Summary of this Page.

The HAWT has evolved very successfully to become a dominant 'monoculture' in converting wind energy into electricity. Many say that it's current design is approaching its limit in size. The HAWT suffers from intermittency and low capacity factors making it a difficult choice for base load electrical supply. A wind powered generator with a far higher capacity factor would be far more valuable.

What's wrong with HAWTs?

Wake effect?

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Animation about the past:
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Currently wind energy used by man can be divided into
two main areas:

1. Traction
where wind is used to pull or drive a vehicle. For instance a sail boat or 'power' kite.

2. Static
where wind, normally, drives a rotating shaft that is used to drive something useful like a pump or electrical generator.

Traction
Today sailing is generally a recreational activity but a notable exception was launched recently by the German company Skysails: www.skysails.de. Their traction kite system reduces the fuel consumption for commercial shipping. There is an explanation of the system at www.gcaptain.com

Static
Currently all static wind energy is derived from two main types of wind turbine that are named after the orientation of their main rotating shafts.

The Vertial Axis Wind Turbine (VAWT) and the Horizontal Axis Wind Turbine (HAWT).

VAWTs have their supporters, who claim they have various advantages over the HAWT. A very significant, apparent advantage, being that the generator can be fixed on the ground rather than up tall tower.

VAWT see glossary

However as can be seen elsewhere; high energy wind graphic the tall tower is generally required anyway to get the blades high up into faster moving (and thus more energy rich) airflows. The generator could still be on the ground but a long propeller shaft would then be required.

The debate continues as to if the VAWT can match or beat the HAWT in certain performance criteria (for example reduced noise). It has been argued that VAWTs might compete more effectively if it was a 'level playing field'. The point being that nearly all the development and investment has gone into the HAWT.

There is currently no dispute as to which is dominant in the market place; nearly all wind turbines are of the HAWT type and for commercial generators the HAWT design is even more dominant.

a surprisingly advanced old fashioned windmill. more...

HAWT see glossary

The basic design of the HAWT generators has not changed in hundreds of years. Recent interest in renewable energy has motivated industry to incrementally refine the HAWT design resulting in progressively lower cost per kilowatt.

The improvements have been mainly due to scaling up the size of each turbine. For example, a 5 MW turbine is less expensive than two 2.5 MW turbines.

The latest HAWTs have a swept area similar to two football pitches. It is generally accepted that HAWTs are not going to further increase in size, significantly, due to practical limits being approached in various parameters. more.
Therefore, turbine manufactures need to develop new schemes to further reduce costs.

5MW HAWT

HAWT's Shortcomings
Despite the HAWT's dominance, it fails to utilise most of the available wind resource. see graphic It also suffers from 'intermittency' failing to do its job of supplying 'dependable' electrical supply for instance in light winds: A well placed HAWT in the UK generally has a capacity factor of little more than 30%. This leads to criticism from those who claim that every HAWT used for base load requires a back up conventional power station. Of course supporters of wind power point out that all power stations require some sort of backup. The percentage of backup required and cost of providing that backup are clearly debateable. However there is no dispute that a wind powered generator with a higher capacity factor, and reduced intermittency, would be more valuable not least because it would require less backup.