Start with your bill, not your roof
It's tempting to think system size is mainly about how much roof space you have. In practice, the more useful starting point is your last 12 months of electricity bills. That tells us your actual average and peak consumption, including seasonal swings from air conditioning in summer.
The inputs that matter
- Average monthly units consumed — the baseline for sizing the array
- Peak season usage — typically summer, when AC load spikes
- Roof orientation & shading — south‑facing, unshaded roof area produces the most
- Available structural space — for panels, walkways and future expansion
- Grid connection type — single or three‑phase, which affects inverter choice
- Budget & goals — full offset vs. partial offset vs. backup priority
Full offset vs. partial offset
A system sized for full offset aims to cover close to 100% of your annual consumption, which usually means a larger upfront cost but a smaller ongoing bill. A partial system covers a portion of your load at a lower upfront cost, still meaningfully reducing what you pay WAPDA each month.
Neither is objectively "right" — it depends on your budget and how quickly you want the system to pay for itself. We usually present two or three sizing options in a proposal so you can compare.
Why oversizing isn't free
A system larger than your net‑metering export limit, or larger than your roof can comfortably support, adds cost without adding proportional benefit. Getting the size right the first time is most of what a proper site survey is for.