Hot water is one of the biggest single lines hiding inside your power bill, commonly around a quarter of a typical household’s electricity use. It is also the easiest big load to point at your solar panels, because water does not care what time of day it gets hot.
We are G-Solar & Electrical, based at 32 Magazine Street in Stratford. We install and service solar across Cairns, Port Douglas, the northern beaches and the Atherton Tablelands, and hot water strategy comes up in almost every consultation we do.
Quick Answer
- Hot water is roughly a quarter of most household electricity use
- Since July 2026 exports earn about 6 cents, so heating water with your own solar beats exporting
- Cheapest fix: a simple timer that runs your electric tank in the middle of the day
- Smartest fix: a diverter that feeds only your true surplus into the tank
- Most efficient heater: a heat pump, which makes hot water from a third or less of the electricity
- Old rooftop solar hot water collectors are a different, mostly superseded technology
First, Clear Up the Confusion: Two Kinds of “Solar Hot Water”
The phrase solar hot water means two completely different things, and mixing them up costs people money.
Old style: rooftop collectors. Water circulates through roof panels or evacuated tubes and the sun heats it directly. These systems still work, but they do only one job, and when the collector or tank fails the repair bills are chunky.
Modern approach: solar PV heats the water. Your ordinary solar panels make electricity, and that electricity runs your water heater during the day. The panels serve every appliance in the house, hot water included, and the hardware doing the heating is a normal tank sitting safely at ground level.
Almost every new Cairns installation takes the second path. Roof space spent on PV panels beats roof space spent on single-purpose collectors, because electricity is flexible and hot water is just one of its jobs. If a collector system on your roof is nearing the end of its life, replacing it with more PV plus one of the options below is nearly always the better rebuild. For how the generation side works, start with how solar panels work.
Option 1: The Humble Timer
The simplest move in home energy, and still one of the best. A timer on your electric storage tank’s circuit shifts its heating window into the middle of the day, when your panels are producing hard.
- Why it works: a storage tank is effectively a battery made of water. Heat it at noon with power that would have been exported for 6.006 cents, and the tank holds that energy until your evening shower.
- What it costs: very little. It is a small electrical job we can fold into other work.
- The catch: a timer is blunt. It heats at the set time whether your panels are producing well or the day is grey. On cloudy wet season days some of that heating power comes from the grid at daytime rates. Our post on cloudy day performance shows what FNQ cloud really does to output.
If your tank currently heats overnight on a controlled load circuit, the timer conversation interacts with your tariff setup, which we cover in our Ergon tariffs guide. For many solar homes, daytime self-powered heating now beats the cheap overnight rate.
Option 2: The Hot Water Diverter
A diverter is the clever version of the timer. It watches your home’s energy flows in real time and sends only genuine surplus solar into the heating element, ramping up and down as clouds pass and other appliances switch on and off.
- Why it works: near-zero grid power for hot water on most days, without stealing solar from the rest of the house. It soaks up exactly the power that was heading out the meter for 6 cents.
- Where it shines: homes on an export cap. Most Ergon-area houses can export only 5 kVA, and a diverter turns trimmed-off power into hot showers. Details in our export limits guide.
- The catch: more cost than a timer, so it suits homes with a decent surplus to harvest. A quick look at your monitoring history tells us which side of the line you sit on.
Option 3: The Heat Pump
A heat pump water heater does not make heat from electricity the way an element does. It moves heat from the surrounding air into the water, the same trick as your aircon running in reverse. The result: the same tank of hot water from roughly a third or less of the electricity.
- Why it belongs in Cairns: heat pumps love warm, humid air, and FNQ supplies it all year. This is close to ideal heat pump country.
- The combination move: a heat pump running on a daytime timer, fed by your solar. Small load, met by your own panels, hot tank every evening. It is the most efficient mainstream setup available in 2026.
- The catch: higher purchase price than a standard tank, softened by the small-scale technology certificates that discount efficient hot water systems the same way they discount solar panels, as covered in our STC rebate guide. Heat pumps also make some noise, roughly comparable to an aircon outdoor unit, so placement needs a thought.
We frame heat pumps as buying advice rather than a sales pitch: our trade is the solar and electrical side, and getting the solar sizing right is what makes any heater cheap to run.
Which Option Fits Which Home
| Your situation | Best move |
|---|---|
| Electric tank, solar on the roof, tight budget | Timer. Biggest saving per dollar in this list |
| Solid midday surplus, export capped | Diverter. Harvests power the cap would waste |
| Tank due for replacement anyway | Heat pump on a daytime timer |
| Old rooftop collector system failing | Replace with PV plus heat pump or tank on timer |
| Planning a battery soon | Do hot water first. It shrinks the battery you need |
That last row surprises people. Hot water is such a large, flexible load that solving it with a timer or diverter reduces your evening grid draw, which means a smaller, cheaper battery covers what remains. It is step one in the wider self-consumption playbook we lay out in using more of your own solar, which matters double now that feed-in credits have dropped.
And if your system needs to grow to carry the hot water load, our panel count guide covers the sizing maths.
Frequently Asked Questions
Is solar hot water still worth it in 2026?
Heating water with solar energy is more worth it than ever, but the modern route is PV panels powering your heater, not dedicated rooftop water collectors. Electricity from PV is flexible; a collector does only one job.
What is the cheapest way to heat water with solar?
A timer that runs your existing electric tank during the day. It costs very little and points a quarter of your household energy use at power you were exporting for about 6 cents.
What is a hot water diverter?
A device that measures your surplus solar in real time and feeds exactly that surplus into your water heater. It maximises self-consumption without drawing grid power, and suits homes with export limits especially well.
Are heat pump water heaters good in Queensland?
Excellent. They pull heat from the air, and warm humid FNQ air keeps them working efficiently all year. Paired with a daytime timer and solar, they are the most efficient mainstream hot water setup available.
Should I fix hot water before buying a battery?
Usually yes. Hot water is a big flexible load, and solving it with a timer or diverter shrinks your evening grid usage, which means a smaller and cheaper battery finishes the job.
My rooftop solar hot water system is old. Repair or replace?
Once collectors or tanks fail, replacement with PV plus a heat pump or timed tank usually beats repairing single-purpose hardware. Get both options priced before spending on repairs.
Point Your Biggest Easy Load at the Sun
We will look at your tank, your tariff setup and your solar surplus, then set up the timer, diverter or system resize that turns hot water into a solved problem. Straight advice, 10 year workmanship guarantee, all across FNQ. Call 07 4039 4914 or book a free consultation.