Australia's solar installation industry processes hundreds of thousands of residential and commercial installations per year, making it one of the highest-volume compliance environments for bookkeepers. The interaction between the Clean Energy Regulator's certificate schemes, the GST system, and consumer guarantee warranty obligations creates specific accounting requirements that differ materially from general trade contracting. Getting the STC treatment wrong means every installation is misposted — and the error compounds across a high-volume operation.
Small-Scale Technology Certificates: The Point-of-Sale Discount Mechanism
Small-scale Technology Certificates (STCs) are created under the Small-scale Renewable Energy Scheme once an eligible system (solar PV, solar water heater, air source heat pump, small wind or hydro) has been installed. The number of STCs depends on the system's size, its location (zone) and the remaining deeming period, which shrinks each year until the scheme ends in 2030. Registering or creating an STC on the REC Registry does not attract GST.
The right to create the STCs belongs to the system owner, not the installer. In the usual arrangement, the owner assigns that right to the installer (or to a third-party REC agent) in exchange for an up-front discount on the purchase and installation price. The customer pays the net amount, and the installer (or agent) then creates the STCs and sells them.
GST on the installer's sale: the full price, not the discounted price
The ATO's position is explicit: the installer calculates GST on the full price of the system and installation, not the discounted or reduced amount the customer pays. The STC discount is not a reduction in the price of the installer's supply. It is the customer paying part of that price with their STC entitlement instead of cash.
The ATO's own example: an installer supplies a solar water heater for a GST-inclusive price of $7,700, shows an STC up-front discount of $1,000 on the invoice, and collects $6,700. The installer's GST is $700, which is one-eleventh of $7,700, not of $6,700.
Applied to a typical solar PV job:
| Amount | |
|---|---|
| System and installation (GST-inclusive) | $10,000.00 |
| Less STC up-front discount | ($2,000.00) |
| Customer pays | $8,000.00 |
| Installer's GST liability (1/11 of $10,000) | $909.09 |
Calculating GST on the $8,000 cash received ($727.27) under-reports GST by $181.82 on this one job. Across a high-volume installer, that error repeats on every residential installation. It is also why the customer's invoice legitimately shows GST of more than 10% of what they paid. The ATO warns homeowners to expect exactly that.
The same rule applies when a separate REC agent, not the installer, takes the STC assignment and pays the discount amount to the installer. In the ATO's example, the installer's GST is still one-eleventh of the full $4,400 price. The $600 the agent pays is part of that $4,400, not an extra supply.
GST credits on the STC assignment: it depends on who the customer is
- Homeowner or other unregistered owner: the assignment of the right to create STCs is not a taxable supply. The installer or REC agent cannot claim a GST credit for the value of the discount.
- GST-registered business owner using the system in the business: the assignment is a taxable supply by the business. The owner pays GST based on the amount of the up-front discount and must issue a tax invoice if it exceeds $82.50 (GST-inclusive). The installer can then claim a GST credit, but only with that tax invoice.
GST on selling the STCs
When the installer or REC agent later transfers or sells the STCs (to a trader, a liable entity, or through the STC Clearing House), that sale is a taxable supply if the seller is registered or required to be registered for GST.
Worked journals: residential job
Continuing the $10,000 example, where the customer is a homeowner and the installer sells the STCs to an agent for $2,000 plus GST:
At installation
Dr Bank 8,000.00
Dr STCs held (asset) 2,000.00 no GST credit (homeowner assignment)
Cr Sales – installations 9,090.91
Cr GST collected 909.09
On sale of the STCs
Dr Bank 2,200.00
Cr STCs held (asset) 2,000.00
Cr GST collected 200.00
The two GST amounts ($909.09 + $200.00) both go to label 1A, and both sales go to G1. Any difference between the discount given and the price the STCs actually sell for is a gain or loss on the STC asset.
Bank-feed coding alone will not produce this result: the bank shows an $8,000 deposit, and coding it as a GST sale gives $727.27. The extra $181.82 has to come from the invoice, either by coding the invoice at its full value or by posting the STC leg as a split or journal.
For a GST-registered business customer, add a GST credit (label 1B) for the GST on the STC assignment, supported by the customer's tax invoice.
Large-scale Generation Certificates for Commercial Systems
For commercial or industrial rooftop systems above 100kW, the relevant certificate is the Large-scale Generation Certificate (LGC) under the Renewable Energy (Electricity) Act 2000. LGCs are created based on the actual generation of eligible generators in megawatt-hours and accredited under the Large-scale Renewable Energy Target (LRET).
For large-scale commercial solar installations, the system owner (the business, not the installer) typically retains and surrenders or trades the LGCs. The installer's revenue recognition is based on the installation contract price — the customer pays for the system and manages the LGC stream thereafter. In these cases, the installer's books are simpler: the full contract price is revenue (taxable supply, 10% GST), and the customer's subsequent LGC creation and trading is a separate matter.
Where an installer does enter into a contract that includes LGC creation and trading as part of the service bundle (for example, a power purchase agreement structure), the LGC component is a separate income stream — assessable at market value when certificates are created or sold, with GST on the LGC sale (they are taxable supplies).
Revenue Recognition on Installation Contracts
Most residential solar installations are straightforward: a single performance obligation (supply and install the system), satisfied when the system is installed, commissioned, and connection approval obtained from the distribution network. Revenue is recognised at the point of commissioning — AASB 15 point-in-time recognition.
Commercial installations with longer construction phases — large rooftop systems on industrial or agricultural sheds, multi-building installations, or multi-stage community solar projects — may involve contracts where revenue is recognised over time (AASB 15 percentage-completion) rather than at a single point. For these engagements, a WIP schedule should be maintained as for any construction contract, with progress claims billed against milestones and contract assets/liabilities recognised for any timing difference between billing and revenue.
GST on Battery Storage Add-Ons
Battery storage systems (e.g., Tesla Powerwall, SolarEdge, Fronius Primo hybrid systems) are taxable supplies — there is no GST-free treatment for battery storage equipment, even when sold as part of a solar installation package.
Where solar panels and batteries are sold as a bundled package, the entire bundle is a taxable supply at 10% GST. There is no legal basis for carving out the solar panel component as "clean energy infrastructure" with a reduced or zero GST rate — the GST Act does not contain such an exemption. Installers who structure invoices to allocate a disproportionate amount to hypothetically "GST-free" components are applying incorrect treatment and risk penalties on audit.
The STC rules described above apply to the bundled package too. The number of STCs is driven by the solar component, but the installer's GST is calculated on the full GST-inclusive price of the whole package before the STC discount, not on the net cash the customer pays.
Warranties and the Consumer Guarantee Provision
Under the Australian Consumer Law (ACL, Schedule 2 to the Competition and Consumer Act 2010), major components of a residential solar installation — the panels and inverter — carry consumer guarantee obligations for a period that reflects what a consumer would reasonably expect for such goods. Industry standard is effectively 10 years for panels and 5–10 years for inverters, based on manufacturer warranty periods and the reasonable consumer expectation standard.
For high-volume installers (50+ systems per month), a warranty provision should be recognised at balance date. The provision represents the estimated cost of future warranty call-outs and component replacements on systems already installed. Under AASB 137 Provisions, Contingent Liabilities and Contingent Assets, a provision is recognised when the entity has a present obligation (the warranty exists), it is probable that a transfer of economic benefits will be required, and the amount can be reliably estimated.
A reasonable methodology is to apply a historical warranty cost rate (total warranty costs incurred ÷ total systems installed in prior periods) to the current year's installations to estimate the provision. If the average warranty cost per system is $150 and 800 systems were installed this year, the provision is $120,000. Adjust the rate as actual experience develops.
End-of-Period Checklist for Solar Installer Bookkeepers
- Review all installations with an STC up-front discount: confirm GST was reported on the full GST-inclusive price before the discount, not on the net cash the customer paid
- Check GST credits on STC assignments: claim them only where the system owner is GST-registered, uses the system in their business, and has issued a tax invoice. Reverse any credits claimed on homeowner assignments
- Reconcile the STCs held account: every STC sale to an agent or the Clearing House should be recorded as a taxable sale, with any gain or loss against the discount value recognised
- Review commercial solar installations above 100kW: confirm LGC creation and trading income is recognised separately if the installer is involved in the LGC stream
- Confirm all battery storage sales are coded as taxable supplies at 10% GST — no GST exemption applies to clean energy equipment
- For contracts in progress at balance date: prepare WIP schedules and assess percentage completion; recognise contract assets or liabilities for timing differences
- Calculate the warranty provision at balance date using historical warranty cost rates; adjust the provision for any warranty call-outs resolved during the period
- Confirm EMDG receipts (if the firm exports solar technology or services) are coded as assessable income, not GST supplies