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Breathing new life into old wind turbines

WORLDWIDE: A key objective for turbine manufacturers is to reduce the cost of the power their machines produce. Technology has allowed manufacturers to increase the rotor size and improve the efficiency of their turbines to harvest the maximum energy from any given wind speed. Now, another key emerging area for reducing wind energy costs is improving the reliability and longevity of turbines.

Programmes to prolong turbine life are growing in popularity
Programmes to prolong turbine life are growing in popularity

As a result, new operations and maintenance (O&M) models such as reliability-centred maintenance and reconditioning programmes are becoming increasingly popular. However, these improvements are just the first glimpse of a much more ambitious and promising opportunity: turbine life extension.

Reliability-centred maintenance

Two years ago, as part of an aim to reduce the cost of energy of its worldwide fleet of turbines by 30% — bringing it close to price parity with other sources of energy — turbine manufacturer Gamesa looked at maintenance, and particularly reliability-centres maintenance (RCM). This is a process that has been used for more than 50 years in other industrial sectors such as nuclear, aeronautics, rail and aerospace. It involves studying failure modes of each component and their possible consequences on a more complex system. RCM optimises maintenance tasks, defining predictive, preventive and corrective actions, and finally determining when a component should be upgraded with the latest design.

So rather than just fixing a broken turbine component with the same component that could fail again, RCM is a dynamic process nurtured by operational experience, which configures each maintenance programme based on the evolution of the turbine, and at the point of its life cycle it has reached. This guarantees optimised maintenance and allows an extension of the original useful life by identifying where it is possible to make some hardware or software upgrades to boost reliability or ease of maintenance.

But RCM is about more than simply upgrading individual turbine components and software systems. Such improvements will certainly increase the time between turbine failures, but the productivity of a wind farm can also be affected by a turbine's regular downtime, and this stems mainly from a lack of parts, limited technical experience of the personnel and low operational efficiency.

Logistics upgrade

With this in mind, another key element of successful RCM is the complete overhaul of logistics networks and the roll-out of cutting-edge mobility solutions to ensure the right components are in the right place at the right moment for swift and timely maintenance work. Advances in logistics processes and tools, for example, now mean that technicians equipped with tablet computers have at their fingertips the necessary systems to identify parts digitally using barcode scanners and order spares, as well as being able to access online user manuals and best practice documentation. Meanwhile, all service tools, such as spare part replenishment and task managers, have been interconnected with an internal weather and lightning forecast tool. As a consequence, all maintenance scheduled tasks are performed on turbines during low wind periods.

Better availability

The profound and continuous transformation of Gamesa's new maintenance — which incorporates design and service process improvements with the aim of delivering 99% turbine availability — was conceived precisely to increase revenue and cut running costs. By the start of this year, more than 25% of the fleet maintained by the company had been upgraded with this new programme, improving the average availability of turbines by 1% in just one year.

Meanwhile, by overhauling the maintenance processes the average downtime of the fleet can be reduced by as much as 71%, finds Gamesa. What's more, reliability-centred maintenance has been found to reduce the impact of preventive maintenance on wind farm revenues by 80% and, overall, wind farms' operating expenditure by 10%.

Reconditioning of major components

The real challenge for the wind industry, in order to achieve a cost of energy comparable with other sources of energy, is to upgrade the existing fleet. Currently, more than 70GW of turbines around the world have been running for more than five years. Upgrading these turbines could make the wind farms profitable beyond their original useful lifetime, with no need for subsidies.

Gamesa's reliability maintenance programme undertakes the reconditioning of major components, such as blades, gearboxes and generators, enhancing their constituent parts or replacing these elements with the latest technological advancements. In some cases, as a preventive measure, or during repairs, the damaged parts are replaced with the same original element.

Gear geometry

For example, reconditioning a turbine gearbox can involve redesigning the gear geometry, reinforcing the crown gear, replacing the existing bearings with a different design, and changing auxiliary systems connected to the gearbox to improving working conditions. This significant redesign can double the gearbox operating life for less than 20% of the cost of a new gearbox. It can also reduce maintenance costs.

Extension of the useful life of wind turbines can be achieved by investing in preventive and corrective activities to keep the turbines working for 30 years, compared to the 20 years of useful life originally envisaged for early models, and giving additional years of revenue from a wind farm.

Additionally, upgrading components with state-of-the-art technology will improve the turbine's efficiency and performance, which cuts running costs and keeps them low over the long term. The useful life extension programme prevents an aging wind farm's running costs steadily increasing over time, stabilising them at the levels of a 10-year-old wind farm and making them compatible with a the €50/MWh price of energy.

Life extension of wind farm assets also allows an automatic increase in the company's asset value, potentially raising the value by 33% for five-year-old turbines to 100% in the case of 15-year-old turbines. The total value of the company (equity) and the profits increase automatically without any need for investment, as asset amortisation and financial costs are spread over a wider period.

Finally, many of the projects in mature markets that were not profitable, with a price of energy at €50/MWh, now become attractive.

WE CAN REBUILD IT, WE HAVE THE TECHNOLOGY: WHY LIFE EXTENSION IS NOW POSSIBLE

In the past 15 years the whole wind industry has drastically increased its technical know-how and operational experience, making a longer operational lifetime possible.

Improved aero-elastic models

Certifying agencies validate manufacturers’ turbine design, ensuring that security margins are sufficient to bear loads during the entire original useful lifetime of 20 years. Eighteen years of operational experience has provided the necessary know-how to improve and cleverly tune mathematical models in order to simulate the evolution of turbine structural elements (frame and tower) over the long term.

Real, useful data

Condition monitoring has been used for many years in power plants and industrial facilities. At the beginning, it was scarcely used in wind turbines because of scepticism about its advantages for end-customers, and even today it is often seen as merely ‘nice to have’ for onshore turbines
However, some manufacturers do use the continuous and critical data from condition monitoring to improve the design of existing main components (reconditioning), and to design new gearboxes and blades for out-of-production turbines, such as Gamesa’s G47 and V47 turbines.

Credit crunch effect

Only five years ago, few people in the wind industry believed in the life extension programme, as the entire market was instead favouring repowering of older wind turbines. As the turbine’s power rating was increasing quickly and financing was not an issue, most of the manufacturers were planning to replace the oldest turbines with new ones.
However, with the recent and potentially long-lasting credit crunch that is being faced by the industry, many customers are no longer willing to take such a risk.
For turbines with nominal power of above 500kW, maximising existing investments at the lowest cost and with complete security is the most appropriate solution, until the economic turmoil finally comes to an end.

IS LIFE EXTENSION SUITABLE FOR ALL EXISTING TURBINES? THE MANUFACTURER'S KEY ROLE

It is possible to extend the life of most wind turbines, and original manufacturers are one of the key stakeholders in the process.

First and most obviously, the original manufacturer must still exist, as it would be difficult for any third party to develop a comprehensive solution that would drive turbines up to 30 or even 35 years of operational life.

Second, in order to develop cutting-edge solutions, the original manufacturers must have all the appropriate resources such as research and development, operational experience, investment capacities, and so on, which could be the real challenge when you plan to extend the operational life of 15-year-old turbines.

The company must also have an adapted service strategy and strong operational experience to be able to offer full-scope maintenance contracts for the next 15 years of operations.

This ability to keep operational expenditures under control over the long term ensures cash flow certainty to banks and investors who might agree to renegotiate loan repayment terms with wind plant owners.

Spare parts

The original manufacturer must have the ability to supply, at a reasonable price, all spare parts for the 30 years of operation. From this perspective, manufacturers that maintain a substantial part of their oldest turbines will have the adapted supply chain to guarantee it.

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