Solar Hot Water Booster, Cheap and (mostly) Easy

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Cartoon by Pete Pascoe

Hey – Jack here from the DaiaSolGaia community to talk about another of my building projects. I am DaiaSolGaia’s “jack of all trades” (yea, i know …  sorry for the pun …).

I want to tell ya about another of our “experiments” that has become pretty integral in our life out here off-grid and away. I’ll also warn you right off the bat that the water heater that we built is a “below the mason dixon line”  water  heater – that is – the kind of solar hot water booster I’m going to tell you about here is not suitable for areas with extended low temps with accompanying extended lack of sun. That said, there are reasonable options for solar hot water boosting depending on the configuration/orientation of your more northern (or higher altitude) house. The links for the pretty good “How To” books are just below.

Hauling propane over miles of dirt roads for hot water is a pain in the …  Now we could get it delivered, but still – it defeats the idea out here – to live off the land and with minimal “civilized” resources that can otherwise be compensated for. Lookin around on the internet we found lots of  (pricey) heat-exchange bla this and bla that water heating options.

If you are in the colder less sunny climes, your house cannot configure for our DIY idea here, or you are competent but not confident when it comes to such building projects, then here’s a couple good books that will give you all kinds of ideas/plans you can draw from:

Do It Yourself Solar Hot Water Plans

DYI Solar Hot water

What we ended up building is a variation of a “batch” hot water heater – and after seeing how well it functions in our sunny environment, we realize that it’s actually a borderline crime (a misdemeanor at the leas t …) that ALL houses built in the southwest don’t have this to at least boost their hot water prior to finishing it up to temp  in their conventional hot water heater. A batch hot water heater is a large tank (or 2 or more) that is painted black and aimed at the sun. The large mass of water heats slowly but it also cools slowly – which meant that a couple of days of not sun will leave you with less boosted water, but will not lead to frozen tanks – especially if you build the right enclosure.

Here’s a picture – please note that this was built A) as an experiment so not very finely finished, B) photographed before I intended to write a blog! I’m in the process of building a 2nd one of these over the bathroom of one of our homes and will do much more detailed pics for a future blog.

Now, there are lots of installation factors that will impact your process here – and since most houses are not organized from the get-go to accommodate a solar hot water booster, you may find this blog more interesting theory than actually useful for you – however if you are creative, you may just find a way …  but here goes:

We built our solar hot water booster using mostly discarded items and did it for less than $150. We saved that much in propane the first 2 months. The concept is very simple – you get 2 discarded hot water heaters (gas or electric) whose integrity has not been compromised (they don’t leak). Most are discarded because the gas valve/burner or electrical coil has failed and it’s just too expensive to bother to fix them (our throw-away consumer society … sigh …). But in this case you can benefit from the discard.

Strip off all the metal jacket, insulation and fittings and generally clean the metal tanks (perfect not required). Now paint them flat black. Next build a framework that holds the tanks in a hot-dog laid-down position and offset by about 1/2 (the top tank overlapping the bottom tank by 1/2). Then rough up your plumbing: water feed in bottom of bottom tank, top of bottom tank to bottom of top tank, then feed back to water heater from top of top tank – draw it out – it’ll be logical. Use galvanized iron pipe – or if you want, CPVC – I prefer the safety of iron in the enclosure as it can get a bit toasty in there.

If you roof access is pretty easy (or you are placing this on the ground outside your basement) make sure you get full sun all day (duhhh). Figure out how to get the water feed that goes to your water heater to the solar heater without it being exposed to potential freezing. The one in the pic was easy – the water heater is directly below the solar booster.

Be critical about the possibility of smaller water passages (pipes) freezing potential – this batch heater will work all winter if none of the feeds freeze. Finish the enclosure with LOTS of insulation in the back and sides (r-50+) and fit the double-pane insulating window on the front. Now all these steps are subject to your own handy/building skills and judgments, of course.

Parabolic Back Reflectors – Good Idea?

Our booster was build, plumbed and tested for leaks before silicon-gluing the window in place. Remember to also organize reflective surfaces all around the sun-exposed interior of the collector to reflect on the tanks. I have seen fancy parabolic reflectors arranged so the sunlight goes in and around the back of the tanks – however I believe this to be questionable. If you have good reflective surfaces sending the sun to the tanks, a well-insulated box, good reflectors outside to direct even more sunlight into the box (important) and the tanks are good and black – then I think it is more valuable to haf the surfaces away from the dank (the back 40%) very well insulated.  My theory is that the heat loss on longer cooler winter nights is more than any heat gain from the parabolic reflectors that would require the back of the tank to be exposed.  The sun that is coming int the box well designed, does not get out – so to leave the tanks 360 degrees exposed is not – I think – the best route.

On a good sunny day (hotter in summer of course, but still hot in winter) our booster water comes off the roof too hot to hold onto the outlet pipe (probably 120 degrees or so).  If you have your conventional water heater set just hot enough, then it will probably not even fire up on such days. The beauty of this design is that – provided you have insulated well and live in a pretty sunny climate – you just do not have to worry about freezing. I have hinged the front reflector so the unit could be closed in the event of a stretch of really cold, cloudy weather, but in 3 years we have not used it more than 2 or 3 times.

Do you have questions? How about ideas for improving/adapting this design? Please leave your comments here:


One Response to Solar Hot Water Booster, Cheap and (mostly) Easy

  1. Jill says:

    Great post! I would love to implement something like this at our homestead… someday maybe! Thanks for sharing this at the Homestead Hop!

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