How net billing changed the economics of rooftop solar
Exported power is now valued at what it is worth to the grid at that hour, not at the retail rate. That single change reshaped payback maths.
For years, a rooftop solar customer exporting power received a credit close to the retail rate. That made the arithmetic simple: every kilowatt-hour exported was worth what a kilowatt-hour bought.
Net billing changed the basis of that credit to what the electricity is actually worth to the system at the hour it is exported. Midday, when rooftop solar is abundant, that value is low.
Why it changed
The prior arrangement was designed when rooftop solar was scarce. As it scaled, the gap between the credit and the system value grew, and that gap was borne by other customers through rates — including customers without the means to install panels.
What it means for a household
Payback now depends on self-consumption rather than export volume. Electricity you use yourself avoids the retail rate; electricity you export earns a lower credit.
That is why storage moved from optional to central. A battery lets midday generation be consumed during the evening peak, capturing the higher value.
“A system sized to export is now sized wrongly. A system sized to cover evening load is not.”
Practical points
- Model self-consumption, not gross generation, when assessing a quote.
- Check whether an existing installation is on legacy terms before changing anything, since modifications can end that status.
- Compare battery quotes on usable capacity and cycle warranty rather than headline size.
- Ask an installer to show the payback under the current tariff, not a historic one.
