STCs are not a separate profit centre for most solar companies. They are a financing mechanism that happens to be tradable, and the money to be made is small per system but real at volume.
The basic mechanics
A customer buys a system. The installer calculates the STCs the system will create, values them at a rate, and takes that value off the quote. Later the installer sells the certificates. Whatever the buyer pays above the value used for the discount is the margin; if the buyer pays less, the installer wears the difference.
For a 6.6 kW system in a zone 3 city in 2026, the system creates 45 STCs. At roughly $38 to $40 spot at the time of writing, that is about $1,700 to $1,800. A one-dollar difference in rate is $45 a system. Across 500 systems a year it is $22,500, which is why serious installers shop rates.
Where installers make or lose money
- Rate spread. Quoting at one price and selling at a better one.
- Time value. If you wait 20 business days instead of 1, you fund the customer’s discount from your own cash for a month. See STC payment terms, 20 days vs 1 day.
- Rejections. A failed claim means the certificate does not exist and you have already discounted the job. See top rejection reasons.
- Falling deeming. Each year the same system creates fewer STCs. See deeming period by year.
What installers actually do
Most sell to a trader or registered agent on a published rate. A few large operators self-register and sell on a book of contracts. Very few hold certificates speculatively, because the clearing house ceiling of $40 limits the upside while spot can still drift lower. See also whether it is worth self registering.
What this means for installers
Treat STC handling as a procurement decision. Compare rate, payment days, held-back amounts and compliance support. Energy Merchants publishes the rate daily on pricing, pays within 24 hours for established partners and charges no fees, so the number you see is the number you get. Open an account through start trading or read how it works.
See the STC trading overview or the FAQ for more.