Energy

Capacity Factor vs the Betz Limit

By Lucian — builder & engineer, LK Forge

A wind turbine can never capture more than 16/27 of the wind’s kinetic energy — about 59.3% — no matter how good its blades or generator. That number gets quoted constantly, but it answers a narrower question than most people think it does. We ran the Wind Turbine lab across a spread of mean wind speeds to see how far a real, wind-averaged capacity factor actually falls below that ceiling.

 ·  5 min read  ·  measured from the power-curve model

59.3%
the Betz-limit ceiling on wind-power extraction
36%
captured at a single 12 m/s snapshot
6.9–57.1%
measured capacity factor across 4–11 m/s mean wind
4–11 m/s
mean-wind range spanned by the benchmark rows

Capacity factor climbs with wind speed, but stays under both ceilings

Sweep the turbine's mean wind speed from a slow 4 m/s to a brisk 11 m/s and the measured capacity factor rises steeply — from single digits to over half — but it stays below both ceilings, and even the windiest sites fall short of the Betz limit. The gap to the Betz line (59.3%) is the built-in momentum loss every rotor pays; the gap to the single-point snapshot (36%) shows what averaging real, variable wind does to an already-realistic power curve.

0% 20% 40% 60% Betz limit 59.3% 12 m/s snapshot 36% 4567891011 mean wind speed (m/s) CF

Capacity factor (amber line and dots) from the benchmark rows, against the Betz-limit ceiling (dashed amber) and the single-point 12 m/s snapshot (dashed grey).

The exact numbers

Every row behind the chart above, straight from the benchmark dataset.

Mean wind speed Capacity factor
4 m/s 6.9%
5 m/s 13.3%
6 m/s 21.4%
7 m/s 30.2%
8 m/s 38.6%
9 m/s 46.1%
10 m/s 52.3%
11 m/s 57.1%

Betz limit: 59.3%. Single-point 12 m/s snapshot capture: 36%. Generated 2026-09-10.

Try it yourself

Open the lab, set the mean wind speed and the turbine's cut-in/rated/cut-out points, and watch the power curve and capacity factor update live.

Open the Wind Turbine lab →
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Related reading

Common questions

What is the Betz limit?

The Betz limit is the theoretical ceiling on how much of the kinetic energy in moving air a wind turbine can extract: no more than 16/27, about 59.3%. It follows purely from momentum conservation — a turbine that captured all the wind's energy would leave the air behind it stationary, blocking the next parcel of air from arriving, so some speed (and some energy) must always pass through unclaimed. It applies to any rotor working in open flow, regardless of blade design, material or generator efficiency.

Why is measured capacity factor so far below the Betz limit?

Capacity factor and the Betz limit answer different questions. The Betz limit is an instantaneous, single-speed efficiency ceiling on energy extraction. Capacity factor is a time-averaged output — actual energy produced over a period divided by the energy the turbine would produce running at full rated power the entire time. Because real wind is rarely at the exact speed that yields rated power, and produces roughly zero below cut-in and nothing above cut-out, the averaged figure sits well under the peak-efficiency ceiling — here 6.9–57.1% across mean wind speeds of 4–11 m/s.

What capacity factor should a real wind site expect?

It depends heavily on the site’s mean wind speed and the turbine’s power curve. In this benchmark, mid-range sites (mean wind roughly 7–9 m/s, typical for many onshore locations) land around 30–46%, tracking the commonly cited 30–45% figure for wind capacity factors; low-wind sites near 4–5 m/s fall to single digits, and only high-wind sites above 10 m/s approach the 50s.