Completing the set: we now have solar hot water

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A shiny new set of 30 evacuated tubes on the roof
A shiny new set of 30 evacuated tubes on the roof

When the feed in tariff for solar electricity was put in place, we were one of the early movers, installing a 1.6kw solar PV system on our roof. With the limited space on our roof, we had to pick between solar electricity and solar hot water, and we chose the former.

Once we finished our renovation, however, we had 99m2 extra of flat roof to play with.

Nonetheless, we’d already purchased a super-efficient instantaneous gas system to replace our 1988-era electric hot water tank. We’d hardly be saving the environment if we threw that away, so solar hot water remained on the long-term to-do list.

With the likelihood of rising gas prices over the next few years, I recently looked back into solar hot water options.

What I discovered is that it was possible to reuse our instantaneous gas system as part of a solar hot water installation.

It’s simple really: the evacuated tubes on the roof heat up the water in a storage tank (shown below). The output of the tank goes through the instantaneous gas system. If the water is already hot, the gas system does nothing. If it’s only warm, it boosts it as required.

So no manual boosting or fiddling around, with a 100% guarantee of hot water.

We ended up purchasing a system with 30 evacuated tubes, plus a 300L storage tank. This is far in excess of what we need for two people, but with the roof partially shaded in winter, the extra tubes were chosen to ensure we take maximum advantage of the morning sun.

We’ll be getting back $1300 from the government for the STCs (solar credits).

On current gas prices, the payback period is 8-10 years, which isn’t great. But I’m expecting the gas prices to rise, which should seriously shorten the payback period.

Anyway, it’s good to complete the set of environment-saving technologies 🙂

PS. after 3+ months of no rain, we had 2 solid weeks of rain immediately after putting in the solar hot water. Not great for our solar generation, but good for the garden I guess 😉

The 300L tank gets squeezed into the side passage of the house.
The 300L tank gets squeezed into the side passage of the house, alongside the instantaneous gas system.
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2 thoughts on “Completing the set: we now have solar hot water

    solarbeez said:
    September 8, 2014 at 3:59 pm

    That looks a little like my Thermomax 30 tube set up. We installed ours in August 2008 in Oregon. We love it. I watch the controller that shows the temps as they heat up and kick on the little pump which brings the heat transfer fluid to the water heater. I use an 80 gal. water heater with a back up heating element. Not as good as yours, but in foggy Oregon, a necessity. The evacuated tubes really do a great job in heating up fast. You will love it!

    Sarah Bingham said:
    March 8, 2015 at 8:42 am

    Very interested to see this – like you I have an instantaneous gas heater & was reluctant to replace it. I might revisit this idea, with 2 teenagers in the house my gas bill is starting to be a cause of concern, not to mention the recent reports on the effects of escaped gas on climate change.

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