Wind turbine rotor blade with in-plane sweep and devices using same, and methods for making same

1. A blade having a torsionally rigid root, a forward sweep of an elastic axis in an inboard section of said blade and an aft sweep of the elastic axis in an outboard section of said blade, said forward sweep is at said root of said blade, wherein said forward sweep is defined as an angle extending between said elastic axis at said inboard section of said blade and a pitch axis of said blade, and said aft sweep is defined as an angle extending between said elastic axis at said outboard section of said blade and said pitch axis of said blade.

2. A blade in accordance with claim 1 wherein said forward sweep is at least 0.25 degrees.

3. A blade in accordance with claim 1 wherein said forward sweep is at least 0.5 degrees.

4. A blade in accordance with claim 1 wherein said forward sweep is at least 1 degree.

5. A rotor for a wind turbine, said rotor having a hub and at least one blade having a torsionally rigid root, an inboard section, and an outboard section, said inboard section having a forward sweep of an elastic axis of said blade and said outboard section having an aft sweep of said elastic axis, said forward sweep is at said root of said blade, wherein said forward sweep is defined as an angle extending between said elastic axis at said inboard section of said blade and a pitch axis of said blade, and said aft sweep is defined as an angle extending between said elastic axis at said outboard section of said blade and said pitch axis of said blade.

6. A rotor in accordance with claim 5 wherein said blade has a forward sweep of at least 0.25 degrees.

7. A rotor in accordance with claim 5 wherein said blade has a forward sweep of at least 0.5 degrees.

8. A rotor in accordance with claim 5 wherein said blade has a forward sweep of between 1 and 3 degrees, inclusive.

9. A rotor in accordance with claim 5 wherein said forward sweep is effective to counter an amount of torsion resulting from said aft sweep.

10. A rotor in accordance with claim 9 wherein an amount of said forward sweep is effective to neutralize a pitching moment built up by blade sweep further outboard.

11. A rotor in accordance with claim 5 wherein said blade has a root, a tip, and a knee at 60% span, and said blade has a 15 degree forward sweep at its root and a 15 degree aft sweep at its tip.

12. A wind turbine comprising a rotor having a hub and at least one blade having a torsionally rigid root, an inboard section, and an outboard section, said inboard section having a forward sweep of an elastic axis of said blade and said outboard section having an aft sweep of said elastic axis, said forward sweep is at said root of said blade, wherein said forward sweep is defined as an angle extending between said elastic axis at said inboard section of said blade and a pitch axis of said blade, and said aft sweep is defined as an angle extending between said elastic axis at said outboard section of said blade and said pitch axis of said blade.

13. A wind turbine in accordance with claim 12 wherein said blade has a forward sweep of at least 0.25 degrees.

14. A wind turbine in accordance with claim 12 wherein said blade has a forward sweep of at least 0.5 degrees.

15. A wind turbine in accordance with claim 12 wherein said blade has a forward sweep of between 1 and 3 degrees.

16. A wind turbine in accordance with claim 12 wherein said forward sweep is effective to counter an amount of torsion resulting from said aft sweep.

17. A wind turbine in accordance with claim 16 wherein an amount of said forward sweep is effective to neutralize a pitching moment built up by blade sweep further outboard.

18. A wind turbine in accordance with claim 12 wherein said blade has a root, a tip, and a knee at 60% span, and said blade has a 15 degree forward sweep at its root and a 15 degree aft sweep at its tip.

19. A method for making a blade for a wind turbine, said method comprising:

determining a blade shape by selecting sweep angles for elements of said blade so as to (a) increase or maximize an amount of twist induced and the distribution of said twist in such a manner as to create a reduction loads, (b) reduce or minimize an increase in blade material necessary to maintain tip deflection, (c) reduce or minimize negative effects on aerodynamics, and (d) maintain structural integrity; and

fabricating a blade in accordance with the determined blade shape such that an inboard section of the blade has a forward sweep of an elastic axis of the blade and the forward sweep is at a root of the blade.

20. A method in accordance with claim 19 further comprising selecting a FIG. of Merit and weighting factors (a)-(d) in accordance with the selected FIG. of Merit.

21. A method in accordance with claim 20 wherein the FIG. of Merit is related to cost of energy.

22. A method in accordance with claim 20 wherein the blade has a tip, and further wherein determining a blade shape further comprises imposing a constraint on a location of the tip and on a maximum sweep angle.