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Build Your Own "Solar Batch Water Heater"

Although not that well known, the SOLAR BATCH WATER HEATER or SOLAR BREADOX, is basically 2 recycled 40-gallon water tanks painted black to absorb heat, and then plumbed into an insulated wooden box that faces south. The front of the unit is angled at about 45 degrees and then glazed with 2 common and inexpensive recycled tempered glass patio panels, each 34"x76". This creates a total "solar aperture" of about 38 SF (6' x6'4"). Underneath this glazing a 2nd layer of the heat shrink plastic film is installed - the stuff people often use on old single pane windows.

Yesterday morning I was passing through Courtenay volunteering a little bit of my expertise to Chris Hilliar (ex BCSEA Chapter Chair of Comox Valley) in regard to a sunspace/greenhouse room he and Molly are considering building. They also want to tighten up the air leaks in their home ( I recommended the Energuide home assessment, which in my opinion, is worth it weight in gold, just for the blower door air test alone!)

We set up my "solar pathfinder and assessment tool" in 3 different locations: first, on either end of the proposed sunroom and then in the centre of their large garden. For future reference, Chris took digital photos of the shading and sunpath images that were created, and it confirmed his idea of taking out 3 large trees on the due south section of his property. This will compensate for the low altitude of the deck, allowing the January sun to penetrate into the existing south facing windows and the proposed sunspace. Currently, very little sun is able to penetrate the trees from November to February. If the trees are removed, the garden will also receive a lot more sunlight, which will increase food yields.

I was really trying to twist Chris' arm to add a simple inexpensive home built passive solar hot water tank, slightly below the sunspace at ground level.

Here are the details of such a unit:

Although not that well known, the SOLAR BATCH WATER HEATER or SOLAR BREADOX, is basically 2 recycled 40-gallon water tanks painted black to absorb heat, and then plumbed into an insulated wooden box that faces south. The front of the unit is angled at about 45 degrees and then glazed with 2 common and inexpensive recycled tempered glass patio panels, each 34"x76". This creates a total "solar aperture" of about 38 SF (6' x6'4"). Underneath this glazing a 2nd layer of the heat shrink plastic film is installed - the stuff people often use on old single pane windows.

In this simple but surprisingly effective unit, there are no pumps or moving parts. When you turn on the hot water tap, cold water enters into the bottom of the tanks, to displace the hot water coming out of the top. For overcast or marginal days of sunshine, it is best to add a valve that will divert the lukewarm preheated solar water into your existing electric hot water. Better yet (if you can afford it), eliminate this manual valve and make the system "user friendly" and more efficient by purchasing an "on demand heater", either electric or natural gas, that will turn on automatically to provide extra heat as required.

One could fine-tune this system in a few different ways:

  • to make it more aesthetically pleasing, disguise the unattractive tanks and plumbing beneath obscure glazing

  • to avoid winter freeze-up on coldest winter evenings either drain the system, or alternatively, put a thermostat inside the box and wire it to an old archaic 100 watt incandescent light bulb, and set it to come on when the temperature in the box drops to freezing (this will also occasionally provide nice ambient evening lighting to the area)

  • one might also consider installing insulating panels to cover the glazing at night, although this is more complicated and relies on the owner to remember to open and close them , morning and evening. Some folk may find this acceptable, but in a busy urban environment, it is not really "user friendly" and may not seem worth the trouble

If any one is interested in building such a unit, feel free to email me for a set of the plans: brucessunrise@xplornet.com.

Many people dont have the skill set, the time, or the desire to build a solar batch heater. However, you may have the economic means and the ethical will to install a more technically advanced solar hot water system. If so, consider enrolling in the BCSEA's SolarBC Program at www.solarbc.ca. On this website you can follow the links to learn about purchasing a subsidized, state-of-the-art solar hot water system.