Vertical array wind turbine

Abstract

A wind turbine with an array of rotors arranged at various heights. Each rotor is optimized for the height at which it is located. Optimization of each rotor could include selection of rated power, solidity, tip speed, blade twist, blade taper, or rotor diameter. Each rotor can also be operated in a manner that is optimized for the wind speed it experiences. Optimized operation parameters could include blade pitch angle or rotor speed.

Description

RELATED APPLICATIONS [0001] This application is a Continuation of co-pending U.S. patent Application Ser. No. 10 / 092,775 which was filed on Mar. 7, 2002.FIELD OF THE INVENTION [0002] The invention relates to the field of wind turbine generators. Specifically, the invention relates to an array of wind turbine rotors on a single tower that are individually optimized to improve the economics of the entire system. BACKGROUND OF THE INVENTION [0003] Wind turbines have gained widespread use for electricity generation in recent years. The cumulative capacity of wind turbines installed worldwide has grown at a rate of approximately 32% per year over the past ten years. As of the end of 2001, the total installed capacity of wind turbines worldwide added up to over 20,000 MW. Future growth prospects for the industry are bright, although the economics of wind energy must continue to improve for the market to grow. There are signs that the potential for economic gains from current wind turbine ...

AI Technical Summary

Benefits of technology

[0015] Another advantage of the present invention is that each of the plurality of rotors is optimized for its individual wind regime. Each rotor can have a unique power rating relative to its swept area. In this way, the blades, hubs, pitch assemblies, and main bearings are similar for all of the rotors and are interchangeable as spare parts. However, the drive train and generator for each rotor would be unique. Other parameters that could be optimized for each rotor include its solidity and tip speed, although if the rotors are to be interchangeable then the solidity must be consistent among rotors. Generally, the rotors toward the top of the tower have a higher power rating, a higher tip speed, and optionally a lower solidity. This allows each rotor to extract the maximum possible amount of energy out of the wind for the wind resource that it “sees.” The energy extracted by a plurality of small rotors is greater than the energy extracted by a single massive rotor because each of the smaller rotors can be better tailored to its unique wind resource.

[0016] Each of the rotors is also controlled individually for the local wind speed that it experiences. Control parameters can include cut-in, cut-out, rotor speed, and blade pitch. By controlling each rotor individually it is possible to achieve a higher overall efficiency compared to controlling a single massive rotor based on the average wind speed that the rotor sees. Each rotor is controlled to be at the appropriate rotor speed and blade pitch to maintain peak efficiency. This allows the entire system to operate at peak efficiency for the entire range of wind speeds experienced from the lowest rotor to the highest rotor. In contradistinction, a single large rotor can only be controlled to operate at peak efficiency for one height and one wind speed while much of the rotor operates at lower efficiency.

[0017] The present invention has further advantages in terms of availability and maintenance. When a very large wind turbine faults offline, its entire production is lost. In contrast, one of the rotors of the present invention can fault offline with the resulting loss of only a small fraction of the total output. For example, if a 1.5 MW wind turbine ex

Problems solved by technology

However, large turbines are also considerably more expensive than smaller machines and the economy of scale does not completely explain the trend to multi-megawatt size wind turbines.

Project developers have demanded larger wind turbines at least partly due to perception issues.

As the size of wind turbines grows, there are several technical issues that adversely affect the economics of wind energy and that can potentially lead to constraints in turbine size.

Another problem with large wind turbines is blade deflection.

The turbine designer must take care so that the blade does not strike the tower, thereby causing catastrophic failure.

However, the loads that cause deflection also increase for longer blades.

However, practical considerations such as tooling, blade weight, and material cost constrain the design so that the blade's chord and thickness are smaller relative to the blade's length for large rotors.

This causes a higher aspect ratio and lower solidity for large rotors.

However, noise issues tend to constrain tip speed ratio so that centrifugal stiffening is less for very large rotors.

All of this points toward blade deflection becoming a limiting design criteria for very large wind turbine rotors.

Another issue with very large rotors is that there is a large amount of composite material in each blade which can lead to material problems.

Statistically, there is a higher probability of a defect existing in a large blade than in a small blade.

If a defect is built into a blade, it can propogate to become a crack which will eventually lead to the blade's failure.

As the thickness of the blade's laminate increases, it becomes more and more difficult to detect flaws in the material.

Therefore, very large wind turbine blades may have a higher statistical probability of failure than a larger number of smaller blades.

Another issue for very large wind turbines is transportation and installation logistics.

Also, the tower h

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