=energy =technology =history
Power from large wind turbines is now cheap. Why didn't it become cheap earlier?
fiberglass
Fiberglass has ~1/5 the density
of steel, and the fatigue strength of fiberglass is about 5x that of steels
used 100 years ago, so its effective strength-to-weight is 25x that of those
steels. If operating at the limit of material strength, that makes turbines
with 25x the diameter possible, which is 625x as much power per turbine.
Today, wind turbine blades are made by putting sheets of fiberglass
soaked with resin on a large mold, generally by hand. There are 2 molds,
each for half the turbine blade, and the 2 blade halves are connected.
Here's an animation
of the process.
Suppose you want to make a large wind turbine blade
from steel instead. In theory, you could take a large sheet of steel and
stamp it to make a blade half, but presses large enough to make modern wind
turbines blades don't exist and would be too expensive. So, in practice,
large steel wind turbine blades would need to have many steel pieces welded
or bolted together. That's expensive and can produce weak points. The
resulting manufacturing costs would be similar to those of aircraft, and
wind turbines are now much cheaper than aircraft.
scale
With massive investment in wind
turbine production, turbine sizes have increased, reducing costs. Why are
large turbines cheaper?
If carrying things with cranes and vehicles,
labor costs are more related to part count than mass, so bigger is cheaper.
Often, the same is true for the equipment used.
The cheapest scales
to operate at are generally:
- things one
person can carry
- as large as industrial equipment can handle
Wind is generally faster at
greater heights, so it's good to put wind turbines on tall towers, but
putting a small turbine on a large tower is impractical.
Large
electric motors are generally cheaper and more efficient than small ones,
for the same reasons large transformers are better.
The main disadvantages of larger wind turbines are:
- tooling
costs
- transportation
- slower rotation increases gear costs
Overall, "the largest blade size that trucks can transport over roads" is a fairly good scale for wind turbines. Offshore wind has larger potential scales, but that certainly doesn't compensate for its cost disadvantages.
power electronics
Wind turbines rotate at variable
speeds. AC power grids use a fixed frequency. Until modern
power
electronics were developed, converting AC frequencies was expensive;
generators and motors were all synchronized, and variable-speed electric
motors were rare.
Today, power electronics using modern
semiconductors can convert AC frequencies with 98% efficiency at low cost.
airfoil design
Old windmills typically used flat boards for the blades. Wind tunnels and CFD simulations are relatively recent developments. Modern wind turbine blades have much higher L/D ratios and operate at much higher speeds, improving efficiency and power density.