6.12 - Wind Energy

Learning Objectives

I. Wind Energy Basics and Generation

• Mechanism: Wind energy harnesses the kinetic energy of moving air, which turns giant blades attached to a turbine.

• Generation process (similar to hydroelectricity):
1. The blades rotate a shaft.
2. The blades turn the wind's kinetic energy into the rotational (mechanical) energy of the shaft. The shaft turns slowly, so a gearbox speeds up the rotation for the generator. (Some newer turbines skip the gearbox and use a large, slow-turning generator instead.)
3. A generator, which shows up in most forms of electricity generation, turns that mechanical energy into an electrical current.

• Capacity factor and intermittency:
• A typical new U.S. land-based turbine is rated about 3.4 MW (2023 average, Berkeley Lab). At a 34% capacity factor, one turbine makes enough electricity for roughly 1,000 average U.S. homes (see the practice calculation below).
• Wind farms have a lower capacity factor than fossil fuel or nuclear plants. Capacity factor is the electricity actually made in a year divided by what the turbine would make running at full power the whole time. U.S. wind averaged about 34% in 2024 and 2025, compared with about 91% for nuclear (EIA).
• Turbines usually make some electricity most of the time, but rarely at full power, because the wind speed keeps changing. They only run when the wind is between about 8 and 55 miles per hour: below that the blades can't turn the generator usefully, and above that they shut down to avoid damage.
• Most turbines have a motor that positions them directly into the wind to optimize production.

II. Wind Turbine Locations

• Wind projects are typically clustered into wind farms in rural areas. Centralizing them improves efficiency for maintenance and for building transmission lines, the wires that carry electricity to population centers.

• Shared land use: Wind farms are unique in that they can share land with agriculture, for example growing crops beneath the turbines.

• Offshore wind: Turbines can be placed offshore in oceans or large lakes.
• Advantage: Offshore wind speeds are typically higher since no landforms block the wind, which means a higher capacity factor. It also takes up no land and does not disrupt land habitats.
• Drawback: It requires building challenging, long, often buried transmission lines to bring the electricity onto land.

III. Benefits and Drawbacks of Wind Energy

A. Benefits

• Non-depletable: Wind is considered non-depletable, which is even better than renewable, because there is no way we could run out of it. The wind will always blow.

• Zero emission: Wind is a zero emission form of electricity.
• It produces no greenhouse gas emissions like carbon dioxide, so it does not contribute to climate change.
• It releases no air pollutants that lower air quality (NOx, SOx, particulate matter, or VOCs), which prevents harm to human health and acid rain.

• Less habitat disruption: Wind farms do not destroy or fragment habitat the way mining for fossil fuels or building large solar farms does, because the turbines sit high up in the air.

B. Drawbacks

• Bird and bat mortality: Wind turbines can kill migratory birds and bats. That said, domestic cats, habitat loss, and pesticides are likely much bigger causes of bird and bat biodiversity loss.
• Scale: One study estimated that U.S. wind turbines kill about 234,000 birds a year, while outdoor cats kill an estimated 1.3 to 4 billion (Loss and others, 2013). Turbines also kill many bats, especially migrating bats in late summer and fall.
• Solutions: Build wind farms away from migration routes, slow or stop turbines on low-wind nights when bats are most active (this cuts bat deaths a lot while losing little power), and paint one blade black so birds can see the spinning blades (a test in Norway cut bird deaths by about 70%).

• Aesthetics and noise: Some people consider turbines an eyesore or a source of noise pollution, which can cause controversy, especially around property values like beachfront property.

• Intermittency issues: Like solar, wind can't generate electricity on demand. Grid batteries are growing fast, but most hold only a few hours of power, not enough to cover several calm days in a row.

• Cannot replace base load power: Because of intermittency, wind cannot replace base load power. Base load sources like fossil fuels, nuclear, and dams are available 24/7, so wind is best used to supplement them rather than replace them entirely.

IV. Practice Calculation: Homes Powered by One Turbine