Enabling change in our Society, Environment and Economy (SEE)

Solar Hot Water Systems

Choosing a hot water system can be tricky and so we asked SEE-Change members what their thoughts were.

QUESTION: If you are a two person house that occasionally changes to a six person house, should you use solar hot water or an instantaneous system?

Following are answers from SEE-Change members in response to this question:

  • Yes. I would suggest that they install a solar hot water system with perhaps 30 tubes (not much more expensive than 22 tubes). The key is to install instantaneous gas boosting rather than electric storage. When the household population surges, no running out of hot water. 
  • We were a 5 person house that often had 10 people (partners staying over in a share house). Hot water was never an issue! Now my family has solar hot water in our place- 2 adults & a toddler. We occasionally have extended family visit from interstate- so 4 extra adults, making it a 6.5 person house- & again, never any issues with hot water! So much better than gas or electricity in terms of supply, & definitely in terms of running cost. However, I can’t comment on purchase price, as all 3 houses I’ve lived in with solar had it already. I definitely recommend to this person to consider it.
  • The only suggestions I would make is to ensure their shower heads are changed over to low-flow and that their solar HW system has a gas booster to cope with having the occasional 6 people.
  • The hot water system I have had installed for some years now, is an Evacuated Tube Array. The set of black glass tubes have a gas which heats up, rises to the top of the array, where the copper pipe takes water to the storage tank. The cylindrical shape of the black tubes get warmth from the Sun’s rays all through the day. It’s smart and efficient. I do have an electric booster on for two short intervals during winter, on a 24 hour timer, and even on the dullest, coldest winter days, that booster only goes on for about 2 hours in the morning and at night. I was told that the amount of electricity would be equivalent to a small room light globe on for hours! Another advantage is that there is no need to top up with any chemicals like glycol as an anti-freeze, as the gas does not freeze. We have had solar panels before, but this Evacuated Tube Array is far more effective. I have heaps of hot water. These solar hot water system tubes have been installed in places like Sydney, where hail storms can be heavy and violent, and the installers said there had been no adverse effects. I have not had any problems at all.
  • My experience with solar HWS is that the return on capital is very long and there are numerous variables so it is not possible to give a definitive answer. But as a general rule the more hot water you use the quicker the return but even so 10-15 years or longer is not unrealistic if you are replacing a perfectly workable electric storage system. On the other hand if your electric storage system is no longer working the recovery period is considerabley reduced as you only need to recover the additional cost of the solar HWS above the cost of replacing your no longer working electric storage system. You also need to be aware that solar hot water systems are more complex and are prone to problems through cold temperatures causing broken glass or tubes, failure of pumps used to circulate hot water to the roof to overcome the threat of freezing during cold nights and believe it or not the failure of the control unit that controls the circulation of water and when the electric boost cuts in. Forget the hype. Here is what I recommend. If your electric storage system needs replacing then go for solar if it makes you feel good but don’t do it for economic reasons as you are unlikely to get your additional costs back within 15 years unless you a have larger family. Go with instantaneous gas. It is more expensive to fit but operating costs are lower as you only pay for what you use as opposed to paying for heating water which you may never use.
  • I am an ex professional engineer (mechanical) and I have a solar hot water system.  I had problems with the installation when it was first installed, and had to do quite a lot of investigation regarding how the system worked, because the plumbing business that installed the system didn’t seem to know what they were doing. My system is a 20 “heat tube” installation, installed several years ago. There are only two people in my house, myself and mature age son. The system has a large storage tank with an electric backup element.  In summer I can turn off the electric backup at the switchboard and only very occasionally have to use the electric backup if there is a run of cloudy days.  In winter, the solar heating is insufficient, and I have to rely on the electric.  I think this (winter) problem is because I should have had many more tubes, at least 30, maybe more. I didn’t have more because before installing I was told by others,  (and another person recently) that in summer and particularly when no hot water is being consumed, a 30 tube system causes such a build up of hot water that the relief valve vents and wastes a lot of water. Probably in winter, the (insufficient) water heating from the installation does reduce the electric power required somewhat. It occurred to me subsequently that the water venting problem with a bigger system in summer, can be fixed by covering say half the tubes (but all, if you are going away for some time,) with a tarpaulin or shade cloth; this means climbing onto the roof.(which is ok really but some might not like to do it.) I could comment a good deal more, but it might bore you!!!. I don’t think the solar hot water system will ever come to a break even point regarding cost, but I thought that it was a step in reducing electricity demand and a good social exercise. At the time, I could have also installed  PV panels on the roof. I didn’t, because I thought that the then enormous subsidy for such installations was grossly unethical and unfair.(there was a small subsidy for the solar hot water system – but not much). I might in future have PV panels, now that the subsidy is greatly reduced, also the panels themselves are more efficient and drastically cheaper. However cost wise, large scale wind power is much better than PV.  It seems not very well known that only about 20% of electric demand is for domestic use, and really household PV panels aren’t a proposition for a large community, as they only contribute a small amount. A PV farm might be a good proposition, but as with personal PV, there isn’t any power when its dark,  so a pump storage system somewhere is required in addition, which cost doesn’t seem to be factored into the equation generally.
  • With only 2 people you will not often have to use a booster – we only do in depths of winter. And if you get short with lots of visitors at times the booster will do the trick.  I believe you can get adjustable timers, or switches that switch it on for an hour, which allows you to manage occasional boosting.
  • I no longer recommend that anyone uses solar thermal systems, as heat pumps have now reached such high efficiency and great tolerance to low temperatures that this is the new solution. It is also cheaper than a quality solar thermal system, never overheats in the sun or freezes in the winter and is cheaper to install. The proviso is that you buy just one type; CO2 heat pumps. The only current manufacturer prepared to bother with Australia at the moment is Sanden sold here by Laros Technologies: www.laros.com.au. A typical cost is $4,000 plus installation. The CO2 technology means the heat pump has a global warming potential of just 1 whereas the next nearest heat pump has a GWP of 1300 (ie pretty bad for the planet) as well it can still provide an efficiency of 250% at –10 degrees which is far better than any other heat pump currently in existence. For those just buying solar PV units you can offset your consumption by buying a little extra for your heat pump and charging up the heat pump during the day rather than sending your electricity back to the grid for a measly 7.5 cents (this is called self consumption).

With thanks to our


  • ACT Government Environment and Planning
  • The Association of Independent Schools of the ACT (AISACT)
  • Catholic Education Office (Archdiocese of Canberra and Goulburn)
  • Education and Training Directorate
  • ACT Government