Heat pumps + solar PV: the daytime-charge trick that drops bills to zero
How to schedule a Reclaim or iStore unit to run in the middle of the day on your own solar export, which is about as cheap as hot water gets.
If you've got solar PV and a modern heat pump, you can run your hot water for free. Literally free. Here's how the daytime-charge trick works.
The principle
Most solar households export more energy in the middle of the day than they use. The feed-in tariff is usually 4-8c/kWh, while the retail rate you're paying to buy back is 30-40c/kWh. That's a huge margin you're giving away.
A modern heat pump uses 500-800 W to heat 250-300 L of water, about 3-5 hours of runtime a day for a family of four. If you schedule those 3-5 hours during peak solar production (roughly 10 am to 3 pm), you're running the heat pump off your own free electricity instead of exporting it.
How to schedule it
The Reclaim CO₂ split with Wi-Fi controller, Reclaim R290 (Wi-Fi is built in), and iStore all let you set a heating window in the app. Point them at 10 am to 3 pm. The tank fills to setpoint during solar hours and holds temperature through the evening on stored heat.
Thermann doesn't currently ship a Wi-Fi controller, so you'd need a mechanical timer on the power point. Slightly clunkier but same result.
Real numbers from a Pakenham install
One of our recent installs, 4-person household, 6.6 kW solar, Reclaim R290 300 L. Their hot water usage was averaging 260 L/day. Before the swap: gas storage tank running them ~$680/year in gas. After the swap and scheduling: heat pump running off solar during the day, essentially $0/year in incremental power cost. The heat pump's 500-800 W draw sits entirely within their solar export headroom.
That's a $680/year saving on top of the ~$1,000 they saved on the install through Solar Homes and the Aus-made rebate. Payback under 4 years.
Gotchas
Cloudy days you're not covered, the heat pump will still run but it'll pull from grid. Over a year the average is 85-90% solar coverage in Pakenham.
Winter mornings are the pinch point, solar is weak and heat pump COP drops slightly in cold air. Some households add a small booster window at 3 am on off-peak power to top up. Adds maybe $30-$50/year.
If you've got solar and you're on gas hot water, we're happy to talk through the numbers on your specific setup, free 20-minute chat, no pressure.
Fixed-price, no obligation, VEU rebate applied at the quote.
We usually reply within 12 hours. Free 20-minute site check for bigger jobs.
