Household electricity consumption for hot water

Hi there,
We have a normal electric immersion heater for water (Rheem) with one element and no booster element. . We also have level 1 off peak electricity supply from Energy Australia.
My question seems simple enough but I can’t get a straight answer.
Does the water tank only get heated during the off peak period?
I’ve always assumed that to be true, but I’ve begun to wonder if it is.
We (senior couple) only need one 300 tank of hot water a day, so do not need it to be continually ‘topping up’ the heat.
Can anyone please advise?


Simple answer is yes.


“We (senior couple) only need one 300 tank of hot water a day, so do not need it to be continually ‘topping up’ the heat”.
As you use the hot water during the off-peak period, cold water enters the tank to replace it and the built-in thermostat turns on the element to bring the tank up to normal temperature. This process is automatic and not consumer controlled.


There are various ways water heating can be done, if you have a dedicated off-peak hot water circuit it may well be turned on by a signal sent into the grid by Energy Australia, or alternatively there could be a clock on it, to only have the element (via a thermostat) energised during the off-peak period.
A better way to save money is to use a PV system to heat the water during the day at zero marginal cost, and a more electrically efficient way to heat it is with a heat pump. Also you can buy evacuated tube manifolds + circulation pump to heat water in an existing tank.


A great option if the site suits, with a 300l storage tank very generous for just two. We managed a family of 5 with a similar sized solar HW system. The electric booster was connected to off peak (night rate). It was easy to monitor how well the solar HW performed. We usually left the power to the booster element turned off. It was only during prolonged periods of heavy cloud and wet that the booster was needed.

Depending on where you are flat plate HW collector which is cheaper than evacuated tubes may be adequate.


Thanks guys for those helpful replies.


That’s a very interesting installation you describe. Do all solar power people do that sort work? It sounds a bit specialised.


Possibly, but perhaps not.

Central Qld but a slightly earlier version,1988.

As @gordon suggested you can upgrade using your existing HW system by adding a Solar HW collector and a circulating pump. The existing electrical HW heater element is your backup/booster.


Likewise - off at the meter box. We might need to turn it on once or twice per year.


If you have not previously found this it may help understanding the options.

If you live in a cold/frost prone area solar is still ok, but needs some extra protection against freezing.

Also worth a read and one place to look for market information.