The sad reality of commodity solar hot water

This looks at issues found with common solar-hot-water systems and regulations in Victoria, Australia.

2021-06-20

By Richard Keech

My experience from assessing homes

I’ve formed the view, from six years of home conducting professional home assessments, that common, budget, solar-hot-water (SHW) systems are highly problematic. During my time doing ecoMaster home assessments, most solar hot water systems I saw were faulty. Looking back, I wish I’d collected data on the specifics to paint a clearer picture.  A typical situation involved the following (remember, this in in Victoria, Australia):

  • I’m assessing a client’s home, for reasons un-related to hot water, i.e., they don’t report having a problem with their hot water;
  • The hot water unit has a flat-panel solar collector on the roof, a storage tank at ground level, and gas-fired instant hot water unit as a booster;
  • I look at their hot water in the course of assessing the entire house and it’s apparent that there’s zero solar warming of the water. I can tell this because, by touching the metal fittings on the tank, there’s no sign that the temperature of the stored water is above ambient;
  • The client’s subjective experience of hot water is still OK because the booster unit is doing all the work of heating the water;
  • There’s no obvious reason for the fault.

Of the 500, or so, houses assessed, there were probably about 10-15 homes with SHW. Most of these cases displayed this problem.

Victorian regulations

Here in Victoria, the building regulations require (for new builds) either gas-boosted solar hot water system or rainwater harvesting. Reference is Victorian Building Authority Practice Note 55 (see excerpt below).

Excerpt from VBA Practice Note 55

Implications. At face value this regulation is good, and encourages more rooftop renewable energy. However, the perverse consequence of this mandatory requirement is that there are lot of installations in place for no other reason than to comply with the minimum standards. This encourages the use of budget hardware. When combined with the fact that consumers may not realise that their solar is faulty, it’s a recipe for a failure of regulation.

What I know about HWSs

I have owned a solar hot-water system for over ten years. Mine is a quality system and has served me well. So, I’m very familiar with these types of systems, how they work, and their idiosyncrasies. My experience and understanding with solar hot water also comes from:

  • Analysing these types of systems in my university studies;
  • Research into hot water system as co lead author of the Zero Carbon Australia Buildings Plan (2013);
  • Working briefly for a company that did analysis of hot-water systems for compliance testing.

As a result, I’m reasonably in tune with what’s on the market and what can go wrong.

Typical solar-hot-water tank installation

An opportunity for data collection

Situation. With my current employer, one job in 2019 presented a unique opportunity to do a little data collection.  The job was to assess 16 homes owned by a large organisation. The homes are used as temporary residences for people associated with the organisation.  All homes were very similar, conventional contemporary, well-maintained residences, and (at the time of inspection) all 5 to 10 years old.  All homes had flat-panel, gas-instant-boosted, solar hot water systems. 

Finding. Upon inspection,  a large fraction of the HWSs were obviously faulty.  However, the gas boosting was masking (from the residents) the underlying faults.
So, of the 16 residences, only five had fully working, undamaged HWS units.  Eight of the 16 had solar units that were completely faulty, i.e., stone-cold tanks.  One was not working when inspected, but just needed to be switched on. Specific data below. 

Year of buildDate of assessmentHot water typeSolar HW functioning?
  20122019-02-05Chromagenworking, but leaky pump
20122019-02-05Chromagenworking, but leaky.  Damaged tank
20122019-02-05Chromagenfaulty solar – tank cold. Damaged tank
20112019-02-07Dux, 322Lfaulty solar – tank cold.
20112019-02-07Dux, 322Lworking OK
20112019-02-07Dux, 322Lworking OK
20112019-02-07Dux, 322Lworking OK
20092019-02-13Rinnaifaulty solar – tank cold
20092019-02-13Rinnaifaulty solar – tank cold
20092019-02-13Rinnaifaulty solar – tank cold
20092019-02-13Rinnaiworking OK
20142019-02-19Chromagen, 200Lprobably OK; once plugged in it seemed to work
20142019-02-19Chromagen, 200Lworking OK
20142019-02-19Chromagen, 200Lfaulty solar – tank cold
20142019-02-19Chromagen, 200Lfaulty solar – tank cold
20152019-02-19Rinnai Sunmaster, 215Lfaulty solar – tank cold
Sixteen residences – eight faulty SHW

Among the 16 systems there were five different manufacturers. However, what these SHW systems all had in common was that they were:

  • flat-panel-collector (i.e., cheap);
  • gas-boosted;
  • common, volume-market brands.

So, these types of system are absolutely typical of the types of systems found on volume-built new homes.

What happened to these systems? All sixteen systems were replaced with Sanden heat-pump HWS. At the same time, Solar PV was installed.

What’s wrong? Other than this particular mode of failure, there are other things that can go wrong with a SHW system that present in ways different to what I’ve observed here. With respect to this mode of failure, there are various underlying reasons that a SHW system might not be working. Reasons include:

  • pump failure (or turned off?);
  • temperature probe failure (or disconnected);
  • controller failure (or turned off).

Conclusion

The obvious inference from this data is that it’s very likely that a non-trivial percentage of all SHW systems installed in Australia are faulty in this way, and that the residents are oblivious.

How to tell? If you have a solar HWS like this then the tank water can be expected to be noticeably elevated above ambient all the time, assuming normal (non-excessive) water usage. Simply by touching the exposed fittings of the tank it should be apparent. If it’s warm to touch then there’s solar boosting going on. Note, this test assumes instant-gas boosting is used (in these systems, the only heating of the tank water is from the sun).

Implications. If it’s borne out that very large numbers of installed systems are, indeed, faulty, then it should, hopefully, make the Victorian state government reconsider the role that SHWs have in this state.

Recommendations. At the very least, I hope that the regulations will be amended to permit heat-pump hot-water systems to be used as an alternative. Permitting heat-pump units in lieu of gas-boosted solar would be a good thing to do in any case, just based on efficiency and emissions. However, if the SHW reliability issue is widespread, as my observations suggest, then it’s doubly important for gas-boosted SHW systems to be removed from the Victorian regulations ASAP.