solar 'water heater'

FreeBrrd · September 2008

I'm building a little camper shell on my truck with a solar panel on top for lights, fans, etc.

I have this really nice flat gallon water bottle that I am going to put inside the roof - put a hinge on the inside roof and put the bottle in there - with the reflective foil insulation under the bottle so the sun will heat the bottle.

I was thinking of painting the roof above the bottle black to help with heating, but I would prefer not to. I'd rather the whole outside be stained gray. So I am trying to figure what would work best to make this as efficient as possible.
1. If I put some of the insulation on top of the bottle with the foil side down, would this help keep the heat in the bottle? Would it insulate from the water getting hot or with the foil that way would it do nothing?
2. Would it be better if I put something black on top of the bottle or make the bottle a black 'sock', but under the roof? Seems that would not do anything, that it would only work for the roof surface being black.

This will also provide gravity feed water pumping rather than using power to do so. I'll have a little bit of warm water at the end of the day to wash up with. The cold water in the morning will do me good

BB. · September 2008

Re: solar 'water heater'

Black paint will allow much more in the way of heat to migrate to your bottle... But, black paint will also allow much more heat to escape when the sun goes down. White paint will let less heat in, but allow less heat to escape. So--neither will be a solution in itself.

The best would be to have an insulated tank and either a thermo siphon (with the collector "low" and the insulated tank mounted "high"). Or to use a small solar panel powering a DC water pump to move cool water from the tank to the collector, and hot water from the collector back to the insulated tank for storage.

Otherwise, for hot water during the sunny part of the day--just place the black water tank on the top of the roof for best heat collection.

My two cents worth--anyway.
-Bill

FreeBrrd · September 2008

Re: solar 'water heater'

With only one gallon, heat retention over night is not an issue. I figure I'll use the warm / hot water before it gets a chance to get cold.

Can't go on top of roof. As a motorcyclist, I'm especially concerned with bits falling off on the road. Trying to use a few pieces as possible (and seriously gluing & screwing everything on).

Another question: I need to have a little clear panel on the roof. I've had problems with plexiglass curling up in the sun. Does thicker plexiglass do ok sitting in full sun or is there other plastic to use? I could go buy a pyrex bowl & use that. It only needs to be about 4.5" in diameter or square. (I should just call Tap Plastics). Prefer flat or slight dome.

BB. · September 2008

Re: solar 'water heater'

Lexan and polycarbonate types, in general, should be OK in the sun. Or, if you can find a nice piece of glass.

Since plastics tend to be componded based on application--you would probably need to check the specs. for any specific sheet you look at to see if it is good for your application or not (also needs to be pretty heat resistant too).

Might want to look at various "clear" roofing materials (like used on plastic green houses)--some have a UV protective on one side to prevent sun damage.

You might see if you can get a piece of polycarbonate from www.solarroofs.com--they sell replacements (10-15 year life?) for their solar thermal panels.

-Bill

mike95490 · September 2008

Re: solar 'water heater'

Lexan / polycarbonate will stand up to the UV, but over 200F, they start to "soften". It's really easy to make a Fusion Powered Oven (solar oven) out of plastic, because it has a low thermal conductivity. But they heat too hot quickly.
Maybe a small chunk of the tempered glass with the wires in it (for restaurant door windows) would work. Plastics are soft and will scratch easily, even with careful washing, after a couple years, you will get frosted plastic.

FreeBrrd · September 2008

Re: solar 'water heater'

I had scrounged a shower door until I found that I can't cut tempered glass.

Hopefully my roof will not reach 200F.

I'm not too concerned with scratches. Don't really plan to be in the camper more than a couple of years. (of course, with the economy, it might become the norm).

It's to let in light. I am making the cat tree hollow, lining it with foil, so the kittens will have light in their 'nest'. I wasn't going to explain because it's a bit out there. It will also provide ventilation. Top will open in attic with clear ?? above it.

I put the two framed walls onto the truck today. I can't park outside now that the project is on the truck. I had measured for it to fit, but forgot to measure height. I just assumed it would be ok. I ended up having to adjust the garage door. Than I had about 5 inches clearance thru the door. Now I have to design the 'cab over' part & drill holes in the roof of my sweet little truck

Doesn't seem like heating too quickly would be a problem with a solar oven. Don't most heat pretty slowly and to a lower heat so you have to cook much longer. I'm not going to build mine until I'm out. Too much to do before.

As unual, thank you all for the help. Think I'll see what Tap has when I get to the roof.

mike95490 · September 2008

Re: solar 'water heater'

FreeBrrd wrote: »

Now I have to design the 'cab over' part & drill holes in the roof of my sweet little truck

DONT DRILL Camper/RV shops have inflatable donuts/cushions that support the cab-over part on the cab roof. No drilling. The Bed of the truck flexes QUITE a LOT (an inch in mine!) as you drive, if you bolt a camper to the bed, AND to the cab roof, you will have TROUBLE.

FreeBrrd · September 2008

Re: solar 'water heater'

Does it just support or does it hold it down, on, also?

I was looking at a truck with a cabover shell yesterday as it drove thru the parking lot. It wasn't supported / attached at all. Had about 4 to 5 inches space.

I'm more concerned with air lifting it up, but with the air flowing up over the windscreen, the air should keep flowing in the same direction and not go under the cabover - as long as the gap isn't too big. The front of the cabover will be angled just a bit more than the windscreen. That should push down on the cabover rather than lift if anything.

ps. found the perfect clear material, an old cover for a mini pyrex dish. It's about 5 inch round with a nice little lip. Lost the dish. Knew there was some reason to not thru the top away

mike95490 · September 2008

Re: solar 'water heater'

The cabover donuts/cushion help keep the jetstream out of the area. They also have an inflatable ring, that goes around the cab/camper crawl-thru, keeps the water and bugs out. Can be used with or without window glass(es). Generally advised to use if no glass installed. Sounds like quite a project.

FreeBrrd · September 2008

Re: solar 'water heater'

It is and this morning I've been wasting time moving the light from above the rear window (outside) into the shell. Almost forgot that the shell is removeable

Glad I just happened to add a plug connector.

I'm putting foam weatherstripping on the front of the shell to go around the window. Don't know yet if there will be glass, depends on finances. A slider would be nice, but have to have access from cab to shell.

Thank you for all the help. Lots of stuff here that I know nothing about (and a bunch more that I know very little about).

I'll probably post some pictures to my site this weekend. I'll send a link. Ya'll deserve some entertainment.

solar 'water heater'

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