Resumo turbinas eólicas

                

[pic 1]

Market, cost, and technical analysis of vertical and horizontal axis wind turbines

[pic 2]

---

Table of Contents

1        INTRODUCTION        1

1.1        Early historical development        1

1.2        The modern HAWT        1

1.3        The modern VAWT        2

2        HAWTS VS VAWTS        5

2.1        Aerodynamic efficiency        5

2.1.1        Drag-based devices        5

2.1.2        Lifting surface devices        5

2.1.3        Comparison of efficiencies        5

2.1.4        Maximizing efficiency        6

2.1.5        Parasitic drag        7

2.2        Capacity factor        7

2.3        Annual energy capture        8

2.4        Effect of scale        9

2.5        Cost breakdown        9

2.6        Rotor mass        10

2.7        Dynamics problems        12

2.8        Drive train design        12

2.9        Installation        13

2.10        Maintenance        13

2.11        Support system        14

2.12        Braking        14

2.13        Technology advances        15

2.14        Offshore design        16

2.15        Certification        17

3        SUMMARY        18

4        CONCLUSIONS        21

5        REFERENCES        21

List of figures

Figure 11. Typical modern 2-bladed HAWT        2

Figure 12. Typical modern 3-bladed HAWT        2

Figure 13. A commercial 2-blade curved VAWT.        3

Figure 14. A prototype straight bladed VAWT        4

Figure 15. A prototype straight bladed VAWT        4

Figure 21. Comparison of aerodynamic efficiencies of common types of wind turbines, from [Hau]        6

Figure 22. Comparison of aerodynamic performance for a VAWT and HAWT        8

Figure 23. Effect of scale on the mass/swept area ratio of HAWTs and VAWTs        11

Figure 24. Possible offshore VAWT configuration        17

List of tables

Table 21. Comparison of annual energy captured from a VAWT and HAWT        8

Table 22. Typical cost breakdown for a 750 kW HAWT installation        9

Table 23. Cost of a typical 250 kW VAWT before installation        10

Table 24. Summary of swept area per unit length of blade, etc.        11

Table 25. Some technology improvements in the wind industry        15

Table 31. Summary of features of typical HAWTs and curved- and straight-bladed VAWTs        19

1. INTRODUCTION

1.  Early historical development

This report attempts to answer the question of why horizontal axis wind turbines (HAWTs) are currently more common and are regarded as more economically competitive than vertical axis turbines (VAWTs).  Some historical review will assist in putting this question into perspective.

The very first records of wind turbines are from Persia around 644AD and from China around 1219 AD.  Both involved the rotation of blades around a vertically oriented axis.  Both used fabic to cover the blades and relied on the drag from the wind to provide force.  The Persian design required a shroud to direct the wind and was not, therefore, completely omnidirectional.  The Chinese design allowed the drag on the advancing blades to be less than that on the retreating blade, did not use any shroud, and was a truly omnidirectional wind turbine [Spera].  Such machines were very simple mechanically since the vertical axle could be used directly to move the stones used to mill flour.

The year 1200 AD is also the approximate date of the first records of horizontal axis wind turbines in England [Spera].  This represented a fundamental change in two ways: first, the horizontal axis had to be converted to a vertical one through a “cog and ring” gear in order to drive the milling stones.  In addition, some yawing system was needed to allow the rotor to face into the wind at all time.  Second, the blades, initially flat boards, were driven by lift rather than by drag from the wind.  This fundamental principle may not have been appreciated by the owners at the time, but it was the underlying reason that these early windmills, known as the Dutch or English design, became prevalent throughout Europe and many other places.  Despite their added complexity and initial cost, they were more efficient than devices that relied on drag.