How it is calculated
- System size (kWp) = monthly use ÷ (daily yield × 30)
- Monthly generation = size × daily yield × 30
- Number of panels = size × 1,000 ÷ watts per panel, rounded up
- Supply: up to 5 kWp single phase; above 5 and up to 15 kWp needs three phase; above 15 kWp exceeds the Solar ATAP domestic cap
Solar ATAP replaced NEM 3.0 from 1 January 2026. To estimate your electricity bill, use the TNB electricity bill calculator.
Worked example
A home using 500 kWh a month, yield 3.5 kWh/kWp a day, 550 W panels:
- Size: 500 ÷ (3.5 × 30) = 500 ÷ 105 = 4.76 kWp
- Panels: 4,762 W ÷ 550 = 8.66, rounded up = 9 panels
- 4.76 kWp is not above 5 kW, so single phase is enough.
A home using 900 kWh with a yield of 4.0: 900 ÷ 120 = 7.5 kWp, which is 14 panels and needs three phase.
Why your number may differ
Actual yield depends on roof direction and tilt, shading, weather and system efficiency; 3.5 is an assumption, not an official figure. Rounding the panel count up gives a slightly larger system. Bill savings and payback are not calculated because the export credit rules are not verified. Get a site assessment from a registered installer.