Why this comparison exists
Under classic net metering, one exported unit cancelled one imported unit — so bigger was harmless. Net billing broke that symmetry: imports cost your full retail tariff while exports earn a much lower rate. The result is a genuine trade-off that a single payback number hides. This tool models both systems with the same assumptions and puts them side by side.
How each scenario is modelled
Both systems generate at your city's sun-hours with real-world losses included. Generation first replaces your daytime usage at the full import tariff; anything beyond it is exported at the export rate. Cost is simply size times your market's installed cost per kW. The marginal line then isolates the extra capacity in the big system — its extra cost, its extra monthly earnings, and how long that specific money takes to return.
Reading the verdict
If the marginal payback of the extra capacity is dramatically longer than the small system's payback, the extra rupees are working lazily — they may serve you better as a battery, a better inverter, or simply staying in your pocket. If you expect your daytime usage to grow (an EV, daytime AC, a home office), re-run with a higher daytime share before deciding.
Is a bigger solar system always better under net billing?
No. Exported units earn a fraction of what imported units cost, so capacity beyond your daytime usage pays back very slowly. A daytime-matched system frequently reaches break-even in half the time.
What is a typical daytime usage share?
For homes empty in the day it can be 25–35%; for homes with daytime AC, pumps and offices it can reach 50–60%. Check your habits — it is the single most important number in this comparison.
Doesn't a big system still save more per month?
Usually yes in absolute terms — but at a much worse return per rupee invested. This tool shows the marginal payback of the extra capacity so you can judge whether that money works hard enough.