Solar for pool heating vs solar PV in Perth: which gives better value?

Perth's climate supports year-round or near-year-round pool use, but unheated pools can be too cold from May to September (average pool temperature can drop to 17–20°C without heating). Two main approaches use solar energy for pool heating: solar thermal collectors (roof-mounted tubes or panels that heat pool water directly) and heat pump pool heaters powered by your solar PV system. Here's how they compare for Perth.

Solar thermal pool collectors

Solar thermal pool heating uses unglazed (or glazed) collectors mounted on the roof that pump pool water through them. The sun heats the water in the collectors, and the warmed water returns to the pool.

How they work:

• Pool water is pumped from the pool to rooftop collectors
• Water absorbs heat as it passes through the black rubber or poly collectors
• Warmed water returns to the pool
• A controller turns the pump on when collectors are warmer than the pool

Perth performance:

• Summer: Very effective — collectors can gain 10–20°C above ambient temperature
• Autumn/spring: Effective for maintaining comfortable temperature (22–25°C)
• Winter (June–August): Limited — overcast days and short daylight hours mean collectors barely warm above ambient; not effective for keeping pools warm in the coldest months

Cost: $2,000–$5,000 installed depending on pool size and roof space. No electricity running cost for heating (the pump runs anyway for filtration, and the solar controller just determines timing).

Roof requirements: Needs 1–2× the pool surface area in collector area. A 30m² pool needs 30–60m² of collectors — a significant roof area that may compete with PV panels.

Heat pump pool heaters with solar PV

A heat pump pool heater works like a reverse refrigerator: it extracts heat from the ambient air and transfers it to the pool water. Powered by electricity from your solar PV system.

Perth heat pump performance:

• COP (coefficient of performance): 4–7 in Perth's mild climate (extracts 4–7kWh of heat per 1kWh of electricity)
• Winter performance: Even in Perth's mildest winter (average July daily maximum 18°C), heat pumps maintain COP 3–5, making them effective year-round
• Power draw: 1–3kW for residential pool heat pumps; run for 6–10 hours daily in cooler months

Cost: $2,000–$6,000 installed depending on size and brand. Ongoing electricity running cost when pool isn't being heated by solar-generated power.

With solar: A 6.6kW solar system generating surplus between 9am–3pm can run a heat pump (drawing 1–2kW) for the entire midday period, effectively heating the pool from solar at zero grid cost. On Midday Saver (9am–3pm rate: 8.8511c/kWh), pool heating cost is minimal even if drawing some grid power.

Direct comparison for Perth conditions

| Aspect | Solar thermal | Heat pump (solar-powered) | |---|---|---| | Installation cost | $2,000–$5,000 | $2,000–$6,000 | | Ongoing energy cost | Near zero (pump already runs) | Near zero if timed with solar | | Winter performance | Limited (May–September) | Year-round effective | | Roof space required | Large (equal to 1–2× pool area) | Small inverter; no roof area | | Heating capacity | Limited by collector area and sunshine | Consistent; can maintain set temperature | | Lifespan | 10–20 years | 10–15 years | | Pool temperature control | Passive (depends on sunshine) | Active thermostat control |

Which is better for a Perth home that has (or will have) solar PV?

If you already have a full solar system filling your available north-facing roof: A heat pump is clearly better — solar thermal competes for the same roof area where PV is generating revenue. A heat pump powered by your existing solar generates no conflict.

If you don't have solar PV and the roof has room for both: Solar thermal for pool heating is cost-effective for spring and summer use, but won't keep a pool warm in Perth's July–August. If year-round swimming is the goal, a heat pump (even grid-powered) is more effective in winter, though higher running cost.

The most common Perth scenario: Adding solar PV to offset the household bill, then timing a heat pump to run from solar surplus, is the preferred approach for new installations. This maximises solar PV roof area and provides active pool temperature control year-round.

Pool pump timing and solar

Whether you use solar thermal or a heat pump, the pool pump scheduling deserves separate attention. A standard 750W–1,500W pool pump running 8 hours/day costs approximately $700–$1,400/year at A1 rates. Timed to run during solar generation hours (9am–3pm), it runs largely at zero net cost.

A good pool automation timer set to 9am–3pm (and a heat pump in the same window) turns your pool heating from a significant electricity cost into a near-zero one.

Gas pool heaters: not recommended for Perth

Gas pool heaters heat pool water quickly (useful for heating a cold pool rapidly before use), but are expensive to run for sustained heating. At WA residential gas rates ($0.70–$1.10/MJ), gas heating a typical 50,000-litre pool from 18°C to 26°C costs $30–$60 per heating cycle. This is appropriate for occasional/event use but not for maintaining pool temperature over winter.

Gas pool heaters also perpetuate a gas connection — if you're considering removing gas from the property (see the guide on switching to induction), a gas pool heater is a reason to keep the connection and its associated supply charge.

For Perth homes with an existing PV system, a heat pump pool heater timed to run during solar surplus is the optimal approach — year-round effective, no roof space competition with PV, and near-zero running cost. Solar thermal is a viable alternative for households without PV who want low-cost spring/summer heating, but it won't maintain pool temperature through winter.