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.

That is the gross figure, with the three loss boxes left empty. Put in a realistic 97% availability, 8% wake and 4% electrical and it drops to about 7,129,000 kWh, a 14.3% haircut that is entirely normal and is the number a bank would want to see.

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. Gross AEP is rated power times hours times capacity factor, with nothing taken off. This page shows that figure and then works down through three separate losses: availability (the time the machine is not running), wake and array loss (the wind the upwind turbines already took), and electrical loss.

That last one catches people out. Transformer, cable and, on small systems, inverter losses take another 5 to 10% between the generator terminals and the meter, so deliverable energy is 90 to 95% of what the drivetrain produced. Project finance models net, and net here means after all three.

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.