South-Facing Solar Hot Water System - Worth It?

I can't find anything on relative efficiencies of solar hot water system that faces away from the equator (i.e. south). I'm in Brisbane.

I'm putting in a solar PV system on a north-facing roof. For various reasons I can't have a solar hot water system on anything except a south facing roof. I want to consider the relative costs and benefits of having a plain electric storage water heater that will be driven from the PV system during the day, vs heat pump and the different kinds of solar hot water systems, but I can't find anything that tells you how much efficiency you sacrifice with a south facing solar hot water system. Obviously the up front cost of an electric storage system will be lowest, but it will draw from the grid for a bit over half of the day.

Does anyone know of a calculator or have experience with the various kinds of south facing solar hot water systems, in Brisbane? How much is each kind of system going to draw from the grid in an average day if it is south facing?



      Will be a good guide as to the effective system loss..

      OP, I suspect you will need to pull out your old Maths textbooks and do some trigonometry…
      Angle of roof, versus angle of the sun (especially in Winter), and work out the apparent heating area. You'll also need to factor out any shaded period.
      ie. 1sq m of solar collector is only going to appear to be 0.5sq m when south facing.

      My guess is that as long as the roof is reasonably flat, you'll be fine provided you spec up an oversized system to factor in the apparent collector size.
      If you've got a peaked roof though, I cant see it working.


      How did my Google-fu fail me so badly!

      Based on that it looks like a south facing system is 78% as efficient as a north facing one in Brisbane. That's not bad. I assume its the same regardless of whether it's PV, evac tube etc.


      I found this too. There's a table if you scroll down.

  • +2 votes

    Why not tilt the panels up

  • +2 votes

    Knock down rebuild

  • +1 vote

    Can you do some of your PV west facing (will push your peak power production a little later in the day) and then your SHW on the north face?


      Definitey worth doing this if you can.

      You wont generate as much power in total, but you'll generate more power when you're using it, so economically you'll be better off.


      Not really - existing HW is on the south side so it would involve re-plumbing all over the place, and it's also not a good side for a tank to be on.


        Not really, It would involve running new feed water and hot water returns to the existing pipework in the roofspace and sealing off the old outlets.
        Might add an additional 30 minutes to the work, plus cost of materials.

        If your pipework is subfloor it might add an additional 15 minutes and extra materials.
        They'd just need to work pipes into the roofspace from the existing location, neither would be hard or add all that much cost.

        I'm guessing the cost to oversize a south facing system would far exceed that of the extra work and materials to have a standard size unit on the north side.


          Maybe so, but for space reasons I don't think I can. I'll probably just go with straight electric storage on the south side and trust that the PV will take care of it during the day. The extra $3-4k for solar and the other headaches it brings just doesn't seem worth it.


    Not worth it. Setting aside from inherent inefficiencies of PV systems, there's not much point if you're getting under 80% of optimal.

    You need to do the calculations for yourself but don't just include the cost of the system, there's other factors like increase wear and tear (more like accidental damage) to the roof and unforseen costs of ownership.


    get some solar installers to do some quotes and ask for their written advice to educate yourself.

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