What is the formula for European Inverter Efficiency?

The European Inverter Efficiency formula is η_EU = 0.03×η₅ + 0.06×η₁₀ + 0.13×η₂₀ + 0.10×η₃₀ + 0.48×η₅₀ + 0.20×η₁₀₀, where η_EU—Weighted European efficiency (0-1 or %); η₅ through η₁₀₀—Efficiency at 5%, 10%, 20%, 30%, 50%, and 100% of rated power.

What does η_EU mean in the European Inverter Efficiency formula?

η_EU is Weighted European efficiency (0-1 or %).

European Inverter Efficiency

Q: How do you calculate European Inverter Efficiency?

Use the formula η_EU = 0.03×η₅ + 0.06×η₁₀ + 0.13×η₂₀ + 0.10×η₃₀ + 0.48×η₅₀ + 0.20×η₁₀₀. The European efficiency is a weighted-average inverter efficiency that accounts for the fact that solar inverters rarely operate at full power. Enter the values you know in the calculator above and it solves for the remaining variable.

η_EU = weighted average of partial-load efficiencies

Calculator

Euro Efficiency

η at 5% load

η at 10% load

η at 20% load

η at 30% load

η at 50% load

η at 100% load

Result

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Formula

η_EU = 0.03×η₅ + 0.06×η₁₀ + 0.13×η₂₀ + 0.10×η₃₀ + 0.48×η₅₀ + 0.20×η₁₀₀

Description

The European efficiency is a weighted-average inverter efficiency that accounts for the fact that solar inverters rarely operate at full power. The weighting factors reflect the typical irradiance distribution in central European climates, where partial-load conditions dominate. The 50% load point receives the highest weight (48%) because inverters spend the most time near this operating point. This metric gives a more realistic picture of annual energy harvest than the peak efficiency, which only occurs at one specific operating point.

Variables

η_EU — Weighted European efficiency (0-1 or %)
η₅ through η₁₀₀ — Efficiency at 5%, 10%, 20%, 30%, 50%, and 100% of rated power

Practical Notes

Modern string inverters achieve European efficiencies of 96-98%. The CEC (California Energy Commission) efficiency uses different weights optimized for sunnier climates. Microinverters and power optimizers have slightly lower peak efficiency but can improve system-level efficiency by reducing mismatch losses from shading or panel variation.

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