5kW vs 6.6kW Solar Systems in Australia — 2026 Comparison

Output and who each size suits

A 5kW array often suits smaller households using roughly 12–18 kWh/day or roofs with limited unshaded space. A 6.6kW system is the popular family default and can deliver roughly 20–33 kWh/day depending on city sun hours before losses. If you work from home, run a pool pump by day, or expect an EV, 6.6kW usually ages better. Shade and orientation still beat raw kilowatts — a clean 5kW north roof can outperform a compromised 6.6kW layout. Keep decisions grounded in your interval data, roof constraints and written DNSP settings rather than national averages or salesperson screenshots. Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Save PDFs of every plan, approval and datasheet — warranty claims years later depend on that trail.

STC and price delta in 2026

Larger eligible capacity creates more STCs. In Zone 3, MrSolar’s table points to about $1,076 for 5kW and $1,435 for 6.6kW at $39.85 as of 2026-08-05; Zone 4 figures are lower (about $917 vs $1,235). After STC, many metro 6.6kW quotes land near $5,000–$8,000 (often $5,000–$7,500 in competitive markets). The incremental hardware cost from 5kW to 6.6kW is frequently modest relative to the extra lifetime kWh — unless export limits strand the surplus. Ask the installer to show the certificate or voucher maths with your postcode, the $39.85 spot assumption (as of 2026-08-05) where STCs apply, and a separate line for any Cheaper Home Batteries Program dollars (~$372/kWh usable since 1 July 2025). Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Photograph your switchboard and roof planes before quoting day to cut variation risk.

Inverters, clipping and export limits

6.6kW of panels on a 5kW inverter is a common Australian design that accepts some midday clipping. On export-limited streets in Sydney, Adelaide or SEQ, clipping may barely matter because you could not export the peak anyway. Ask your DNSP pathway via the installer. If you are firmly export-capped at 5kW and have little daytime load, jumping to 6.6kW needs a self-consumption story — or a future battery plan. Model bill outcomes with a conservative FiT (often 3–5c/kWh stress-test) and your real weekday daytime load — exported energy rarely beats displacing retail imports in 2026. Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Save PDFs of every plan, approval and datasheet — warranty claims years later depend on that trail.

Battery and EV headroom

If a battery is likely, slightly more daytime PV helps charge storage after the Cheaper Home Batteries Program discount (~$372/kWh usable since 1 July 2025). EV daytime charging similarly favours 6.6kW over 5kW when the roof allows. Do not buy unused capacity “for later” without a switchboard and inverter pathway. Size usable kWh to your 4pm–9pm consumption, confirm CEC listing, and keep federal (~$372/kWh usable) and any state battery support itemised — never as one mystery “government discount”. Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Photograph your switchboard and roof planes before quoting day to cut variation risk.

Decision rule

Pick 5kW when space, budget or tiny loads dominate. Pick 6.6kW when family loads, modest future growth and competitive pricing align. Compare three CEC-accredited quotes on MrSolar with identical inclusions so the size debate is about energy, not missing scaffolding lines. Keep decisions grounded in your interval data, roof constraints and written DNSP settings rather than national averages or salesperson screenshots. Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Save PDFs of every plan, approval and datasheet — warranty claims years later depend on that trail.

Roof layout and future expansion

If your roof can host 6.6kW cleanly today, installing 5kW “to be safe” often leaves the cheapest expansion opportunity on the table — second visits cost scaffolding twice. Conversely, forcing 6.6kW across shaded hips just to hit a marketing size wastes STCs on underperforming modules. Bring a roof photo set and preferred panel wattage to each CEC-accredited quote via MrSolar. A site assessment with photos, stringing plan and shade notes beats brochure layouts; mismatched orientations need separate MPPTs or module-level electronics. Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Photograph your switchboard and roof planes before quoting day to cut variation risk.

Bill modelling checklist before you choose

Compare displaced imports at your retail rates, not FiT income. Stress-test both sizes with a 3–5c export assumption and your actual weekday daytime load. If a battery is likely under the Cheaper Home Batteries Program (~$372/kWh usable), note how each array fills storage by late afternoon. Keep decisions grounded in your interval data, roof constraints and written DNSP settings rather than national averages or salesperson screenshots. Use this comparison to brief installers with a clear preference and a fallback — then price both options with the same CEC-accredited shortlist via MrSolar so hardware choices stay constant. Save PDFs of every plan, approval and datasheet — warranty claims years later depend on that trail.

Compare 5kW and 6.6kW side by side — request up to three CEC-accredited quotes on MrSolar.

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