Hot water is one of the biggest energy users in an Australian home, so the system you pick at contract stage keeps costing (or saving) you money for the next 15 years or so. Direct PV solar hot water is one of the newer options, and it's worth understanding before your builder defaults to whatever is on the standard spec sheet.

How direct PV solar hot water works

A direct PV system uses its own set of solar panels, separate from any rooftop solar that powers the rest of the house. The panels feed DC power through a controller straight to a heating element in an electric storage tank.

The controller usually includes maximum power point tracking (MPPT), which squeezes the most out of the panels as the sun moves and clouds pass. Most tanks also have a second element connected to mains power as a backup, so you still get hot water after a run of overcast days.

There's no inverter feeding the grid, no water pumped up to the roof, and no heavy tank sitting on the rafters.

The other two options worth comparing

PV diverter. If you're already putting rooftop solar on the house, a diverter sends your surplus solar to a standard electric tank instead of exporting it to the grid for a few cents per kWh. It uses panels you already have.

Heat pump. A heat pump works like a reverse air conditioner, pulling heat from the air into the water. It typically uses around a third to a quarter of the electricity of a standard electric tank. Run it on a timer during the middle of the day and it pairs well with rooftop solar. Most heat pumps aren't designed to run straight off a variable DC solar supply, so they're used with a normal rooftop system rather than a direct PV setup.

Traditional roof-mounted solar thermal (panels with water running through them) is still an option too, but it's become less common in new builds as solar PV prices have dropped.

Pros of direct PV

  • Simple and reliable. A heating element is about the simplest bit of kit you can buy. Few moving parts, nothing pumped around the roof.
  • Flexible panel placement. Panels can go on any roof face or a ground mount. Useful where the roof can't take the weight of a roof-mounted tank, or where the best roof face is already used by your main rooftop solar.
  • Works off-grid. For rural or off-grid homes it takes a big load off the batteries.
  • No grid export. Because it isn't connected to the grid, it doesn't eat into any export limit on your main solar system.

Cons of direct PV

  • Less efficient than a heat pump. A resistive element turns one unit of electricity into one unit of heat. A heat pump turns one unit into three or four. That means you need more panel area for the same hot water.
  • Extra panels. You're buying a second set of panels and a controller, which can cost more than simply adding a few panels to your main system and fitting a diverter.
  • Backup still costs. In a wet week the mains element does the work, at normal tariff rates unless it's on an off-peak circuit.

What it costs

Pricing moves around a lot by brand, tank size and region, so get quotes. As a rough guide, conventional solar hot water and heat pump systems commonly come in somewhere between $3,000 and $7,000 installed before rebates, and small-scale technology certificates (STCs) usually knock some of that off. Direct PV kits sit in a similar band once you add panels, controller and tank. A diverter is often the cheapest add-on if you're already installing rooftop solar.

Must-knows for any hot water system

  • 60°C storage. Australian plumbing standards require stored hot water to be kept at 60°C or above to control Legionella. Whatever system you choose must be able to get there, including through winter.
  • Tempering valve. Hot water delivered to bathrooms is limited to 50°C to prevent scalding, so a tempering valve goes in the line.
  • Energy rating. Your hot water system counts toward the NCC whole-of-home energy assessment that sits alongside the 7-star NatHERS requirement. A more efficient system can free up the budget elsewhere in the energy rating, so ask your energy assessor how each option scores.
  • Tank location. Put the tank close to the kitchen and bathrooms. Long pipe runs waste water and heat while you wait for it to run hot.

Is direct PV right for your new home?

Direct PV makes the most sense when:

  • you're off-grid or on a large rural block with plenty of space for panels
  • you want hot water separate from your main solar system
  • the roof can't take a solar thermal tank

For a typical suburban Queensland home that's already getting rooftop solar, a heat pump on a midday timer or a PV diverter on a standard tank will often do the same job for less.

My advice: ask your builder or plumber to price a heat pump, a PV diverter and a direct PV system side by side before you lock in your hot water. It's a lot easier to change on paper than once the plumbing is roughed in.