Are you getting the most from your solar hot water system?


A solar hot water system can reduce your power bills dramatically - but only if it's used and installed properly. Image: Norbert Nagel / Wikimedia Commons - License: CC BY-SA 3.0.

A solar hot water system can reduce your power bills dramatically – but only if it’s used and installed properly. Image: Norbert Nagel / Wikimedia Commons – License: CC BY-SA 3.0.

Hot water is power hungry

It takes a lot of energy to heat water. To raise the temperature of a bucket of water by one degree, you’d need to add more than twice the energy than if it was, say, a bucket of oil – or a huge 3500 times more than if it were a bucket’s worth of air (volumetrically speaking).*

This makes it easier to understand why such a huge proportion of home electricity usage is due to hot water. If you have an electric hot water heater, it could be responsible for around a third of your power bill. And that’s why a lot of Australian households have found it’s economical to install solar hot water heater systems on their roofs and use the sun to power their hot showers.

A solar hot water system can reduce your hot water cost by 30 to 80 percent – but to get the most out of it, it has to be installed and used correctly.

CSIRO’s study: how to supercharge your solar hot water system

CSIRO was interested to see whether there are things households can do to improve the performance of their systems, so we carried out a pilot study in collaboration with the City of Newcastle and the University of Wollongong.

Thirty households took part in the study, which aimed to investigate how households used their solar hot water systems, how those systems were installed, and where future savings could be made.

Based on the results of the pilot study, CSIRO’s put together a simple checklist for owners of solar hot water systems and people looking to install or upgrade.

Two of the top tips for getting the most out of your system are:

  • making sure your pipes are insulated
  • keeping an eye on how you use your booster switch.

These simple things can make a huge difference to your energy usage, carbon emissions, and power bill.

A CSIRO pilot study into how households use their solar hot water systems led to this simple checklist. Following the tips will help you get the most out of your system. (Click to enlarge.)

Read more in CSIRO’s solar hot water factsheet, or visit the great solar information page at for more solar tips.

Did you know CSIRO played a large role in the development of solar hot water technology? Read more in this previous blog post or on CSIROpedia.


* Interesting side note: because of this fact, staying in the shower to keep warm on a cold winter’s morning uses 20 times as much energy as stepping out and standing under a two-lamp heater instead. (This factoid from the excellent CSIRO home energy saving handbook.)

14 Comments on “Are you getting the most from your solar hot water system?”

  1. Huw Morgan says:

    Reblogged this on News @ CSIRO and commented:
    How to supercharge your solar hot water system.

  2. Lloyd says:

    I love my Solarhart hot water system. I use the electricity booster sparingly. Now that the kids have left home my wife and I can use our solarhart unboosted for about nine months per year. I do wonder what the booster’s thermostat is set to and what its optimal setting would be?

    Strangely the takeup rate for solar photovoltaic systems is greater than it is for solar hot water. Why is this?

  3. Bill says:

    “Strangely the takeup rate for solar photovoltaic systems is greater than it is for solar hot water. Why is this?”

    Solar PV is exposed to the chilly winds of international competition. The local solar hot water industry has managed to insulate itself from these winds. Google something like “cost of Solar water heaters in China” and you will see what must give them nightmares and the rest of us expensive solar hot water. Then set Google to “images” and go again.

    • Chris says:

      I agree with Bill and add two more factors:
      1. humans operate visually & “see” power usage when a light is left on or a heater is used to heat the home while they can save power by properly insulating the home or by wearing more clothes.
      2. the recent Federal Gov’t subsidy provided a “call to action” with the sunset accelerating last minute sales (power bills are also highly visual!) while the respective State Gov’t HW subsidies have been less prominent & limited in absolute $ terms per household (typically $1500) plus one only qualifies if replacing an electric HW system & many had already converted to gas.
      Furthermore, while it is true that a SHW system can generally save 1/3 of total household energy consumption, people see PV as a “whole of household” approach. I chose an evacuated tube system which works very efficiently & was relatively simple to install.

  4. Chris says:

    More on evacuated tube SHW: However, I have been very disappointed with after sales service. To date I have replaced the storage tank (made in Australia by a leading manufacturer) twice due to failure along the welded seam! Recently I replaced the circulation pump (40 W unit) due to it being starved of water with the flow meter becoming fouled with Ca. A word of warning to you – wherever heated water is circulated beware of liming – a little known quality of calcium is its reverse solubility curve: the bane of heating/cooling systems. The individual elements of this system are of good quality – I believe it was the overall design of the system which let down the overall package. My plumber says he won’t do any more installations of this brand but has plenty of orders for another brand. All systems need some maintenance & perhaps I should have been more vigilant. The Chinese made collector tubes are really very good but I wonder if I might not have been even better off (considering Adelaide’s town supply) going for Israeli made stainless steel units. ATA’s Renew magazine does regular reviews on all these types of technology; well worth a look. When I look at older flat plate systems I commonly see them leaking which is indicated by moss proliferating along the lower edge of the collector. These are much more susceptible to hail or frost damage & can reverse syphon at night losing heat unless a check valve is fitted.

  5. More Info says:

    I love my Solarhart hot water system. I use the electricity booster sparingly. Now that the kids have left home my wife and I can use our solarhart unboosted for about nine months per year.

  6. liamandrew says:

    Yes, actually solar hot water systems are more efficient than electric ones…
    And, ya also help to save electricity bill…

  7. Michael van Kampen says:

    Is it a fair comparison between solar HWS and PVC; without the test means being known it is difficult to be conclusive; how far down the chain do you or did you analyse the involved losses? the source is a constant the target is what will be the challenge, and perhaps surface area will be more important to the SHWS, given the water is not individualised into small spaces such as the PVC so the volumes are not the same. I would like to experiment with the use of a polished surface to reflect onto the PVC array to take full advantage of the afternoon sun as I have a peak roof patio opposite my PVC array which faces north. The best angle? given the reflective surface would be unchanging.

  8. path12 says:

    Yes, very true solar hot water systems not only save electric bill but also environment which is most important. We have to make use of more and more natural sources rather than artificial ones..
    Thanks for sharing such informative post..

  9. stephen says:

    I love my solar hot water system.It’s a pitty the rights to the system were sold by Sydney Uni in the early eighties.

  10. Jez says:


    I’m surprised the CSIRO’s Solar Hot Water Guide doesn’t suggest the installation of a timer switch for the booster. Ours is programmed to come on between 23:00 and 06:00.
    This ensures that the booster only comes on if the solar collector couldn’t provide enough heating during the day and ensures that hot water is always available for morning showers, etc. We no longer have to fuss about when to turn the switch on or off.
    An added benefit of our timer switch is that it is metered separately and we pay off peak rates for it. Although it was originally programmed to come on between 10:00 and 15:00 as well as the evening cycle, ACTEWAGL (Canberra energy provider) was able to send out a technician to reprogram the meter for us. This prevents use of electricity for the intensive ‘recovery’ of the HWS after morning showers and gives the sun a chance to do the work for us.

  11. Very useful content for hot water installation. Thanks for sharing such interesting information.

  12. IB says:

    On a full sun day in winter in Sydney should we need a boost? We run out of hot water on a daily basis. Largest tank, no hot water usage after 11;00am but still have only warm water in evening. We have offpeek boost at night. Collector is in sun 8hr/day in winter and faces north.

    • Solar@CSIRO says:

      A few trouble-shooting tips that might be able to help:

      • Ensure the insulation around the pipes and hot water tank is sufficient.
      • The insulation on the pipes that go from the panel to the tank and back is very important. Without it your pipes are basically a radiator which the hot water is continuously pumped through during the day.
      • The tank and collector ratio might not be appropriate, i.e. the tank is too big and the solar collectors are not able to heat the full tank with winter sun
      • It’s good that your collector faces north but you may want to check if it is getting full sun. Dust or shading from buildings or trees may be obstructing direct sunlight.
      • Check to make sure you don’t have any leaking hot water taps. They use a surprising amount of water.

      Inappropriate insulation and appropriate system size can reduce the efficiency of solar hot water installations. Further info specifically on hot water systems can be found at

      One last tip – an electrician may be able to check that the heating elements are working at full capacity, and that the off-peak switch is functioning correctly. If the electric heating wasn’t operating at full capacity, you could get a layer of hot water stratified at the top of the tank, and cold water below it. This would give a hot shower in the morning, but it’d all mix together during the day as it circulated, giving only warm water at night if there was insufficient solar energy to heat it all up.

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