Why dont wind turbins have more wind blades if they have more then they catch more wind and create more enegy.

Question

Why dont wind turbins have more wind blades if they have more then they catch more wind and create more enegy.

Answer 1

Rotational Momentum.  The greater the mass and the further away it is from the spin axis, the more energy it takes to get moving.  If you had a constant source of high wind, multiple  blades might harness more energy.  But with off and on winds, in many places you would never have a high enough gust to get the thing spinning in the first place, and not harness the lower velocity winds that prevail.

Don't know all the physics behind it, but you do NOT need a whole lot of blades to capture the energy of the air moving through their area.  There also also issues with bearing friction and loading to support more blades.  And additional turbulence between them probably causes losses.

Answer 2

Cost. Like most highly engineered systems, windpower systems are designed for the minimum cost system meeting the required specifications.

2 properly designed blades absorb roughly 85% to 90% of the wind energy in their swept area. Adding more blades gets very little more, but also adds drag, weight, and much more cost. The cost is not only for the blades, but also for the pitch control hub and system, and the heavier structure required for the greater topside weight. You're talking less than 5% additional energy possible, then subtract the additional drag. So, say you're designing a 100kW wind power generation system. Better to use a 2% or so longer 2 blade system (for extra 4% or so power) than to use 4 or 6 blades, because it generates the power you target at lower capital and operating costs.

There were old windmills with many blades, used on farms usually to pump water. These used very cheap sheet metal blades of modest efficiency, with a simple frame from rings to hold them. Not adjustable pitch, so used rudder system to turn blades away from the wind when the speed got too high. Lots of ways to approach a problem, usually only one is the most cost effective though.

Answer 3

There is an optimum number of blades given the speed of rotation and size of blade. The blade size is obviously chosen based on material type and cost to produce.

Carbon fiber blades for windmills are very expensive, so minimizing the number is good. Plus if the pitch of the blades needs to be controlled for varying wind speed, it would be easier to do for fewer blades.

I don't think more blades would make it harder to get started. The weight of one blade is balanced by weight on the other side. It just has more momentum when spinning.

Why don't helicopters have more blades?

Prop planes easily fly with two blades, i think more is overkill

Answer 4

You have a good question and I agree with Flipperw but what about lighter weight materials? Like the light weight plastic that is used on childrens swirly sticks  that spin with the wind. Example: bhttp://www.windandweather.com/category.a...  Those have more than four paddles. Wouldn't this concept work?

Answer 5

with more blades the windmill blades shall move much slower thereby creating or generating less energy(this is because with more blades there shall be more weight which shall make it difficult for the wind to make the blades move very vast)

Answer 6

Weight.  The blades are heavy and more might make it more difficult for the turbine to start.

Vertical axis turbines often can use less wind to start - they simply have some designb problems to overcome before they become commonplace.

DK