What if a turbine had a small generator?

A wind turbine has big blades and a generator. The blades catch the wind and spin.

The generator turns the spin into electricity. What if the generator were small?

We often think of a wind turbine as its giant blades. But the blades are joined to the part that actually makes electricity: the generator.

Every generator has a top limit, its rated power, the most electricity it can make. So what happens if a turbine with long blades has a small generator? Will it still make lots of electricity in a strong wind? In this lab, you keep the blades and the wind the same and shrink the generator.

Wind turbines are specified by both rotor size and generator rating (nameplate capacity). The rotor sets how much power is available at each wind speed; the generator sets the ceiling on what can be delivered.

This lab holds a 40 m rotor with Cp = 0.4 in a steady 12 m/s wind and reduces the rated power from 15 MW to 1 MW. It examines the power output, the share of the wind's power caught, and the energy over a day.

With a big generator, the turbine uses all the spin the blades can give.

In a strong wind, it makes lots of electricity.

In the model, the wind blows at a steady 12 meters per second. The air through the circle swept by the 40-meter blades carries about 5.32 megawatts of power, and the blades catch 40% of it.

With a big 15-megawatt generator, nothing holds the turbine back. It makes about 2.13 megawatts, and in a full day of that wind, about 51.1 megawatt-hours of energy. The generator has plenty of room to spare.

At v = 12 m/s, ½ρπr²v³ ≈ 5.32 MW passes through the disc. With Cp = 0.4 the rotor can deliver 2.13 MW, far below a 15 MW rating, so the turbine operates on the rising part of its power curve: 40% caught, rotor speed about 20.1 rpm and about 51.1 MWh over 24 hours.

With this rotor, the 15 MW generator would only become the limit at about 23.0 m/s, close to the model's 25 m/s cut-out.

Now Olly puts in a small generator. The blades still catch lots of wind.

But the generator can only make a little electricity. The rest of the wind's push goes unused.

Swap in a 1-megawatt generator. The blades could still deliver 2.13 megawatts, but the generator can only make 1. So the turbine holds its output at exactly 1 megawatt, and the share of the wind's power it uses drops from 40% to about 19%.

A day's energy falls from about 51.1 to 24.0 megawatt-hours. And blowing harder doesn't help: at 20 meters per second the small-generator turbine still makes just 1 megawatt, while the big one would make about 9.85.

With a 1 MW rating the output is clamped at 1.00 MW. The rotor would reach that at about 9.33 m/s, so from there up to the 25 m/s cut-out the curve is flat. At 12 m/s the captured share falls to 19% (from 40%) and daily energy to 24.0 MWh (from 51.1 MWh); the model also slows the rotor to the speed it had at the rated wind, about 15.6 rpm.

Below 9.33 m/s nothing changes: at 6 m/s both turbines make 0.266 MW, because the generator is not yet the limit.

The blades can only give the generator so much work to do. And the generator can only do so much!

Whichever is smaller sets how much electricity you get.

Think of a turbine as a team. The blades collect energy from the wind, and the generator turns it into electricity. The team's output is set by whichever part reaches its limit first.

In gentle winds, the blades are the limit, so a bigger generator wouldn't help. In strong winds, a small generator becomes the limit, and real turbines then turn their blades to spill the extra wind. Our model keeps the wind perfectly steady and uses one fixed power coefficient, which real turbines don't.

Output is min(Cp·½ρAv³, P_rated), set to zero below cut-in (3 m/s) and above cut-out (25 m/s) in the model. The wind speed where the two terms meet, the rated wind speed, scales as the cube root of P_rated / (Cp·½ρπr²): about 9.33 m/s for 1 MW and 23.0 m/s for 15 MW with this rotor.

Model limits: steady, uniform wind over the disc; a single Cp standing for all aerodynamic and electrical losses (real Cp changes with wind speed and blade angle); fixed cut-in and cut-out speeds; and constant air density. Real winds vary all the time, so real yearly output is far below a steady-wind calculation.

Real turbines also stop at a top power. When the wind gets very strong, they turn their blades to let some wind slip past.

In a big storm, they stop to stay safe.

The U.S. Department of Energy describes a real turbine's power curve. The blades start turning at a cut-in speed, often between 6 and 9 miles per hour. More wind brings more electricity until the turbine reaches its rated power. After that, the power stays the same while the blades feather, turning to point into the wind.

Generators have grown too. Berkeley Lab, a U.S. Department of Energy national laboratory, reported that new U.S. land-based wind turbines installed in 2024 had an average rating of 3.5 megawatts.

DOE's description of the power curve matches the model's shape: a cut-in speed (typically 6 to 9 mph), rising output to the rated speed where the turbine produces its rated power, then constant output until a cut-out speed, which varies by turbine (55 mph in DOE's example), when it shuts down to avoid unnecessary strain. Above rated speed the blades feather, pointing into the wind to reduce their surface area.

DOE also notes that a gearbox can speed up the rotor's rotation and allow a physically smaller generator, and DOE reported that newly installed U.S. turbines averaged 3.4 MW in 2023, 375% more than in 1998–1999. Berkeley Lab's 2025 data update for DOE puts the 2024 average at 3.5 MW.