Gross cost and net cost (solar)

Written and checked by the Energy Merchants desk · Reviewed 3 October 2026

Gross cost is the full price before the STC discount. Net cost is the price after it. Quotes use both terms, sometimes loosely, which makes comparison harder than it should be.

The basic sum

Gross cost minus the STC discount equals net cost. A 6.6 kW system with a gross price of $7,500 and a discount of $1,710 has a net cost of $5,790. The customer pays the net figure.

Why quotes differ

Two quotes can look far apart for reasons that have nothing to do with quality. One may price STCs at $40 and another at $34. One may include GST and one not. One may show a net price including a state rebate that the other leaves out. Only by putting both on the same basis can a customer tell which is cheaper.

In practice

For installers, the discipline is to show gross, discount and net on one line each, and to say how the STC value was calculated: the system size, the zone, the deeming period and the price per STC. See zone rating. If the discount is based on a number that you cannot get, you are the one who will pay the difference. The STC calculator works out the quantity, and the daily rate on pricing tells you what each is worth.

Worked example

Quote A: gross $7,500, discount $1,710, net $5,790. Quote B: gross $6,800, no discount shown, net $6,800 for the same system. Quote B looks cheaper on the gross and is dearer on the net. The customer who compares gross to gross gets the wrong answer.

Common confusion

Net cost is not the system’s true cost. The customer is also paying, indirectly, for the market value of certificates they have handed over. And net cost is not the same as the payback, which depends on usage, tariff and export.

See point of sale discount, what is an STC worth, STC trading and the glossary.