Heat pump HWS vs electric with large PV system

Slopshua on 06/12/2022 - 09:31
Last edited 06/12/2022 - 09:32

Hi all,

Just had a large 10.5kw PV system installed on my house. Currently have a 21 year old electric hot water service that's showing no signs of slowing down but is probably due for replacement.

Hence I've been looking into heat pump hot water services to replace the old electric unit but the cost of a good quality, well reviewed unit has got me thinking that it may not be the right option.

For a quality heat pump HWS it's going to cost around 4.5k supply and install after rebates! Yes - these are high end units but the reviews for mid tier units seem to get exponentially worse and the last thing I want is unreliable hot water. Especially considering my 21 year old unit hasn't missed a beat in all the years I've owned it.

Obviously in terms of efficiency the heat pump unit will perform significantly better than a traditional electric element but if I run a traditional unit during the day on my solar power, when household usage is low as no one is home, then I cant see any real upside of the heat pump unit in my case?

Home & Garden

Comments

  • Fozdog on 06/12/2022 - 09:45
    +2

    Imo unless you have a really high hot water usage or your system is failing, it's not worth replacing. Just run the old one on a daytime timer (assuming you old one is a storage tank setup)

  • JimmyF on 06/12/2022 - 09:55

    Obviously in terms of efficiency the heat pump unit will perform significantly better than a traditional electric element but if I run a traditional unit during the day on my solar power, when household usage is low as no one is home, then I cant see any real upside of the heat pump unit in my case?

    HP HW are very low power uses but do come at a cost. If you have excess solar then a traditional HW unit is cheaper up front.

    The issue mostly is in winter when your HW usage is up and solar output is down, the traditional HW units power requirement might not be met from the solar unless you have a really big system. Traditional HW units are around 3.6kw for fixed units, but these can be dropped to 2.4kw.

    You can also use a solar diverter for the HW so it only uses excess solar power to heat the HW.

    • Slopshua on 06/12/2022 - 12:45

      This is the question I wont really be able to answer until next winter. This morning where I live it was maybe 6/8 overcast at 14 degrees and I was getting around 3.0wk which would be enough for a 2.4kw unit but only just.

  • highon2str on 06/12/2022 - 10:22

    We had a 12 yo gas-boosted electric HWS that needed the anode replaced. We were getting rid of gas at the time so it made sense to go with a heat pump HWS. Got a Sanden installed and haven't looked back since!

    In your case though, I'd probably use it till it stops, since there doesn't seem to be any real incentive?

    • Slopshua on 06/12/2022 - 13:24

      I agree - right now the numbers arent stacking up for a HP HWS

      However, I went with the largest PV system I could justify as I am planning on taking full advantage of bidirectional vehicle charging when it becomes available in the country. At that point i'll buy either a PHEV with a large battery or an EV and hopefully charge the car when the suns out and then use the cars batteries to power the house when the sun goes down. Nice idea in principle..

      Therefore I suppose you really need the most efficient appliances generating your houses needs which obviously includes hot water.

      • Jono05 on 13/01/2023 - 15:15

        What happens if you want to drive the car but it’s powering the house? Wouldn’t it be better to just get a battery?

        • boretentsu on 14/01/2023 - 22:12

          Buy another one

  • bym on 06/12/2022 - 10:28
    +1

    I'm in the same boat and came to the conclusion that the large outlay for a quality HP HWS wasn't worth it. I just run my element HWS (315l) on a timer.

    • saliya on 06/12/2022 - 11:41

      Do you know how many kWh your system uses vs how much water it actually heats? I'm looking at doing a similar thing (converting gas to electric storage).
      How many people does 315L service (I have 2 teens in the house)?

      • bym on 06/12/2022 - 11:57
        +1

        Family of four and have the timer set from 10am - 3pm. On ave. it kicks in for 1-2hrs in the morning then a couple of short bursts of about 15min throughout the remaining time and I've never run out of HW. I'm in Cairns though and it's a 3.6kW element.

        • saliya on 06/12/2022 - 20:40
          +1

          Cheers. Looks like for your energy usage (say 8kWh/day) and assuming a 12c FIT (approx $1/day) a $4500 heat pump that used only 30% as much power would still take about 17 years to pay back vs your existing working element system.

          If we were comparing a new $1500 element system vs a new $4500 HP system then the HP only takes 12 years to pull ahead!

          Practically, an element HWS is a cheap battery - you store ~8kWh of energy as hot water…

          • bym on 06/12/2022 - 21:17

            @saliya: Thanks for doing the maths for me, I suspected as much but never bothered adding it up!

          • Jono05 on 13/01/2023 - 15:17

            @saliya: Who pays a 12c FIT? They’re about 6c these days. Heat pumps use about 80% less energy.

            • Cheapshots on 14/01/2023 - 13:37

              @Jono05: Powershop in nsw for me in 12c fit

              • Jono05 on 14/01/2023 - 20:38

                @Cheapshots: Not many pay above 10c, most are around the 6-7c mark if you’re lucky.

                • Cheapshots on 14/01/2023 - 20:46

                  @Jono05: Yeah I was with netcr as I found a sign up bonus. Was only 4c feedin though.
                  Still had out of pocket energy bills (new 6.6kw solar installed).
                  Made the switch to Powershop as lower daily, better feed in and only slightly higher std usage.
                  Their app is a bit crappy. Tells you daily usage and total month usage and daily feedin, but not the overall usage less feedin.
                  My month is up tomorrow so I assume they calculate it then.

                  If I’m right i should basically have no charge this month (and a $75 sign up bonus on top haha)

                  • Jono05 on 14/01/2023 - 20:56

                    @Cheapshots: Good find. I’m with Alinta and only get 6.7c FIT.

  • Switchblade88 on 06/12/2022 - 10:38
    +1

    If you had a smaller solar system, then a heap pump upgrade would make sense so you don't exceed your solar output too much. In your case, I'd stick with the old system and get a heat pump in several years once it dies (and they'll be cheaper by then hopefully).

  • Jono05 on 13/01/2023 - 15:29
    +1

    What if there’s a wait for supply and installation of the heat pump? If your current HWS could die any day now being 21 years old. Wouldn’t be good with no hot water especially during winter.

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