5 kW vs 10 kW Solar System: Which Should You Buy?
This is the most common upgrade question, and net billing has changed its answer. Doubling the array no longer doubles the benefit, because the surplus you export earns far less than the units you import. Here are both systems side by side.
| 5 kW | 10 kW | |
|---|---|---|
| Panels needed (585 W) | 9 | 18 |
| Clear roof area | 300–350 ft² | 600–700 ft² |
| Average daily generation | 21 kWh | 42 kWh |
| Average monthly generation | 636 units | 1272 units |
| Typical inverter size | 6 kW | 12 kW |
Generation assumes 5.3 peak sun-hours and a 0.8 performance ratio — real losses included. Your city changes these numbers: run your own in the complete calculator.
When the 5 kW is the right choice
A 5 kW system fits a household with moderate daytime usage — one or two ACs used selectively, fans, fridge and lights. Under net billing it is often the better return, because almost everything it makes is consumed at home at the full tariff rather than exported cheaply.
When the 10 kW is worth it
A 10 kW system suits large homes running multiple ACs through the day, families with heavy daytime pumping, or anyone planning an electric vehicle. It needs roughly twice the roof, and it only pays well if the extra generation is consumed rather than exported.
Why net billing changed this decision
Under the old rules an exported unit cancelled an imported unit, so a bigger system was never wrong. Now imports cost the full retail tariff while exports earn a much lower rate — so capacity beyond your daytime usage earns a fraction of what the first kilowatt earns. Before doubling, check what the extra 5 kW actually returns on its own.
Is a 10 kW solar system worth it?
It is worth it when your daytime consumption can absorb most of what it generates — multiple ACs running through the day, daytime pumping, or an EV. If the extra generation would mostly be exported, its return is far weaker than the first 5 kW under net billing.
How much roof does a 10 kW system need?
Roughly 600 to 700 square feet of clear, unshaded roof — about double a 5 kW. Structures, water tanks and parapet shadows reduce the usable area, so measure the clear space, not the total roof.
Can I start with 5 kW and expand to 10 kW later?
Often yes, but plan it at the start: the inverter, cabling and net-metering paperwork all need to allow for it. Expanding a system that was designed as final usually means replacing the inverter.
Decide with your own numbers rather than an average household's: size your system in the complete calculator, then test whether the larger option actually pays in the net billing comparison.