Solar Inverter Sizing Calculator
Determines the right inverter size for a solar array by factoring in panel capacity, orientation, climate, and DC:AC ratio. Use this when designing or auditing a rooftop or ground-mount solar system.
About this calculator
A solar inverter converts DC electricity from your panels into AC electricity for home use. Oversizing or undersizing the inverter wastes money or clips energy production. The key formula is: Inverter Size (W AC) = (totalPanelWatts × panelOrientation × climateFactor) / dcacRatio. The DC:AC ratio — typically 1.1 to 1.3 — accounts for the fact that panels rarely produce their full nameplate wattage simultaneously. A higher ratio means a smaller, cheaper inverter but risks more clipping on sunny days. Panel orientation and climate factors adjust for real-world losses from suboptimal tilt, azimuth, and local irradiance. Getting this ratio right maximises energy yield and protects the inverter from overload.
How to use
Suppose you have 6,000 W DC of panels, a mixed-orientation factor of 0.95, a climate factor of 0.98, and a desired DC:AC ratio of 1.2. Step 1 — multiply panel watts by orientation: 6,000 × 0.95 = 5,700 W. Step 2 — multiply by climate factor: 5,700 × 0.98 = 5,586 W. Step 3 — divide by the DC:AC ratio: 5,586 / 1.2 = 4,655 W AC. You would therefore select a 4.6–5 kW AC inverter for this array.
Frequently asked questions
What is a good DC to AC ratio for a residential solar inverter?
Most residential systems use a DC:AC ratio between 1.1 and 1.3. A ratio of 1.2 is considered a safe industry standard because panels rarely produce their full nameplate wattage in real conditions. Going above 1.3 can cause the inverter to clip production on very sunny days, losing energy. Going below 1.1 means you paid for more inverter capacity than you need.
How does panel orientation affect solar inverter sizing?
Panels facing directly south at the optimal tilt (in the Northern Hemisphere) produce the most power, so their orientation factor is close to 1.0. East- or west-facing panels may have an orientation factor of 0.85–0.95, meaning they produce less peak power. When panels face multiple directions, a blended orientation factor is used. A lower factor means you may be able to use a slightly smaller inverter without significant clipping.
When should I resize or replace my solar inverter?
You should reconsider inverter sizing when you add panels to an existing system, as the new DC:AC ratio may fall outside the optimal range. Inverters typically last 10–15 years, so a replacement is often needed mid-system-life. If your monitoring data shows frequent clipping or the inverter is consistently hitting its AC output limit, upsizing may recover lost production. Climate changes or shading from new obstructions can also shift the optimal sizing calculation.