How STC Values Change Over Time
Why people get confused about “STCvalue”
When people say “theSTC rebate is dropping”, they often mean two different things.
· The number of STCs a new system can create can reduce over time because the deeming period steps down.
· The dollar value per STC can move because STCs are traded.
Understanding the difference helps you make sense of headlines and makes quote comparisons much easier.
The STC count steps down over time
For solar PV systems,the number of certificates you can create is tied to a deeming period. That period reduces over time as part of the scheme design.
The practical effectis straightforward: all else equal, a system installed later may create fewer STCs than the same system installed earlier.
In plain terms, the scheme assumes a solar system will generate renewable energy benefits over aset number of years. Each year, that assumed period steps down a little. Fewer years means fewer certificates.
You will often hear that the deeming period reduces by one year each year until the step-downcompletes. The exact schedule is set by the scheme, so it is worth confirming the current rules when you are close to installing.
A simple example to make it concrete
Say two households install the same sized system in the same location, but one installs earlier and one installs later after a step-down. The later system can create fewer STCs, which means a smaller discount if the STC price is similar.
That does not automatically mean the later household made a bad decision. Electricity prices, feed-in tariffs, and household usage might have shifted in the meantime. The step-down is just one piece of the puzzle.
Location affects the STC count too
STC calculations use zones to reflect different expected solar generation in different parts of Australia. That means the same system size can attract a different STC count indifferent locations.
This is one reason it is hard to compare “rebate amounts” between friends in different cities. It is better to compare system quality and on-site usage than to chase a single headline discount.
The dollar value per STC can move
STCs have a market value because they are traded. That means the dollar value used in quotes canchange.
Many installers use a conservative STC price in quotes to reduce surprises. Some lock in the STC price for a period. If you are comparing quotes, ask what price has been assumed and when it is locked.
You may also hear mention of an STC clearing house. The clearing house provides a pathway for STCs to be sold at a set price mechanism, but it can involve waiting periods. Many businesses trade STCs through the open market, which is why quote assumptions can vary.
For homeowners, the practical action is to ask the installer how they have priced STCs and whether the discount is guaranteed.
Which date matters for STCs
Homeowners sometimes assume the date they sign a quote locks in the STC value. In most cases, the installation date is what matters because STCs are created for an installed and commissioned system.
If you are close to a step-down date, it is worth discussing scheduling and realistic installation timeframes. A reputable installer will not promise an impossible timeframe just to win the job.
What this means for homeowners deciding when to install
It is natural to wonder whether you should rush to install before the incentive reduces. In practice, the decision is usually bigger than the STC step-down.
Good reasons to movesooner include:
· You are already paying high electricity prices and your roof is suitable.
· You are planning electrification upgrades and want solar in place first.
· You want to lock in a design before changing tariffs or export conditions.
Bad reasons to rush include signing with an installer you do not trust, or accepting a poor design just to chase a deadline.
How to compare quotes across time
If you are comparing aquote you received last year to one you receive now, differences in STC discount might not be a sign that someone is ripping you off.
To compare fairly, ask for the same system size and similar assumptions, then compare:
1. System design and roof allocation
2. Included electrical work and compliance
3. STC price assumption and lock-in timing
4. Warranties and monitoring access
Decision traps to avoid
· Assuming a bigger STC discount automatically means a better system. Design quality still matters more.
· Chasing a deadline and ignoring roof shading, exportlimits, or future upgrade plans.
· Comparing quotes with different system sizes or different STC price assumptions and treating it as apples-to-apples.
If you keep the comparison clean and focus on long-term fit, the STC changes become manageable rather than stressful.
How to protect yourself when STCs arechanging
1. Ask for the STC price assumption in writing.
2. Ask when the STC price is locked in and what happens if the market moves.
3. Confirm the expected installation timeframe and whether any step-down dates may apply.
4. Compare quotes on design quality and include delectrical work, not just discount size.
If you do these four things, STC changes over time become a normal planning factor rather than asurprise.
Bottom line
STC benefit changes over time for two reasons: the number of certificates reduces as the scheme steps down, and the value per certificate can move with the market.
Use the incentive as one input, not the only input. The strongest long-term value still comes from good design and correct installation.
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