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A new wave of efficiency

Published:  02 July, 2014

The technologies for generating energy from wave and tide are developing rapidly. For the long term viability of the ocean energy sector, however, reducing the cost of energy (COE) to a level that is competitive with offshore wind and other traditional power generation methods is absolutely key, says Phil Burge, country communication manager, SKF.

Currently, incentives such as the Renewables Obligation Certificates (ROCS) help to create a cost balance against more established power generation methods in the field of renewable energy. However, ROCS will close to new generation in 2017, which will create greater uncertainty in the industry and a need for greater self-reliance.

The manufacturers and, most importantly, the operators of wave and tidal energy systems will therefore need to develop methods of reducing total cost of ownership throughout the life cycle, and given the harsh environment in which these systems operate, asset reliability, availability and maintainability will be key factors. Companies with a stake in the future success of wave and tidal therefore need to design effective life cycle management tools into ocean energy systems from the outset, starting from the components level upwards.

Experience gained within the established wind energy sector can be applied to ocean energy systems, in particular, highlighting the importance of building in reliability at a component and system level, and the value of evolving holistic condition monitoring and management techniques that reduce lifetime operating costs and extend system life.

A powerful machine condition monitoring system offers a vital level of insight into machine condition, as well as a much greater degree of flexibility for a condition monitoring engineer to analyse the data. In wind energy, identifying a fault can save hundreds of thousands of pounds, plus a lot of potential downtime. Like wave and tidal, the cost of wind turbine maintenance is high, even when it is onshore, and for example, if a crane is required in a remote location, it can be a logistical nightmare as well as a huge expense. For operators, profitability can only be maximised if turbines are available at all times and condition-based maintenance (CBM) is key to achieving that.

The methods and tools deployed for condition monitoring in the wind sector can be utilised to great effect in the emerging wave and tidal Industry, providing not only short-term but significant long-term benefits. For example, advanced tools are now available that allow the capture and codification of machine component exceptions and failures on a day-to-day basis. The “mining” of this historical database enables consultants to identify and quantify trends of poor reliability in machines and components that can be fed back to OEMs, who can then work collaboratively with solutions providers to help improve machine design.

Total cost of ownership is also reduced by innovations in component technology. SKF High Endurance Slewing Bearings, with enhanced sealing capabilities and redesigned internal geometry, offer increased resistance to harsh environmental conditions. The SKF High Endurance Slewing Bearing was developed to meet the challenges of extreme weather, heavy loads, remote locations and increasingly powerful designs - just a few of the operational challenges affecting turbines. Featuring enhanced sealing capabilities and redesigned internal geometry, this next-generation bearing can help increase turbine reliability while reducing operating and maintenance costs. The new internal bearing geometry in the cage and raceways reduces friction and increases turbine and pitch control performance. A new, polyurethane-based seal material can provide better resistance to ozone, UV and salt water, reducing wear and providing longer service life than traditional nitride-based sealing solutions. The seal design is less sensitive to ring deformation during operation, reducing grease leakage and water ingress to help improve robustness and lower maintenance costs.

Development in bearing design to meet the needs of the wind industry has had to address the handling of minimal load conditions and quick acceleration and deceleration. These conditions can cause conventional bearings to suffer smearing due to high levels of wear, potentially leading to bearing failure. To combat this challenge, advanced high-capacity cylindrical roller bearings are now available, optimised with the addition of an inner ring cage guidance mechanism and a lower weight brass cage, for low inertia of the roller set. Separable high-capacity cylindrical roller bearings combine the advantages of conventional cylindrical roller bearings and high-capacity cylindrical roller bearings. These are sized to match standard original bearings, yet feature extra rollers for increased load-carrying capacity. In addition, they offer the ability to separate the inner ring from the rest of the bearing components, without the risk of the rollers becoming disengaged. A separable bearing design such as this also enables easy mounting and dismounting, which reduces costly replacement and maintenance times during top-of-turbine repairs.

These are exciting times in the development of wave and tidal energy and by building on the expertise of established manufacturers of renewable energy power generation components the potential is there to build a robust, profitable industry. Though oil and gas will undoubtedly play a key role for many years to come, with operators finding new ways of extracting more hydrocarbons, this alone is simply not sustainable for future generations. This reinforces the case for alternative energy generation from renewables, with wave and tidal having an important role to play.

Within the wave and tidal industry, it is recognised that reducing the cost per unit (KWhr) towards a level that is truly competitive with traditional means of power generation is key to long term viability. Considering reliability, availability and maintainability at the prototype design stage are absolutely vital in order to have a positive financial impact in the array production phase. Lessons learned from the oil and gas sector show that by adopting a least Capital Expenditure (CAPEX) approach at concept and design stage will undoubtedly have detrimental consequences in terms of Operational Expenditure (OPEX) throughout the life of the asset through to decommissioning. With a full and carefully implemented investment programme in new component and maintenance technologies, operators can effectively control the occurrence of planned maintenance and more importantly, help eliminate unplanned maintenance levels. This will have a positive impact on running costs and ensure that wave and tidal power will continue to be both a viable economic solution for energy production for the future and a benefit to the environment.

SKF works collaboratively with prototype device developers, to help them design in reliability at an early stage, thus ensuring they meet their future availability and production targets. It also takes into consideration maintenance strategy and maintainability, recognising the harsh and inaccessible environments in which these devices operate.

For further information please visit: www.skf.co.uk

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