Running heat pump hot water off your solar

A hot water tank is a store. Heat goes in when it suits you and comes out when you turn on the shower, hours later. That makes hot water one of the easiest loads in the house to line up with rooftop solar, and a heat pump is well suited to the job.

Why the middle of the day suits a heat pump twice

A heat pump water heater works like a reverse cycle air conditioner on its heating setting. It draws heat out of the outside air and puts it into the water, which is why it uses much less electricity than an element heating the water directly.

Running it in the middle of the day helps in two ways. Solar Victoria's advice to owners is that the heat pump should run when your rooftop system is generating the most, and that this also improves efficiency because the air is warmer. The same guidance notes these systems use more energy when the outside temperature is colder, and that running overnight may not save money in winter.

That second point matters up here. A frosty night in Trentham or Daylesford is about the hardest work you can give a heat pump. The middle of the day, when the panels are producing and the air has warmed up, is the easiest. Lining the two up gets you the cheap power and the better efficiency at the same time.

Why your own solar is worth using

Victoria has had no minimum feed-in tariff since 1 July 2025. Retailers set their own export rates, and the Essential Services Commission's only rule now is that they can't go below zero. A kilowatt hour your heat pump uses from your own panels is one you don't buy back from the grid at night. A kilowatt hour you export may earn you very little. Heating water at midday is one of the simplest ways to keep more of your solar in the house.

Three ways to time it

A piece written for SolarQuotes by Baran Yildiz, a senior lecturer at UNSW's School of Photovoltaic and Renewable Energy Engineering, sets out the options well.

1. The heat pump's own timer. Many models have one built in. Some offer a solar window, such as 9am to 3pm, and some can change the window with the seasons. This is the simplest option when it is available.
2. An external timer. Solar Victoria says that if your heat pump has no timer, an electrician can fit a digital timer at the switchboard.
3. A daytime controlled load circuit. Some retailers and networks now offer a cheaper controlled load rate during a daytime window. Yildiz points out that this option doesn't let a household use its own rooftop solar behind the meter, so it suits a home without panels better than one with them.

Getting the window right

The timer window has to be long enough for the heat pump to finish reheating the tank. Too short, and you can run short of hot water if the family uses a lot outside the timer hours. Too long, and some of the heating spills out past the best of the solar. Yildiz notes that trade off directly.

There is also a mechanical point. A heat pump cut off partway through a heating cycle can be damaged in some models, which is why a plain switch on a timer isn't always the right answer. Check the manufacturer's guidance for your model before setting anything up, or ask us to.

A few things we look at when we commission a system:

• How the household uses hot water. A family that showers at night needs the tank to carry the day's heat through the evening, so tank size matters.
• What the solar actually produces in winter. Short days and low sun mean a narrower useful window in June and July than in January.
• Where the unit sits. A heat pump draws heat from the air around it, so a cold, shaded corner of the yard is a harder spot than a sunny wall.

The Midday Power Saver

From 1 October 2026 the Victorian Government's Midday Power Saver offer will be available to households with a smart meter, with no charge for the power you use between 11am and 2pm. A heat pump on a timer is exactly the kind of appliance it suits, with or without solar. You have to opt in through your retailer, and it won't suit every household, so compare it against your current plan first. We cover how it works in the Midday Power Saver and your air conditioner.

Replacing an old system

If you are still on gas or an old electric storage tank, a heat pump is the natural replacement, and it is often the second step in getting off gas after the heating. We go through that order in going all electric and dropping the gas connection. Discounts are available under the Victorian Energy Upgrades program for eligible heat pumps, applied by an accredited provider, and you can ask us if your job is likely to qualify. See the VEU discount for heat pump hot water for how it works.

We install heat pump hot water across Central Victoria, set the timer to suit your panels and your household when we commission it, and measure up and quote before anything is ordered. If you'd like us to take a look, contact us or ring 0417 734 206.