale#Modern_scale

Some real world windspeed measurements showing upper end outliers of 8 times average speed: http://www.wind-power-program.com/wind_statistics.htm

That assumes that the turbine have the same efficiency over all wind speeds. Realistically, it will not - but your point stands none the less.

I think there is optimization pressure between the size of the generator and the median amount of power produced. Wind speed probably has some sort of log distribution.


  wind speed  hours/year
  0-10        4000
  10-15       2700
  15-20       1100
  25-30       600
  35-40       300
  40-50       50
  50-55       15
At some point the cost analysis says the extra power generated isn't worth the cost of the oversize generator needed to extract it so just feather the turbine.

Yeah there are certainly options out there but at some point the blades will be simply spinning too fast to be safe and it will need to be actively braked.

The other problem is adding the mechanical complexity all up in the nacelle of the wind turbine, where it is hard to service and maintain.

I would have guessed that any large wind turbine would have to have variable pitch blades. You need to be able to feather the blades in case of high wind/overspeed, maintenance, or other need to stop/slow the rotational speed.

While the idea is new to me - using friction in a windmill to heat your house - the practical use in Western Europe could be limited. Installing a 12 meter windmill in my backyard is not going to happen... And then efficiency. A heatpump has a COP of around 4 or 5, so every 1 kW into the system results in 4 or 5 kW out. A heatpump uses electricity, which can be generated using a windmill, but also via solar panels. And a heatpump is relatively easy to link to your general central heating system. Now if you'd want to link your water-brake windmill to the central heating I guess it would be a 'different biscuit'. And since the smaller systems generate 3.5 kW with a firm breeze, you need backup. Suppose you'd not use a water-brake but a generator and heatpump; wouldn't the overall system efficiency be better in that situation? Or at least more convenient if you add solar panels in case there's no wind?

The article talks about this; it says the most efficient system is a mechanical heat pump (where the wind provides direct mechanical power to the compressor), but only for local generation, since heat transfer is much less efficient than electricity transfer.

If for some reason (I don't know, heating a blimp perhaps?) you were restricted to an air-sucking heat pump you could go wild and route the intake (or some fraction of it) of the heat pump through the generator and motor: this should recapture all the losses. A worthless optimization since the waste avoided would be free (just build a slightly larger turbine), but technology for low intensity heat is uniquely simple, but why not use three opportunity to make it amazing ("conversion losses? Yeah, they are taken care of")

> (I don't know, heating a blimp perhaps?)

Actually, given the recent interest in tethered blimps hosting high-altitude turbines, that's not as dumb an idea as it sounds. The prototypes shown so far generally use helium which is expensive and in limited supply.

Yes, my thought was to use the windmill to run the heat pump, then buffer the heat as hot water in an insulated tank to heat the house. Not really practical unless you live in a place with fairly regular wind in the winter. Where I live, winter air tends to be fairly still with occasional exceptions and I could be wrong but I doubt it would be a great way to heat the house.

Same with solar, in the dead of winter the sun is at quite a low angle in the sky, not even above the tree tops, and I doubt there's much to be gained either from photovoltaic solar or using it to directly heat water for the house.

Electricity production in winter can definitely be lower, but it depends on latitude. As you might guess, near the equator there's almost no difference in season.

According to the US Office of Energy Efficiency and Renewable Energy:

"Countries such as the United States, which lie in the middle latitudes, receive more solar energy in the summer not only because days are longer, but also because the sun is nearly overhead.

The sun's rays are far more slanted during the shorter days of the winter months. Cities such as Denver, Colorado, (near 40° latitude) receive nearly three times more solar energy in June than they do in December." [1]

Looking at these maps [2][3] for solar production in January and July, it seems like a lot of places drop by around 50% summer to winter. So it's a significant drop, but unless you're extremely far north, there's still energy to be harvested.

[1] https://www.energy.gov/eere/solar/articles/solar-radiation-b...

[2] January: https://www.nrel.gov/gis/images/map_pv_us_january_dec2008.jp...

[3] July: https://www.nrel.gov/gis/images/map_pv_us_july_dec2008.jpg

You could go all-out with an angled thermal collector panel (double-glazed or possibly vacuum insulated like some fancy solar hot water systems) which heats water to be piped back inside into a storage tank, then pump the heat from the storage tank into the air when required.

(For some scenarios this might even be a good solution without the heat pump, just run the water through a radiator. Is this something that people have tried?)

I'm inclined to agree. Domestic wind turbines never took off compared to solar. And solar thermal has been overtaken by solar electric. I don't think combining two technologies that failed in the marketplace are going to change that.

Solar thermal and solar electric have different uses. Id much rather use solar thermal to heat my water than solar electric.

My understanding is that currently the payoff for pv is quicker than thermal, which is why most people now go for it.

Now I don't know whether an equivalent pv system is cheaper in absolute terms than a thermal system, but from what I can work out, the marginal cost of adding extra pv to cover hot water is cheaper that adding a separate thermal system.

So yes they have different uses, pv generates electricity which can be used for a variety of things, thermal just generates heat. So if pv is cheaper or has a quicker payback, it seems like a no brainer to me.

The efficiency is MUCH higher for thermal over PV (~80 vs ~25). Its not an either/or thing. If you want heat, you use solar thermal, if you want electricity, use PV. Theres nothing stopping you having both.

Edit: Not sure what you mean by 'pay-off'. Solar thermal can be as simple as a black bucket sitting in the sun. It doesnt get much cheaper than that :D

A number of recent studies have shown that PV used to heat water is actually cheaper and more efficient.

It's counter-intuitive, but the reality is that PV has become much cheaper, while solar hot-water panels plus plumbing are expensive.

Plus you can use any surplus PV for multiple purposes.

I think it depends on the requirement and configuration.

A simple passive open-loop system is very cheap, and adequate for a hot water during warmer seasons (if you dont need hot water in the morning, i may add :D)

During colder seasons, you would need a closed loop system with a heat exchanger (often a heat pump, which you can power by PV) and insulated storage. Thats when it starts to get expensive, and the effective efficiency can be decreased if you are pumping more heat than you consume. This is an alternative to the air-source heat pump that your research probably used for comparison.

That said, I can totally see how PV could fulfill a hot water need right through the year, its just WAY more expensive than a low-tech solar thermal system (and likely less efficient in the summer).

Again, no harm in using both if you have the funds (and space) :D

A pv at 25% efficiency attached to a heat pump with a COP above 4 is still above 100% so still beats thermal. And yes you can have both, but the cost to have the installers add a few extra KW of pv is less than getting other installers out to do an entire solar thermal system, so what's the point?

Payoff as in if you buy a pv system it will pay for itself quicker than a thermal system. Electricity is more expensive and valuable than 'heat' (read gas substitute) so even if the pv system is more expensive, the savings are greater, which offsets the higher purchase price.

Hey if you want to shower under a black bucket, go for it :)

> A pv at 25% efficiency attached to a heat pump with a COP above 4 is still above 100%...

Could you name the particular brands and models of PVs you are using that produce 25% in the field? 15% under ideal conditions is more typical and your 25% is above current state of the art available for home installation. Also interested in your heat pumps above 3. Are these geothermal? If not, who makes them?

Normal set up is going to be 15% max on the PV and 3 on the heatpump, for 45% max, but more typically 25% as the PV is seldom set up to capture ideally.

I was quoting my parent on the 25% efficiency figure.

"The COP for heat pumps range from 3.2 to 4.5 for air source heat pumps to 4.2 to 5.2 for ground source heat pumps"


The COP of a heat pump hot water heater is strongly dependent on the ambient and current water temperature. You get the best COP heating from cold, but it's not often that you have to reheat an entire tank of cold water. The actual achieved COP in normal use is more like 2-2.5.

Sometimes all you need is a black bucket. If you want to throw an 8KW solar array and a $3000+ heat pump at a shower then go for it! :D

> (~80 vs ~25)

The most efficient panels are at 22% right now, and that's with no overcast conditions or rain, sun directly overhead, and full tracking. The 22% are significantly more expensive. Most panels have around 15% efficiency, when new, under ideal seasonal, weather, tracking and lighting conditions. Quite a bit less when not.

I have a self built solar water heater and a house designed around passive solar. This handles heating and cooling sufficiently without grid inputs. My house stays at temperate conditions year round and my monthly energy bill, consisting of non-heating uses, is around $25/month on average.

Typical solar thermal installations are a bit more complicated that black buckets and require professionals to install. They usually don't work for free.

My PVC pipe solar shower begs to differ.

Why not both!? It increases electric output by cooling PV panel and makes you some hot water!

Using solar electric to run a heat pump is more efficient in most climates.

Agreed. Plus in moderate climates you can use a standard reverse cycle split system for cooling as well as heating. Granted you could do the same mechanically but it would be a custom design as opposed to commodity AC.

The Joule Machine was originally conceived as a measuring apparatus. James Joule built it in the 1840s for his famous measurement of the mechanical equivalent of heat: one Joule equals the amount of energy required to raise the temperature of 1 cubic centimeter of water by 1 degree Celsius.

Although this confuses the definition of joule with calorie, Joule's experiment was brilliant and laid the groundwork for the laws of thermodynamics:


A weight was suspended from a rope and allowed to fall. The falling weight was mechanically coupled to a paddle in a pool of water. As the weight fell slowly, it turned the paddle. Given that the mass of the weight and the water were known, the work performed by the falling weight and the heat absorbed by the water could be quantitated.

Here's a kitchen test of the principle where a household blender is used to boil water:


I suspect some heat transfer from the motor through the blades, but it's very surprising the water boils. He could have run a calculation, based on the power output of the blender, to see if the temperature increase was reasonable.

Joule's apparatus can be seen at the Science Museum in London. https://commons.wikimedia.org/wiki/File:Joule_Apparatus.jpg

It's a beautiful device, worth googling around for the various photos that are online. I would embed a few choice images that I found but of course HN doesn't allow that. rolling eyes emoji

There's also an old Open University programme which reconstructed his experiment (conducted on his honeymoon, allegedly). It doesn't appear to be on YouTube.

Related: Boil water with a blender: https://www.youtube.com/watch?v=GjcOobt9Ef8

I wonder if this was ever used in a MacGyver episode.

> one Joule equals the amount of energy required to raise the temperature of 1 cubic centimeter of water by 1 degree Celsius.

I believe he meant 1 calorie, in Joules would be 4.184.

This impeller design is clever, but it seems that a DC generator and a resistive load would be an easier way to brake the windmill and generate heat. The first advantage is off-the-shelf parts. Electric generators and resistive loading are well known technologies. You can locate the resistive load (literally, an electric heating element) close to where you need the heat and there will be very little mechanical wear.

You are missing something important: they are storing enough heat to last for a couple weeks of no wind (or a cold snap). Enough DC batteries to heat a house that long are expensive and dangerous (fire hazard). A large water tank (10 tons of water or more!) is a lot safer to have around the house. The water tank also means the ability to locate your load anywhere isn't important: either way you have to design your system around the tank.

Also, DC is less efficient as the losses at your generator is heat that isn't captured. Generators are typically 80-90% efficient. This is pedantic though and doesn't matter (if this was the only concern DC is wroth the losses because you can divert it to lights or something else that is also useful)

> You are missing something important: they are storing enough heat to last for a couple weeks of no wind (or a cold snap). Enough DC batteries to heat a house that long are expensive and dangerous (fire hazard). A large water tank (10 tons of water or more!) is a lot safer to have around the house.

Why would you use batteries? That’s silly, you’d simply heat water in both scenarios.

I didn't spell everything out. I never suggested you store the electricity in batteries. The electric heater would be used to heat some mass, like a tank of water or bricks. I look at this impeller and I see a custom mechanical design, with seals that are prone to failure. You replace that with an off-the-shelf DC motor and a resister bank in a tank of water, and you can put the tank of water in your basement or wherever you already have the heater for your hot-water heating system.

They also discuss an "eddy current retarder" design, which uses a magnetic mechanism that sounds vaguely like an electric generator but generates heat directly, as an alternative to the water break/impeller design. Sounds like maybe you get the best of both worlds, in terms of a smaller package but avoiding the motion -> electricity -> heat conversion losses due to the extra step.

10 tons of boiling hot water? What could possible go wrong? https://en.wikipedia.org/wiki/Great_Molasses_Flood

It's ten cubic meters, not as crazy as it sounds. Yes it would flood your basement if it burst, and you probably wouldn't want to be directly under it, but not going to drown you.

Water is heavy!

this is not boiling water AFAIK, it's more like warm water

I think heat storage for domestic use is a red herring--the point isn't to replace all forms of gas/electric heating, but rather to reduce the usage. So, all the turbine heat is essentially consumed immediately, and the conventional methods kick in to fill the gaps.

The easiest way to accomplish this is feed your lukewarm turbine water into the water heater intake. Every joule added to the input is a joule the gas heater doesn't have to deliver.

Seems like generating power to feed to a heat pump would still be more efficient, despite electrical losses, considering that good heat pumps can be 3x more efficient than friction/resistive heating.

One of the main benefits of the water brake system is the storage of heat. With a sufficiently large insulated tank, you can retain head for days to weeks when the wind subsides. The water brake gives you a little more insurance compared to electricity generation for an off-grid solution.

Why couldn't you use a heat pump to heat an insulated tank and get the same benefit?

The problem is wind can be unreliable. With a electrical system you are way more flexible.You can use the generated electricity if you don’t need heat and if you are in the winter in a period without much wind you can fall back on solar or grid.

Unless you live in an area with very steady wind during the winter and a more or less equal need for heat all year around, the electrical solution is more practical even if it is less efficient.

I could imagine this for warm water with a different system used for heating or something like that.

Electricity conversion: pretty darn efficient.

Conveying the heat from a brake to a building: not so much.

Yeah, this article seems like bad engineering, especially when the opening paragraph is trying to compare mechanical energy to solar heat.

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.

> 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

How so?

I'm also puzzled. I guess one angle is if the losses from a generator are captured, you get a bit more utility from having more of the total energy as electrical energy? Maybe they're picturing all of the generation and conversion inside the building envelope to capture losses.

I agree it is mostly bad engineering, but they are correct in one point: to make wind work you need to store the energy somehow. Water is a lot better than batteries if the goal is to heat your house for a few weeks of no power input (batteries are expensive and a fire hazard).

That doesn't imply that the water must be heated directly by the braking system, however.

Water's heat capacity means you'll need a lot of water in order to keep a house heated for weeks, in a temperate climate.

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.

I admit my understanding of these things isn't perfect but I'm not sure the idea of having a generator is as simple as your making it sound.

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.

Speed requirements are going to affect both systems equally. A water chamber driven by a mixer is going to have to reach a certain speed to generate enough heat to overcome heat loses in the gearing,chamber, and tubes and would also need an ancillary breaking system to avoid going too fast and destroying the whole assembly.

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.

Are insulated pipes burried 6ft underground going to lose that much heat?

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.

> 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.

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.

> 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.

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.

Generate AC then use diodes to turn it into DC

Until it breaks down? The water+tubes is a low-tech solution that will survive the apocalypse.

Wait, by "water" did you mean "electrons" and by "tubes" you meant "wires"?

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...

Plumbing is like DC electricity. If we used alternating current in the plumbing, that would get complicated too.

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.

Yet all the remote mountain cabins I know of usually have less problems with their electricity than with their pipes, drains and such. Especially because they are higher mainrainance during cold winters (expanding ice bursts pipes, while wires just happily work quite independent of temperature if done right)

Places with less-cold, less-mountainous winters get more bio-problems, like a nest of fire ants inside the meter or main breaker panel, or squirrels chewing through the telecom/television/Internet cables.

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.

Yeah, I know about EM. FWIW it's usually only a material issue in fuses & semiconductors.

Firstly, are you proposing that people should have windmills that have no generator at all, only a brake for generating heat?

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.

Few moving parts but many electronic components that will fail eventually.

At small scale, why wouldn’t it be efficient?

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.

Conveying mechanical energy: reasonably efficient over modest distances.


Are you proposing some sort of chain, belt or shaft drive, such that the brake is actually housed inside the building?

Yes, that's what I was getting at. You can have the windmill located on a high point on the property (or just far away enough to be out of the way) then convey that energy back to near the house and use a brake to generate the heat near where it is needed.

You either live in a warmer climate or don't have electric heat.

This gets thrown out on HN often about any topic regarding heating. There's a reason why nobody in cold places has electric heat or air heat pumps -- they are either too expensive or not effective enough to run.

It sounds like air-to-water pumps may offer a new alternative, but it's still more expensive than gas in many scenarios.

We ditched our gas and have an air to water heat pump, costed around €6000 ex subsidies (I live in Amsterdam so not the coldest weather, we also have solar thermal and PV).

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...

Montreal, and the rest of Quebec, uses electric heating, because electricity is cheaper than gas here (due to the hydroelectric dams along the st lawrence). There are regions electricity is cheaper than gas.

How is electric expensive, if you're getting electricity for free from your wind turbine? No matter in what form you get energy out of it, it's about the same, modulo efficiency.

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.

The wind doesn’t always blow. And storing electricity is expensive and capital intensive.

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.

It is more effective to use 100% of generated electric to pump 300% heat with a heat pump than it is to use that electric to generate heat by resistive load.

note that heat is already transported from one building to another when using central heating.

For example - Prague is (partly) heated by waste heat from Mělník power plant.

Kind of a tangent, but also check out the Ranque-Hilsch vortex tube, "a mechanical device that separates a compressed gas into hot and cold streams" - https://en.wikipedia.org/wiki/Vortex_tube

Can anyone explain to the ignorant among us (i.e. me) why converting to heat is so much more efficient than converting to electricity? The article makes the claim but doesn't back it up. What are the losses involved with each approach?

Ultimately all approaches convert to heat with 100% efficiency. However the in between stages and what you do with the heat are in question.

A Generator is 80-90% efficient in general, then you have battery charging losses (which I do not know), then battery discharge losses, finally, you have power transmission losses to get the electric around. All of the above losses are not captured. They are claiming that because everything is converted directly to heat near where it is used their total losses are less. (they assume insulation here)

The losses in their system are gears (some of which exist in most generator systems), and tank losses over time.

It is plausible they are right. However it all depends on local install factors which can be manipulated either way.

I think the main point the article was eluding to was that if you use wind power to first generate electricity then convert this into heat, you have two conversion steps with loss: wind to electricity, and then electricity to heat. The overall efficiency is then the product of the efficiencies of the two steps. If you produce heat directly from wind, you cut out one conversion with its associated inefficiency.

I always figured electricity to heat was nearly 100% efficient, it's the generating of electricity where the losses occur.

There are two stories for this URL:

https://news.ycombinator.com/item?id=19263814 (this one)



I would have expected the anti-duplicate-submission mechanism to prevent one of these from being created, redirecting the later submitter to the already-existing story, given that these were both submitted around the same time.

TL;DR: Everyone knows that solar can provide electricity at 20% efficiency or heat at 80% efficiency. Almost no one is aware that windmills can do the same.

Instead of connecting a windmill to an electric turbine, you can have it churn a pool of water where friction raises the temperature without the conversion loss.

Fascinating article. I had never considered this.

I am not a builder, but I wonder if tech like this is stymied by the nature of the housing market?

From what I understand, housing is one of the most-regulated sectors, and one which has also seen not much innovation (compare to computers or autos).

Were I a Bill Gates, I'd sponsor housing projects where innovators could be rewarded based on sustainability and cost. I guess, in order for anyone to live in them, I'd also have to sponsor some politicians to get government to then allow it.

From an efficient resource allocation (in other words, economic) perspective, there appears to be almost noone solving sustainibility problems. What I mean is, sustainability per dollar spent should be at the forefront of our minds, and I'd be very surprised this kind of tech did not find a place in the market if that were allowed to prevail.

I believe there are entities that benefit far more from keeping the status quo as-is, instead of innovating. While I've only worked in large real estate enterprises in my past, and not actual housing (though the two industries are quite linked), never forget that beyond the science and conventional challenges of innovation, there exists human elements who block forward progress; because - sadly - some of these humans gain too much ($POWER or $MONEY, etc.) in the legacy world.

I'm convinced this is one of the biggest problems with our generation--corporatism or cronyism, whatever it is. It is the fact that the private sector and government collude to keep the status quo profiteers safe from innovators obsoleting them.

It should be the opposite. The government should work to resolve market failures.

This is one of those issues which is not left vs right, but rich vs poor... That just gets completely ignored, whether by accident or design...

Electric motors/generators are typically much more than 20% efficient, the usual range is 75% to 95%. And you can use that energy for things besides heating on warm days.

EDIT: The overall wind turbine isn't that efficient, that's the efficiency of the conversion of the mechanical rotation to electric power. There's a good deal of loss between the wind itself and rotation to vortices and whatnot.

My thoughts as well (most of the other top-level comments got it wrong).

The other important feature of this is that anyone can build a Savonius (or other) turbine and impeller at home, meaning that there is no lower floor on cost, meaning it's one of the only scalable uses of wind power that I've seen.

Free energy in the form of heat is all around us (orders of magnitude more than humanity uses currently, even considering a 20% electricity conversion efficiency). I'm in mourning that there is still no off-the-shelf supplier of Stirling engines for the world. Which is probably by design, considering how detrimental something like that would be to oil stocks hahah.

I wonder if you could do even better having it turn a fan and compressor on a heat pump.

The article talks about this in the "Retarders and Mechanical Heat Pumps" section.

Great concept to reduce the losses in transmitting and converting energy, and reducing the weight, complexity, and cost of the wind system. But there are issues.

1) It takes a rather large system and stiff breeze, "a rotor diameter of 5 meters and a height of 9 meters – produced 3.5 kilowatt of heat at a wind speed of 11 m/s", ~25mph wind, to produce a modest heating output. that is the equivalent of two small 1750 watt heaters, which would barely heat a decent size room in cold weather.

2) The system is completely dedicated to heat production, and will be a waste of space over half the year. In the summer, most of the wind will be of essentially no use except for warm tap water. In contrast, you can use electrical generation any time.

The best system I've seen of this was at a remote boarding school in Florida. On the roof, they had black serpentine pipes in flat black boxes with glass lids, so mini-greenhouses. In the utility area, they had large insulated water storage tanks. They could get the water to 180F, and had to warn people to be careful when using the tap or taking showers. Pretty impressive, and this was decades ago.

It occurs to me that this could be combined with a standard wind turbine.

I assume turbines already generate heat, and they also require brakes for when wind speed gets too high. Best case you could be generating maximum electricity and using the brake to generate useful heat. I guess this would aid dispatchability of the electricity, certainly with regards to limiting output as well.

Whenever I read anything about wind turbines I'm reminded of this article. It's a shame the photos are missing at the moment. Maybe Jacques is around somewhere and can restore them.


The photos are working in the Wayback Machine:


Another model could be to run an air compressor from the turbine. Compression will give you a heater, and then releasing the compressed air will give you cooling.

Thinking about it some more, you should also be able to get kinetic energy out (or electricity) and water, by running a turbine on the compressed air and collecting moisture from the cooled air.

Essentially one of these: https://en.wikipedia.org/wiki/Heat_pump_and_refrigeration_cy... - they're not technically as efficient as a phase change, but if it's simpler and there are fewer moving parts, it might be a win.

The point of the article is that (unlike people would expect) THERE IS a direct way how to convert mechanical energy to heat. It can be even more effective (in theory) than heating via electricity from wind, because there is only one energy conversion (motion -> heat unlike motion -> electricity -> heat).

Big downside is that heating with water brake is somewhat impractical and unexplored territory.

However big plus of this approach is that you can make water brake with middle-age technology.

I've heard several times that electrical heaters of any kind are expensive and much less efficient than other heat sources and I feel like I am throwing money out of the window when I turn them on.

This doesn't make any sense to me though. Can someone with a better understanding of physics than me explain to me why this would be the case? I would imagine electricity to be just about the most efficient way to transfer energy. And furthermore, as I understand it, lost energy tends to become heat!

The thing about electricity is that it's perhaps the most "useful" form of energy. Not only can you use it to heat your house, but also to drive your car or run your phone or your power tools etc.

On the other end of the spectrum, you have "low grade waste heat", take for instance the heat from running a computer. Almost all the (useful) energy input as electricity gets turned into hot air coming out. You can use that to heat your room, but nothing else.

So because electricity is so useful and high grade energy, we prefer not to use it "just" for resistive heating. Running heat pumps is an example of a much better use (you can get 4-5 times as much heat out).

>you can get 4-5 times as much heat out [...]

..but why?

The second law of thermodynamics says that the amount of energy won't change, it can only change form, right? (Correct me if I'm wrong, I'm not sure). So the electricity should either remain electricity or turn into heat?

I get that it might not happen at the place where we want it to. For instance, we don't want to be heating up the ground between the power plant and my house where the cable runs. And I also get that turning heat into electricity (as it happens at the power plant) might not be efficient. But I still feel that it should perform better than running a pipe with hot water which seems more likely to leak heat into the ground along the way.

>>you can get 4-5 times as much heat out [...]

> ..but why?

Because you are literally pumping heat from outdoors to indoors. You are reducing the energy of the outdoor air and increasing the energy of the indoor air.

The electric energy spent is used to drive a motor that is pumping a fluid round in a loop. The pump is placed where you go from outdoors to indoors. Opposite the pump in the loop, you have a pressure reduction valve, and together these give you a higher fluid pressure on the indoor side, say 40 bar vs 20 bar. The trick is that this pressure difference means that the low pressure fluid is also cold, so it can be heated by the outside air, and the high pressure fluid is warm, so it can release heat to then indoor air.

The thing about running hot water (e.g. district heating) is because you use heat that is literally free. E.g. if you have a waste incineration plant burning all the garbage, that's a lot of free heat. Or if you have a big data centre, lots of waste heat. Let's use it!

In systems like the OP post, the water acts as both energy storage and a convenient way to distribute heat. No DC/AC inverter, etc.

> And furthermore, as I understand it, lost energy tends to become heat!

AFAIK the whole problem is that "waste" heat happens at the coal/gas plant where heat is converted into electricity in the first place, and (to a lesser extent?) in the transmission lines, not at your house where it'd be useful.

Ok, this I can understand. If the cost is in fact in the initial conversion rather than in transportation, it makes sense. In that case though, we are not nearly as good at turning heat into electricity as I thought.

http://insideenergy.org/2016/06/20/ie-questions-can-we-turn-... is an interesting read. The efficiency of a basic coal plan is pretty dismal - converting a mere third of the released heat into useful electricity if I'm understanding right. And even if you build a state of the art combined heat & power system (requiring steam pipes to heat houses, not just electric lines) we're still looking at only ~85% efficiency.

Because in order to get the electricity to your house the power plant had to first do whatever it needed to do to generate the electricity.

for example if the power plant is burning oil, and converting that to electricity, then you convert that electricity to heat you're going to get much less heat than just burning the oil yourself.

> for example if the power plant is burning oil, and converting that to electricity, then you convert that electricity to heat you're going to get much less heat than just burning the oil yourself.

OTOH, the power plant probably has a rail connection or pipeline for oil, and the marginal energy cost of transporting an additional unit of oil to the power plant is probably quite low compared to the marginal energy cost of transporting the same additional unit of oil to your house.

While technically correct, this is the wrong way to look at it. The energy density of oil is large, so transmission losses per unit of energy is low. Any modern house furnace will be at least 80% efficient, and 96% isn't unheard of. The most fuel efficient power plants are around 60%, (combined cycle coal plants) but any plant running oil is probably less, plus you have all the transmission losses for electric (8%). In the end if you are burning fuel for heat it is both cheaper and a better use of energy to burn it locally.

Of course that isn't the full picture either. Electric can come from many sources (wind, PV), and scale means they can mix sources cheaper. (imagine a coal furnace, gas furnace, oil furnace, PV heat, and a windmill all at your house - it is obviously ridiculous, but large utilities have this)

You also don't have to burn for heat directly. Electric leaves open the option of a heat pump which can be >100% efficient when it isn't too cold.

>OTOH, the power plant probably has a rail connection or pipeline for oil, and the marginal energy cost of transporting an additional unit of oil to the power plant is probably quite low compared to the marginal energy cost of transporting the same additional unit of oil to your house.

Uh, I have a natural gas pipe coming directly into my home, along with nearly everyone in my state, and also region.

Electric heating is more efficient than natural gas, but electricity is more expensive per BTU, at least where I live.

I'm not sure about that.

I usually get about 125 gallons at a time. And since heating oil is just diesel with dye in it, we can just add deliver costs in gallons. Even assuming im the only delivery, I doubt it would take more than a gallon of gas to travel to my house. But to be safe lets say 5.

With the above assumption, the question is Could 130 gallons burned at a power plant generate more heat in my house via electricity. Than 125 gallons burned in my house directly.

I dont know enough to give an answer but my gut says no.

Oh, I'm not saying distribution efficiencies necessarily outweigh transmission losses, just that if you weigh the cost of getting energy from the place to your house you should also make sure you consider the cost of getting fuel to each location.

Natural gas delivers more heat per dollar spent.

I've come across this concept before. I think it might have been another post on the same site where they talk about direct mechanical use of hydro-power which made me look further into it.

I wonder what the efficiency of using direct hydro / wind power to power an air compressor (say rejecting the excess heat to preheat the hot water supply) and releasing the compressed air for air conditioning.

I nearly flunked thermodynamics in college, so take this as the harebrained scheme/Burning Man hack that it would be.

But I've wondered if you could get a useful amount of cooling/greywater disposal/hot clean water supply by mounting a wind-powered vacuum pump on top of a tall (11m +) column of water so that the water in the column would boil at ambient temperature.

It turns out that water boils quite slowly at room temperature and low pressure, so you’d need a very large surface area.

Why do we keep trying to come up with ways to heat things when a human is a 100 watt heater at rest?

Just insulate the building properly and then you can use rooftop solar to cool it down on those days when it gets too hot - largely because the sun is shining.

Moving heat is generally easier than generating it.

Unless you live in a styrofoam box, you're going to need heating. Also, people like windows.

PassivHaus standard can be warmed with a 1Kw heater at -10 degrees celsius. They have windows, doors and mechanical ventilation.

I just read about Passive House, thanks for citing it. The standard requires less 15kWh/m^2 per year. I live in the U.S. in a 1200 sq ft apartment, small for U.S. standards, and that comes to ~4.5kwH per day. To put that in perspective, an 80 Watt computer running all day uses up nearly half of that margin. A small 6000 BTU A/C (good enough for a small bedroom) uses up the entire allowance if you run it for 8 hours in your bedroom while sleeping. An electric dryer will use up the entire allowance if you do two loads of clothing.

I love that people are thinking about this, and I truly hope that it becomes standard, but it's not exactly reasonable for folks to expect such a level of efficiency without paying through the nose.

This seems like a reasonable argument for wearing a jumper.

I think you're firmly into diminishing returns if you're insulating your house to be warmed purely by body heat through the depths of winter.

Plus what happens if you have a child? Do you remove insulation, run the AC through winter?

You run the AC as required.

An argument against that is that the work energy counts against the operation of an AC unit, whereas it works for the operation of a heat pump. So you get a better CoP heating.

The obvious critique is that people in extreme poverty deserve every attention moment they can get, to derive a benefit with the lowest cost (to them) possible. But, when this represents an ad-hoc, it can often leave them stranded on a low increment from zero. So, adding proper drains to a favela is good because it reduces child mortality from bad drains, but its still a slum: the fix is unclear but probably involves a revolution.

These mechanisms are good because they can be easily understood and whilst they will require patching and hacking and repair and are inefficient and can't do all things, if they can provide a stable heat source to remove the burden of burning things, which actually kills more women and children because of lack of oxygen, CO/CO2 poisoning, asthma and other effects, there is a huge positive upside.

But, as has been said since at least the 1920s what we really need is soviet power, plus electricity.

I am curious about the potential for a hybrid wind turbine (clutchable):

Generate electricity during peak hours (high price) / Generate storable heat during off-peak hours.

Or would it be better to generate e-power all the time if the turbine is capable of it?

What I don't quite understand is: heat will be a byproduct of using electricity anyway, since it is always the waste product in the end. So why not generate electricity that can be put to good use first?

>The owner of this website (www.lowtechmagazine.com) has banned your IP address (x.x.x.x).

Anyone else getting this? I'm just going to read it on archive.org but it seems weird. I'm coming from a Digital Ocean NYC IP

Some sites block VPS's to mitigate bot abuse. Some just send you to endless captchas. Others block in haproxy. Some just 'ip route add blackhole ${ip}'

I didn't see mention of the noise levels - I know that wind farms are noisy, I wonder how noisy a single windmill would be.

I have never found wind farms to be particularly noisy. Certainly not any more so than having a road nearby.

I did some research after I made that comment (as one typically does) and I wondering about use in an urban setting - it looks like the ambient noise would be much more obnoxious than anything the windmill puts out.

Cities can be surprisingly quiet at night.

I wonder if this could be scaled up to provide district heating for villages and small towns.

They discuss this: yes but small is key here. It doesn't scale to large towns much less a city. (though if you take each neighborhood separately...) Losses from transmission are high.

But no? It says small city. In my town we have residential heating for 100k people. It's a power plant dumping all of it's heat into the hot water grid. (Co-generation.) If there were windmills, at the power plant, or really just along the heat distribution waterworks, they could dump their heat into the hot water grid.

Presumably your small city is using waste heat, so efficiency isn't as important: the goal is electric and the heat is just waste heat that needs to be dumped anyway. When there isn't the co-generation involved efficiency matters more.

Note too that nobody has defined the actual size. Your idea of a small town could be larger than my idea of a large city. Local factors matter in this definition as well.

Or, wind -> electricity -> heat pump (1:5) -> lots of heat?

Post links to front page. Direct link to article:


I don't know how that happened but now it won't let me update the URL now.

Updated. Thanks!

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