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Notes -
The energy in the wind scales as the cube of the wind speed. It looks like it ought to be the square of the wind speed, because kinetic energy is one half m v squared. But what is the mass here? It is the mass of air passing the wind turbine, so that is proportional to the wind speed.
This makes intermittency a huge problem. When the when is blowing at half speed, you only get one eighth of the energy. Imagine planning for low winds by over provisioning by a factor of two. You have built twice as many wind turbines as you need for a day with the designed for wind strength, expecting that you will make it through low wind days without black outs. But when the wind strength dips to 79% of design nominal, you are already down to half power, taking up the entire margin provided by over provisioning. The wind drops to 78% and you have to start shedding load :-( Or at least drawing on storage.
I keep seeing critics of wind power asking "what do you do on calm days?". That is a bad question. It leads to boosters and critics both worrying about the occasional calm day when the air is still. But we need to worry about the half strength days. And those are common place days when the wind is still blowing and we expect the turbines to turn and the electricity to stay on.
A credible wind power system would have eight fold over provision, and weeks of storage. The occasional day when the wind is above design strength all day would be a cause for celebration: we have captured a weeks worth of energy in a day! And we could start feeling that we had a secure energy supply. We are nowhere near facing the challenge of intermittency nor the expense of intermittency.
This is true in theory, and a decent model for small wind turbines in relatively slow winds.
It's not useful for large modern turbines (let's say 3 MW and up), since it assumes that higher wind speed automatically results in faster rotor RPM. But since rotor RPM is critically limited by blade tip velocity, a large turbine reaches max RPM in ultra light wind. After that point, power scales linear with wind speed. See this power curve, first example I found
Add to that, that a large turbine reaches nameplate capacity at around 10 m/s wind speed (and goes linear at around 3 m/s, shuts down at around 30 m/s), and it's really not that much of a problem in a modern park.
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