Inverter sizing & DC/AC ratio

Your array makes DC; the inverter turns it into AC, capped at its rated output. The relationship between how much DC you install and that AC cap — the DC/AC ratio — is one of the most misunderstood design choices. A little oversizing is good; too much wastes panels.

The DC/AC ratio

Divide your array’s DC watts by the inverter’s AC watts. A 8 kW array on a 6.4 kW inverter is a 1.25 ratio. Ratios above 1.0 (oversizing the array) are normal and usually smart, because…

Why oversizing helps

Panels almost never hit their lab-rated (STC) output — heat, angle, haze, and dirt mean they mostly run well below nameplate. So an inverter sized to the array’s peak would sit half-empty most of the year. Installing more DC than the inverter’s rating fills more of its capacity for more hours, raising total energy — especially valuable in cloudier conditions and shoulder seasons.

The limit: clipping

Push the ratio too high and on the brightest few hours the array briefly produces more than the inverter can pass. The inverter simply caps output and the excess is lost — that’s clipping. A small amount of clipping is fine (those peak hours are rare, and you gained energy everywhere else). A lot of clipping means you overpaid for panels whose peaks you throw away. Typical residential designs land around 1.1–1.3, depending on orientation and goals.

String vs. hybrid inverter

• String inverter — solar only; simplest and cheapest if you’re not adding storage.
• Hybrid inverter — also charges/discharges a battery. Pick this if a battery is in your plan now or later (Module 7).

Next: batteries — capacity vs. power, parallel units, and backup sizing.