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August 12, 2009

The Economics of Wind Turbine Maintenance
Author: Sean Keller, Business Unit Director, DEX Renewables

When wind turbines are first installed the maintenance costs are comparatively low.  However, like any other piece of electro-mechanical equipment parts start to fail over time.   The typical life span of a wind turbine is around 20 years or the equivalent of 120,000 hours operation.  As the turbine ages, the greater the probability of parts failing.

For first generation turbines the annual maintenance costs were estimated at 3 per cent of the original investment in the turbine.  Newer turbines which tend to be larger, cost approximately 1.5 to 2 per cent in annual maintenance costs (according to the Danish wind energy association).  This can be a significant sum with a typical turbine costing 1m euros.  Of this cost around 25% is service and spare parts.

If a part fails under warranty it is normally replaced by the manufacturer.  However, there is a growing issue with parts which fail outside the warranty period.   In most cases operators have no choice but to buy a new part from the Original Equipment Manufacturer (OEM).  This can be an expensive option with the cost of buying new up to 50 per cent greater than repairing the part.   In other sectors such as IT and medical equipment there is a sophisticated structure for repair and maintenance external to the OEM which has matured over the past decades.  However, as yet there is little cooperation between wind turbine OEMs and third party repair and logistics companies.  This has made it difficult to obtain technical manuals and specifications to efficiently repair faulty parts.

Companies such as DEX, through its DEX Renewables division, are addressing this issue by building up an extensive bank of specialist technical expertise in the repair and maintenance of wind turbines.  The electronic components used in rotor current controllers, for example, are highly complex and proprietary to the manufacturer of the turbine.  Each repair solution is therefore bespoke and requires specialised tooling and testing equipment to be developed as well as intensive training of engineers and technicians.  Nonetheless, it is still more cost-effective to repair or refurbish an existing part than buy new with potential cost savings of up to 50%.

The consequences of part failure can be extreme.  If no spare part is readily available the turbine can be rendered redundant, the operator loses revenues and must purchase peak rate power from the grid to honour power purchase agreements. 
The cost of downtime could potentially hit revenues to tune of 1,000 euros per day per turbine.

In one case a major European wind farm operator experienced a failure on a rotor current controllers.  The operator discovered that there was a five-month lead time for this particular part.  As a result the operator was forced to purchase additional power from the grid to meet its contractual obligations.  The cost of the extensive downtime was estimated at 250,000 euros.  We have subsequently worked with the operator to establish a full test and repair solution for the entire rotor current controller system so that this situation does not arise again in future.

This example highlights the difficulty operators frequently have in sourcing spare parts.  Parts for discontinued models can be particularly hard to find.  For this reason we have developed a global parts sourcing service which has access to a network of over 4,000 validated vendors who compete daily to offer the best prices on parts.  Allied to this is our procurement service which can supply parts through global inventories and sources.

The most common parts to fail on wind turbines are the control system electronics.  According to a report compiled by the Institut fur Solare Energieversorgungstechnik around half the repairs on large wind turbines are related to electrical components.  This can include parts such as rotor current controllers and IGBTs modules (insulated gate bipolar transistors).  IGBTs are increasingly used in frequency converters in turbines. Although they are highly efficient reliability issues are common. It is a feature of this technology that newer revisions of converter often utilise higher specification IGBT components. This affords an opportunity for owners to proactively upgrade converters to the higher spec IGBTs.  Consequently DEX have developed an option to implement an inventory upgrade program in conjunction with repair options for IGBT converters.

It is also vital to keep track of inventory.  We have found that in many cases spare parts are stored in inappropriate environments.  Usually this is in a shed or cabin close to the wind farm site.  If not protected properly from the elements, these parts (especially electronics) can deteriorate leading to problems with non-functioning parts when they are required.  The solution is to have a proper inventory system which can track the location and condition of parts across the fleet.  Ideally once a defective part is replaced it should be taken away, repaired and kept in stock so there is always an adequate reservoir of parts.

Repair of parts, however, is only one side of the coin.   If a particular part is consistently failing or performing below par it is essential that analysis is carried out to find the root cause.  This involves the construction of special test jigs to simulate wind turbine operations in the workshop so that the part can be subjected to a wide variety of operational and stress conditions.  Detailed analysis of the results of this testing can highlight any inherent weaknesses.  Field testing and onsite monitoring can also be carried out to determine the cause of performance or reliability issues.

In summary wind turbine downtime due to repair and maintenance issues can be expensive, time-consuming and very inconvenient.  Having the right repair and parts procurement strategy in place can help operators avoid this nightmare.

About the Author
Sean Keller is business unit director of DEX Renewables.

DEX Renewables is a division of DEX.  DEX is an international specialist engineering company with a 30 year pedigree providing optimal solutions for the Technology Supply Chain including logistics, repair, parts procurement and asset recovery services. DEX operates in high-tech industries including computer, industrial and medical equipment.  The company has a global presence with a number of facilities in the US, Europe and Asia.  It counts dozens of Fortune 500 companies among its clients.

The new division applies this world-leading expertise to the European renewable energy sector, initially focusing on wind turbine solutions.

For further information please visit www.dex.com/renewables or call +353 1 848 6555.

Marketing inquiries, please contact:

Randy Hudson
Marketing Director
805-388-1711 x146
Email: rhudson@dex.com

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