Wind turbine blade

1. A wind turbine blade which comprises: a blade body extending from a blade root area to a blade tip and defining a blade cavity, said blade body adapted for use in a wind turbine and adapted to connect to a wind turbine rotor hub at said root area, said blade body including a blade surface comprising a suction side and a pressure side; and a drain for draining off water that condenses inside said blade cavity, wherein said drain comprises at least one hole formed on said surface of said wind turbine blade and communicating with said blade cavity, said at least one hole being located at said wind turbine blade root area.

2. A wind turbine blade according to claim 1 wherein there are two of said holes, at least one hole being located on said suction side of the blade, and at least one hole being located on said pressure side of the blade.

3. A wind turbine blade according to claim 2 wherein said drain holes are both located at said root area.

4. A wind turbine blade according to claim 3 wherein there are two of said holes located on the same side of the blade but not on a same longitudinal line of the blade.

5. A wind turbine blade according to claim 1 wherein there is provided an enclosure member inside the blade at the root area; said enclosure member extending from the inside surface of the suction side of the blade to the inside surface of the pressure side of the blade to provide structural strength.

6. A wind turbine blade according to claim 5 wherein said enclosure member separates the interior of said blade into two compartments, one nearer the root and one nearer the tip, and said drain comprises at least one hole located at one side of said enclosure member and at least one hole located at the other side of said enclosure member.

7. A wind turbine blade according to claim 6 wherein at least one of said holes is located within 5 cm from said enclosure member.

8. A wind turbine blade according to claim 1 wherein said at least one hole has a circular shape.

9. A wind turbine blade according to claim 8 wherein the diameter of said at least one hole is greater than 8 mm.

10. A wind turbine blade according to claim 1 wherein said at least one hole is provided with a protrusion protruding outwards from the outer surface of the blade.

11. A wind turbine blade according to claim 1 wherein said at least one hole is from 8 mm to 15 mm in width.

12. A method of draining the interior of a wind turbine blade, said method comprising: providing a wind turbine blade having a root area adapted for being connected to a wind turbine rotor hub; forming a drain communicating with the interior of said blade in the region of said root of said blade; and draining water from said blade through said drain while said blade is operating slowly in an idling condition.

13. A method as in claim 12 wherein said drain includes an internal structural enclosure member in said root area, said enclosure member separating the interior of said blade into a first region at said root and a second region nearer said tip, and said forming comprises forming a first drain communicating with the interior of said blade in said first region on one side of said enclosure member and forming a second drain communicating with the interior of said blade in said second region on the other side of said enclosure member.

14. A method as in claim 12 wherein said forming said drain further comprises forming a hole communicating with the interior of said blade and forming a protrusion communicating with said hole, and said method comprising using said protrusion to prevent water on the exterior of said blade from entering the interior of said blade via said hole.

15. A wind turbine comprising a rotor hub and three wind turbine blades attached to said rotor hub, each of said wind turbine blades including at least two drain holes, both of said drain holes in each of said blades located at the root area of said blade.