1. A Savonius rotor assembly for interacting with a moving fluid, comprising:

(a) a support framework; (b) a rotor mounted on the support framework for rotation about a central horizontally extending axis, the rotor having two blades disposed symetrically about the central horizontally extending axis, each of the blades having an outer edge and an inner edge with respect to the central, horizontally extending axis, the outer edges of the blades lying on a circle defining a diameter of the rotor, the blades further having a first curved portion and a second curved portion, the first curved portion beginning at the outer edge and ter- minating at the second curved portion with the first curved portion defining a surface generally concave with respect to the central, horizontally extending axis, the first curved portion having a radius of curvature which becomes progressively less from the outer edge to the second curved portion, the second curved portion coming progressively closer to a plane containing the central, horizontally extending axis and the outer edge of the blade as the second curved portion extends from the first curved portion to the inner edge of the blade, the maximum displacement of the blades from the plane being less than one-quarter of the diameter of the rotor; and

(c) a deflector member extending substantially along the length of the rotor and positioned on a side of the rotor facing the direction from which the fluid is flowing, a top edge of the deflector member being positioned below a substantially horizontal plane extending through the central, horizontally extending axis of the rotor.

2. A Savonius rotor assembly in accordance with claim 1, the Savonius rotor assembly further including an airfoil member disposed proximate the top edge of the deflector member and extending substantially along the length of the rotor, the airfoil member being pivotable about an axis substantially parallel to the central, horizontally extending axis.

3. A Savonius rotor assembly in accordance with claim 1, wherein the point of tangency of the first curved portion with the second curved portion is closer to the circle defining the diameter of the rotor than the point of tangency of the second curved portion and a circular arc which is tangent to the circle defining the diameter of the rotor at the outer edge of the blade and having its center at a -point on the plane containing the central, horizontally extending axis and the outer edge of the blade.

4. A Savonius rotor assembly in accordance with claim 1, the second curved portion of each of the blades having a uniform radius of curvature and terminating at the inner edge before crossing the plane containing the central, horizontally extending axis and the outer edge of the blade.

5. A Savonius rotor assembly in accordance with claim 1, wherein the support framework is mounted for rotation about a substantially vertical axis.

6. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member extends beyond the ends of the rotor.

7. A Savonius rotor assembly in accordance with claim 1, wherein the first curved portion has a shape charac¬ teristic of part of an ellipse whose major axis is skewed.

8. A Savonius rotor assembly in accordance with claim 1, wherein the second curved portion terminates at a location on either side of and removed from the plane containing the central, horizontally extending axis and the outer edge of the blade by less than one-tenth of the diameter of the rotor.

9. A Savonius rotor assembly in accordance with claim 1, wherein the second curved portion, if extended along an imaginary surface, crosses the plane containing the central, horizontally extending axis and the outer edge of the blade at a location removed from the central axis by less than one-third of. the diameter of the rotor.

10. A Savonius rotor assembly in accordance with claim 1, wherein a bottom edge of the deflector member extends down substantially to ground level.

11. A Savonius rotor assembly in accordance with claim 5, wherein the support framework is mounted for rotation about the substantially vertical axis on wheel means for travel along track means.

12. A Savonius rotor assembly in accordance with claim 5, wherein the support framework is supported for rota¬ tion about a substantially vertical axis by central ver¬ tical shaft means.

13. A Savonius rotor assembly in accordance with claim 2, wherein the airfoil member extends beyond the ends of the rotor.

14. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a substantially vertical flat plate member.

15. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a substantially flat plate member facing the fluid at an angle.

16. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a convex sur¬ face facing the fluid. .

17. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a partially curved portion with a convex side facing the fluid and a partially flat portion.

18. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a partially curved portion with a concave side facing the fluid and a partially flat portion.

19. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a concave sur¬ face facing the fluid.

20. A Savonius rotor assembly in accordance with claim 1, wherein the deflector member includes a curved por¬ tion with a convex side facing the moving fluid, a top edge portion of the deflector member extending substan-

tially parallel with the direction of the fluid flow and of substantially the same height as the height of a plane of fluid flow through the rotor axis.

21. A Savonius rotor assembly in accordance with claim 20, wherein the curved portion of the deflector member makes an angle within +_ 10° of the direction in which the fluid is flowing, the top edge of the deflector member extending not more than 0.15 of the diameter of the rotor beyond a mid-section of the rotor.

22. A Savonius rotor assembly for interacting with a moving fluid, comprising:

(a) a support framework; and

(b) a rotor mounted on the support framework for^* rotation about an axis, the rotor having two blades disposed symetrically about the axis, each of the blades having an outer edge and an inner edge with respect to the axis, the outer edges of the blades lying on a circle defining a diameter of the rotor, the blades further having a first curved portion and a second curved portion, the first curved portion beginning at the outer edge and terminating at the second curved por¬ tion with the first curved portion defining a surface generally concave with respect to the axis, the first curved portion having a radius of curvature which be- comes progressively less from the outer edge to the second curved portion, the second curved portion coming progressively closer to a plane containing the axis and the outer edge of the blade as the second curved portion extends from the first curved portion to the inner edge of the blade, the maximum displacement of the blades from the plane being less than one-quarter of the diameter of the rotor.

23. A Savonius rotor assembly in accordance with claim 22, wherein the axis of rotation is horizontal.

24. A Savonius rotor assembly in accordance with claim 22, wherein the axis of rotation is vertical.

25. A Savonius rotor assembly for interacting with a moving fluid, comprising:

(a) a support structure;

(b) . a rotor mounted on the support structure for rotation about a central, horizontally extending axis, the rotor having at least two blades; and

(c) a deflector member extending substantially along the length of the rotor and positioned on a side of the rotor facing the direction from which the fluid is flowing, a top edge of the deflector member being positioned below a plane substantially parallel to the direction of the fluid flow and extending through the horizontally extending axis of the rotor.

26. A Savonius rotor assembly in accordance with claim

25. wherein the rotor has three blades.

27. A Savonius rotor assembly in accordance with claim 25, the Savonius rotor assembly further including an airfoil member disposed proximate the top edge of the deflector member and extending substantially along the length of the rotor, the airfoil member being pivotable about an axis substantially parallel to the central, horizontally extending axis.

28. A Savonius rotor assembly in accordance with claim 25, wherein the support framework is mounted for rota¬ tion about a substantially vertical axis.

29. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member extends beyond the ends of the rotor.

30. A Savonius rotor assembly in accordance with claim 25, wherein a bottom edge of the deflector member extends down substantially to ground level.

31. A Savonius rotor assembly in accordance with claim 28, wherein the support framework is mounted for rota¬ tion about a substantially vertical axis on wheel means for travel along track means.

32. A Savonius rotor assembly in accordance with claim 28, wherein the support framework is supported for rota¬ tion about a substantially vertical axis by central ver¬ tical shaft means.

33. A Savonius rotor assembly in accordance with claim 27, wherein the airfoil member extends beyond the ends of the rotor.

34. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a flat plate member facing the fluid at approximately a right angle.

35. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a substan¬ tially flat plate member facing the fluid at an angle.

36. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a convex sur¬ face facing the fluid.

37. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a partially curved portion with a convex side facing the fluid and a partially flat portion.

38. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a partially curved portion with a concave side facing the fluid and a partially flat portion.

39. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a concave sur¬ face facing the fluid.

40. A Savonius rotor assembly in accordance with claim 25, wherein the deflector member includes a curved por¬ tion with a convex side facing the moving fluid, a top edge portion of the deflector member extending substan¬ tially parallel with the direction of the fluid flow and of substantially the same height as the height of a plane of fluid flow through the rotor axis.

41. A Savonius rotor assembly in accordance with claim 40, wherein the curved portion of the deflector member makes an angle within +_ 10° of the direction in which the fluid is flowing, the top edge of the deflector member extending not more than 0.15 of the diameter of

42. A Savonius rotor assembly for interacting with a moving fluid, comprising:

(a) a support structure;

(b) a rotor mounted on the support structure for rotation about a central axis oriented at an angle with the horizontal, the rotor having at least two blade; and

(c) a deflector member extending substantially along the length of the rotor and positioned on a side of the rotor facing the direction from which the fluid is flowing, the top edge of the deflector member being positioned below a plane substantially parallel to the direction of the fluid flow, the top edge of the deflec¬ tor member extending not more than 0.15 of the diameter of the rotor beyond a mid-section of the rotor.

43. A Savonius rotor assembly in accordance with claim 42, wherein the top edge of the deflector member does not extend beyond a mid-section of the rotor.

44. A Savonius rotor assembly in accordance with claim 42, wherein the central axis is vertically extending.