When you buy a solar system, the government rebate is calculated as if the system were going to produce power for a fixed number of years, and it pays you for all of them at once. That number of years is the deeming period.
In plain terms
A solar system produces electricity for 25 years or more. The rebate scheme does not wait that long. It estimates how much clean energy the system will generate over a set number of years, converts that into certificates called STCs, and your installer turns the certificates into a discount on your price.
For 2026 the deeming period is 5 years. For 2027 it drops to 4, and it falls by a year every January until it reaches 1 in 2030. The scheme closes on 31 December 2030.
What it means for the rebate
The rebate is the system size, times a zone rating for your postcode, times the deeming period, times the price of a certificate. For a 6.6 kW system in zone 3 in 2026, that is about 45 certificates. At roughly $38 to $40 each, that is about $1,700 to $1,800. In 2027, at 4 years, the same system earns about 36 certificates, worth about $1,370 to $1,440.
What it does not mean
It does not mean your panels stop working after 5 years. It does not change your warranty. It does not change how much you save on bills. It only affects the discount you get on the day you install.
Another way to see it
Imagine the rebate as an advance on five years of generation, paid on day one. The government decides how many years it will advance, and that number is shrinking. In 2030 it advances one year only, and then the scheme closes. The panels continue to generate after that, and you continue to benefit on your bills.
What this means for you
If you are planning solar, the rebate is largest this year, but the decision should still stand on your usage, roof and bills. See should I install solar now or wait, the schedule by year, and the deeming period resource. Our STC trading pillar explains how installers turn certificates into your discount.