Extending lifetime is often the best option

WORLDWIDE: Years ago as part of a seminar on sustainable project development, I attended a presentation by a major bank on its striking new high-rise headquarters, claimed to be a benchmark for energy efficiency and sustainability.

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The speaker discussed the building's design and innovative features, stressing that the bank had made use of the latest, most environmentally friendly technology in materials separation and recycling when demolishing the old 1960s headquarters.

However, I once read that renovating a building generally takes 10-15 times less cumulative energy input compared with constructing a new structure for the same use. And a study by the National Trust for Historic Preservation in the US found that the energy balance between demolishing an existing office building and an energy-efficient replacement building incorporating the latest "green technologies" would still require up to 65 years to neutralise the energy lost during the demolition, even if 40% of the materials were recycled.

Wind turbines are commonly developed for a 20-year life, but a number of recent initiatives indicate that this may shift, albeit gradually, to 25 years and longer. The single biggest envisaged benefit is that this will drive down lifecycle-based costs of energy (CoE). A wider overall benefit to societies as a whole is improving the sustainability of the product and project. There are several main components in wind turbines, such as transformers and copper (ground) cables for electricity transport, that can last for over 50 years, or even as long as 100 years, as in the case of concrete towers. Spreading payback over a longer period thus positively contributes towards lowering CoE and improving project sustainability.

Initiatives to extend turbine lifetime are not new, but so far have produced mixed results. I remember meeting an official of former US wind-turbine supplier Zond at Germany's Hanover international industry fair in the mid-1990s. He proudly pointed at a new 750kW Z-750 model with an impressive integrated drive train on display and claimed it was the world's only turbine with a GL-certificate for a 30-year design life certificate. Unfortunately, the Z-750 developed major issues with key components such as gearboxes soon after its introduction and a complete redesign of the turbine was carried out. But there are other examples of turbine models that have successfully operated for over 20 years.

In the pioneering days of the wind industry, limited know-how and experience hampered progress. And huge market pressure for bigger turbines allowed insufficient time to develop lengthy experience and thus more reliable turbines. And from an owner/developer perspective, it was often considered attractive to replace older turbines well before they had reached their technical lifespan and install larger, more powerful new products.

Design longevity

It was not until the emergence of utility 1.5-2MW and above turbines that upscaling pressures lessened. Several volume products have now been on the market for a decade or longer in different model, with thousands in operation. The Siemens 2.3MW series, for example, has been on the market for ten years, but available rotor diameters have increased four times.

At the recent European wind conference in Denmark I spoke with a Gamesa expert responsible for a new business dedicated to turbine reconditioning and future lifetime extension to 25 or even 35 years. These turbines, he told me, can be older kilowatt-class models operating at sites with height, infrastructure or other restrictions that block repowering. They can also be more recent megawatt-scale turbines with other issues.

Lifetime extension projects typically involve a technology condition scan after around 15 years of operation, he said, which then forms the basis for a production improvement plan of additional years.

Modern wind turbines recover their cumulative energy inputs within three to eight months of electricity generation, which can be expressed as "energy payback period". This contributes to a sustainability performance figure that shows the lifecycle energy output-input ratio - called the harvest factor. So, a 20-year turbine lifetime with six-month energy payback results in a harvest factor of 20x12/6=40.

Classic-build photovoltaic panels in moderate European climate regions, lasting 25 years, with energy payback quoted in the 2.5-year range, produce a harvest factor of around 10. A building generating no "internal" power can never achieve a positive harvest factor.

Expanding turbine operating spans to 25-30 years can also boosts the harvest factor, providing that upkeep costs and turbine performance remain in line with industry expectations. This is a clear win-win situation and fits into the key role that modern wind power can and does already offer the world.

Eize de Vries is Windpower Monthly's technology and market trends consultant.

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