時差N小時:風力發(fā)電機(下)

　　Turbines with one or two blades are actually evenmore efficient. But because they’re also lighter andtend to spin faster, they’re also noisier. Thesedesigns also require a special tilting hub that acts asa sort of shock absorber, which is expensive. On theother hand, having more than three blades raisesother problems. For one thing, the extra materialneeded to build the blades raises the cost. And themore blades there are, the lighter and thinner theyneed to be. Relatively thin blades are moreflexible, making them prone to bend and break.Three-bladed turbines aren’t perfect, but they avoid many of these problems. They’re powerfulenough without being overly expensive. And they’re less noisy than their two bladed cousins.

　　帶一個或兩個葉片的渦輪機實際上更有效率。但是因為這樣重量較輕，旋轉(zhuǎn)速度更快，噪音也就更大。設計還需要一個特殊的作為一種減震器的傾斜輪軸，它很貴。另一方面，如果葉片超過三個也會引發(fā)其他問題。一方面，建造更多的葉片需要更多的材料，這提高了成本。而且葉片，葉片就要更輕，更薄。很薄的葉片也更靈活，但容易彎曲和斷裂。三個葉片的渦輪機并不完美，但會避免這些問題。他們造價不高，但是功率足夠了。而且兩個葉片的渦輪機噪音小。