Wind Turbine Annual Energy Production (AEP) Calculator

AEP = Rated Power × Hours per Year × Capacity Factor. Hours per year = 8760. Rated power is what the turbine produces at its design wind speed (usually 11 to 15 m/s). Capacity factor is the fraction of that rated output you actually achieve over a year.

Capacity factor is the number that matters. A 2 MW turbine running at 100% would produce 17,520 MWh per year. Real turbines do not reach that. Land-based modern turbines are 35 to 45%. Best offshore sites push 50 to 55%. A weak land site can drop to 20%. The same hardware on a windy ridge versus a sheltered valley can differ by 3x in annual output.

Why capacity factor varies.

• Wind speed cube law: power scales with v³, so doubling wind speed gives 8x power. A 7 m/s mean site produces hugely more than a 5 m/s site.
• Cut-in and cut-out: most turbines start producing at 3 m/s and shut off above 25 m/s for safety. Time outside that window is zero output.
• Wake losses: in a wind farm, downwind turbines see slower wind because upwind ones extracted energy. Typical farm-level loss is 5 to 15%.
• Availability: maintenance and faults take 2 to 5% of the year offline.

Worked example. A 2.5 MW turbine on a Class III site (mean wind ~7.5 m/s at hub height), capacity factor 38%:

• Rated kW × hours × CF = 2500 × 8760 × 0.38 = 8,322,000 kWh per year
• That is enough to power roughly 750 average US homes for a year.

Sanity check on capacity factors.

• Class IV / poor site: 18 to 25%
• Class III / fair: 25 to 35%
• Class II / good: 35 to 42%
• Class I / excellent: 42 to 50%
• Offshore typical: 40 to 55%

Small wind turbines drop further. Residential 5 to 20 kW machines on towers below 100 ft typically hit 15 to 25% capacity factor unless the site is a windy ridge or coastal plain. Anyone advertising a capacity factor over 30% on a small turbine is either lying or measuring at the wrong height.

Net versus gross. This calculator gives gross AEP — energy at the turbine terminals. By the time you account for transformer losses, transmission losses, and inverter losses, deliverable energy is 90 to 95% of gross. For project finance, model net not gross.

Capacity factor versus efficiency. People confuse these. Efficiency is what fraction of wind energy the rotor converts (Betz limit caps it at 59.3%, real turbines run 35 to 50%). Capacity factor is what fraction of rated output you achieve over time. Different concepts.