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Solar Geysers With Back Up Options


Our final installation of a three part series looking into solar geysers / solar water heating systems. In this article, we’re looking at different types of back up options to use in conjunction with a solar geyser.


In Part one, we got to grips with some terminology and types of solar geyser systems, as well as their pros and cons.

In Part two, we looked at climate and environmental considerations when choosing a system, and a brief look at prices here in South Africa.

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 two options for combining a solar powered geyser with a backup option. Using gas, or using wood fire.

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Solar Geyser and Gas Back Up

Gas Pros and Cons

Gas is a great water heating option.

It only goes into action the moment you turn on a tap. The 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, and no energy is expended on keeping any water warm until the next demand.

This is much, much more efficient than traditional and solar geysers that typically have to keep a large storage tank full of water constantly warm. Whether in use or not, energy must be expended at all times to keep the water temperature high in these systems.

Here in South Africa, we don’t have an option to have gas plumbed to our house (whether we’re living off or on grid). Instead, we have to drive to a gas shop (which generally is not at the petrol station – although that’d make so much sense to do) to fill up bottles.

Example of a thermo gas geyser

Is Gas Sustainable?

This has it’s pros and cons. As a pro, we’re not dependent on supply from government infrastructure which is fallible. We can store gas in bottles on our own property. Of course, that is also a con, considering the safety hazard. And we are still reliant on supply of gas, albeit not directly through government/municipal routes.

Gas is considered the “greenest of fossil fuels” and is said to “burn clean”.

Despite that, 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! 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:

Backup Gas Options

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 & Cons

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 Geyser and Wood Fire Backup

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.

How To

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 thermo-siphoning 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.