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 😉