Solar Geysers / Water Heating Systems – Part 3

Final installation on solar geysers / solar water heating systems (for now) – looking at back up systems

Ok, so far I’m a little underwhelmed about solar geysers / solar water heating systems, I have to be honest. But I’m not ready to rule it out as a viable option just yet. I’d already been thinking about some back up system options – alternative ways to heat the water if the solar heating wasn’t cutting it (for example, in an extended cold snap in winter). Here are some rough ideas.

Solar and Gas

Example of a thermo gas geyser

Gas is a great water heating option. It only goes into action the moment you turn on a tap – pilot flame ignites, cold water runs through the pipes heating up instantly, and hot water comes out. Turn off the tap, flame goes out, no more gas used, no energy expended on keeping any water warm til the next demand. Compared to traditional geysers and solar geysers that have to keep a large storage tank filled with water hot constantly, for those minutes of use!

Despite gas being considered the greenest of fossil fuels and ‘burning clean’, I don’t feel comfortable switching everything over from coal-generated electricity to gas burning. I’d still be dependent on the system, and I’d be supporting the devastating effects of deep well drilling and fracking. Would I really have changed anything?

An example of fracking in Wyoming. Four fracking pads for every square kilometer.

I’ve looked into harvesting our own bio-gas and that looks really interesting, but for right now our plates are a little full, so it’s something I’ll look at again further down the line when we have main processes up and running. In the meantime, I’m not opposed to supplementing our power and heating needs with some gas use. Ok ok ok, now that I’ve got that off my chest, let’s look at ways to supplement a solar water heating system with gas.

Bosch have a clever product available called the “Gas Water Heater Solar Kit” (I’m going to call it GWHS for short), which I first came across on Sustainable. It acts as the gateway between your solar geyser and your gas geyser. Your main water supply enters your solar geyser, which heats up the water and holds onto that heat to the best of its ability. When the hot tap is turned on, the water flows down the pipe and into the GWHS which then measures the water temperature.

If its below a certain temperature, the GWHS opens a valve, directing the water through your gas geyser. Gas geyser activates, heats up the water, and sends it back to the GWHS. The GWHS then mixes the hot water with the cold water supply (depending on what taps you’ve turned) and sends it up to the tap.

If the water coming from the solar geyser into the GWHS is at or above a certain temperature, then it opens a different valve, bypassing the gas geyser and sending it on its merry way.

Pros: You only use gas when you need it, and the whole process is automated for you.
Cons: Its a very expensive set up. You need the solar water heater system, the GWHS, and a (Bosch only) gas geyser.

If you’re a qualified plumber/electrician/gas installer (or just extremely handy and confident), you’d probably be able to create your own version of this system for less. You could also set up two separate systems that both connect to a main mixing valve, both with manual on / off switches, so you could manually switch from one to the other as necessary.

Solar and Wood Fired

Burning wood is again not as bad as conventional fossil fuels, but still not great for the environment. Assuming you’re using invasive species or wood pellets as your fuel source, the main concern is contributing to air pollution. I have to admit, I LOVE LOVE LOVE fires. I love a fire’s heat, I love cooking on a fire, I love the beautiful dancing amber light of a fire… So yes, I’m a little biased here. What appeals to me about using fire to heat water is the opportunity to multi-task. With the right set up, a single fire can simultaneously heat water, warm the home *and* cook food. Now that’s efficient.

Obviously it wouldn’t be super efficient to light a fire every time you needed hot water, though. So a solar water heating system with a fire heating back up could be just the ticket. Setting up a water heating system using fire is well documented in the off grid living community, and I’ve found a plethora of useful and interesting articles and videos about the topic.

In its simplest form, heating water via a fire involves a water storage tank (ideally insulated so as to retain the heat for as long as possible), copper piping and, well, a fire. The copper piping exits the lower end of the tank, then coils around an open firepit or stove chimney, then re-enters the tank towards the top end. As the water heats up in the pipes, the hot water begins to rise, creating a thermosiphoning effect with hot water entering through the top of the tank, cooler water sinking down and exiting the tank, getting heated up, rising, and so on. Note that you’d ideally want a pressure valve on the water storage tank, and a temperature gauge to avoid scalds.

In the same way that you could combine solar water heating with a gas geyser, you could have copper piping from the fire feeding into and out of your solar water storage tank, either with a fancy system controller or just manual taps that you could switch on and off.

I know how much ya’ll love my badly-drawn sketches so here’s a truly terrible one

Do you have any other back up system ideas to combine with a solar water heater? What do you think of these ideas? Let me know! Check out the next post on Rocket Stoves to see an awesome water heating solution.

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