How to Choose a Wind turbine?

How to Choose a Wind turbine?

Wind energy is one of the most established renewable energy industries. Despite this, the small wind market suffers from a lack of regulation, combined with the availability of cheap, low-quality Wind turbine manufactured in the Far East and sold at meager prices online.

There is a massive difference between models of wind turbines, both in regards to the quality of the product and the performance of the turbines. This is particularly true of the tiny wind turbines -turbines with a rated output of 2kW or less. Many of the very low-cost wind turbines routinely sold on eBay are not constructed to cope with many years of outdoor life and often have inferior performance levels.

Wind turbine manufacturers do not have to carry out field tests on their products before they go to market, and performance ratings vary from manufacturer to manufacturer. Certification schemes do exist, but none of them are mandatory. Many of the wind turbines that come from the Far East have not undergone any independent testing and self-certify their performance figures.

With wind turbine manufacturers, think quality. You’re going to be using your wind turbine for the next twenty years and buying cheap is a false economy. Talk to the experts, use long-established companies, and make sure you use certified products.

There have been reports of some wind turbine manufacturers making claims for their products that break the laws of physics with exaggerated across.

Our wind turbines don’t need to be mounted so high up because we have a better rotor design

Wind speed increases the higher you get, and the speed is cubed to calculate the potential wind power. After 2,000 years of wind turbine development, creating a rotor design that is so efficient that it can overcome such a huge difference in potential power is not possible.

We have a vertical wind turbine design that can work efficiently even at ground level

There is not enough power in turbulent wind to make a wind turbine of any design work efficiently at ground level. If your turbine is large enough, you may be able to produce a few watts of power to charge a mobile phone, for example, but that is probably about the limit.

We use smaller rotor blades, but we have six of them rather than three, which means we can capture as much power as our competitors using a much smaller rotor

Excellent idea, but it’s wrong. More rotor blades equal more drag and more turbulence created by the blades themselves. It is the swept area of the rotor that is important for capturing the power of the wind, not the number of the blades.

Our rotor design is 60% efficient

It can’t be, that would break a law of physics. Betz Law, published by German Physicist Albert Betz in 1919, calculated that the maximum amount of power that could be extracted from the wind by a turbine, independent of turbine design, is 16/27ths of the kinetic energy of the wind. 16/27th is 59.3%. This figure is known as Betz’s coefficient.

If a salesperson makes any claims that their small wind turbine is more than 35% efficient, query the figure. While larger, utility-scale wind turbines can be as high as 45% efficient, smaller wind turbines struggle to get much beyond 35%. It could be that they are making their claim against the Betz’s coefficient figure rather than the overall kinetic power of the wind. In this case, their efficiency figure should be multiplied by Betz’s coefficient value of 59.3%. In this instance, a claim of 60% efficiency is 60 X 59.3%=35.58%.which is still high enough to attract suspicion.

Standards performance of the wind turbine

There are certification schemes in place within the wind industry. These require the manufacturers to conform to standards for performance ratings and need the wind turbines to be field tested, generally by a third-party certification council.

The most common certification schemes are:

IEC 61400 certification

These are a series of standards covering engineering and longevity tests to ensure the wind turbine is engineered to withstand hazards within the planned lifetime, along with noise and performance tests.

MCS 006 certification

UK Microgeneration Certification Scheme wind turbine certificate for wind turbines of up to 50kW. This is a superset of the relevant IEC 61400 standards specifically for smaller wind turbines. If you are based in the United Kingdom and are looking to connect your wind turbine to the grid and receive payments through the feed-in tariff scheme, your wind turbine must conform to the MCS 006 standard and be installed by an MCS accredited installer.

AWEA 9.1:2009 certification

American Wind Association Small Wind Turbine Performance and Safety Standard, covering performance, sound, strength, safety, and duration testing. Like the MCS 006, this is a superset of the requirements of IEC 61400.

Small wind certification council

A US certification scheme for small wind turbines, ensuring that turbines conform to required standards (either AWEA or IEC 61400) and have been independently tested. SWCC also provide like-for-like information for wind turbines so consumers can compare turbines from different manufacturers.

Not all wind turbines will have undergone all the different tests. Most of the tests are based on the international IEC 61400 standards, which are then modified for specific applications. ‘When looking at specification sheets for wind turbines, you should look out for conformance to at least one of these standards. This is particularly important for grid-tie applications, as you are unlikely to be able to link into the power grids unless you have certified equipment.

Unfortunately, few tiny wind turbines, typically those rated at 2kW or below, have been certified under any of these schemes. These turbines are most often used in off-grid applications, and most turbine manufacturers seem to have decided that it is not worth the expense of putting these turbines through the same accreditation tests as the larger products. If you are in the market for a tiny wind turbine, you will generally find that the companies that also produce more giant, fully accredited wind turbines, provide full specification sheets for their smaller turbines that at least conforms to the IEC-61400 standards applied to the larger machines. If in doubt, ask the manufacturer for clarification.

The small wind turbine ISO certification

You may also see companies listing ISO 14001 or ISO 9001/ISO 9002 as accreditations against their products. ISO 14001 is a criterion for environmental standards, while ISO 9001 and ISO 9002 are quality standards. Both standards are organizational standards and not standards specifically relating to wind turbines. They are not a substitute for product tests. If you see cheap wind turbines on sale on eBay with no other standards listed other than ISO 14001 or ISO 9001 or ‘CE approved for sale in Europe,’ this means they the turbines have not undergone specific external testing to rate their performance. Likewise, wind turbines advertised as TUV Approved or BSI Approved mean nothing without knowing which standards they have been approved against.

Building wind energy installations

To the casual observer, installing a wind turbine on a building sounds like an ideal combination: the electricity is generated on the building it is being used in, the wind turbine is at the height where the wind is stronger, and if mounted on a roof-top, the concentration of wind should be intensified.

In reality, however, installing wind turbines on buildings is to be avoided. Buildings create turbulence in the air, which dissipates the energy; in the wind and makes it unsuitable for HAWTs and less efficient for VAWTs. Performance of building-mounted wind turbines is weak, and many people who have installed them have been disappointed with their performance. In some cases, people who have installed wind turbines on their homes in built-up areas have discovered the wind turbines do not even generate sufficient energy to power their control electronics.

Besides, wind turbines contain moving parts and create vibrations. Because the speed of the wind turbine is not constant, the frequency of the noises and vibrations created by wind turbines are not consistent, making them difficult to dampen. Consequently, it is not uncommon for wind turbines to create resonances within the building, which are then amplified through the walls. Living or working inside a building with these resonances would be impossible.

What to take on consideration when you install Wind turbine?

The only instance where a building installation may be considered is on a remote agricultural building in an open field where a small amount of electricity is required to power lighting. In this case, a small wind turbine with a rated output of no more than 1kW could be mounted on a tall pole, clamped to a supporting structure at one end of the barn, facing the prevailing winds. For much of the United Kingdom, the prevailing winds come from the South-West. The turbine should be mounted so that the lowest point of the rotor blade is at least ten meters (32 feet) above the highest point of the building. You should expect to get 50-70% of the energy that you would from an identical wind turbine that has been installed on a freestanding pole in an open location.

Rated power and annual energy production figures

As the official fuel economy figures for your car, rated power, and yearly energy production figures may or may not relate to the amount of power, you can reasonably expect to get from a wind turbine once you have installed it. Instead, these figures work in much the same way as the official fuel economy figures for your car: they allow you to compare your vehicle with another one to make comparisons between them.

Compare the figures that you calculated for your wind production with the power graphs. They should show similar figures, but they almost certainly will not be the same. If you want to make your figures more accurate, you will need to ask the manufacturer to provide you with their power coefficient rating for their rotor and their generator efficiency. Based on this, you can then rerun your calculations to get a clearer idea of the expected power output from this turbine.

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