Solar ovens and solar water heaters/showers

[tomas_maly]

Anyone here have experience with solar wall ovens and solar water heaters/solar showers?

I'm thinking of making a solar oven (wood box) hanging from one of the window frames (with the glass removed). My challenge is finding one that works well (I've seen a lot online that are either parabolic, which wouldn't fit the rectangular shape I need, or only get up to 200 degrees), I also want to fit it out the side window frame and yet be light enough to remove and/or pull inside (ie hinged) for storage while I'm driving.

I'm also thinking of having solar heated hot(-ish) water via a black-painted barrel (polyethylene) put on the roof. I have water hookups on my driver's side, which will go through some filters on my driver's side, and am thinking of having a pipe go up through the roof and then attach to my 5-gallon polyethylene barrel on the roof. The barrel is going to be on it's side, with one hole above the other. The water would be pumped in through the "top" hole, and gravity would feed water out the "bottom" hole, once I open a valve inside (across from the sink, on the passenger side). Besides the mechanics I also have to think about maximizing the temperature. I'm thinking in weather like this just being on the roof, in the sun would make it quite warm?

In the winter months I will be using my on board wood stove to cook and also use to heat water (coils wrapped around flue) - but would like to avoid using the stove in the summer.

I'm looking through youtube for general, and getting some ideas. I wasn't sure if someone had a tutorial here, etc. I'm trying to keep my bus low-tech, so I can minimize fuel and electric needs.

[family wagon]

Regarding the solar water heat.. I haven't studied it for mobile application at all, but have done a lot of reading and thinking on fixed use (ie home space and domestic water heat) so my comments are guided by that background.

For maximum output temperature the usual thing would be to draw hot water off the top because that's where the hotter water will be found. I'm not sure how much stratification you'll get in a 5-gal cube container though; probably it's less important here than in an 8-ft tall wall-mount collector. Will you fill the container once in the morning, or will you top it off during or after each hot water use? Topping off during use will cause the output temperature to fall quickly as the hot and cold mix together in the container.

You'll probably do best to have the parts of the jug that are exposed to sun also in contact with the water -- otherwise heat must pass from light to the plastic to the air inside and finally into the water (air doesn't conduct heat very well). If the jug isn't kept completely full, so that there isn't even a little bit of air bubble across the top, then I think the heat gain will be reduced quite a lot. It would probably be helpful to insulate the bottom and north-facing sides of the jug since you can only lose heat through those surfaces. Probably insulate the east face and maybe the west too; there's so little sun exposure there that I imagine there'll be more heat lost on those sides through the middle of the day than is gained in the early morning and late afternoon hours.

A water container might not be the best fit for this -- generally they're designed to have minimal surface area because that translates to cost of plastic to mold the thing. In a solar heat gain application, surface area is king. If it were me I'd be thinking about something like a flat plate collector on the wall or on the roof. Something elevated off the roof surface just a bit might be nice; all that heat gain would go into your water and much less would find its way into the bus body. A plate collector could be as simple as a garden hose laid out and filled with water, or maybe that 1/2" drip irrigation main line stuff. If it's for potable use though then use copper or other NSF-PW rated material, not the irrigation stuff.

If the wall collector is an option then you could also think about an insulated holding tank near the ceiling (above the top of the collector) -- it could be configured so that thermosyphon carries hot water from the collector to the tank, and colder water is drawn from the tank to the bottom of the collector to be heated.

[Diesel Dan]

In the same spirit as family wagon, I would recommend a longer, more narrow tube so there is more surface area exposed to the sun relative to the amount of water to be heated. I plan on using something like a 20 foot long 4" black plastic pipe for that purpose.

Regarding the solar oven, I suppose that would be practical if you are staying in one place for at least an entire day. As you probably know, they cook very slowly.

I am also looking forward to using active solar panels to help charge my batteries, but that is another topic altogether.

[roach711]

viewtopic.php?f=9&t=4885&hilit=smitty+solar+water& start=795#p63420

Here's a solar water heater from Smitty's Bus. A page or two farther on in his thread he said that if he was to do it again he'd insulate the box better and pack the piping in tighter.

[lornaschinske]

The older articles from Mother Earth News would be a good place to find info. If you read the articles from the 1970's & 1980's you will find more of the DIY stuff as opposed to the "buy this product from our advertiser" info. None of it is really portable. You might want to try searches for these solar systems that have been adapted to marine applications. The marine world is much larger (and older) than the RV world.

[thrash]

Your friend is http://builditsolar.com. Lots of solar hot water collector design experiments and discussions. An excellent resource for DIY.

[family wagon]

Originally Posted by lornaschinske

The older articles from Mother Earth News would be a good place to find info

Originally Posted by thrash

Your friend is http://builditsolar.com

x2 -- I've learned a lot from both of those resources. Like Lorna says much of it is designed for fixed applications. But if you're willing to invest the time to read about and understand the designs there then you could adapt and invent to create something rugged and resilient for your mobile use. The concepts are pretty simple -- surface area, heat transfer, thermosyphon, etc.

Thinking more about your initial question, I realize the ideas I originally suggested might be over the top depending on your needs. If all you're looking for is a warm shower at the end of the day then a simple black jug might do the job fine. But if that's the case, if it were me, I'd probably set the jug on the ground outside the bus rather than on the roof, or even just buy a camping solar shower bag and be done with it. Unless you wanted it to heat while driving during the day, of course.. in which case you'll want insulation around the container to reduce heat lost into the wind... there I go again!