Solar thermal vs heat pump hot water in Perth: which is better in 2026?

For much of the 1990s and 2000s, solar thermal hot water was the recommended upgrade for Perth homeowners. Perth's sunshine makes it ideal for thermal collectors — the panels absorb solar radiation and transfer heat directly to water via a fluid circuit.

Heat pump hot water systems have transformed the economics of this comparison. As of 2026, heat pumps are the default recommendation for most Perth households considering a new hot water upgrade.

Here's an honest breakdown of why, and when solar thermal might still make sense.

How each system works

Solar thermal

Solar thermal systems have roof-mounted collectors (flat plate or evacuated tubes) that absorb solar radiation and heat a glycol fluid. The fluid circulates (either gravity-fed or pumped) to a heat exchanger in the storage tank, transferring heat to the water.

Variants:

• Flat plate collectors: Glass-covered panels with copper tubes and a black absorber. Lower cost, slightly lower efficiency, suitable for Perth's predominantly clear weather.
• Evacuated tube collectors: Each tube is a vacuum-sealed glass cylinder containing an absorber. Higher efficiency, better in cold and cloudy conditions, more expensive.
• Thermosiphon (passive): Tank mounted on the roof above the collectors; gravity circulates the fluid. No pump required. Most Perth solar thermal systems are thermosiphon.
• Split system (active): Tank at ground level; pump circulates fluid. More aesthetically flexible but adds complexity and maintenance.

Heat pump hot water

A heat pump extracts heat from ambient air using a refrigerant cycle (same physics as a reverse-cycle air conditioner) and transfers it to the water tank. It uses electricity — approximately 1kW — and achieves a coefficient of performance (COP) of 3–5: for every 1kWh of electricity consumed, it delivers 3–5kWh of heat to the water.

Cost comparison

Upfront cost

| System type | Installed cost range | |---|---| | Flat plate thermosiphon (small) | $2,500–$3,500 | | Flat plate thermosiphon (large) | $3,500–$5,500 | | Evacuated tube thermosiphon | $4,000–$7,000 | | Heat pump (mid-range, e.g. Reclaim Energy, Rheem) | $2,500–$4,000 | | Heat pump (premium, e.g. Sanden CO2) | $3,500–$5,500 |

Both options attract government rebates via the Small-scale Renewable Energy Scheme (SRES) — STCs are generated for both solar thermal and heat pump systems. The number of STCs varies by system, but both typically deliver a $400–$1,500 rebate applied at point of sale.

Running cost

Perth's advantage for solar thermal is its excellent solar resource — flat plate collectors can produce hot water for free on sunny days. However:

• Solar thermal still needs a booster element: For cloudy periods, mornings before the collector has heated the tank, and periods of high demand, an electric booster (resistive element) in the tank activates. On Perth's ~30 overcast/rainy days/year in winter, the booster carries a meaningful fraction of annual load.
• Heat pump: Runs on electricity, 24 hours a day. Designed to heat from whatever ambient temperature is present (heat pumps work down to -5°C, well below any Perth winter temperature). A heat pump timed to run 10am–1pm on solar power costs approximately $100–$180/year.

| System | Annual hot water energy cost (Perth) | |---|---| | Solar thermal (flat plate, electric boost) | ~$150–$280/year | | Solar thermal (evacuated tube, electric boost) | ~$100–$200/year | | Heat pump (timed to Midday Saver 8.85c/kWh) | ~$100–$180/year | | Heat pump (A1 tariff, no timing) | ~$250–$350/year | | Resistive electric | ~$600–$900/year |

Heat pump timed to solar hours or Midday Saver is competitive with the best solar thermal systems — and can beat them in Perth winter when boost element usage climbs for solar thermal.

Reliability comparison

Solar thermal

Pros: No moving parts in thermosiphon systems (the most common). Proven 20+ year lifespan if maintained.

Cons:

• Glass collector panels can crack in hailstorms (rare in Perth but not unknown)
• Glycol fluid needs replacement every 5–10 years ($200–$400)
• Frost valve can fail in rare Perth cold snaps (though Perth rarely has genuine frost)
• Tank and collector on roof add structural and aesthetic considerations
• If the pump fails in an active split system, no hot water production
• Hard to access for maintenance — roof access required for collector service

Heat pump

Pros:

• Ground-level or near-ground installation (tank at ground level, heat pump unit mounted low)
• No roof penetrations or roof-mounted hardware
• Easier maintenance access
• Modern units have 10+ year compressor warranties (Sanden: 10-year, Reclaim: 10-year)

Cons:

• Compressor is a mechanical component that will eventually need replacement (unlike the all-passive thermosiphon)
• Heat pump units generate operational noise (~50 dB at 1m) — placement away from bedrooms matters
• Slightly less efficient in very cold conditions (below 5°C) — irrelevant in Perth

When solar thermal still makes sense

Off-grid or extremely grid-constrained properties: A solar thermal thermosiphon system generates hot water without any electricity. In a property with no grid connection and a small solar system, thermal systems reduce electricity demand for hot water to near zero.

Replacing an existing solar thermal system: If you already have solar thermal collectors in good condition, replacing just the tank is far cheaper than switching to heat pump. Continue using the existing collectors.

Very high hot water demand: Large families or households with very high hot water demand benefit from large-capacity thermal systems. Solar thermal tank sizes reach 400L+ easily; heat pump tanks typically max at 270–320L.

The 2026 recommendation for most Perth households

For a Perth household:

• Replacing an old resistive electric hot water system
• Connected to the grid
• Has or is getting rooftop solar

Heat pump hot water is the default recommendation. It:

• Achieves comparable or better running costs to solar thermal when timed to solar/Midday Saver hours
• Costs similarly installed (after STCs)
• Is simpler to install (no roof penetrations, no glycol, no structural load on roof)
• Has no glycol servicing requirement
• Is compatible with any solar system (it's just an electrical load you can time)

Solar thermal remains the better choice in specific scenarios — particularly off-grid and existing-collector situations.

Running costs based on Perth tariff rates effective 1 July 2026 (A1: 33.26c/kWh, Midday Saver super off-peak: 8.85c/kWh). System costs are installed price ranges before STC rebate. Rebate values vary; consult your installer for current STC amounts.