Going with the wind

IEC International Standards support wind power’s remarkable expansion

By Morand Fachot

As demand surges for clean power generation to meet the world’s growing energy need, the renewable energy sector is set to expand rapidly. Wind energy is currently the most cost effective new renewable energy source. Many countries have goals for wind to supply more than 20% of their energy generation by 2030, with offshore turbines playing a significant role in some countries. With the growing demand for more efficient and reliable wind turbines, IEC International Standards prepared by IEC TC (Technical Committee) 88: Wind turbines, are ever more central to the successful development of the industry.

Fast growth and major economic stakes

In 2009 the world relied on renewable sources for over 13% of its primary energy supply and renewables accounted for nearly 20% of global electricity generation, according to IEA(International Energy Agency) statistics.

Wind power now supplies the greater part of the world’s non-hydropower renewable electricity capacity. Global wind power capacity was 238 GW (gigawatts) at the end of 2011, up from just 18 GW at the end of 2000, with a CAGR (compound annual growth rate) of over 25% over the past five years. According to Pike Research, a firm that provides in-depth analysis of global clean technology markets, that capacity is expected to reach 562.9 GW by 2017, representing a USD 153 billion global industry and cumulative investment in new wind power capacity of USD 820 billion.

The supply of wind turbines is a global business, with the six largest producers all based in different countries and the 10 top manufacturers accounting for nearly 80% of global production.

Demand for reliable products to feed the fast growth of this industry is satisfied primarily by the products' compliance with IEC 61400Wind turbine generator systems, the series of 19 International Standards and Technical Specifications which have become the world's de facto standards for the industry.

Environmental and other challenges

The increase in wind energy capacity has come from the installation of greater numbers of turbines and also from the availability of larger, more efficient turbines.

IEC 61400-1 outlines design requirements for wind turbines. It isn't limited to the design of mechanical, electrical and electronic parts, but also takes into account a thorough assessment of the following site-specific environmental and other conditions:

  • topographical complexity of the site
  • wind conditions
  • wake effects from neighbouring wind turbines
  • earthquake conditions
  • electrical network conditions
  • soil conditions
  • structural integrity by reference to wind data
  • structural integrity by load calculations with reference to site-specific conditions

All these factors determine the optimum and safe choice of sites on which to install wind turbines

Technical challenges

The origin of wind turbines dates back to several centuries BC when windmills were used to pump water or mill cereals. It is estimated that some 100 000 windmills were scattered throughout Europe during the 18th and 19th century before wind power was displaced by steam engines and other sources of mechanical power. In America, farmers and rural communities relied extensively upon small electricity-generating wind turbines which first appeared in the late 19th century.

For most uninformed observers, the term wind turbine evokes an image of a large three-blade propeller-like mechanism rotating on top of a tower. In fact wind turbines are complex installations that may come in different shapes and include structural (tower), mechanical (gearbox, drives, etc.), electrical (generator, motors, cables, etc.) and electronic (control, monitoring) systems.

The huge increase in electricity from wind power in recent years is the result of the greater number of turbines installed as well as of the launch of larger turbines. The average capacity of turbines is now greater than 2,5 MW; some now even achieve 7,5 MW with rotor diameters that can exceed 160 metres. The introduction of these very large turbines means that many technical challenges have to be overcome to ensure safe and proper operation of the devices.

Wind turbines can be set up on land and offshore. Their components share most design requirements but specific conditions for offshore installations are dictated by the marine environment.

IEC 61400-3Design requirements for offshore wind turbines, includes assessments of the external circumstances at an offshore site, such as wind conditions, waves, currents, water level, tides and storm surges, sea ice, earthquake conditions and seabed movement. This International Standard also details recommendations for the assembly, installation and erection of offshore turbines as well as for their commissioning, operation and maintenance.

Other International Standards in the IEC 61400 series cover many additional aspects such as the measurement of mechanical loads and acoustic noise, structural testing of rotor blades, lightning protection, communications for monitoring and the control of wind power plants for maintenance, conformity testing and certification.

Small is beautiful too

If the ten-fold increase in wind power cumulative capacity between 2001 and 2011 (from 23,9 to 238,4 GW) results mainly from the installation of large turbines, small wind power installations can also provide cost-effective electricity on a highly localized level, both in remote settings as well as in conjunction with power from the utility grid.

TC 88 has prepared IEC 61400-2Design requirements for small wind turbines, to deal "with safety philosophy, quality assurance, and engineering integrity" and to set out "requirements for the safety of SWTs (Small Wind Turbines) including design, installation, maintenance and operation under specified external conditions".

IEC 61400-2 "applies to wind turbines with a rotor swept area smaller than 200 m2, generating at a voltage below 1 000 V a.c. or 1 500 V d.c.". This part of IEC 61400 is similar to IEC 61400-1, but "does simplify and make significant changes in order to be applicable to small turbines".

Pike Research forecasts that the global market for small wind systems will have more than doubled in value between 2010 and 2015, from USD 255 million to USD 634 million.

During the same period small wind system installed capacity additions will nearly triple to 152 MW. "The payback period for a small wind system can be 5 to 10 years in a region with adequate wind resources", says Pike Research senior analyst Peter Asmus, adding: "these economics provide a strong value proposition for a variety of commercial, industrial, and residential applications"..

IEC standards unlock expansion and boost investors' confidence

IEC International Standards have proven essential to meet the complex challenges and set of issues faced by the wind power industry. The global nature of that industry means that International Standards play a vital role in ensuring the proper production, testing, worldwide installation and acceptance of wind power turbines, whether large or small and installed on land or offshore.

Sandy Butterfield, founding CEO (chief executive officer) and CTO (chief technical officer) of Boulder Wind Power and Chairman of IEC TC 88, notes that when he started in the wind turbine business in the early 1980s, the absence of harmonization and consistency in the design process meant that many important design features that would ensure the manufacture of reliable products were missing. As a result there was a lack of confidence on the part of stakeholders and a reluctance to fund projects. All this changed when the industry started objective testing based on standards developed by the IEC, Butterfield says.

"Standards offered the financial community a way of believing that the machine had been designed according to some objective third party process and that it had been reviewed according to some rules that the entire industry agreed upon." He adds, "Ultimately, in the wind energy business, all wind turbines end up being certified. It's a market imperative. If you don't understand the standards, you have a more difficult time meeting the certification".

The IEC 61400 series of International Standards and associated referenced documents ensure the wind power industry has all the information needed to allow it to manufacture products that are internationally certified, accepted and marketable.

Siemens SWT-3.0-101 DD 3 MW direct drive turbine with 50% fewer parts (Siemens press picture) Siemens SWT-3.0-101 DD 3 MW direct drive turbine with 50% fewer parts (Siemens press picture)
Offshore wind farm installation (Photo: London Array Limited) Offshore wind farm installation (Photo: London Array Limited)
Vertical axis wind turbines can be found on top of office and commercial buildings (Photo: DARcorporation) Vertical axis wind turbines can be found on top of office and commercial buildings (Photo: DARcorporation)