Three illustrative quote checks

These are invented worked examples to explain the method—not customer quotes, market averages, testimonials or current offers.

1. The bigger battery with a cheaper unit price

Quote A: $8,200 for 13.5 kWh = $607/kWh. Quote B: $10,500 for 20 kWh = $525/kWh. B has the lower unit price but costs $2,300 more. With 12 kWh of daily solar export and 7 kWh used at night, our 90%-efficiency model supports about 8 kWh of useful daily storage. Both may be larger than the household can routinely use. Extra capacity needs a separate backup or tariff case.

2. The cheaper quote without backup

Two 10 kWh systems cost $7,000 and $8,000. If only the second includes backup hardware and the required circuits, the $1,000 gap is not a like-for-like price difference. Ask both installers to itemise the same scope.

3. The rebate counted twice

A 13.5 kWh eligible May–December 2026 installation estimates 91 STCs. At an assumed $37 per certificate, that is $3,367 before fees. If a quote already says “$8,200 after rebate”, enter $8,200—not $4,833—in the payback tool.

Get these inclusions in writing

  • Exact battery and inverter models, usable capacity and continuous output.
  • Final installed price, GST, certificate count and certificate value.
  • Backup circuits, reserve settings, metering, switchboard work and approvals.
  • Battery throughput limits, retained-capacity warranty, labour and call-out cover.
  • Payback using your interval data, not a generic household.

Our comparison does not verify installer accreditation, electrical compliance or product reliability. Read the methodology and the Australian Government solar guidance.