# Why Wind Power Is Best At Night

Why wind turbines often make more power at night: sun\-heated ground, mixing, the night inversion, wind shear and tall towers

By Ham Sandwich

Topic: Energy

[Open the interactive Jig](https://ask.jig.com/j/g8EiPvz06Dxu)

## Guide

### 1. Wind after dark

On the Great Plains, wind farms often make the most electricity at night, even though the wind you feel on the ground is usually stronger in the afternoon\. The coloured streaks are the wind, faster streaks run warmer, and the arrows above the profiler on the left measure it every 25 metres\. Drag the sky or the ground to look around\.

The turbine is a typical new US onshore model: 3\.4 megawatts, a hub about 103 metres up and blades 65 metres long\.

### 2. Sunlight heats the ground

By day the sun heats the ground, and the ground heats the air just above it\. Warm air rises in bubbles called thermals while cooler air sinks to take its place\. Raise the afternoon temperature and watch the ground glow and the thermals climb higher\.

On a sunny afternoon the ground surface gets much hotter than the air around you\. In this model the afternoon high is the air temperature near the ground\.

### 3. Mixing evens out the wind

Thermals stir the lowest few hundred metres like a spoon\. Fast air from aloft is pulled down and slow air near the ground is lifted, so the wind changes little with height\. The ground breeze is lively, but the air at the rotor is only a little faster than at the treetops\.

Meteorologists call this an unstable, well\-mixed boundary layer\. One study measured daytime shear exponents of 0\.12 to 0\.2\.

### 4. Night: the ground cools

Let the sun set\. The ground loses its heat to the clear sky, and the coldest air settles at the bottom, under warmer air: an inversion\. Mixing stops\. Friction slows the air near the ground, while the air above slides freely and speeds up into a low\-level jet, a band of fast wind a few hundred metres up\.

Jet cores are usually 50 to 500 metres up, around 230 metres on average, at 8\.5 to 9 metres per second\.

### 5. Power grows with the cube

A turbine's power grows with the cube of the wind speed: 20 percent more wind gives about 70 percent more power\. Switch between afternoon and night and compare the readout and the glowing pulses running from the turbine to the substation\. The faint curve on the profiler is the other time of day\.

Measured jets raised average turbine output by 53 to 80 percent at two German sites\. Real turbines cap their output at a rated power\.

### 6. Taller towers reach faster air

Wind gets faster with height, most of all at night\. A taller tower lifts the rotor into faster air: by day this makes up for some of the wind lost to mixing, and at night it reaches deeper into the jet\. Change the hub height, or drag a turbine's nacelle up and down\.

The average new US hub rose from 98 metres in 2022 to 103 metres in 2023\. Designs expected by 2030 reach 100 to 140 metres\.

### 7. Your wind farm

Now it is yours\. Pick a time of day, then set the hub height and the afternoon high in the panel above, or drag a nacelle\. Watch the profile, the rotor band and the power column\. Try a hot afternoon with short towers, then a clear night with tall ones\.

This is a simplified model\. Real nights vary: jets are not present every night and are strongest in regions like the Great Plains\.