Producing hot water off-grid is a surprisingly energy-intensive activity, and although it looks simple on its surface it can get quite complicated especially when used in large scale for something like providing hot water for an entire home. When using combustion to heat the water there needs to be proper venting as well as control of the fuel, and even storage of the hot water needs to be meticulous to avoid certain pathogens. [Greenhill Forge] has built an off-grid solution for heating hot water that doesn’t necessarily rely on any combustion, though, provided he can find something to spin his custom electric machine.
The machine in question is, of course, an induction heater. It works similar to any simple electric motor, generator, or transformer except in this case the eddy currents generated are exploited rather than minimized. Normally these currents, generated when a magnet passes by a metal, are wasted heat in other machines but in this induction heater it’s the goal. The machine’s stator is built from copper tube wound in a spiral which allows water to flow through and absorb heat. The tube is soldered into one electrically solid mass to maximize the eddy currents. The rotor is taken from a previous generator built by [Greenhill Forge] which holds the permanent magnets.
During the initial tests using a power drill to drive the generator, he was able to heat 1.5 liters of water from 7.9C to about 24.4 C in three minutes. The math works out to providing 575 watts of power to the heater, and with something that could spin the generator faster it might have the potential to provide around 14.5 kW. Provided that there’s a source of energy around, such as a wind or water turbine, this could be a fairly sustainable way of generating hot water in off-grid situations. Some of [Greenhill Forge]’s other projects are centered around this idea as well, like one of his builds which uses waste sawdust to heat his workshop with a custom-built stove.
A longer article on the same or related topic, featuring a different version of the same idea:
https://solar.lowtechmagazine.com/2019/02/heat-your-house-with-a-mechanical-windmill/
Induction is less efficient than resistive elements, they both produce heat, but induction has other losses.
Why?
Why not?
If you use a small hydroelectric generator to power a resistive element, you have a more complex and expensive system, but it still has significant losses from induction, they just originate from producing electricity instead of heat. Not to mention waste heat from the generator, etc, etc.
There are a lot of experiments and projects we do that aren’t optimal, but by doing these things we learn. That’s why.
By making this project he may have learned something that he can use to develop another project.
It also may be the first step to optimising this approach using stuff he’s learned from other projects.
It’s a limited approach to say I know that’s not efficient, I won’t do it.
Because “heating water with a resistance doesn’t drag Youtube views. Yet, it’s the simpler (no mechanical failure), faster (you reach 100% efficiency here), cheaper (a waterproof resistance cost pennies), so better in all aspect.
There’s a reason why your home heating system is using a resistance and not a fancy induction cooking table.
“There’s a reason why your home heating system is using a resistance and not a fancy induction cooking table.”
Yeah because your home heating system is attempting to heat a large volume of air. Induction heats metal. Transferring heat from metal to fluid is fairly easy since most fluids have a high thermal conductivity. Water conducts heat ~24 times faster than air. Using an induction hob and a metal heat exchanger is a very efficient means of heating water on demand. It would be quite difficult to design a heat exchanger that be heated by induction, not melt, and have enough gas channel surface area to transfer heat into air. Its much simpler to just let air flow over glowing hot wires. Two very different scenarios.
He meant that water heating boilers normally use electric resistors you “genius”!
It is about input energy and output useful heat- induction is not that energy efficient in this case.
That’s an americanism specifically, though – here in the UK, our boiler (aka furnace in US English) heats water, which is circulated to radiators in each room (or underfloor heating if you’re fancy) – the main advantages to it are small (15mm) pipes to circulate water through, rather than the large ducts you’d need to circulate air
Many UK homes are older, brick-built structures with high thermal mass, which are not designed to accommodate the large ductwork required for forced-air HVAC systems.
Most US homes are newer Stick built structures with low thermal mass and are designed to accommodate ductwork.
The UK has an extensive, widely available natural gas network, making gas boilers highly accessible and inexpensive to run compared to electricity.
Roughly half of US homes do not have gas lines at all. It much easier for the UK to provide gas with a population density of 289 people per square kilometer compared to the US 38 people per square kilometer.
The average residential home in the UK is approximately 800 to 1,000 square feet.
The average new single-family home in the U.S. is approximately 2,300–2,400 square feet.
Forced-air systems are popular in North America largely because they also provide cooling, whereas the UK only needs efficient heating..
YES, As am American, on an American website, My comments are naturally from an American perspective.
You live in a teeeny little country about the size our state of Oregon in which youve packed 1/5 the US population. With an average house age of approximately 50 years and upwards to 25% are 100+ years old. Your perspective of housing standards and technology naturally quite different.
Your comments are quite Eurocentric. Unfortunately for your aging empire you havent been the center of the world for a century of two. Dont worry though, Our empires exceptionalism is rapidly failing as well.
DurDurDur should move to Texas, or maybe not. Gas is common and widely used. DurDurDur’s comments are quite DurDurDur-centric and are insulting to both the person he is speaking to and the people who he purports to represent; even he acknowledges how widespread gas is in the United States, and his statistics seriously mis-state matters in his favor. It is even more skewed if one focuses on suburban and rural locations that are most likely to find a use for this project.
There are actual good reasons why you might have rotary energy but no easy option of making enough electricity to usefully heat water. (for example, not enough copper wire to make an electromagnetic generator). Copper tubing and copper wire might have the same mass of copper, but are otherwise not inter-fungible for this task.
Practicing thinking outside the box when it’s optional can help build the problem-solving skills needed when the box itself is unavailable.
Is this message useful? Maybe not. But if DurDurDur has the right to act like a DurDurDur, I certainly have the right to point it out to anyone who missed the obvious :D
If your home heating system using resistive heating, then look into getting a heat pump!
Heat pumps still require a booster element to get to the final temperature. At least the ones I’ve seen installed.
Very much situational/locational, and very much depending on the details of your heat pump. A vertical deep-well heat pump can be surprisingly effective, but those are of course not the kind most people install, often without even running the numbers to check for local suitability and capacity.
A poorly-chosen heat pump will certainly not give heat pumps a good reputation. And if we are considering “heat pumps as are commonly and widely installed”, perhaps this reputation is not undeserved.
It’s a failure in applied engineering, not the technology itself; anyone who bothers to properly engineer it (or to hire competent engineers to do it right, rather than checkbox-compliant “yup, it’s a heat pump”, will find out that they’re often (but not always) suitable, and when they’re suitable, they’re pretty awesome.
But when they’re not, don’t force it. Find a more appropriate solution, because an inappropriate heat pump is a bigger waster of power than a well-done non-heatpump solution, if you add up all the inefficiencies and losses.
Did you even read the article or watch the video? There is zero electronics involved, it converts mechanical power from a wind or water turbine directly into heat.
You really think having a generator power a resistor is more efficient or reliable then this? No you don’t, you just assumed it was a ZVS induction heater because you triggered on the title and didn’t bother to look at the article.
I didnt “trigger” at all. My post wasnt an attack as yours seems to be. It was a discussion of the nature of heat transfer efficiency. Im fully aware that the article is about a cobbled together mechanical induction heater, a construction that poorly represents the potential efficiency of induction, Hence my inclusion of reference to an optimized representation of the technology. Take your meds, Touch some grass, Talk to someone who cares about you. Theres no need to remove the pins from your hinges. Its just the internet.
Eh, it’s just the internet, and the internet is not a one-way street.
Things on Hackaday are here to spark inspiration. They’re rarely useful or ideal as-shared, but worked-examples of out-of-box thinking can be very helpful when the box itself is unavailable. And once that happens, it’s too late to begin training your brain to consider what’s available, not what’s ideal.
This article (and idea) has merit for that alone, even if it truly sucked as a water heater.
And, I have seen a very similar heater system used in an industrial environment. It takes a bit of iterative refinement, but they can be quite a bit more efficient than you’d initially think.
After that system was pulled out of service, the plant engineers spent a few weeks having pointless fun with it: a couple of hundred kilowatts of shaft power can make some very dry steam, which can spin a moderate-sized steam turbine quite well. High-torque low-rpm shaft power -> high rpm turbine -> nearly a hundred kilowatts of electric power. Which is surprisingly more efficient than what you’d get trying to generate electricity directly from the low-speed shaft, or via the gearing necessary to couple it to a reasonable generator. It was for shits and giggles, with no real need, but the plant engineers did power most of the facility with their lash-up for a day, while the place was being retooled for the next big project. They did it as an example to the juniormost engineer, that practical efficiency is often very different than theoretical efficiency. If you can’t make it happen, the efficiency is zero.
I didn’t (or didn’t mean to) reply to you, but to the parent comment by sweethack, who said it was just induction for the YouTube views and resistive heating was better in every way. Sorry if something went wrong there.
The point is to centralise the heat generation to where it can be usefully used. e.g. an electric system incurs 20% losses in the generator, which is typically somewhere useless like at the top of a wind turbine.
I do wonder how this compares to a simple Joule Machine, though (a simple friction-based water heater that just vigorously stirs the water until it heats up). They’re both 100% efficient, so the only difference is ease of construction and cost. Would the induction heater allow, say, directly coupling the generator to the turbine? That’d be an improvement over needing gearing.
So you take the output of the inductive process and power some resistive elements with it to assist the setup.
And then somehow rig the whole thing up with a heat pump to boot. :)
I’m not sure but i feel like maybe the other replies are missing the point?
A resistive element is 100% efficient at producing heat from electricity, but isn’t the point of this hack to harvest kinetic energy rather than electric energy? I mean it seems to me like you could run the kinetic energy through a generator (i.e., an induction step), and then you could run that electricity throuh a resistive heating element…hey wait! That’s exactly what’s happening here, just the generator and the resistor are a single physical component. Isn’t it just a question about whether his magnetic heater is more efficient than the magnetic generator?
At the end of the day this is just a question of how to generate friction without creating wear surfaces, i think.
I think you’re seeing it clearly.
If you have a source of shaft power, this induction machine is likely the most efficient way to convert energy into heat. Otherwise you will incur loss from generation and potentially rectification (15-20%) to supply a resistive heating element.
However the distinction is moot, as heat conversion is capped at 100% efficiency. 100% efficiency sounds good, but it is relatively inefficient as compared to a heat pump, that does not convert energy into heat, instead it moves heat around, achieving >400% efficiency.
When using a heat pump, the 15-20% generation/rectification loss in converting shaft power to electrical power is more than worth it.
Yes. Resistive heating is 100%. Making the electricity is not 100%. In many practical cases, the whole-system efficiency can be lower than a system like this, at least after it has had some iterative optimization. And in this case, any heat produced goes directly into the water, rather than some being lost at the generator.
Induction has far better heat transfer efficiency than resistive. Giving it the edge that makes it desirable. Yes resistive is 100 percent efficient converting electricity to heat but then loses by throwing that heat everywhere as well as as intended target.
heating water of grid is remarkably easy and doesn’t require something like this. You simply get an electric water heater and connect it to the power coming from your solar cells. And if you you don’t have enough power from your solar to do that then
1) put a timer on it for times when you do.
2) put a smarter controller on it to only turn it on when you have enough power.
3) put a smaller element in it – many of them are made with 1.2, 2.4, 3.6KW elements and you can swap them..
I was going to do (2), but ended up doing (1) and (3)…
“1) put a timer on it for times when you do.”
and a bell to alert you that you have hot water so you better hurry up and wash the dishes, your clothing, and bathe.
Most people want hot water on demand, they dont want to plan around the periodic availability of hot water.
That’s a good point, but at the same time, we’re not on HaD to solve for the common case. Most people just buy something, then toss it out whenever they want something different. If you have the money, or you have no interest in the complexity and no joy from solving a problem, that’s a reasonable choice.
But, once again, HaD.
sure, but as it says in the video description, this setup was specifically intended to
a) not require solar, but be powered directly by something like hydro or wind.
b) provide continuous heat while running, not be limited to a fixed storage tank.
In 2002 I discovered the joy of POINT B.
I had purchased a truckload of goods for resale from home depot through a liquidator. There was a pallet of 12 recalled tankless water heaters. It turned out there was a manufacturing defect on the control board that caused them to fail, a bad/weak trace that required a small wire patch and some solder to repair. I kept 8 of them and sold the rest, as well as most of the goods in the truckload.
Our family property runs on a large battery bank, and a pelton wheel that were installed in the 1950s, so I cant say much about the power savings there. But the one I installed in my city condo appears to have shaved about $10-15mo from my electric bill.
My father had installed our first electric water heater in the 80s, we had previously used a wood fired water heater. That was a huge improvement but still had the usual tanked drawbacks of long delays in hot water to tap, pressure drops from other users, and the inevitable running out of hot water in the middle of a shower.
One of these tankless heaters would have probably been sufficient on our homestead based on their ratings but since they were basically free we went all in.
We installed one for the kitchen, one for the laundry, one in an outbuilding we use for meat processing, and two on opposite sides of the house each of which feeds into two bathrooms. Total overkill, but now instead of waiting minutes to get hot water to the further away faucets, its HOT flow in a few seconds. No one ever has pressure drop because of someone starting laundry. And no matter how long you go the showers never get cold. LOVE THEM!
Now ours are resistive heater tankless systems, so not quite the same.
Ive heard good things about the newer generation induction heater tankless systems but unless I stumble into a half dozen of them for free I dont see us upgrading.
TL;DR: Doing things without electricity is easy, just buy generation equipment.
Also, this presumes you can order the components when you need them. Not rejecting that situation, it’s nice when you have it.
But sometimes what you have is a random pile of junk and a real desire for a hot shower. Thinking inside the box will leave you shivering and irritable, so why not find a way to solve the problem you have, with the junk you also have? If nothing else, you never get better at what you don’t practice, and practice is often worth it even if the results are pointless at the moment. There is not always a box to think inside of, even if the box would be really convenient, and might be delivered in a brown van, if it were to exist in the first place.
ITT: Are you AI, High. or just dim with delusions of adequacy?
“Practicing thinking outside the box when it’s optional can help build the problem-solving skills needed when the box itself is unavailable. ”
“They’re rarely useful or ideal as-shared, but worked-examples of out-of-box thinking can be very helpful when the box itself is unavailable. ”
“Thinking inside the box will leave you shivering and irritable, so why not find a way to solve the problem you have, with the junk you also have ”
“There is not always a box to think inside of, even if the box would be really convenient,”
You can also heat the water by direct mechanical action, just by having something spin in it.
But with way more work/Watt. This one is about a simple but effective means to heat water.
More work per watt? What are you saying, work is measured in watts. Are you saying it’s less efficient? In that case, where is the extra power going? It has to go somewhere…
Yeah, came here to post this. Everyone forgets that fluids have friction.
But efficiently coupling work to a fluid depends on viscosity and velocity. If you have a lot of torque but not a lot of RPM, it’s not going to couple well. And even if you can gear it, the kind of variable drag that a fluid stirrer deals with tends to be harder on bearings and gears than a big flywheel mass that has only angular drag.
And, just to be fair, there are situations where a paddle heater is a better solution than an induction heater. They’re simply a bit less common. For example, high viscocity fluids that easily overheat and harden sometimes should be stir-heated, not directly induction heated. Molasses is a poor fit for a flow-through induction heater but can be effectively stir-heated if you really have to.
“If you have a lot of torque but not a lot of RPM, it’s not going to couple well.”
Uhh, you just have to make the paddle bigger. It’s just like changing the diameter of the diaphragm on a speaker.
This guys is a master shape rotator, the stuff he works out in his head is very impressive.
What’d make this interesting is if they managed to make a tank water heater sized vacuum flask and heated the water without contact to prevent heat loss.
Then you have a tank of water that’ll stay hot for a long time with no use.
So you want a big thermos with induction base for heating….
Mmm sun is providing heat too…
i built a whole elaborate system for heating water directly (like how a garden hose gets hot in the sun) from the sun. it’s a more more effficient use of roof real estate to do this instead of converting sunlight to electricity and then to heat, as going directly to heat is three or four times more efficient, even with the most efficient photovoltaic panels. of course there is the pain of running plumbing to your roof and then you have to worry about what happens in the winter (antifreeze, baby!)
http://asecular.com/projects/homebrewsolar.php
If you had a creek running through your property and added a waterwheel to drive this device you could have both hot and cold water coming from the creek. Quite elegant Actually
the problem is that it still takes a lot of watts to heat water no matter how you do it, and a powerful microhydro plant can generate maybe 500 watts, which will take a looooooong time to heat up a bathtub of water. i’d rather just have the electricity, since 500 watts is plenty for most non-heating household needs
I have a tankless water heater that cost $80, and the BBQ tank I get filled for $15 lasts 6 months.
The trick is to get a handle on the power being put into the device vs the power output. The battery powered drill does it but at what power and when kind of water flow or air flow to get enough power to generate enough heated water to make a difference.
Because why wouldn’t you just turn a compressor of a heatpump use the laws of thermodynamics as is so popular these days. I’m thinking it’s going to require a good sized water-wheel or turbine setup or a rather large windmill.
Great experiment though.
Because this is simple, doesn’t require refrigerant gas, and will still work after it’s been outside for 15 years and dropped of a cliff twice.
As it turns out—light alone can evaporate water:
https://news.mit.edu/2024/how-light-can-vaporize-water-without-heat-0423
https://www.nanowerk.com/nanotechnology-news3/newsid=69299.php
https://phys.org/news/2026-04-space-boost-links.html
https://phys.org/news/2026-03-chiral-metasurfaces-free-space.html
So, how to combine all these….
Using magnets to heat water is easy.
Using them to cool water is real science.
(This isn’t a shit post, there is a slow, but usable method to do this, and I only know of one company doing it in production)