Heat pumps + solar PV: the daytime-charge trick that drops bills to zero
How to schedule a Reclaim or iStore unit to run during the day on excess solar, the cheapest hot water in the country.
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.
