Passive solar water heater?
Posted by Own_Cardiologist_989@reddit | preppers | View on Reddit | 25 comments
One of the things I would like to work on next is reducing my energy usage so my current setup can stretch further. I have a propane burner and electric stove I can use in a grid down scenario, but I would like to be able to reduce the amount of fuel/electricity required to heat up water for cooking or maybe even a quick but comfortable shower. I don't expect to boil water, but if I could raise the temperature by a helpful amount then the propane/battery backup doesn't have to work as hard.
Has anyone here had any experience with a passive solar setup that could heat water? I've seen some ideas online about using black piping to absorb the sun's rays, and I've been thinking about trying something out with that. Just thought I'd come here first to see if there was any experience with it.
Excellent_Math_1121@reddit
I actually built something similar few years back using black garden hose coiled up in old glass window frame I found. Put it at angle facing south and man, water gets pretty warm even in winter days when sun is decent
The trick is having good insulation around the coil and maybe some reflective material to bounce more light into it. Mine wasn't perfect but definitely took load off my propane when I was testing off-grid setup. Just remember you need some way to circulate the water or it gets stagnant in the pipes
silasmoeckel@reddit
They exist they numbers don't tend to line up.
Solar PV has gotten very very cheap.
Heat pump hot water heaters are a thing and pricing for units is reasonable.
While direct solar hot water is quite expensive, china isn't pumping them out by the millions like PV panels.
DIY black pipe works in summer but not so much 3 other seasons. So your looking at a water to water heat exchanger to keep the antifreeze separate and probably a heat pump (water to water heat pumps are expensive, because they are uncommon).
Put that together and upgrade to a reasonable modern heat pump hot water heater then power that with solar. A bit of control logic and you can have it heat up when you have good sun.
EddieBull@reddit
This.
My house (Netherlands) had a solar water heater when we moved in, and it works quite well, but its complex, driven by a pump, and uses glycol so it doesnt freeze, and then exchanges heat to water in a reservoir. In summer its enough for all our hot water needs, the other seasons it helps when its sunny, which is not too often.
Maybe in most scenarios it harvests more heat than the same surface area PV would be able to heat with simple electric heat elements, but its far more complex, and much more expensive.
So PV is cheaper, less complex, and electricity is far more versatile than hot water and imo much better suited for most prep scenarios.
JRHLowdown3@reddit
There are specific solar water heaters, I thought that was what you were talking about. We don't have one, although when we built our addition I did plumb for one if we ever needed to add one in the add on.
As far as a homemade system I've tinkered with a couple things like this around the homestead for use in outside buildings.
On our recent greenhouse build in the trusses I laced black flexible irrigation pipe back and forth throughout the ceiling area, tied into greenhouse piping which is fed both by a 12v on demand pump from the rainwater catchment tank on the side of the greenhouse as well as being tied into our main water grid for the homestead. Turn one ball valve off, open the ball valve for the others and it's coming in from the catchment tank instead of the main water grid. The water from the black irrigation flexible pipe in the ceiling gets the water pretty damn hot and since it's not used as part of the normal irrigation system in the greenhouse, the water stays in there warming except in the winter when I keep that part drained so freezes don't break fittings.
We have similar thing with black flexible pipe that is threaded back and forth around the roof of a small building near one of our firewood sheds and garden areas. The roof of is has some solar panels on it and the black pipe snakes around those in a large loop and terminates in both a hot water shower as well as going to a big "laundry" type sink that we use when we are butchering, cleaning a lot of produce, etc.
One last thing that we can tie into this as well is a 55 gallon metal barrel I bought that was surplus from a local honey place. I put iron pipe fittings on it and a hose bib. I had a couple of old Lowes wheel barrows that had go to Helene Handbasket's house, but the metal frames were still good. So I removed the buckets which broke in a really short period of time, I think we looked at them wrong or something (POS construction, didn't last)... and mounted the 55 gallon metal barrel to the metal frame of the wheelbarrow. After the barrel is filled with water, you build a small fire under the wheel barrow/metal barrel and it heats the water quickly because the barrel is thin metal. A small 12V on demand pump pulls the hot water out and can feed to any hose or via a hose into the shower system for that building.
It worked good during Helene, we used rainwater from a catchment tank to fill it- you just want to be careful with the rainwater as far as washing "parts" and all :)
Serious-Ad2573@reddit
works extremely well in the tropics as summers here can go up to 45C.
dakotamidnight@reddit
We used one when I was a kid. 100 ft of black hose spread on top of a 28ft RV in South texas. I highly recommend using a mixing tank or something similar with a temperature gauge - it will absolutely get hot enough to seriously burn.
dittybopper_05H@reddit
I did something similar when I was a kid. Dad worked as a machinist at a catheter plant, and we ran a motel up in the Adirondacks. Even in the summer, pool would be pretty cool, sometimes at the beginning and end of the season, downright cold.
So he brought home a whole bunch of endotrach tubing which had been rejected for one reason or another, and he had me build a wooden frame and coil it up inside, and spray paint the whole thing black. Then we covered it over with clear plastic.
It definitely got seriously hot on a sunny day, but it was a large pool so while it took the edge off a bit, it didn't make it into bath water.
Looking back on it now, using metal pipe definitely would have been more efficient, but a lot more expensive. We were basically improvising using scraps.
overgrown@reddit
I worked on residential and commercial scale (~7 acre) systems from '08-'16 roughly, and I will add my .02 with the caveat that I am just now dipping my toe back into the solar thermal waters after years away from the subject.
The fundamental piece of information is that we reached price parity a while back in terms of nominal cost for water heating with pv vs thermal, so subsidies, components, and contractors disappeared for the most part in the middle of the last decade. YMMV by state and region, that said, if you're willing to throw some valves and/or put together some diy automation there is a good amount of energy to be collected at little relative cost. You can start simple, and there are various levels of complexity in projects laid out pretty well by hobbyists in every climate. The black plastic pool heating systems are rated for three seasons but you can push that with some clever design and they're pretty cheap and easy to repair. You can still get high end flat plate and evacuated tube systems, and for that price point you probably also want to consider tanks, differential controllers, and certainly integration with whatever existing energy systems. I am a proponent of multi-tiered systems that are site specific, e.g. solar - wood - hydronic floor. In terms of free advice, I would recommend finding a differential controller with inputs that suit your needs and building a modular system around that. Include a high point air vent and a low point drain, and valves to isolate parts of the system wherever you can. pex-al-pex is a product you may find interesting. Here for questions, possibly also answers.
Winter_Persimmon_110@reddit
The evacuated tube solar thermal collectors are worlds better than the old style panels or the homemade deal. Photovoltaics can beat them for price, and it is a bit of a thing to plumb, but they do in fact provide higher energy density for unit area so it's a good thing for small spaces.
MGyver@reddit
What climate do you live in?
Own_Cardiologist_989@reddit (OP)
Good question. I'm in Indiana, so I know at least half the year I'd have issues in the cold. I did anticipate this being more of a late spring to early fall type of thing to utilize.
MGyver@reddit
Sure, just thinking that if there's water circulating then it'll need to be drained before the freeze. Alternately, look at "drainback" systems but these require a pump
Chemical_Dog3418@reddit
My parents have a solar water heater in their home in Mexico along with a solar electrical generator. Other than cleaning the area that gets heated up they have not had any problems, their gas consumptions is basically null.
I will say though for anything above say Arkansas it’s probably not worth using. The heat would not be enough, at that point you could maybe use it to pre heat water but it’s not really that effective since your water heater is already doing that work and it would just be a more complex setup
TwiLuv@reddit
🤪🤪🤪have you been to the piedmont to coastal regions of NC or SC in summer?
Upper 80’s all the way to 100’s, & sunny, sunny, sunny.
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Adorable_Dust3799@reddit
Lots of solar water heaters here in so-cal
wanderingpeddlar@reddit
That depends on your budget.
The latest generation of Passive water heaters are good stuff. A closed loop glycol with evacuated tubes is a solid, robust choice
You collect sunlight in vacuum collection tubes. It is circulated to a heat collection tank say 300gal your house plumbing collects heat there. The heat collection tank acts very much like a home water heater. The more tubes you add the more heat you get.
You can also use a wood boiler to heat the same system to the same effect. I know a guy in North Dakota that uses both. He heats his water and his house.
The solar collection tubs are cheaper all told. And you have to feed the wood boiler.
Either way can work
V1ld0r_@reddit
I have a thermosyphon solar system and it's all we use year round. In the winter we do need to turn on the built-in heater element to have warm water for showering when there are multiple days in a row with cold temperatures. It doesn't freeze where I'm at but it regularly gets to 0ºc or just below. Family of 2, 150L tank.
J_Thompson82@reddit
I used one of those solar showers (think black bag that you hang up with a short hose and shower head in the end. In the heat of British summer it got up to a very pleasant temperature. But during the winter here, no dice.
But I have seen houses here in the UK with large black rectangle on their roof, filled with black pipes. I assume these are solar water heaters.
Covert__Squid@reddit
I’ve used them in countries where they are the standard. Basically you get 5-10 mins of hot water for a shower and then it’s lukewarm. They look like solar panels and draw the water through capillaries to heat it.
-Thizza-@reddit
Here in Spain you can buy one with a tank ranging from 100-500 liters and can provide heat to a house or an entire apartment block. You often see them daisy chained on flat roofs. I plan on installing one on my roof with a 150 liter tank. I'm not in a hurry because I use a regular water heater as a solar dump so I already have free hot water.
Backsight-Foreskin@reddit
When Carter was president he had solar thermal panels installed in the roof of the White House.
dawn_thesis@reddit
these things exist. do a google search, and a youtube search
Own_Cardiologist_989@reddit (OP)
Yup, I know. Came here to see what experience people have had with them