Wind: The Cube Law, Capacity Factors and Siting

Wind made about 10 percent of U.S. utility-scale electricity in 2025, roughly 464 billion kilowatt-hours, according to EIA. Texas, Iowa, Oklahoma, Kansas and Illinois together produced about 52 percent of it. All of that comes from a simple trick: put a big propeller in moving air, let the air push the blades, and turn the slow, strong rotation into electricity.

Where the power comes from

Moving air has kinetic energy. The power flowing through a circle of air depends on the air's density, the circle's size and, above all, the wind's speed.

Power in the wind (watts) = 0.5 x air density x swept area x speed cubed
P = 0.5 x rho x A x v^3

rho at sea level = about 1.225 kg/m3
A = pi x (blade length)^2

The area term explains why turbines keep getting bigger. Blade length enters squared, so a rotor with blades 20 percent longer sweeps 44 percent more air. The speed term explains everything else.

The cube law, with real numbers

A = 3.1416 x 65 x 65 = 13,273 m2

Two limits keep real turbines below those raw numbers. The first is physics. In 1919 the German physicist Albert Betz showed that a turbine can capture at most 16/27 of the wind's kinetic energy, about 59.3 percent. Capture all of it and the air behind the rotor would stop, blocking new air from coming through. The second is engineering. Every turbine has a rated power, the most its generator can make. Above the rated wind speed, the blades pitch to spill extra wind. DOE says a typical controller starts the machine at roughly 7 to 11 mph and shuts it down above roughly 55 to 65 mph to avoid damage.

Why the average wind speed lies

Because of the cube, an hour at 12 m/s is worth eight hours at 6 m/s. Take a site that blows 4 m/s half the time and 10 m/s the other half. The average speed is 7 m/s. Plug 7 into the formula and you get 343 units (7 x 7 x 7). Average the cubes instead: half of 64 plus half of 1,000 is 532 units. The gusty site makes about 55 percent more energy than its average speed predicts. Developers measure wind for a year or more with met towers or lidar to get the full distribution. When a project brochure quotes only an average speed, it is leaving out the part that matters.

Capacity factor: the number to ask for

A 3-MW turbine does not make 3 MW all day. Capacity factor compares what it actually produced with what it would have made running flat out every hour of the year.

Capacity factor = actual MWh / (nameplate MW x 8,760 hours)

Example: a 100-MW wind farm produces 300,000 MWh in a year
300,000 / (100 x 8,760) = 300,000 / 876,000 = 0.342, or 34.2 percent

Idaho had about 1,128 MW of wind at the end of 2024, after adding 160 MW that year, and wind made about 15 percent of in-state generation. Newer turbines with taller towers and longer blades reach steadier, faster wind higher up, which is why new projects often post better capacity factors than old ones. A one-year number also bounces: Idaho's fleet went from 27.3 to 31.5 percent between 2023 and 2024 partly because of the weather and partly because of the new machines.

Siting: where the fights happen

Good wind and cheap land often sit far from the cities that use the power, so most wind arguments are about place.

Wildlife

The U.S. Fish and Wildlife Service estimates human-caused bird deaths each year: about 2.4 billion from cats, 599 million from building glass, 214 million from vehicles, about 25.5 million from power line collisions, and about 234,000 from land-based wind turbines (a range of 140,000 to 328,000). Those numbers date from 2017 and the wind fleet has grown since, so the turbine figure today is higher. Both sides misuse this table. Turbines are a small share of total bird deaths. But totals are the wrong lens for eagles, raptors and some migratory bats, where a handful of deaths can matter to a population. The fair framing names the species, the site and the mitigation (curtailing turbines at low wind speeds during bat migration, for example, or careful siting away from raptor flyways).

Land, views and neighbors

Turbines themselves and their roads cover a small slice of a project's lease area; most of the land can still be farmed or grazed. But a project's visual reach is huge, turbines are lit at night for aircraft, and nearby residents report noise and shadow flicker. County zoning setbacks are where these complaints become rules, so read the ordinance.

Federal approvals

Projects on federal land need federal sign-off, and that can flip. In December 2024 the Bureau of Land Management approved the Lava Ridge Wind Project in southern Idaho at up to 231 turbines on about 57,447 acres, for 1,000 MW. On August 6, 2025, Interior announced it would cancel that approval, citing what it called legal deficiencies in the approval, complaints from Idaho state agencies about a lack of consultation, and a policy of ending what it called preferential treatment for intermittent power sources. Supporters of the project pointed to jobs, lease revenue and new power supply; opponents pointed to its size and its effects on ranching, wildlife and nearby historic and cultural sites. Anyone following the project can get the record of decision, the environmental impact statement and the cancellation documents and read each one, then check BLM's project page for where the rescission stands now.

Transmission

Without lines, wind is stranded. Lawrence Berkeley National Laboratory's 2026 Queued Up report counted about 220 GW of wind among roughly 2,060 GW of projects waiting to connect to the grid at the end of 2025, and found that the median project built in 2025 took over five years from its interconnection request to operation. Only about 13 percent of capacity that applied from 2000 to 2020 was built. EIA reported that developers planned 11.8 GW of new wind for 2026, including the 3,650-MW SunZia project in New Mexico, which was built alongside its own long transmission line.