Does anyone here have a solar water heating system on their bus? I'm thinking about having such a system on my bus, but at this stage I'm mightily confused about what type of system is best for a bus. I still have space for two tiltable solar water panels at the end of my PV panels, but I don't have much space left for a drain-back tank etc. I know that I can run excess PV power through my inverter to power the electric heating element in my Suburban water heater, but ideally I would prefer something that is largely separate from the PV system. Any thoughts, anyone?
Thanks, John
Interesting idea John. As Clifford would tell you and others, some places don't require a water heater in the summer months. I am currently in my bus in South Texas for the summer, and I haven't turned on my water heater in the past two months. When the ambient temperature is in the triple digits during the day, the water comes out of the shower warm enuf to take a good shower. That being said, today is the first day it has dropped below 101 degrees during the day in the past two months, so going forward I may have to fire up the Aqua-Hot for a few minutes each day.
It will be interesting to see what people here have come up with. I have been in the bus business for several years now and have not seen any designs for heating water yet. However, my system and many buses with Aqua-Hot and other systems have a manifold that connects into the engine cooling system that heats the house water whilst driving down the road. So when you park for the day, your water is hot. A hot water heater is so simple and reliable. But I know you like your 12V systems. But maybe consider a diesel hot water heater? It only takes a few minutes to warm up a tank of water.
I would think it would be easy to run black PVC tubing in a circular pattern on the roof, or run parallel black pipe with a circulating pump on part of the roof to heat the water a bit. Your problem is that your roof is covered with solar panels (Have you been on your roof lately? (see belos) ;D ), except for the walkway down the middle. You have limited real estate, so you will have to be creative, as you can't have your cake and eat it too.
Don't forget: a circulation pump will draw power from the battery bank unless you only run it when the sun is shining on your solar panels, which is probably when you want to run it anyway. But then again, aren't some of these off-grid systems self-circulating?
Then, will you have an insulated tank so you can also have a hot shower in the morning? Where will you squeeze that in your school bus?
I did find this thread that you may be interested in, though.
https://www.skoolie.net/threads/solar-hot-water-panels-bus-cabin-heater.663166/
Let me know what you come up with, and maybe we can patent it/ ;D
Hi Gary!
I forgot about when you climbed up through my roof hatch at Paul's house to take a photo of my PV panels - that's a great photo.
My intention is to make a simple water pre-heater system that will supplement my existing propane/electric Suburban water heater. Probably in summer it will completely heat water by itself, and in winter it should reduce my propane usage. I'll keep my present heater, and also use it as an insulated storage tank for the solar panels. The only complication is the need to drain the panels after they've heated the water enough; obviously I can't just switch off the pump and leave the water inside them, because on a hot day it will boil or even flash into steam very quickly, and that's no bueno. Designing a simple drain-back system is the tricky part; the rest of it is just basic plumbing and adding some valves and a pump. I'm beginning to get some ideas now for the drain-back side of things, such as ensuring that ALL water can freely drain out of the panels (that means that coiled pipe or hose won't work because it traps water, nor can the panels tilt for obvious reasons!), or choosing pumps that allow water to back-flow through them when they're switched off, and some other arcane details that I would never have considered before now. I'll come up with a workable plan, but I'm still on the vertical part of my learning curve. Above all, it has to be basically simple, and not affect the present hot water system if it should fail or explode or something.
When I built my roof walkway for the PV panels I deliberately set aside some space at the end of the walkway for two water panels. I can only fit small panels there, but they should be enough for my modest needs. At least I have plenty of electric power from the PV panels to run the new pump and some solenoid valves; the pre-heater system conveniently will only work when the PV panels are also making power, so it probably won't draw any power at all from the batteries.
John
Either do that, John, or use non-toxic ethylene glycol in your closed-loop system and a manifold to circulate water through the manifold and the insulated hot water tank. I believe off-gridders do this to prevent freezing in the winter, and then you don't have to worry about it getting too hot when it is not circulating.
That being said, knowing you as I do, you will probably use a thermostat in your tank to shut off the circulation pumps (you will need 2 now), once the water temp heats up.
Heck, maybe you should consider installing the same heating system in your floor if you can afford the height in your bus without a raised roof.
That said, it is like solar electric: you have to park in the sun for it to work, which means the inside of your bus will be hot in the summer too. The alternative is to make a portable box to set out in the sun and run the hot water through houses into your bus tank. But then, you will have to carry extra hoses with you.
Bottom line, with all your solar panels, it may be better to heat your water with electricity, primarily during the middle of the day, and store that hot water for night use. I would want at least a 10-gallon tank, and preferably a 20-gallon if you do a lot of dishwashing, or if you have 2 people in the bus. This eliminates a lot of extra equipment you have to lug around, and every pound you cut will mean more MPG you will get with your bus.
More on my solar pipe-dream (or maybe I'm a moron for even considering it?).
I sketched out a basic direct (i.e. only using water) drain-back system that would work in my bus, but it's clearly not even close to being cost-effective. My initial design needs 2 pumps (one an expensive hydronic-style), 4 solenoid valves, 2 check valves, 2 temperature switches, 2 timers, some relays, an insulated tank, and a partridge in a pair of trees. It would definitely work, in theory, but simple it ain't. I could even make it, but just because I could doesn't mean I should. This doesn't include the two panels themselves that really need to have copper tubes with a million soldered joints, plus the cost of making two enclosures with glass lids, and all the miscellaneous extra odds-and-sods that always end up costing way more than you would ever guess. It would be a financial disaster, even though it would actually work.
To avoid all this complexity I thought of using electrochromic glass (like a Boeing 787's window shades) to block the sun from the panels' heating tubes, but that's REALLY expensive, even though it would eliminate needing all the drain-back faff. I even thought of purely-mechanical shutters that slide over the panels when the water is hot enough, but my bedroom roof hatch would get in their way; that's too bad, because otherwise they would work, and I do enjoy making mechanical things more than doing plumbing or electrical stuff. They would even allow the water panels to be tiltable, just like my eight PV panels.
So, it's back to Plan A, using electrons from photons to heat water electrically. It's MUCH cheaper and simpler to do that, even though it's really not what I wanted. Or I could buy an awful lot of propane for the cost of any water pre-heating system. Once again I am impaled on the horns of a dilemma (or whatever that expression is). I'll sleep on it for now, and see if I suffer from any more inspiration.
John
Yes, in reality, it may not be worth the effort unless you plan on having about 6 kids in the near future. I have been studying bus conversions for a few years now, and I have never heard of anyone setting up a solar water system, but that doesn't mean they haven't. In an off-grid house, sure, but with a bus, it may not be feasible. A bus moves and has limited real estate.
Going down the road shaking all over means you have to build a pretty rugged system, and based on the parts list you presented, it could get pretty costly; again, it is one more thing to maintain, and that can go wrong, and pumps fail after a while.
My Aqua-Hot system works off electric and diesel fuel. If I have free electric, I will use that. When I use diesel, I can fire it up, and in a few minutes I will have a shower full of hot water, and I am already maintaining that system.
The other thing is, because you stay mainly in the Southwest, you don't have much of a difference between cold (actually warm) water and water hot enough to take a shower. So even turning on your electric water heater for 15 minutes before you jump in the shower once or twice per day should be sufficient. I always wanted to put a timer on my water heater, as there is really no need to leave it on all day, and sometimes I forget to turn it off.
Because you already have a killer solar system with tilting panels, you may want to just use those same electrons to heat your water with your electric water heater, and on cloudy days, use propane if you have a propane/electric water heater.
My 2 pesos' worth.
I have 7 solar water panels on the side of my bus barn to HELP in the heating of the garage.
Kinda simple system if the sun does it's part
Sun heats the panels that heats the food grade antifreeze that runs through 2 rad forced heat exchanges than repeat
1 solar water pump and a $50 Amazon controller
1 have seen the antifreeze temp at the last panel as hot as 255 degrees f.
So only pex solar pipe and crimp fittings
A simple way in a coach would be to add a small electric marine waterheater and run the solar through it with a pump and a controller and 1 or 2 panels on the roof but my panels are about 65"x 72" each so way too big for a coach
Use you solar electric
2 cents worth
Quote from: sledhead on October 03, 2026, 08:00:52 PMI have 7 solar water panels on the side of my bus barn to HELP in the heating of the garage.
Kinda simple system if the sun does it's part
Sun heats the panels that heats the food grade antifreeze that runs through 2 rad forced heat exchanges than repeat
1 solar water pump and a $50 Amazon controller
1 have seen the antifreeze temp at the last panel as hot as 255 degrees f.
So only pex solar pipe and crimp fittings
A simple way in a coach would be to add a small electric marine waterheater and run the solar through it with a pump and a controller and 1 or 2 panels on the roof but my panels are about 65"x 72" each so way too big for a coach
Use you solar electric
2 cents worth
The problem I cannot solve is how to make a simple drain-back system to empty the panels of water once they've reached the maximum temperature, to prevent Exciting Things happening when the water boils (which it surely will do in the hot desert Southwest). Unless I can resolve that issue, I think it's best to think of other ways to heat water. What works well for a house usually won't work properly for a bus. IF I ever come up with something that A) works well, B) is simple, C) is cost-effective, and D) I can make myself, then I'll give it a try, but until then I'll just focus on other more pressing things!
John
I think solar hotwater heating makes more sense for an actual house, but not an RV as we are volume limited.
We would be better off storing the entergy in Litumn batteries and have a high power inverter. I just upgraded my to a 5000VA Victron.
I have seen DIY designs in passing for a instant hotwater heater with a heating element from a hot water heater in an iron pipe.
Though I think controlling it would be problem. There's a number of DIY examples on YouTube though.
There is also a discussion thread on a 48V hotwater heater at:
48V hotwater thread (https://diysolarforum.com/threads/instant-hot-water-heater-with-48v-dc.20282/)
This web site perports to have an inexpensive solution:
Instant hot water (https://hubeva.com/products/tankless-water-heater-for-instant-hot-water-supply)
There is something a bit off on their specifications it shows using a wall plug which on a 120V 15amp circuit would be 1800 watts and they specify the power level as 3000 watts.
A potentionally more reliable source would be:
Amazon Instant hot water (https://www.amazon.com/Tankless-Electric-ThermoMate-Temperature-Certified/dp/B0FWKD9LD1)
Though with either solution I would add an anti-scald valve to the design as a safety backup.
Temperature control valve (https://www.amazon.com/Thermostatic-Mixing-Connections-Temperature-Control/dp/B08L17P49P)
I have also seen discussions on a DWHR waste water heat recovery for the shower on YouTube.
Website on this:
Snower Heat Recovery (https://showersave.com/)