Solar Water Heater

[harold8041@yahoo.com]

Good afternoon,

I am considering using a solar water heater for my hot water needs in my 37' Skoolie. Does anyone have any experience with solar water heaters?

Harold

[jimmythomas]

They don't work at night or in the early morning. They can freeze in cold weather.
Ok if you can deal with the limitations.

[Iceni John]

I've left space at the end of my PV arrays for two solar water panels that will hinge up to face the sun, just like their PV neighbours do now. I plan on making them myself, each one using a large roll (50 ft?) of black PVC or PEX 1/2" tubing in one continuous coil inside a shallow box covered with glass (maybe old shower doors?). They'll need to have a drain-back system when the water gets hot enough, which it definitely will in the summer, to prevent any non-circulating water in them from flashing into steam, or worse. Essentially, when the water isn't circulating through the panels it won't even be in the panels at all. I'll use a small 12V hydronic or solar circulation pump that's intended for hot water, and I'll have a small (12 gal?) electric water heater under the kitchen sink as a secondary hot water storage tank, plumbed into my Suburban 6-gal propane/electric water heater. In summer I anticipate having all my hot water heated by these solar panels, and in winter they should reduce propane usage by preheating the water somewhat before it feeds into the Suburban heater.

At least, this is the plan! Maybe I'll come up with a better design, but I think this should work fairly well for minimal cost outlay.

John

[dzl_]

I have heard--and I emphasize heard as its just something I heard in passing--that given limited space for solar, one is better off maxing out the number of solar panels and using solar power (electricity) to heat water as opposed to using solar water heating directly. I don't know if this is correct or not, but it is what I heard.



And as is often said on this forum, propane water heating is one of the most reliable, simple, and practical solutions.

[dzl_]

@Harold you should probably see if you can change your username or make a new account, you probably don't want your e-mail address so publicly visible to the Wide World of the Web

[Jolly Roger bus 223]

i have installed several commercial solar water systems.
drain back and closed loop systems.
the storage tank actually has a coil wrapped around the exterior of the tank inside the insulation and jacket.
the systems uses ethylene glycol/antifreeze through the solar loop.
one to help with the overheating and freezing of the panels.
two to help retatain the heat accumulated longer.
even on a fancy system with all the temperature probes all over the place and a computerized controller programed properly they can still be a pain in the butt.
the storage tank is also a standard electric water heater for periods of no solar gain.

[LargeMargeInBaja]

For showers, we use a three-gallon 'Torpedo' keg, a match to the retired five-gallon stainless-steel Pepsi kegs we use to carry water.
.
To heat water, we use 'sous vide' circulation heaters designed for cooking.
Some brainiac calculated the photovoltaic to replenish the 120vac draw for a nice shower... less than a half-hour mid-day.
.
I think the complications of roof-mounted solar-heating or warming a tank of water would quickly exceed my patience.
We simply do not use water at that rate.

[Doktari]

We used to install STDHW (solar thermal domestic hot water) but we dont any more. Why have two systems if you can have one? And PV panels are much less expensive these days. There’s a possible upside if the solar photovoltaic system is broken and the STDHW system is still functional. But how often does that happen. We simply add a extra PV panel or two to the system with a powerful enough inverter/charger. And large enough battery cables and battery bank to handle the extra current drawn by the hot water heater. If the solar photovoltaic system is already built then the numbers need to be crunched to see if it can handle adding a hot water heater. There’s a “hot rod” heating element already made for RV tanks that inserts into the drain plug. They come in 400 or 600 watt model. This is called a “diversion load”. The more expensive charge controllers and inverter/chargers have a “auxillary relay” that can be programmed to turn on a load at a certain voltage. Ive not yet tried mine but my friend has several loads that turn on automatically. One is his heat pump.
I sometimes run my Honda eu2200i inverter generator in the morning to make coffee, heat hot water, and start the “bulk charge” on my battery. It depends if it’s sunny outside. Most days I don’t need to run the generator. And with lithium it’s even less frequent. Lithium doesn’t need the “absorb charge” stage that lead acid batteries need so reaching a 100% full charge isn’t needed.
In plumbing design they discuss “recovery time” of the hot water heater. Generally in a bus we are conserving water and not draining the hot water very fast anyway so I dont concern myself with recovery time. It takes as long as it takes. But I wild camp and am seldom plugged into the grid. There’s exceptions to every rule. A grid connected bus might be designed differently. I’d consider placing a coil of tubing in the sun sometimes. Or some people like to place the bus in the shade and place panels in the sun. So it all depends on circumstances and preferences.