Battery STC (BSTC) Calculation Method – Explained
This resource explains how Battery Small-scale Technology Certificates (BSTCs) are calculated under the Australian Government’s Cheaper Home Batteries Program, including how the calculation method is changing from 1 May 2026.
It is intended to help installers, retailers, and homeowners understand how installation timing and battery size affect the value of BSTCs.
What are Battery STCs (BSTCs)?
Battery STCs (often referred to as BSTCs) are certificates created under the Small-scale Renewable Energy Scheme (SRES) for eligible battery systems installed in conjunction with solar PV.
Each certificate represents a unit of government support and is usually applied as an upfront discount to reduce the installed cost of a battery system.
Background: Why the calculation is changing
In December 2025, the Australian Government announced an expansion of the Cheaper Home Batteries Program:
- Program funding increased from $2.3 billion to $7.2 billion over four years
- The program is expected to support around 2 million battery installations by 2030
- An estimated 40 GWh of additional storage capacity expected nationwide
As part of this expansion, the Government confirmed changes to BSTC calculations to:
- Ensure the scheme remains viable through to 2030
- Reflect reductions in battery technology costs over time
- Maintain an average upfront discount of around 30%
Key dates
Changes announced: December 2025
Changes take effect: 1 May 2026
BSTCs are calculated based on the battery commissioning date. The commissioning date determines which STC factor and rules apply, and the value is locked in at that time.
How BSTCs were originally calculated
Under the original method, the number of BSTCs created was based on:
- Usable battery capacity (kWh)
- A government-set STC factor
- A fixed formula converting capacity × factor into certificates
In simple terms:
Higher usable capacity × higher STC factor = more BSTCs
The STC factor was originally designed so that the discount equated to approximately 30% of the battery’s upfront cost.
What changes from 1 May 2026
From 1 May 2026, BSTC calculations change in two important ways:
- More frequent reductions to the STC factor
- Tapered STC value based on battery size
Both changes apply only to batteries commissioned on or after 1 May 2026.
1️⃣ More frequent STC factor reductions
From 1 May 2026:
- The STC factor will be reduced every six months
- Reductions will occur more rapidly over time than originally proposed
The applicable factor is determined by the commissioning date, not the sales date or contract date.
STC factor changes
| Year | Period | Existing STC factor | Proposed STC factor |
|---|---|---|---|
| 2026 | January – April | 8.4 | 8.4 |
| 2026 | May – December | 8.4 | 6.8 |
| 2027 | January – June | 7.4 | 5.7 |
| 2027 | July – December | 7.4 | 5.2 |
| 2028 | January – June | 6.5 | 4.6 |
| 2028 | July – December | 6.5 | 4.1 |
| 2029 | January – June | 5.6 | 3.6 |
| 2029 | July – December | 5.6 | 3.1 |
| 2030 | January – June | 4.7 | 2.6 |
| 2030 | July – December | 4.7 | 2.1 |
These factors are subject to confirmation by the Clean Energy Regulator and should always be checked at the time of installation.
2️⃣ Tapered STC value by battery size
From 1 May 2026, BSTC support will taper based on usable battery capacity:
- 0–14 kWh (inclusive): STC value applied at 100%
- Greater than 14 kWh up to 28 kWh (inclusive): STC value applied at 60%
- Greater than 28 kWh up to 50 kWh (inclusive): STC value applied at 15%
This means that larger batteries still receive support, but the marginal BSTC value reduces as capacity increases.
Worked examples
Example 1: 14 kWh battery
If one 14 kWh battery is commissioned during a period where the STC factor is 6.8:
14 kWh × 6.8 = 95.2 BSTCs
Rounded down to 95 BSTCs
Example 2: 26 kWh battery
If one 26 kWh battery is commissioned during the same period:
First 14 kWh at 100%
14 kWh × 6.8 = 95.2
Remaining 12 kWh at 60%
12 kWh × 6.8 × 60% = 57.12
Total BSTCs
95.2 + 57.12 = 152.32
Rounded down to 152 BSTCs
What this means for installers and homeowners
Installation timing matters
- Earlier commissioning dates generally result in higher BSTC values
- BSTCs are locked in at commissioning, not at quote stage – properties such as houses under construction may result in changes to the eligible STCs based on construction timelines.
Battery sizing matters
- Typical household battery sizes receive the highest proportional support
- Larger systems still qualify, but with reduced marginal certificate value
This is important when designing systems and explaining expected discounts to customers.
Using this page with customers
This resource may be shared with homeowners to help explain:
- Why BSTC values change over time
- Why different battery sizes receive different discounts
- Why installing earlier may result in a higher upfront discount
For exact certificate numbers, always refer to the official Clean Energy Regulator Solar Battery STC Calculator.
Important note
BSTC eligibility, STC factors, and calculation rules are set by the Australian Government and administered by the Clean Energy Regulator. Figures provided here are indicative only and may change. Final certificate numbers should always be confirmed at the time of commissioning.