Search “milestone payment billing software for solar installers” and every result is the same: a vendor feature page or a listicle showing screenshots of an invoicing dashboard. Not one of them explains how a milestone structure actually works before pitching you a subscription. That is backwards. The software is the easy part. The hard part is getting the payment stages, the deposit limits and the contract wording right, because that is what decides whether you get paid on time or spend three months chasing a final invoice.

I have spent twenty years around the business side of solar: sales, supply, admin, and trading certificates. The single most common way I have watched otherwise good install businesses bleed cash is not a bad job. It is a payment schedule that does not match how the money and the work actually flow. So before we talk about software, let us talk about the structure it is supposed to support.

What a milestone payment structure actually is

A milestone structure breaks the total contract price into staged payments, each one triggered by a defined event in the job rather than by a calendar date. For a standard residential solar install, the sequence usually looks like this:

That last stage is where most installers get the wording wrong, and I will come back to it, because it is the single most important line in the whole schedule.

Staged progress payments are not a solar invention. They are standard across the construction trades and are backed by security of payment legislation in every state (Queensland Building and Construction Commission, n.d.). Solar just has its own rhythm: the STC assignment, the distributor connection approval, the supplier lead times. A generic invoicing tool does not know any of that. It will happily let you send a “50% on completion” invoice that ignores the two weeks your cash is stuck waiting on a metre.

The deposit: where consumer law bites first

The first milestone is the one most likely to land you in trouble, because it sits directly on top of consumer protection rules.

Under the Australian Consumer Law, most solar sales that happen in the customer’s home count as unsolicited consumer agreements, which carry a cooling-off period (commonly ten business days) during which the customer can cancel and get their money back (Australian Competition and Consumer Commission, n.d.). Cooling-off rules and deposit handling also vary by state, and the practical mechanics of a cancellation are messier than the law makes them sound (Sprintlaw, n.d.). If you have taken a fat deposit and ordered stock inside that window, a cancellation can leave you carrying the cost.

On top of that, deposit caps apply in various forms depending on the state and whether the work is classified as residential building work. Several state building regimes limit deposits on larger residential contracts to a set percentage of the contract price, so you cannot assume a big up-front payment is always allowed. The safe operating rule is simple: keep the deposit modest, know your state’s cap before you set it as a default, and never let the deposit be so large that a lawful cancellation puts you underwater. I have written more on getting this balance right in solar deposits and consumer rights and on cooling-off and cancellation.

The point for your billing setup: the first milestone is not just a number you like. It is a number the law constrains, and it should be one your software can validate rather than one you eyeball each time.

Why the final milestone must be tied to connection, not “install complete”

Here is the line that saves the most disputes. Tie your final payment to grid connection sign-off, not to “installation complete”.

“PTO”, permission to operate, is American shorthand. In Australia the equivalent is permission to connect: the distributor (your DNSP) approving the system to energise and export after the install and the required paperwork are done. The gap between “panels on the roof” and “approved to operate” can be days or it can be weeks, and almost all of that delay is outside your control.

If your contract says the balance is due “on completion of installation”, you have handed the customer an argument. The panels are up, the job looks finished, and they will happily pay you, except the meter has not been reconfigured, the system is not exporting, and now they are withholding the final payment over something you did not cause. You end up financing the distributor’s queue.

Word it the other way and the problem inverts in your favour. If the final milestone is triggered by connection approval, everyone understands from day one that the last payment follows the distributor’s sign-off. When the connection lags, the customer is not surprised, and you are not accused of leaving the job unfinished. Same delay, completely different conversation, purely because of one clause.

Contract wording and payment sequencing the competitors ignore

None of the ranking software pages tell you how to word a milestone clause or how to sequence your own outgoings against it. That is the actual work.

Two wording principles carry most of the weight. First, define each trigger by an objective, verifiable event: “materials delivered to site”, “installation of panels and inverter complete”, “connection approval received from the distributor”. Vague triggers (“substantial completion”) are dispute fuel. Second, state clearly what happens when a milestone stalls for reasons outside your control, so a distributor delay does not become a payment default.

Then there is sequencing, which is where cash flow quietly lives or dies. Your milestones on the customer side have to be set against your obligations on the supply and labour side. You are usually paying suppliers for panels and inverters before or at delivery, and paying subbies at or shortly after install. General contractor payment terms in Australia lean toward shorter cycles than most operators plan for (Asanify, n.d.). If your progress payment at delivery does not cover your supplier bill for those materials, you are funding the gap out of your own working capital.

And your STC cash is its own milestone that customers never see. The certificates are created and assigned around the install, but the cash from trading them lands on its own timeline, which is why late paperwork on that front is one of the most expensive habits in the trade. I have written separately about the STC lodgement cash flow gap and how it interacts with your progress payments. For the record, STCs are not a rebate: they are tradeable certificates created from a system’s deemed generation that liable entities must buy and surrender to the Clean Energy Regulator under the Renewable Energy Target. That distinction matters when you are forecasting when the money actually arrives.

When a milestone stalls: your recourse

Even with clean wording, a customer will sometimes withhold a payment they owe. This is where installers underuse the strongest tool they have.

Security of payment legislation gives you a statutory right to claim progress payments and to escalate through adjudication if a valid payment claim goes unpaid, without going to court (Queensland Building and Construction Commission, n.d.). The catch is that the process is strict on form and timing: a payment claim has to be worded correctly and served within the right window, or you lose the protection (payclaim.com.au, n.d.). Guides written for the broader building trades walk through the adjudication steps in detail (Boss Lawyers, n.d.).

Two practical takeaways. Structure your milestone invoices so each one can stand as a valid payment claim if it comes to that, which means clean records tying each invoice to a completed, evidenced stage. And know that if you engage subbies, retention and trust-account rules may apply to money you hold back on their work (Housing Industry Association, n.d.). Getting paid and paying your crew correctly are two sides of the same audit trail. I have covered the crew side in managing solar subcontractors.

What this means for the software you choose

Now the software conversation makes sense, because every requirement falls out of the structure above rather than out of a feature list.

Most invoicing tools marketed to solar can send a staged invoice (smarfle, n.d.; trustpro.io, n.d.), and there are plenty of options to compare (Service Business Academy, n.d.). The gap is that generic invoicing does not understand the solar payment calendar, which is exactly the working-capital squeeze that quietly kills margins (SurgePV, n.d.). This is the problem I am building CurrentFlow to solve: billing that follows the real deposit, permitting, install and connection stages of a job rather than treating them as generic line items. It is the tool I wanted when I was watching good operators lose money to admin they did not have time for. If you are done running billing out of three disconnected tools, that three-tool problem is worth reading too.

Get the structure right first. The software should enforce a payment schedule you have already thought through, not invent one for you.

References

Asanify. (n.d.). Payment terms for contractors in Australia: Key points. https://asanify.com/blog/contractor-management/payment-terms-for-contractors-in-australia/

Australian Competition and Consumer Commission. (n.d.). Contracts. https://www.accc.gov.au/consumers/buying-products-and-services/contracts

Boss Lawyers. (n.d.). Security of Payment Act Queensland: How to use the BIF Act to get paid. https://bosslawyers.com.au/security-of-payment-act-queensland-bif-act-guide/

Housing Industry Association. (n.d.). Requirements for retention trust accounts. https://hia.com.au/resources-and-advice/working-with-contractors/requirements-for-retention-trust-accounts

payclaim.com.au. (n.d.). How to write a payment claim under the Security of Payment Act. https://payclaim.com.au/how-to-write-a-payment-claim-under-the-security-of-payment-act-australia/

Queensland Building and Construction Commission. (n.d.). Contracts and payments. https://www.qbcc.qld.gov.au/home-owner-hub/build-renovate/contracts-payments

Queensland Building and Construction Commission. (n.d.). Industry guide to security of payment laws. https://www.qbcc.qld.gov.au/sites/default/files/documents/guide-security-payment.pdf

Service Business Academy. (n.d.). Top 6 invoicing software for solar companies 2026. https://servicebusinessacademy.org/top-6-invoicing-software-solar-installation-companies-2026/

smarfle. (n.d.). Solar invoicing software. https://www.smarfle.com/business/solar/invoicing

Sprintlaw. (n.d.). Cooling-off periods in Australian contracts: Essential legal guide. https://sprintlaw.com.au/articles/cooling-off-periods-in-australian-contracts-essential-legal-guide/

SurgePV. (n.d.). Solar installer cash flow management. https://www.surgepv.com/blog/solar-installer-cash-flow-management

trustpro.io. (n.d.). Solar installer software: Proposals, milestones and payments. https://www.trustpro.io/crm-for-solar

FAQ

What is a standard milestone payment structure for a residential solar install?

A common structure is four stages: a modest deposit on contract signing, a progress payment at materials delivery or permitting, a progress payment when the physical install is complete, and a final payment when the system receives grid connection sign-off. The exact percentages vary, but the principle is that each payment is triggered by a defined job event rather than a calendar date, so your billing tracks the work and the cash you have tied up.

It depends on your state and how the work is classified. Several state building regimes cap deposits on larger residential contracts at a set percentage, and consumer law adds a cooling-off period for in-home sales during which the customer can cancel and reclaim their money (Australian Competition and Consumer Commission, n.d.). Check your state’s rules before setting a default deposit, and keep it small enough that a lawful cancellation does not leave you out of pocket on ordered stock.

Why tie the final payment to grid connection instead of install completion?

Because the gap between the panels going up and the system being approved to operate is usually outside your control, and it can run to weeks. If your contract says the balance is due “on completion of installation”, a customer can withhold it while the distributor’s connection is still pending, effectively making you finance the delay. Tying the final milestone to connection sign-off sets that expectation from day one and removes the most common final-payment dispute.

What can I do if a customer refuses to pay a milestone invoice?

Security of payment legislation gives you a statutory right to claim progress payments and escalate to adjudication without going to court, provided your payment claim is worded correctly and served within the required timeframe (Queensland Building and Construction Commission, n.d.). The practical requirement is that each milestone invoice is backed by clean, timestamped evidence of the completed stage, so it can stand as a valid payment claim if you need it to.

Do I need dedicated solar billing software, or will generic invoicing do?

Generic invoicing can send a staged invoice, but it does not understand the solar payment calendar: supplier bills falling due before delivery, STC cash arriving on its own timeline, and connection approvals lagging the physical install. Software built around the real deposit, permitting, install and connection stages can trigger invoices off job events, validate deposit limits, and flag at-risk milestones automatically. This is exactly what CurrentFlow is designed to do, and you can join the waitlist to follow along as it is built.