Rooftop Solar's Wholesale Value Fell Further Than the Solar Farms'

The larger fleet, and the one that rarely turns down

The utility solar value factor measured what an hour of solar farm output is worth against the average wholesale price. Rooftop solar is the larger fleet. AEMO estimates it produced 28,862 GWh across the four mainland regions in 2025, against 18,133 GWh from solar farms. It is also the fleet that mostly does not respond to price: a household system generally keeps exporting when the wholesale price goes negative, where a solar farm can reduce its output.

The measure is the same. Each half hour of AEMO's estimated rooftop output is weighted by that half hour's wholesale price, and the result is divided by the time-weighted average price. At 1.00, rooftop energy is worth the average; below it, rooftop energy arrives when the market is cheaper than usual; below zero, it arrives, on average, when the market is paying to take energy away.

From near average to near nothing

In 2019 rooftop solar was worth between 0.78 and 0.98 of the average price across the four regions. By 2025 its value factor was 0.31 in New South Wales, 0.14 in Queensland, 0.02 in South Australia, 0.14 in Victoria. South Australia's rooftop output was worth 2 per cent of the average price for the year.

In 2023 the annual value factor went below zero: South Australia at -0.003 and Victoria at -0.102. Across that whole year, the wholesale price at the times rooftop solar produced averaged less than zero.

Below the solar farms in every region

Rooftop solar's value factor has been below utility solar's in every region in every year since 2020. The gap is widest in South Australia, where solar farm output was worth 53 per cent of the average price in 2025 and rooftop output 2 per cent.

Two differences are consistent with the gap, though this report does not measure either. Rooftop panels are mostly fixed and peak sharply at midday, where many solar farms track the sun and spread their output towards morning and evening. And farms that reduce output at negative prices drop those half hours out of their own weighting, which, as the utility report notes, flatters their value factor; rooftop systems keep producing into them.

Checked against AEMO

AEMO publishes two estimates of rooftop output for every half hour, one upscaled from a sample of metered systems and one derived from satellite imagery. This report uses the measurement-based estimate, because it reproduces AEMO's own published figures: computed average output in Q4 2025 is 1,513 MW in New South Wales, 1,354 MW in Queensland and 956 MW in Victoria, the distributed PV averages AEMO reports in its Quarterly Energy Dynamics for that quarter. In Q4 2025 the satellite estimate read 1 to 8 per cent higher in output, and in other periods it reads lower, but it gives the same picture: its value factor is within 0.06 of the measurement estimate's in every region and year.

What these numbers are not

• Not what households are paid. Rooftop owners are paid a retail feed-in tariff and save their own retail price on what they use, not the wholesale price. This is the wholesale value of the energy at the times it is produced.
• An estimate, not a meter census. AEMO estimates rooftop output from a sample of metered systems and installed capacity. Its level can be revised; the value factor is a ratio and is far less sensitive to that than the energy total.
• Half-hourly. Rooftop output is estimated per half hour, so it is weighted by each half hour's mean price rather than by the five-minute prices the utility report uses.
• The NEM only. Western Australia's SWIS runs a different market, and none of these figures describe it.