STC factor (battery)

Written and checked by the Energy Merchants desk · Reviewed 2 October 2026

The STC factor is the number you multiply a battery’s usable capacity by to find its STCs. Under the Cheaper Home Batteries Program, it is 6.8 per kWh for batteries installed in 2026 and steps down to 5.7 on 1 January 2027 and 5.2 on 1 July 2027. It keeps stepping down every six months to 2030.

The formula is short: usable capacity (kWh) x STC factor = STCs.

Worked example

A 10 kWh usable battery installed in 2026 creates 10 x 6.8 = 68 STCs. The same battery installed in January to June 2027 creates 10 x 5.7 = 57. At roughly $38 to $40 per STC at the time of writing, the 11 certificates lost are worth about $420 to $440. For a larger battery the gap grows with the size.

Remember the program’s limits: the battery must have 5 to 100 kWh usable capacity, up to 50 kWh counts, it must be CEC-approved and VPP-capable, installed by an accredited installer, and there is one battery per property. It works with new or existing solar.

In practice

The factor is the battery equivalent of the solar deeming period: a yearly step down that pulls forward demand. Installers who have batteries in the pipeline in late 2026 are watching the December calendar, because the installation date decides the factor. See deeming period for the solar version.

That makes the date of installation critical evidence. Photos, the written statement and the registry entry should all agree. And it means the input has to be right: the factor multiplies usable capacity, not nominal. See nominal capacity for why that matters.

The Cheaper Home Batteries Program installer guide covers the eligibility steps, and the battery submission guide covers evidence.

Common confusion

The STC factor is not the STC price. The factor tells you how many certificates a battery creates. The market price tells you what each is worth. Both move, but for different reasons: the factor on a published schedule, the price with the market.

It is also not the same as the zone rating, which is a solar concept. See zone rating.

For the full process see battery STCs, and for related terms the certificate trading glossary.