What is a deeming period?

The deeming period is a fixed window set under Australia's Small-scale Renewable Energy Scheme (SRES) that determines how many years of Small-scale Technology Certificates (STCs) a solar photovoltaic system can claim when first installed. Rather than earning certificates over time as the system generates electricity, owners receive the full certificate entitlement upfront, based on the deeming period in place when the system is installed.

Each year, the deeming period shortens by one year. A system installed in 2024 can claim STCs for approximately eight years upfront. By 2025, new systems will have roughly seven years. This decline continues annually until the deeming period reaches zero on 1 January 2030, when no new systems will be eligible for upfront certificate claims.

The deeming period directly affects the rebate size because more years of certificates mean a larger upfront discount. As the period shortens year to year, the financial incentive for installing solar diminishes, which influences purchase decisions across Perth Metropolitan and Australia. For householders and businesses evaluating solar investments, understanding where the system falls in the deeming period countdown is critical to calculating the total net cost after rebates. Government-registered retailers and installers use the deeming period to calculate how many STCs each system qualifies for and convert that to the cash rebate available at the point of sale.