Wind Farm Annual Energy Yield Calculator
Calculates the gross annual energy production (AEP) of a wind farm given fleet size, turbine capacity, capacity factor, and availability. Use it during project feasibility studies to size a farm and project revenue.
About this calculator
A wind farm's annual energy production (AEP) depends on how many turbines are installed, how large each one is, how often the wind blows hard enough to generate power, and how much time the turbines are actually available to run. The formula is: AEP = numberOfTurbines × turbineCapacity (MW) × 8,760 h/yr × (capacityFactor / 100) × (availabilityFactor / 100). The 8,760 figure represents the total hours in a year. Capacity factor accounts for variable wind, while availability factor deducts planned and unplanned maintenance downtime — typically 95–98% for modern turbines. Multiplying these two percentages together yields the net utilisation of the installed nameplate capacity. The result is in MWh per year, which can be directly converted to revenue by applying a power purchase price.
How to use
A 20-turbine farm uses 5 MW turbines, has a 38% capacity factor and 96% availability. Step 1 — nameplate capacity: 20 × 5 MW = 100 MW. Step 2 — maximum possible generation: 100 MW × 8,760 h = 876,000 MWh/yr. Step 3 — apply capacity factor: 876,000 × 0.38 = 332,880 MWh/yr. Step 4 — apply availability: 332,880 × 0.96 = 319,565 MWh/yr. At a power price of $50/MWh, that represents roughly $16 million in annual gross revenue.
Frequently asked questions
What is a realistic capacity factor for an onshore wind farm?
Modern onshore wind farms in good locations — such as coastal plains or elevated ridgelines — typically achieve capacity factors of 30–45%. Sites in lower-wind inland areas may only reach 20–28%, while exceptional sites or taller turbines with larger rotors can exceed 45%. Offshore wind farms benefit from stronger, more consistent winds and routinely achieve 45–55%. The capacity factor is the single biggest driver of project economics, so accurate wind resource assessment before construction is essential.
How does availability factor affect wind farm annual energy production?
Availability factor represents the percentage of hours per year that turbines are mechanically ready to generate, accounting for both scheduled maintenance and unexpected breakdowns. A 96% availability means turbines are offline for roughly 350 hours per year. Since availability multiplies directly with capacity factor in the AEP formula, dropping from 97% to 93% availability on a 100 MW farm at 38% CF costs roughly 3,500 MWh of lost generation annually. Proactive maintenance programmes and remote monitoring systems are key tools operators use to maximise availability.
Why does a wind farm produce less energy than its nameplate capacity suggests?
Nameplate capacity is the maximum output under ideal, continuous full-power conditions — a theoretical ceiling that is never sustained year-round. Wind speed varies constantly, so turbines spend most hours operating below rated power or not at all. Wake effects between turbines in a farm also reduce the wind resource for downwind machines, typically cutting farm-level output by 5–15% compared with isolated turbines. Maintenance downtime adds a further reduction, which is why the product of capacity factor and availability factor gives a much more realistic picture of actual production.