Heating A Home With Sunlight… And Water

The sun is a tremendous source of energy, and while photovoltaic panels are an easy way to harvest some of that energy especially now that prices for them are incredibly low, there are plenty of other ways to tap into that free energy as well. [Engelbert] was looking for alternative ways to heat his house since traditional methods were prohibitively expensive, and ended up building a heat exchanger using solar-heated water to cover his home heating needs. (Google Translate from Dutch)

The system uses several large roof-mounted hot water heating panels. The heat captured by them is then pumped into an underground pipe network which is able to warm up a large area of earth in the summer. In the winter, that heat is able to be extracted back out of the earth and used to heat his home. The system includes almost three kilometers of pipe which are buried two meters below grade, so this will probably not be a weekend project, but it still cost much less than the €80,000 to install gas heating in his home.

[Engelbert] is able to use this self-built system to keep his home and another smaller building at a constant 23°C all year. He actually overbuilt the system slightly and has since disconnected almost half of the pipes, but we certainly understand the desire to over-engineer things around here. The only problem he has had is with various government entities that are slow to adopt energy-efficient systems like these. Perhaps the Dutch government can take some notes from the Swiss when it comes to installing geothermal systems like these.

Thanks to [Jero] for the tip!

64 thoughts on “Heating A Home With Sunlight… And Water

  1. I can relate to his woes with the government – I wanted to do something as simple as putting hydronic inslab heating in my workshop shed when it was built and the inspector just couldnt get his head around it – The concept of putting water pipes in the concrete was too much for his little brain to comprehend.

    After he was given all the paper work for the inslab heating pipe he eventualy shrugged his shoulders and passed it.

    And this was only about 6 years ago….

    1. How does in slab heating work?

      I know almost nothing of foundation work, so please ignore my ignorance.

      Doesn’t heating the slab mean that you heat the ground below it? In my mind it sounds better to put an insulating layer on top of the slab, followed by heating and floor.

      1. I can’t speak for Saabman, but where I live (Germany), hydronic floor heating is quite common. Typically, it is not the structural slab that is heated. Instead, you would have a layer of insulation (styrofoam) on top of the structural slab, followed by a couple of inches of concrete screed.

        The water pipes for heating sit in the screed so that only the actual floor is heated. The styrofoam limits the loss of heat into the ground (or the ceiling of the floor below).

      2. You put the insulation under the slab and around it. he slab becomes part of the insulated area of the building.
        The insulation is quite capable of taking the weight of the slab as a distributed load. That is 4″ or 100mm and upwards of PIR board, not rockwool :)

        Again this is a hard concept to get UK building control to understand. The same people I dealt with questioned if metal is “substantially non combustible”. And on raft foundations.
        They are stuck in the past, jobs for the boys.
        Dont want to deal with individuals but it’s the building firms that are the real cowboys.
        Sadly it’s part of the system of dumbing down rather than enabling people to do their own work.

        1. Too true, see it all the time… we do it that way because we always have, or we buy that system because we have an account with that company. Had a friend who had similar when trying to get a rain water harvesting system “passed” the inspector just couldn’t get past why you didn’t just let the rain water go down the drain, and that was before he saw the storage tank, which he then referee to as a water butt in his report.

    1. There’s ways of building greenhouses where you can do it directly, where the water table isn’t high. You dig it 4ft into the ground, and make a north wall earth berm with the spoil. Then any solar gain at all warms up the north wall “sink” and re-radiates when cold.

    2. Warm greenhouse similar method dig trench length of greenhouse about metre wide 75cm deep Insulate sides run waste pipe filled with holes. Fill trench with large stones. Cover to prevent soil entering and filling air gaps between stones. One end pipe to green house roof other floor level. Add fan. Preferably solar powered. In summer air heats stones in winter stones heat greenhouse

  2. Could someone fact check the claim (also in the original article) that this system is storing the heat in the soil for months at a time? It seems unlikely to me that soil would be insulating enough to have that effect.

    My impression is that this is really just a geothermal heat pump with solar boosting the ground temp a little. This works even without the concept of long term heat storage.

    But honestly I suspect it would be more efficient just to use the solar-warmed water as an input to your hot water heater. The more directly you “use” the warmed water, the less opportunity it has to lose heat.

      1. Great for winter. What do you do in summer?
        Your thermal panels are generating tons of heat, your heat pump is in cooling mode and generating tons of heat.

        What are you going to do with that waste heat ?
        You could run a steam turbine :)

        1. There is no need for a reversible heat pump with such a large earth basin. Even while storing heat from the thermal panels, the return water temperatur from the basin will be lower than ambient temperature and can be used for cooling.

    1. I can only say its very plausible, remember its not storing all the energy at all – its going to be very lossy of the freely available fusion by-products blasting down on his abode… But with the right geology capturing significant energy and not loosing all of it for months is quite believable, the downside being geology good for longer term storage are necessary going to be less thermally conductive so it will be harder to get the energy in and out. Also consider how long the kettle/pan full of boiling water lasts compared to your teacup (or coffee if you insist), and that’s with a rather active liquid distributing its heat to the edges really fast, usually in a container that makes for a better radiator of energy than the cup – big mass can stay hot a long time just because its bigger.

      You are definitely correct any storing of the heat incurs losses so if you can get away without it great – but much like your phone/laptop would be more efficient without a battery it would also be rather less functional, perhaps not up to the task at hand (I mean my phone almost never leaves me desk so I wouldn’t really notice, but I understand most folk like to be connected 100% of the time on leaving the house, and are glued to their phone enough to never forget it), and this is energy freely available for the capture. It also can’t kept at the source till we need it, the sun is beyond our control.

      I’m not entirely sold on actively catching and storing heat in the ground, seems like the environmental impact of such a scheme could be hard to measure and I’m not convinced its better for the global climate troubles we are causing than other options. Done right its a durable, reliable system though so its probably sound enough in practice, I’d just be more comfortable capturing the heat inside more controlled environments, where the losses can be lower, the environmental impacts monitored, my inner control freak satisfied, etc.

    2. I do wonder whether someone’s got the wrong end of the stick here. Surely photovoltaic panels running a heat pump would be a more immediate benefit. Cooling the house in the summer, dumping excess heat from the house (not the roof) into the ground, and warming the house in the winter by drawing heat from ground. You might not get much assistance from the PV during the winter, but you also don’t make it more difficult to cool the place in the summer.

    3. I too doubt how much heat he is putting into the ground.. I suspect if he only turned it on in winter he would get about the same heat out of it..

      The australian way of doing something is much simply, as we don’t really need much heating. You just wack enough solar sells up to run your air con, pool pump, with enough left over to put a bit back to the grid.. You then just use a bit of that power in winter (with the lower solar coming in) to run your air con on heat mode..
      And a separate solar hot water..

      Mind you, I’ve got a really cheap solar hot water in my holiday house, which I found out by accident about a decade ago. We shifted the electric hot water tank around the corner to the North/East side of the house – I hadn’t put solar on as I was about to rebuild the roof – and I forgot to ‘plug’ it back into the electricity. About 4 weeks later I found out when doing something else – but had hot water all that time because just the tank sitting in the sun was enough to give me hot water all day :-)

      1. “About 4 weeks later I found out when doing something else – but had hot water all that time because just the tank sitting in the sun was enough to give me hot water all day :-) ”

        I can second you on that. I tried it back when I was 20 in my country of birth in South America. I painted the electric heater matte black for a better effect :D

    4. Yup, absolutely. Relatives in South Wales (U.K.) – known for cloudy rainy weather – had solar water heating installed. Got the water to about 40C even in mid-winter when there was no sun to be seen for days.

      1. Not sure about the hygienic aspecs of storing (potable) water over a longt time at a temperatur that’s warm enough for all kinds of germs to grow in but too cold to kill them.

        Water code in my area requires boilers to heat to above 70 °C in regular intervals to avoid growing legionella

    5. Seems unlikely to me as well. The article talks about a heat pump (at least the Dutch source). Haaksbergen has sandy soil with relatively high water flow through it, and 2 meters is not really much when you wish to store the heat. If storage was the intention, i’d expect a large plastic wrapped amount of soil at a bigger depth. It seems to me that it is just a relatively large thermal mass for the heatpump. My guess is that only a small part of the winter heat in the house was stored in summer.

    6. Ive read several studies and real world examples on people doing this and noticing a change in long term soil temperature.
      And lots of people saying it doesn’t work – but who haven’t tried it.
      Google is your friend.
      it also featured on a Grand Designs Australia episode.

      I plan to put my money where my mouth is when it comes to upgrading the heating on my house. I already have solar thermal for hot water, and a little PV, but that needs to grow in order to be effective as interseasonal soil temp increase.
      I will be adding more thermal panels and testing a heat pump solution with PV to offset much of the power requirements. Added bonus, summer cooling of the home adds even more heat into the ground.
      However my biggest problem is my older house is lacking insulation – this is the first step.

      The typical soil temp for the UK is say 8C. Heating it during summer might take that up to 12C for a localised area; so what?
      That is driving winter efficiency for the heat pump as it’s not adding those extra 4deg of temp to the working fluid. All from the summer period which was previously “waste heat”.

      In June/ July/August even in the UK; once you’ve got 200L of hot water on tap and a warm swimming pool by 1pm, what do you do with the rest of the 90C temp of water coming out of the vac tube panel till 5pm?? :)

      One thing I ponder about is how heat pumps are generally disconnected systems.
      If you had a working fluid at a set temp and every device needing (or benefiting from) a heat pump was connected, you’d be adding or removing heat through all appliances much more efficiently than each separate appliance dumping that waste heat into the air.

      Just have to do the math to see if it’s viable.

    7. Soil has insulation R value of about 0.125 – 0.25 per inch. So the soil that is under the center of a house, with 8 feet of soil between it and the outside is insulated to a similar rating as a typical wall: R13-R23. Remember that his pipes are buried about 6 feet deep, so ~ R9-R18. Details are light in the article – it seems that he has a fairly typical heat-pump system to pump heat into the ground, and then return it via radiators, and that his pipework extends beyond the house footwork. More importantly, soil has a high heat capacity compared to air. It takes a lot of energy to heat up and cool down, so is able to buffer changes in air temperature very effectively.

      A recent Grand Design’s episode (British Channel 4 architectural series) showcased someone building this to an extreme. No exterior radiators, solar collectors, or forced air heat anywhere. The entire earth-buried home was designed to collect summer heat via solar gain through windows, with the concrete structure used to collect it in the summer and radiate it back during winter. They estimated it would take 3 years to get to living temperature. https://www.dailymotion.com/video/x7yyqig

    8. The temperature at 2m below ground is pretty constantly within 2-4C of the surrounding soil except where permafrost exists or the water table is within this depth. As to “storing” the heat, not so much. Consider the mass of a cubic meter of soil and it’s clear why this is the case — how many watts are required to raise the temperature of such a mass 1C, and then how do you prevent that heat from conducting away? In the US it’s common to dig a well 30-60m down and then run 300+ m of tubing into it, sometimes using multiple wells. You then use this pretty constant temperature of fluid as the “base” from which you heat or cool against — so you are always heating up from 12C or cooling using the same, but you are warming or cooling from the much colder or warmer outside air. It works better for air conditioning obviously.

    9. Good Day, Mr. Abrahams. Thank you for your posting.

      Solar supplemented hot water seems very sensible, and if the containment can be insulated (and secured against puncture) ‘geo’ thermal does not have to dig too far, and may even be contained in a basement. Same with chiller cold storage. How can I learn more and participate in this? Watching winter do Kansas was hard, and when you multiply that by tens of thousands of farms and add tornadoes, solar panels seem really impractical. So I am deeply interested.

  3. Utrecht University in Holland has something I think is similar. They are claiming energy savings of around 3%. https://www.uu.nl/en/organisation/sustainable-uu/operations/heating

    And at the Centre for Alternative Technology in Wales I remember seeing solar water heaters made from matt black-painted central heating radiators (many years ago now). The problem here in the UK is freezing, just when you need some heat the most. Well worth a visit to CAT though when conditions allow, lots of very DIY hacky projects!

  4. Come on! 80,000 euros to put a gas furnace in? Either that is just out and out Bull or it includes extending a natural gas main a few miles. Never heard of propane? Or are Europeans are being taken to the cleaners? You could put in a couple geothermal heat pumps (water to air) for that in NY and have money left over. The 6 month storage thing is a stretch too but non zero possibility given constant input and the right geology, not normal soil (think large geothermal cooling system in Texas “chalk”).

    1. Propane isn’t cheap at least here in the UK, in fact it’s more expensive than electric resistive heating if ordered a few kilograms at a time. Can’t speak for bulk pricing.

    2. He lives on the Dutch-German border and extending a gas pipe to his home costs 80k. He has a really specific situation, a relative small well insulated house on a extreme large property (for this region). But most neighbours are heated by gas and there is no financial reason not to.

    1. Even with study they can work very well – as you point out its ‘free’ so as long as it does the job, and keeps doing it there isn’t anything to complain about. Sure your mythical magic tech 100% efficient mass to energy room heater (or real world high efficiency options) are very impressive, but they still have maintenance and fuel costs – there are lots of other metrics that make them potentially much much worse options than making use of freely available resources.

      1. Correct. But a heatpump (water/water) has a COP of arond 5 so you get all heating while you need to pay for only 20% of it. In The Netherlands there is a big advertisement of air/water heatpumps problem is that when you realy need that energy the air temp is to low to get a COP above 1.
        Have calculated a simular system with freezing a basis when heat is needed and then in summer unfreeze it by using the heat coming from the ‘forced’ coold PV pannels (they get to 80+ Celsius), for my house (210 MWh) it needs a 220 m3 basin to get the energy for the whole year, now it’s coming from 2100 m3 Natural Gas. At this moment the needed investment has don’t give a positive result :(

  5. So in the summer time, he is removing the heat from his roof (in effect cooling his roof), that would normally be re-radiate into his home, and dumping it deep underground. He is shunting the thermal energy away from the living space keeping the temperature at 23°C (73.4°F).

    And in the winter time because the temperature deep underground is nearly constant (~10°C; 50°F at that depth in that location, according to the article ) all year round, he is using that as thermal source to warm his house. The panels on the roof are unused during the winter.

    That would be my interpretation of what is happening. Lets say that the soil is wet clay with a density of 2300 kg/m^3 and that all three kilometers of pipe warming up a 1m x 20m x 20m (~ 3’3″ x 33′ x 33′) If you spent 6 months warming up that volume of 920,000 kg (~1014 US ton) of soil even if the temperature was only half a degree that would still be an insane amount of energy. Lets assume that it is all water, instead of soil, clay and water. The specific heat capacity of water is 4,200 Joules per kilogram. So 920,000 kg of (water) could store about 4,200 x 920,000 joules of energy (~3,662,365 BTU) if the temperature could be raised by 1°C (1.8°F).

    1. If I’m not mistaken that’s about 4GJ, divided by 3600 seconds/hour for about 1000kW.hours, for the equivalent of running a 1kW electric bar radiator, for 1000 hours, ie about 40 days (per degree C) and assuming 100% efficiency in transferring the heat from the soil to the house.

      1. I don’t know, but given the low temperature differences in such a system my feeling is that achieving an efficiency of 10% might be the limit of practicality in transferring that heat, so we’re looking at heating a reasonably sized, well insulated Dutch bedroom during winter for somewhere between a couple of days and a couple of weeks.

      2. If you are sucking the energy from the ground, and your ground loop is deep enough (at least 1 meter below ground in my area), you can get efficiency of 3-5 times the energy invested. In other words for every 1kW of power spent on running the heat pump i ground loop pump, you get 3-5kW of heat pumped in. The whole thing can work all year round efficiently because ground temperature beneath certain depth stays constant all year round. Efficiency increases in summer when you are pumping heat from warmer place (house) to colder place (ground)…

        Watch Technology Connections videos on heat pumps. He knows stuff and explains it well…

        1. Dude, that’d work just the same even without the roof mounted panels and the earth storage now wouldn’t it? What makes you think that I am not aware of that? How does it effect what I said? Geez, what a struggle.

  6. This does seem to merely be a distributed, lossy (and probably expensive) heat store, coupled to what’s presumably a good heat pump. And as someone else mentions, it appears to just boost the temperature of the loop.

    This is all rather vague and there’s not a lot of referable figures or design info, so how can it be viewed as an invention? Also, if it is just the summation of the above, it doesn’t seem very new. These ideas seem to have been very well discussed by the passive house community which has been around way longer than this project. Can’t reference any of my books on the subject as they’re in storage – which is also vague :) but a lot of them are well over 10 years old. Also I remember looking into something similar for a much larger instillation at UKAEA, also over 10 years ago. Unfortunately, the ground water where the facility was built (Culham) is super high (between 0.5 and 1.2 m below surface) which would make storage impossible as all the heat would flow away. It was also not at all cost effective to store heat seasonally compared with upping the insulation a bit and going with gas. Admittedly, the gas infrastructure was in place.

    Maybe a different prospective is – why is HAD reporting on what is very probably a wealthy implementation of a whim by an aging armchair scientist? There’s no content here apart from his house is overly warm and he spent a lot, then rattled against whatever authority he could.

    Please can we get back to stuff with some detail, coolness and positivity?

      1. You can read “Solar Building Architecture” edited by Bruce Anderson, 1990, MIT press, ISBN 0-263-01111-5. Pages 233-266 discuss instrumented and documented systems of a similar nature, implemented between 1972 and 1986, for a few other examples.

        I am sitting in a room that’s 21C in the late afternoon thanks to nothing more than solar thermal gain. Haven’t run a heater in over 6 months, and am at ~35S latitude. The hot water is purely solar heated 9 months of the year too.

        Am yet to plumb in pipes in the slab for circulation of solar heated water, because, well, lazy.

        Most of the principles of passive solar design were figured out in the 1970s.

        With a decently insulated building envelope, appropriately implemented glazing, and some attention to thermal flywheel techniques, energy use for space heating can be quite frugal.

  7. I know someone here in the U.S. that did something similar. When the home was built it included a lower basement level which was highly insulated and filled with River rock with tubing running through it. The stone stored the heat. The system also furnished all the hot water needs year round. The heating portion of the system was only used during the winter months. There was a backup system that would provide heat if needed due to lack of sunlight to heat the rock. In 30 years the backup had never been used. Even if there was no Sun for as much as 8-10 days, or more, there was still sufficient stored heat to keep the home comfortable. The system circulated water through tubing in the floors. It was a great system.

    I don’t see how nothing more than tubing buried in soil could possibly be sufficient to heat a home. It would seem any heat gained would be lost rather quickly. A heat exchanger, or heat pump, would accomplish the same thing without the need for solar panels on the roof. Also a heat pump with water lines buried under the ground would also take care of any cooling needs in summer. I’m no rocket scientist but I see a lot of problems with the system as described.

  8. I saw a house in Australia that included a huge water reservoir in its center. The many thousands of liters of water acted as the thermal battery to smooth out the temperature fluctuations. It should provide a much cheaper and more efficient storage solution . Not sure if that extended to 6 months though.

    1. I’ve seen such a building as well in Germany – this goes by the name of “Sonnenhaus” – it was covered in many thermal solar panels for collecting as much heat during the summer as possible. In the center of the building there was a massive two story water tank (50 m^3) with good insulation that reached about 90C by the end of the summer.
      You only need electricity for a few water pumps and valves for intelligent loading and layering of temperatures.
      Having this massive thermal storage in the house means that any losses due to non-perfect insulation will not be lost but also heat the house.

      Unfortunately, such a massive water tank is also expensive…

      The loop of pipe 2m below the ground is a typical setup for heat pumps around here (a friend of mine has this) . This does not require special permits (in contrast to digging 90m), can be done yourself and is more efficient than air heat pumps (especially in winter). You can certainly dump heat during the summer – but not for storing heat for the winter.
      For autumn and spring a few thermal solar panels can provide heating with only pumping water (I have this) – but this does not last through the winter.

  9. I think I saw a heat storage system being sold by LG but it was a large well insulated tank underground. I totally agree that the dutch gentleman will not be storing energy in his heather patch over 6 months or anything like it. I would be interested though how well it could work with a tank insulated in a similar way to a dewar flask (hundreds of thin layers of aluminized polymer fabric). Of course the losses would drop dramatically with scale. Maybe a good strategy for a new estate of houses would be to have one huge shared underground well insulated tank at it’s centre.

  10. Now, spray the tank with black paint :-)

    I’ve got a hydronic system. Small-scale, but expandable.

    Rayburn wood-burning kitchen range with a boiler. Runs 24×7 during colder months, but it was boiling the HWS. I installed a thermostat-controlled loop with a circulator pump, interrupting the HWS heating loop, to send excess hot water to the bathroom, through a towel rail, and back to the HWS, somewhat cooler than when it left. One of these days I’ll add some bedroom radiators as well.

  11. Solar heat can be collected during the summer and stored in bore hole for use until the next summer. These bore hole fields may take a couple of years to “charge” and provide a fairly stable energy source all year long. The end of summer temperature can be high (80 C in the example) and the thermal loss during the year is about 50% . Here is one in Alberta, Canada: https://dlsc.ca/. About the bore hole field of this example: https://dlsc.ca/borehole.htm

    1. The Drake Landing project is interesting. They have loads of sunshine and lots of collectors; a megawatt peak thermal power! The single borehole thermal battery is more efficient than individual storage for 80 houses.

  12. I live in a condonium with 143 flats at 60 degrees north.
    We have 16 bore holes down to 300 meter each in to granite bedrock.

    As the ground water is not moving fast we can add energy to the bedrock during summer.

    This as we reclaim ventilation heat in to the system with passive heath exchangers and circulation pump during non heating season.

    We have large heat pumps that increase the water temperature to 60 degrees Celsius for our water based radiators.

    This system works down to around -15 Celsius.

    This was installed 5 years ago and has cut our early heating cost by 40%, taking the investment cost in to acount.

    This in Stockholm Sweden

  13. Back in the 90’s my dad played with this. Built a box out of plywood, painted the inside black, put a 4″x1’x8′ radiator in (painted black with stove paint), and put reclaimed double-paned windows over the top. We hooked up garden hose for the test run, and melted a hole in the exit hose. He didn’t have the time or inclination to run copper pipe out to it and rig up some kind of cover to keep it from overheating in the summer. The project was scrapped as too effective.

  14. I’d like to know a few more details than this popular press article reveals. Like, what’s the temp and flow of his pipes, how much electricity does he use in the heat pump, that sort of thing. And why didn’t he just put a water tank in the basement to tide him over a week with no sun?

  15. The system uses several large roof-mounted hot water heating panels. The heat captured by them is then pumped into an underground pipe network which is able to warm up a large area of earth in the summer.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.