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What's the best type of solar water heater? Answered

I am in the process of renovating a bathroom that hasn't been used since before i was born, which currently lacks a water heater. Being poor, it is very unlikely that i will be able to buy an on-demand heater for this bathroom, and i know how inefficient normal water heaters are, so i am looking into solar water heaters. I live in a sub desert climate, so catching sun is not a particularly big issue, but i am looking to find out what type of heater is most efficient, both as far as heating water, and cost. would i be better off with a passive, or active system, and what other recommendations do you have for solar water heating?


Just do a search for solar water heater or solar batch water heater here on instructables. There are more examples than you can use. Personally I am going to build one with a 55 gallon plastic drum in an insulated wood box with glass or plastic covering siting in the sun. Water in from city through batch heater, up to house water heater, to house pipes. When the water in the inside water heater gets cold it will flow back out to the batch water heater and the hot water will flow up to the inside water heater naturally via heat induction.

For a DIYer, you could build an aluminum collector panel, which can absorb the heat onto its surface (probably going to be a black surface), conduct it into a tube soldered to its surface, and then the water will be heated by convection. The water could possibly then be pumped to wherever you want in your home, or to a tank for later use. Another solar water option (it may be a little expensive) would be thermal stratification. This is a convective heating tool rather than a conductive one. As water is heated, it tends to rise. The hottest water would be at or near the top of your tank. If your solar collector has a storage tank above it, your warmer, heated water will flow into that storage tank, while the cooler water will flow into the collector, waiting to be heated up. As a result a thermosiphon is created. In a more simpler sense, the sunlight acts as a transporter for heat distribution. The thermosiphon causes hot water to rise into the tank, drawing cooler water down through the collector.

Um, like this:
/\ /\ /\ /\ /\
0 0 0 0 0

Cross-section. '0' = clear tubing, '\/'s = mirrors (set close over the tubes). Set in a black box w/ plexy cover, fill w/ water. Black mirrors work WAY better but their expensive too. Regular mirror is easy to come by. Works like the mirror sunning things old ladies use on their faces. Also, BLACK grit or (better yet) shiny black stone in the bottom under the tubes heats it up WAY more too. The idea is to concentrate the sun's light so it heats the heck outa the water instead of passive collection. Thus the clear tubes surrounded by directed mirrors and black everything. The longer the tube, the more water, duh, and, um, just tilt the box a little Equator ways and it works better.

Sorry, the little \/---/\ thingie came out wrong. the mirrors sit between and around the tubes directed toward em. The angles are basic geometry.

Honestly, I'm not sure i understand what you mean with that,so, the mirrors are offset a little bit so that they bounce the light onto the pipes from both sides?

yup. and actually, even a simple mirror backing would suffice. Just so long as your collecting more than just the direct sun only, after all, why waste all that extra light just bouncing around?

We have an off-grid cabin we spend a lot of time at. We live on a shoestring but the easiest way to heat water is to coil a black colored hose and coil it flat on a surface receiving sun. If the elevation of the hose in the sun is overhead you just empty the hot water through the hose fitted with a shower head or whatever you might need.

So, could I plumb this in to a house, and would it be more effective if it were under a pane of glass?


9 years ago

If you wanted warm water available at all times, I suspect that you would need a few of the large roof-mounted radiant water heaters (just black plastic through which the water flows), along with a storage tank and a pump to keep the water circulating through the panels and always warm. Why can't you just attach the bathroom to the existing hot water supply in the house?

I would attach the bathroom to the main water, except that it is in the garage of our house, which is a separate building that my grandpa built to live in while he built the proper house. It has water attached to it, but not from the house, so there's not hot water, and to run the water from the heater would be a 40+ run of insulated pipe underground, so the easiest route is just adding a new heater. Now, as for the type of heater you are talking about, it's an active system, right? Isn't it possible that the pump would end up detracting from the overall energy efficiency?

Ah, yes, I see how a separate heater would be a good idea. The pump could be made to run intermittently or as required (if the temperature of the tank drops below a certain level, begin circulating the water to get more heat). As for the efficiency compared to an on-demand system, I cannot say. I only know how it works, not how well. ;) Does the garage need heat, too? Perhaps you could expand your project to include a radiant heat floor for the "live-in" part of the garage. That would take care of the heating issues AND the hot water all at once.

it's an interesting idea, definitely, but doesn't radiant heating have to go in the floor? the garage has a giant concrete slab for a floor, so while radiant would be pretty awesome, I think it's out. but yeah, if there are other ideas on combining things like that, I'd love to hear them, i am basically taking this space from scratch, and trying to get it rentable. as it stands it's pretty much some walls on a slab, there's not even sewer hookups for the shower/toilet, so i know i have to use gray water for the shower, and composting for the loo. does anybody have other ideas on ways to make the space usable?

Yup, the radiant heat floor goes on top of the concrete slab. There is an instructable on how to build a workshop out of hay bales, and they used radiant heat floors. Perhaps that would be a good place to get some info.