How to read and compare solar quotes in Perth

Getting three solar quotes is standard advice. But if you don't know what to look for, comparing quotes from three different Perth installers is like comparing three menus written in different languages — the totals don't mean the same thing.

Here's how to read a Perth solar quote and find the genuine differences.

Core components every quote should specify

Panels

A quote should name the panel brand, model, power rating (Watts), and number of panels.

What to look for:

• Tier-1 vs budget panels: "Tier 1" is a common claim but isn't a regulated certification. Check the panel brand's reputation, warranty terms, and whether it has CEC approval.
• Power rating: a 410W panel vs a 420W panel on the same string — small but calculable difference
• Efficiency (%): higher efficiency = more power per m² of roof area. Matters if roof space is limited
• Product warranty (materials, usually 10–15yr) vs performance warranty (output, usually 25yr). Both should be in writing from the manufacturer, not just stated by the installer

Inverter

What to look for:

• Brand and model number specifically
• Inverter capacity (kW): must be ≤ 133% of panel array capacity under CEC guidelines (6.6kW panels → 5kW inverter is standard; 13.3kW panels → 10kW inverter)
• Warranty: most quality inverters carry 5–10yr manufacturer warranty; extended warranties to 15yr are available for some brands
• Monitoring: does the inverter include online monitoring? Web portal vs app? Check the ongoing cost — some monitoring platforms charge a subscription after the first year

Installation and Western Power fees

This is where quotes diverge most. Items that should be listed separately:

• Installation labour (panel mounting, wiring, switchboard work)
• Scaffolding or roof access equipment (if needed)
• Western Power connection application fee (usually passed through at cost)
• Smart meter upgrade (if required — this is a WP charge, typically $250–400)

Quotes that lump these together are harder to compare.

STCs and how they affect the bottom-line price

Small-scale Technology Certificates (STCs) are the federal government's solar rebate mechanism. For a Perth (Zone 3) 6.6kW system installed in 2026:

• STC count: approximately 6.6 × 1.382 (zone factor) × 5 (deeming period) × 4.3 × [STC spot price ~$34–$38] = approximately 70–80 STCs × $34–$38 = approximately $2,400–$3,000 of value
• Installers almost always assign STCs to themselves and discount the quote price accordingly
• The STC "discount" is displayed as a reduction on the quote

What to check: the STC calculation should be disclosed in the quote. If two quotes show different STC discounts for the same system size, they may be using different deeming assumptions or spot-price estimates. Ask for the calculation if it isn't shown.

Generation estimates in quotes

Most Perth solar quotes include an estimated annual generation figure (e.g. "your 6.6kW system will generate approximately 9,500 kWh/year").

What to verify:

• Does the estimate account for your roof orientation and tilt? A quote using generic "north-facing" assumptions for a system that will actually face north-west will overestimate.
• Does it assume 100% system efficiency or a realistic 79–82% derate? Systems lose approximately 15–20% between panel nameplate and actual generation due to inverter efficiency, temperature, soiling, cable losses, and mismatch.
• Is the estimate from a modelling tool (PVWatts, PVsyst) or a rough calculation? Ask what tool was used.

A realistic Perth estimate for a north-facing 6.6kW system: approximately 9,000–9,800 kWh/year (depending on shading, efficiency, and modelling assumptions).

Comparing quotes: the right method

1. Standardise the system: compare quotes for the same panel count and inverter size. If one quote has 20 panels and another has 18, you're not comparing the same thing.

2. Compare $/Wp (dollars per watt-peak): divide the total quoted price by the total panel wattage. A 20 × 410W = 8,200Wp system at $7,380 = $0.90/Wp. This normalises for system size.

3. Separate hardware from labour: some premium products (Fronius inverter, Tier-1 panels) cost more but deliver longer warranties and better monitoring. A cheaper quote might be saving on labour (faster installation, less care) rather than hardware.

4. Check what's excluded: is the WP connection fee included? Is scaffolding included? Is monitoring included? One quote might appear $400 cheaper but exclude a $350 WP connection fee.

5. Check installer CEC accreditation: CEC accreditation is required for the system to be eligible for STCs and for WP connection approval. Verify via the CEC installer finder (a free online check).

Red flags in solar quotes

• No manufacturer warranty documentation (only installer's verbal warranty)
• System size that exceeds CEC guidelines without explanation (e.g. 13.3kW panels on a 5kW inverter)
• No Western Power connection application mentioned (system may not be legally commissioned)
• STC discount not itemised
• Generation estimate significantly above realistic Perth norms without explanation
• Payment in full required before installation begins (reputable installers typically require a deposit then final payment on commissioning)

STC values change with spot market pricing. Estimates current for Zone 3 Perth, June 2026.