That's good if you have a peak demand for electricity in the winter for

heating versus summer but when you get into the south, for

instance, you would like to have more electricity, and need more electricity,

in the summers for air conditioning.

So wind energy, in particular, where you have summer peaking energy demand,

electrical demand, it doesn't really match the annualized load.

But we'll look at the annual average on wind maps like we looked at

the wind maps for solar but they're a little more straight forward because this

time it doesn't depend on the orientation.

We can always point the wind turbine into the wind.

These turbines will pivot around the pylon on huge bearings and

so they're always pointing into the wind.

And that's not a big deal.

By the way, you notice the blades.

In that case, the case we're looking at here is pictured that

they're basically perpendicular to the wind.

So that's in the stop lock position.

If the wind gets below a certain speed, or it gets above a certain speed,

that could cause damage to the turbine.

They turn the blades into the wind and lock it down to prevent damage.

But, let's look at how we classify winds.

You classify winds by wind power class one through seven, and

that indicates the range of wind power density.

And that's the watts per, when it says there of Class 1,

0 to 200 watts of kinetic energy in the wind

per square meter of the area that you're capturing of the wind.

So if your rotor blade is in its circumference and

this circle is capturing 10 square meters,

then that means that the total watts of kinetic energy or

power in that 10 square meters

is up to 200 watts up to 2,000 for the class one.

The power density is a little bit non intuitive.

You would think that the because of the kinetic energy,

we think about as always one half m v squared,

that as the wind speed goes up the power would go up to the square of the velocity.

But it actually goes up with the cube, and the reason it does because the kinetic

energy per unit mass of air goes up as the speed goes up.

So if you double the wind speed of kinetic energy per unit mass,

goes up by a factor of 4.

2 squared is 4, 2 times 2.

But the power density goes up by the cube ,because the amount of

mass is flowing through the wind turbine goes up in proportion to the velocity.

So the power density in watts goes up by the cube,

which really makes the higher wind speeds pay off liberally.

Because if you double the wind speed, the power that you get out of

the turbine in kilowatts, a given turbine, will go up by a factor of eight.

If you double the wind speed,

the power coming out by the generator it goes up by a factor of eight.

So it's really sensitive to wind speed, the economics of wind farms is really,

sensitive to wind speeds because of that cubic relationship.