Should you improve energy efficiency before getting solar in Perth?

There's a common debate in Perth solar: should you reduce your household energy consumption first, then buy solar sized to your lower consumption — or buy solar first and deal with efficiency later? The answer depends on your specific situation, but the logic of efficiency-first has merit for certain improvements.

The efficiency-first argument

Reducing consumption before sizing solar can shrink the system you need.

If you reduce annual consumption from 9,000kWh to 7,000kWh before sizing solar, you might need a 10kW system instead of a 13.3kW system — saving approximately $2,000–$3,000 on the solar installation. That's money that might otherwise go to solar panels sitting on your roof for 25 years, doing work that a $200 LED light switch prevented the need for.

The flaw in this argument: solar panels get cheaper every year, and oversizing slightly doesn't hurt you (excess generation exports at 10c/kWh). The calculation depends on the marginal cost of adding more solar capacity vs the marginal cost of the efficiency improvement.

Which efficiency improvements come before solar

LED lighting (do this before solar): If you have halogen or incandescent downlights, replacing them with LED is a near-zero-regret move at any time. Payback: typically 6–18 months at Perth electricity rates. A typical Perth home with halogen downlights spends $200–$400/year on lighting — LEDs reduce this by 70–85%.

Cost of LED retrofit (20 downlights): approximately $300–$800. Annual saving: $140–$340. Payback: 1–2 years.

Ceiling insulation (do this before solar in an uninsulated home): Perth's summer heat means uninsulated ceilings dramatically increase air conditioning consumption. A ceiling with R3.5+ insulation can reduce summer cooling loads by 20–30%.

Cost of ceiling insulation (typical Perth home): $1,500–$3,000. Annual saving (reduced AC load): $300–$600 at Perth electricity rates. Payback: 3–5 years — and reduces the size of solar needed for your AC load.

Hot water system (usually do alongside solar, not before): Replacing an old electric resistance hot water system with a heat pump hot water system typically saves $500–$900/year. This can be done alongside solar rather than before — and makes solar economics better (less load to cover means more export or smaller required system).

Appliance upgrades (targeted, not systematic): Replace appliances only when they're near end-of-life and there's a high-efficiency alternative. A working 7-star fridge doesn't need replacing because you're getting solar. A failing 2-star fridge does.

What NOT to prioritise before solar

Draft sealing (order: after solar): Wall and floor draught sealing has paybacks of 5–10+ years in Perth's climate (milder than cold-climate cities). Worth doing eventually but not a priority before solar.

New windows (no, not before solar): Double glazing in Perth's climate has very long paybacks (15–25 years). Perth winters are mild. Don't invest $10,000+ in windows before solar.

Removing a ducted gas system (don't do this before solar): If you have a working ducted gas system, don't remove it pre-solar just to reduce reliance on gas. After solar, you can model whether switching to reverse-cycle ducted RC (running on solar) makes economic sense. Gas removal is an ongoing operational saving, not an upfront efficiency improvement.

The honest order of operations for a Perth home

1. Replace halogen downlights with LED — quick, cheap, immediate saving ✓ Do before solar
2. Insulate ceiling if un/under-insulated — meaningful AC load reduction ✓ Do before solar
3. Replace near-end-of-life electric resistance hot water with heat pump — can be simultaneous with solar
4. Install solar (correctly sized for current + near-term consumption) ✓ The main event
5. Add battery storage — at install or 1–3 years later when prices fall further
6. Gas electrification — replace gas appliances with electric over 5–15 years as they reach end of life

When efficiency improvements make solar sizing simpler

The efficiency-first argument is strongest when:

• You have halogen lighting throughout the house (significant improvement available)
• You have an uninsulated ceiling (high AC load reduction achievable)
• Your current electricity bill is very high (> $3,000/year) and you can't identify specific large loads — fix the loads first so solar is sized to your true base load

For households where the high consumption is from known large loads (EV, pool, ducted AC on a good insulation base), efficiency improvements may be less impactful. Size solar and battery to cover those known loads directly.

A worked example

Household: 4-person Perth home, 10,000kWh/year, halogen lighting, uninsulated ceiling.

| Improvement | Annual saving | Cost | Payback | |---|---|---|---| | LED retrofit (20 downlights) | ~$280/year | $500 | 1.8yr | | Ceiling insulation (R3.5) | ~$420/year | $2,200 | 5.2yr | | Reduced consumption: | 8,300kWh/year | — | — |

Solar system needed after improvements: 10kW (vs 13.3kW before) = saving approximately $2,500 on solar installation.

Total investment in efficiency before solar: $2,700. Solar saving: $2,500. Net cost of efficiency work before solar: effectively $200 — with LED and insulation continuing to pay back thereafter.

In this scenario, doing LED and insulation first is clearly worth it. The key variable is whether your high consumption comes from addressable inefficiency or from unavoidable large loads.

Ceiling insulation and LED lighting are the two Perth efficiency improvements worth doing before solar if you haven't already done them. Both reduce solar system sizing requirements while paying back independently. Everything else — windows, draught-sealing, appliance swaps for working appliances — generally doesn't change the solar calculation enough to justify delaying installation.