Is your hot-water tank already a battery?

That makes it worth checking the system you already have before assuming that every kind of energy storage requires a home battery.

You can heat now and shower later

An insulated tank keeps water warm between heating cycles. The better the timing suits your household, the more opportunity you have to separate when electricity is used from when hot water is needed.

For scale, heating 250 litres of water by 20°C stores about 5.8 kWh of heat. That calculation assumes the full volume is heated through that temperature difference and ignores heat losses.

It describes thermal energy. A conventional electric element and a heat pump may need different amounts of electricity to add the same amount of heat. Heat pumps move heat from the air into the water, so you cannot read the 5.8 kWh figure as a universal electricity cost.

An instantaneous system works differently: it heats water as you use it and does not have a large tank of stored hot water.

Can I heat water using solar or off-peak electricity?

Some electric storage systems and heat pumps have built-in timers. Depending on the model and installation, they may be able to heat during a solar surplus or a cheaper electricity period.

Think about the busiest hot-water period, not just how many people live there. Several showers close together need enough usable stored water and enough recovery time. Ask what happens after that peak, particularly when a timer restricts the heating hours.

A timer knows the time, not how much solar is available. A scheduled daytime run can draw grid electricity when generation is low. Compare that grid rate and the feed-in payment you give up, as well as the hot water available when you need it.

Check the hot-water tariff on your bill. A separate controlled-load circuit can have different supply times and rates from the rest of the house. If your account is with ActewAGL, we can explain its tariff; otherwise, ask your retailer. Your installer should confirm whether the exact heat pump and circuit are suitable for the schedule you want.

What if I am replacing the hot water system?

For a heat pump in colder parts of the region, ask about the exact model’s winter operation and booster use. The ACT buyer guide recommends checking heat-pump-only operation down to minus 5°C. Also compare tank capacity, recovery time, noise, placement and the complete installed price.

If the existing tank works, compare a suitable schedule with replacing it. A new appliance is a different investment from changing when a working one heats. Keep the same household demand, tariff and service requirements in both estimates.

Keep the hygiene controls working

Keep the system’s approved storage temperatures and hygiene cycles. Hot water that is too cool can allow Legionella bacteria to grow. Water stored in the tank and water delivered at a tap also have different safety requirements. Follow the model instructions and licensed plumbing advice.

Leave the system’s approved temperature settings and sanitation cycles in place. Ask a licensed plumber or the manufacturer how scheduling works for your exact model. A timer must not prevent the system completing the heating it needs for safe operation.

Find the model number, tank size and hot-water tariff. Ask the manufacturer or licensed installer whether heating can move to a better period while still supplying the busiest shower time and completing the required hygiene cycle.

If it can, you may already have a practical way to store some energy for later. You will still need to account for heat losses and the electricity used to reheat the tank, but the upgrade could begin with a setting or a suitable control rather than a new storage system.

Related advice: Heat-pump hot-water rebates in the ACT and NSW: what will I actually pay? · How do I use more of the solar I already have? · What size hot-water system do I need?

Check your tariff or upgrade options

For an ACT household considering replacing gas hot water, our heat pump upgrade page (opens in a new tab) explains eligibility and the approved-installer quote route. Check the requirements for your address and account. Keep model suitability, recovery time and hygiene controls in the conversation with the installer.

Work out your hot-water system size