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- Category: Articles
A Design Study
Wind turbines in use today are not able to catch the abundant flow of wind energy a kilometre or so above our heads. This article describes a design for a wind turbine of up to 500MW capacity that could be deployed at many places throughout the world.
By Dr J.M.E. Beaujean, Bogey Venlo BV, The Netherlands
Wind turbines in use today are not able to catch the abundant flow of wind energy a kilometre or so above our heads. This article describes a design for a wind turbine of up to 500MW capacity that could be deployed at many places throughout the world.By Dr J.M.E. Beaujean, Bogey Venlo BV, The Netherlands
- Category: Articles
Wind Turbine Power Performance Analysis and Optimisation
The wind industry is striving to develop new technologies to improve the economic performance and reliability of wind turbines and wind farms. The Lidar (light detection and ranging) technology, mounted on wind turbine nacelles to measure the wind upstream of the turbine, is a promising new tool to reduce uncertainties in annual energy production, reduce O&M costs and optimise power performance.
By Samuel Davoust and Thomas Velociter, Avent Lidar Technology, France
Wind measurements are crucial throughout the life cycle of a wind farm, whether for resource assessment, power curve measurements or wind turbine control. Cup anemometers, wind vanes and sonic anemometers are commonly used today to measure the local wind.
The IEC 61400-12-1 standard describes the procedure for power performance measurement. According to this standard, the horizontal wind speed should be measured at hub height from two to four rotor diameters away from the rotor plane, using a mast-mounted cup anemometer. However, the installation and dismantling of a met mast can be long, difficult and expensive (up to € 50,000 for an 80-metre tower, excluding equipment cost). This cost increases dramatically for taller masts, in complex sites and offshore. As a result very few power curves can be measured (two to four turbines maximum) when a wind farm is commissioned or during its subsequent operation.
New Perspectives Offered by Lidar Remote Sensing
Introduced several years ago, the portable ground-based Lidar is a remote sensor that is a cost-saving alternative to met mast measurements. This technology is now mature, and the IEC 61400-12-1 standard is currently being revised to include such remote sensing measurement devices.
By measuring entire vertical wind profiles up to 200 metres (a region that is out of reach of mast-mounted cups), these 'towers of light' provide crucial additional information to further reduce uncertainties for resource assessment and power curve measurements. For power performance applications, just as with a mast, ground-based Lidar can cover only a selected wind sector in front of each turbine. By utilising a nacelle-mounted Lidar, however, the measured wind is always aligned in the direction of the turbine: wind is measured as turbines experience it.
Specific Features of Nacelle-Mounted Lidar
Nacelle-mounted lidars should be designed under specific constraints imposed by the turbine operating environment. The Lidar needs to be very robust due to the additional challenges of up-tower operation (vibrations, lightning, electromagnetic fields, etc.). The high cost of interventions on wind turbines demands a high Lidar reliability, and therefore Lidar architectures with no moving parts are preferable. As with any turbine operation, safety should come first, and nacelle-mounted lidars need to be designed so that the mounting and un-mounting can be easily and safely performed.
Wind Iris Turbine Performance Analysis Lidar
Avent Lidar Technology manufactures and sells the Wind Iris, a two-beam Lidar that measures the horizontal wind speed and direction at hub height and at ten distances from 40 to 400 metres upwind of the turbine, simultaneously measured with an acquisition frequency up to 10Hz (see Figures 1 and 2). Designed specifically for turbine operations based on operational experience, this Lidar is robust and easy to deploy. Its first purpose is to reproduce the met mast hub-height measurement, which guarantees that the measurements are useful immediately. However, in addition to this, the flexible pulsed Lidar technology opens up many new possibilities. But first, as with any new measurement instrument, solid field validations need to be obtained.
Field Validations
The reliability and the precision of the instrument have been proven in the field by industry experts. A measurement campaign at the Alpha Ventus wind farm located off the German coast, performed in collaboration with DEWI and Areva Wind GmbH, proved the robustness of the instrument in harsh offshore conditions (ref. 1). A test campaign performed at Risø’s Hovsore test site (ref. 2) has shown that this two-beam nacelle Lidar could measure the horizontal wind speed with a difference of less than 1% compared to an IEC 61400-12 met mast set-up (see Figure 3). Current research focuses on submitting a detailed measurement protocol in order to include nacelle-mounted Lidar power curves in a future revision of the IEC 61400-12 standard.
Reducing Cost, Uncertainty and Duration of a Power Curve Measurement
With installation taking no more than half a day, the cost of measuring power curves using the Wind Iris is drastically less than with a met mast, especially offshore. Figures 4 and 5 show two power curves that have been measured under exactly the same conditions using a IEC set-up mast and the nacelle-mounted Lidar. There is a good agreement between these two power curves and a reduction in the dispersion of data points for the one measured by Lidar. Power curves are thus measured with less uncertainty because of the permanent upwind alignment of measurements. Also, more wind sectors can be considered: regions where the mast was previously in the wake of other turbines or obstacles now provide valid measurements. Power curves can be obtained more quickly.
Extending Power Curve Measurements
Reduction in the cost and duration in power curve measurements leads to improvements in several applications. Firstly, wind turbine prototypes can be tested quickly and in various sites. Secondly, more power curve measurements can be performed during wind farm commissioning, reducing uncertainties further and thereby reducing the cost of wind farm projects. Finally, in operating wind farms the Wind Iris can be moved from turbine to turbine in order to assess and monitor performances, leading to faster decisions for maintenance operations.
Turbine Performance Optimisation
Beyond performance monitoring, nacelle-mounted Lidar are valuable wind turbine optimisation tools. Upwind wind speed and direction measurements can be used to calibrate correction functions for nacelle-based instruments of new turbines, or to adjust those on existing under-performing turbines. For example, permanent yaw errors can be detected and corrected.
Taking a whole wind farm, wind sector management can be optimised by detecting wind speed deficit and turbulence intensity perceived by each turbine as a result of nearby wakes. This leads to new strategies for global power optimisation and exclusion of wind sectors.
Conclusion
Nacelle-mounted Lidar designed specifically for use with wind turbines is a new tool available to the market. Power performance analysis applications, which previously needed a mast, can now be extended to areas that were inaccessible and performed at a reduced cost. New power performance optimisation applications, making a complete use of the instrument output, are also emerging.
At a later stage, retrofitting turbines with Lidar-assisted control using this technology will bring adaptive solutions for under-performing wind farms in difficult sites, until a new generation of wind turbines integrating Lidar as a core component emerges.
Further Reading
Samuel Davoust is Scientific Product Manager at Avent Lidar Technology. Prior to joining Avent, Samuel was investigating rotating turbulent flows with laser-based techniques at ONERA, the French Aerospace Lab. He holds a PhD in fluid mechanics from École Polytechnique in Palaiseau and an MSc in aeronautical engineering from ISAE, Toulouse, France.
Thomas Velociter is Directeur Général of Avent Lidar Technology. In 2008, Thomas joined Leosphere, leader in Lidar atmospheric observations, to undertake the development of wind turbine mounted Lidar activity, leading to the creation of Avent. Thomas holds a degree in optical engineering and high-tech business management from Institut d’Optique Graduate School, Palaiseau, France.
Avent Lidar Technology is a joint investment of Leosphere and NRG Systems dedicated to developing, manufacturing and selling nacelle-mounted lidars.{/access}
The wind industry is striving to develop new technologies to improve the economic performance and reliability of wind turbines and wind farms. The Lidar (light detection and ranging) technology, mounted on wind turbine nacelles to measure the wind upstream of the turbine, is a promising new tool to reduce uncertainties in annual energy production, reduce O&M costs and optimise power performance.By Samuel Davoust and Thomas Velociter, Avent Lidar Technology, France
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}The Wind Iris is the first of a new generation of nacelle-mounted lidars designed and tested in the field as wind turbine diagnosis tools. These instruments can be moved from turbine to turbine to perform cost-effective power curve measurements, performance monitoring and the adjustment of turbine static parameters.
Wind Measurements in the IndustryWind measurements are crucial throughout the life cycle of a wind farm, whether for resource assessment, power curve measurements or wind turbine control. Cup anemometers, wind vanes and sonic anemometers are commonly used today to measure the local wind.
The IEC 61400-12-1 standard describes the procedure for power performance measurement. According to this standard, the horizontal wind speed should be measured at hub height from two to four rotor diameters away from the rotor plane, using a mast-mounted cup anemometer. However, the installation and dismantling of a met mast can be long, difficult and expensive (up to € 50,000 for an 80-metre tower, excluding equipment cost). This cost increases dramatically for taller masts, in complex sites and offshore. As a result very few power curves can be measured (two to four turbines maximum) when a wind farm is commissioned or during its subsequent operation.
New Perspectives Offered by Lidar Remote Sensing
Introduced several years ago, the portable ground-based Lidar is a remote sensor that is a cost-saving alternative to met mast measurements. This technology is now mature, and the IEC 61400-12-1 standard is currently being revised to include such remote sensing measurement devices.
By measuring entire vertical wind profiles up to 200 metres (a region that is out of reach of mast-mounted cups), these 'towers of light' provide crucial additional information to further reduce uncertainties for resource assessment and power curve measurements. For power performance applications, just as with a mast, ground-based Lidar can cover only a selected wind sector in front of each turbine. By utilising a nacelle-mounted Lidar, however, the measured wind is always aligned in the direction of the turbine: wind is measured as turbines experience it.
Specific Features of Nacelle-Mounted Lidar
Nacelle-mounted lidars should be designed under specific constraints imposed by the turbine operating environment. The Lidar needs to be very robust due to the additional challenges of up-tower operation (vibrations, lightning, electromagnetic fields, etc.). The high cost of interventions on wind turbines demands a high Lidar reliability, and therefore Lidar architectures with no moving parts are preferable. As with any turbine operation, safety should come first, and nacelle-mounted lidars need to be designed so that the mounting and un-mounting can be easily and safely performed.
Wind Iris Turbine Performance Analysis Lidar
Avent Lidar Technology manufactures and sells the Wind Iris, a two-beam Lidar that measures the horizontal wind speed and direction at hub height and at ten distances from 40 to 400 metres upwind of the turbine, simultaneously measured with an acquisition frequency up to 10Hz (see Figures 1 and 2). Designed specifically for turbine operations based on operational experience, this Lidar is robust and easy to deploy. Its first purpose is to reproduce the met mast hub-height measurement, which guarantees that the measurements are useful immediately. However, in addition to this, the flexible pulsed Lidar technology opens up many new possibilities. But first, as with any new measurement instrument, solid field validations need to be obtained.
Field Validations
The reliability and the precision of the instrument have been proven in the field by industry experts. A measurement campaign at the Alpha Ventus wind farm located off the German coast, performed in collaboration with DEWI and Areva Wind GmbH, proved the robustness of the instrument in harsh offshore conditions (ref. 1). A test campaign performed at Risø’s Hovsore test site (ref. 2) has shown that this two-beam nacelle Lidar could measure the horizontal wind speed with a difference of less than 1% compared to an IEC 61400-12 met mast set-up (see Figure 3). Current research focuses on submitting a detailed measurement protocol in order to include nacelle-mounted Lidar power curves in a future revision of the IEC 61400-12 standard.
Reducing Cost, Uncertainty and Duration of a Power Curve Measurement
With installation taking no more than half a day, the cost of measuring power curves using the Wind Iris is drastically less than with a met mast, especially offshore. Figures 4 and 5 show two power curves that have been measured under exactly the same conditions using a IEC set-up mast and the nacelle-mounted Lidar. There is a good agreement between these two power curves and a reduction in the dispersion of data points for the one measured by Lidar. Power curves are thus measured with less uncertainty because of the permanent upwind alignment of measurements. Also, more wind sectors can be considered: regions where the mast was previously in the wake of other turbines or obstacles now provide valid measurements. Power curves can be obtained more quickly.
Extending Power Curve Measurements
Reduction in the cost and duration in power curve measurements leads to improvements in several applications. Firstly, wind turbine prototypes can be tested quickly and in various sites. Secondly, more power curve measurements can be performed during wind farm commissioning, reducing uncertainties further and thereby reducing the cost of wind farm projects. Finally, in operating wind farms the Wind Iris can be moved from turbine to turbine in order to assess and monitor performances, leading to faster decisions for maintenance operations.
Turbine Performance Optimisation
Beyond performance monitoring, nacelle-mounted Lidar are valuable wind turbine optimisation tools. Upwind wind speed and direction measurements can be used to calibrate correction functions for nacelle-based instruments of new turbines, or to adjust those on existing under-performing turbines. For example, permanent yaw errors can be detected and corrected.
Taking a whole wind farm, wind sector management can be optimised by detecting wind speed deficit and turbulence intensity perceived by each turbine as a result of nearby wakes. This leads to new strategies for global power optimisation and exclusion of wind sectors.
Conclusion
Nacelle-mounted Lidar designed specifically for use with wind turbines is a new tool available to the market. Power performance analysis applications, which previously needed a mast, can now be extended to areas that were inaccessible and performed at a reduced cost. New power performance optimisation applications, making a complete use of the instrument output, are also emerging.
At a later stage, retrofitting turbines with Lidar-assisted control using this technology will bring adaptive solutions for under-performing wind farms in difficult sites, until a new generation of wind turbines integrating Lidar as a core component emerges.
Further Reading
- Cañadillas, B. and Neuman, T. First test of a nacelle-based 2-beam wind LiDAR system under offshore conditions. DEWI Magazin no. 39, August 2011.
- Wagner, R. et al. Power performance measured using a nacelle Lidar. EWEC Proceedings 2011.
Samuel Davoust is Scientific Product Manager at Avent Lidar Technology. Prior to joining Avent, Samuel was investigating rotating turbulent flows with laser-based techniques at ONERA, the French Aerospace Lab. He holds a PhD in fluid mechanics from École Polytechnique in Palaiseau and an MSc in aeronautical engineering from ISAE, Toulouse, France.
Thomas Velociter is Directeur Général of Avent Lidar Technology. In 2008, Thomas joined Leosphere, leader in Lidar atmospheric observations, to undertake the development of wind turbine mounted Lidar activity, leading to the creation of Avent. Thomas holds a degree in optical engineering and high-tech business management from Institut d’Optique Graduate School, Palaiseau, France.
Avent Lidar Technology is a joint investment of Leosphere and NRG Systems dedicated to developing, manufacturing and selling nacelle-mounted lidars.{/access}
- Category: Articles
The Need for Setting Standards
Reliable operation, consistent performance, reduced maintenance and improved safety are key drivers for the wind turbine business. Consequently, Labkotec Oy decided to put its latest generation of ice detector, the LID-3300IP, through a rigorous independent testing regime to ensure that it would meet the standards demanded by modern wind energy operators.
By Jarkko Latonen, Chief Technical Officer, Labkotec Oy, Finland
Reliable operation, consistent performance, reduced maintenance and improved safety are key drivers for the wind turbine business. Consequently, Labkotec Oy decided to put its latest generation of ice detector, the LID-3300IP, through a rigorous independent testing regime to ensure that it would meet the standards demanded by modern wind energy operators.By Jarkko Latonen, Chief Technical Officer, Labkotec Oy, Finland
- Category: Articles
The Concept and its Potential
After ten years of dedicated and innovative technology development 'Bucket Foundations' are now being 'rolled out' into the commercial market. The expectations are that this concept will reduce the cost of energy, especially when that energy is to be produced in deeper waters.
By Henrik L. Nielsen, Universal Foundation, Denmark
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}The Bucket Foundation concept combines the benefits and main proven assets of a gravity base foundation, with a monopile and a suction bucket. Importantly the design also includes a patented installation system, which controls the vertical alignment of the total foundation as it sucks itself into the seabed, reducing the overall installation time significantly.
In brief, these new foundations consist of an up-ended bucket, which, via a closing lid is connected to a shaft that, in turn, connects to the wind turbine tower, met mast or other offshore surface installation. Once installed the ‘bucket’ encloses a large volume of sediment, which helps provide a high load-bearing capacity (see Figure1).
The development of this new concept began back in 2001 at Aalborg University, Denmark, with analytical studies, numerical modelling and laboratory tests that eventually led to pit tests of 2 x 2 metre and 4 x 4 metre buckets. Installation methods and techniques were developed from these prototypes using suction and skirt-tip injection. The installation of Bucket Foundations can be divided into two phases: (1) self-penetration of the bucket and (2) penetration of the bucket by means of suction. In phase 1 the skirt penetrates into the seabed by gravity. In phase 2 the penetration is increased by applying suction to the inside of the ‘bucket’. The suction creates an upward flow in the sediments within the ‘bucket’, reducing the effective stresses in the sediments beneath the skirt edge, and results in a net downward force on the top of the bucket, as illustrated in Figure 2.
The reduction in effective stresses greatly reduces the penetration resistance, allowing the skirt to penetrate the sediments further. The suction applied is limited by the gradient that causes piping channels in the soil within the bucket (i.e. the critical gradient at which the effective stress equals 0). Once piping channels are created the suction can no longer be sustained. If the suction is kept at a minimum, and does not cause piping in the soil, the soil will regain its strength when pumping is ceased. The critical gradient , where gw is the unit weight of water and g' is the submerged unit weight. The exit hydraulic gradient i can also be expressed in terms of the applied suction p and the seepage length s as . The critical suction resulting in formation of local piping channels is therefore . Combining these formulae with empirical experience the critical suction can be expressed as , where D is the diameter of the bucket, and h is the penetrated length of the skirt. Thus, if h is known, the critical suction can be controlled.
In 2002 the first full-scale Bucket Foundation was installed using the suction technique. A Vestas V90, 3MW turbine was erected on top of a full-scale prototype of the Bucket Foundation, with a diameter, D, of 14 metres, and a skirt height, d, of 6 metres. The turbine is still in production, and now, after nearly ten years of performance data has been acquired, it is possible to say that 'Bucket Foundations' are one of the most proven foundation technologies available.
In 2009 a Bucket Foundation was installed at Horns Rev 2 as support for a met mast. Here the suction installation technology was reversed as a tilt of approximately 1 degree out of vertical was reduced to less than 0.1 of a degree. The ‘bucket’ was simply lifted 1 metre and reinstalled within the given tolerances (see Figure 3).
In conjunction with the installation requirements given above, geotechnical and structural design will cover all the limit states of Bucket Foundations under combined loads from wind, waves and currents. From these considerations a design approach can be developed covering the basic design, followed by a conceptual design, and finally a detailed design. This design procedure is verified by DNV, to fulfil the requirements given in the Offshore Standard DNV-OS- J101, 'Design of Offshore Wind Turbine Structures'.
The flexibility of these foundations lies in the variety of possible designs, and this has a direct bearing on the ‘universal’ prospects of the concept. Depending on the actual ground, meteorological and ocean conditions and the load regime, the bucket skirt height (d), the diameter (D), and shaft dimensions can be varied to give the optimal material usage and still provide an adequate bearing capacity and stiffness as required by the integrated turbine foundation system.
Recent participation in the Carbon Trust foundation competition – Offshore Wind Accelerator – yielded a promising result: 'Bucket Foundations' were chosen as one of the winning concepts out of a total of 104 entries. 'Bucket Foundations' show an estimated cost reduction for a final installed foundation of 15–30% over other competitor systems.
With a strong industry player involved as the major shareholder, the potential now exists for introducing 'Bucket Foundations' as the solution for large-scale wind farms. 'Bucket Foundations' are aimed directly at the offshore wind energy sector, enhancing technical performance while also reducing the significant costs for offshore foundation installations. With the acquisition of Universal Foundation, Fred. Olsen related companies are now positioned to provide a full, packaged solution for offshore wind farm foundations – from feasibility study/design to the finished installation of an integrated system of foundation and turbine.
About Universal Foundation
First Olsen, the engineering arm of Scandinavian shipping firm Fred. Olsen, acquired 60% of the Danish company Universal Foundation A/S (formerly known as MBD Offshore Power A/S) in August 2011. The remaining interests in Universal Foundation are held by the Danish utility company DONG Energy Power Holding A/S, Novasion ApS and Aalborg University, with whom the concept foundations were developed and tested.{/access}
After ten years of dedicated and innovative technology development 'Bucket Foundations' are now being 'rolled out' into the commercial market. The expectations are that this concept will reduce the cost of energy, especially when that energy is to be produced in deeper waters.By Henrik L. Nielsen, Universal Foundation, Denmark
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}The Bucket Foundation concept combines the benefits and main proven assets of a gravity base foundation, with a monopile and a suction bucket. Importantly the design also includes a patented installation system, which controls the vertical alignment of the total foundation as it sucks itself into the seabed, reducing the overall installation time significantly.
In brief, these new foundations consist of an up-ended bucket, which, via a closing lid is connected to a shaft that, in turn, connects to the wind turbine tower, met mast or other offshore surface installation. Once installed the ‘bucket’ encloses a large volume of sediment, which helps provide a high load-bearing capacity (see Figure1).
The development of this new concept began back in 2001 at Aalborg University, Denmark, with analytical studies, numerical modelling and laboratory tests that eventually led to pit tests of 2 x 2 metre and 4 x 4 metre buckets. Installation methods and techniques were developed from these prototypes using suction and skirt-tip injection. The installation of Bucket Foundations can be divided into two phases: (1) self-penetration of the bucket and (2) penetration of the bucket by means of suction. In phase 1 the skirt penetrates into the seabed by gravity. In phase 2 the penetration is increased by applying suction to the inside of the ‘bucket’. The suction creates an upward flow in the sediments within the ‘bucket’, reducing the effective stresses in the sediments beneath the skirt edge, and results in a net downward force on the top of the bucket, as illustrated in Figure 2.
The reduction in effective stresses greatly reduces the penetration resistance, allowing the skirt to penetrate the sediments further. The suction applied is limited by the gradient that causes piping channels in the soil within the bucket (i.e. the critical gradient at which the effective stress equals 0). Once piping channels are created the suction can no longer be sustained. If the suction is kept at a minimum, and does not cause piping in the soil, the soil will regain its strength when pumping is ceased. The critical gradient , where gw is the unit weight of water and g' is the submerged unit weight. The exit hydraulic gradient i can also be expressed in terms of the applied suction p and the seepage length s as . The critical suction resulting in formation of local piping channels is therefore . Combining these formulae with empirical experience the critical suction can be expressed as , where D is the diameter of the bucket, and h is the penetrated length of the skirt. Thus, if h is known, the critical suction can be controlled.
In 2002 the first full-scale Bucket Foundation was installed using the suction technique. A Vestas V90, 3MW turbine was erected on top of a full-scale prototype of the Bucket Foundation, with a diameter, D, of 14 metres, and a skirt height, d, of 6 metres. The turbine is still in production, and now, after nearly ten years of performance data has been acquired, it is possible to say that 'Bucket Foundations' are one of the most proven foundation technologies available.
In 2009 a Bucket Foundation was installed at Horns Rev 2 as support for a met mast. Here the suction installation technology was reversed as a tilt of approximately 1 degree out of vertical was reduced to less than 0.1 of a degree. The ‘bucket’ was simply lifted 1 metre and reinstalled within the given tolerances (see Figure 3).
In conjunction with the installation requirements given above, geotechnical and structural design will cover all the limit states of Bucket Foundations under combined loads from wind, waves and currents. From these considerations a design approach can be developed covering the basic design, followed by a conceptual design, and finally a detailed design. This design procedure is verified by DNV, to fulfil the requirements given in the Offshore Standard DNV-OS- J101, 'Design of Offshore Wind Turbine Structures'.
The flexibility of these foundations lies in the variety of possible designs, and this has a direct bearing on the ‘universal’ prospects of the concept. Depending on the actual ground, meteorological and ocean conditions and the load regime, the bucket skirt height (d), the diameter (D), and shaft dimensions can be varied to give the optimal material usage and still provide an adequate bearing capacity and stiffness as required by the integrated turbine foundation system.
Recent participation in the Carbon Trust foundation competition – Offshore Wind Accelerator – yielded a promising result: 'Bucket Foundations' were chosen as one of the winning concepts out of a total of 104 entries. 'Bucket Foundations' show an estimated cost reduction for a final installed foundation of 15–30% over other competitor systems.
With a strong industry player involved as the major shareholder, the potential now exists for introducing 'Bucket Foundations' as the solution for large-scale wind farms. 'Bucket Foundations' are aimed directly at the offshore wind energy sector, enhancing technical performance while also reducing the significant costs for offshore foundation installations. With the acquisition of Universal Foundation, Fred. Olsen related companies are now positioned to provide a full, packaged solution for offshore wind farm foundations – from feasibility study/design to the finished installation of an integrated system of foundation and turbine.
About Universal Foundation
First Olsen, the engineering arm of Scandinavian shipping firm Fred. Olsen, acquired 60% of the Danish company Universal Foundation A/S (formerly known as MBD Offshore Power A/S) in August 2011. The remaining interests in Universal Foundation are held by the Danish utility company DONG Energy Power Holding A/S, Novasion ApS and Aalborg University, with whom the concept foundations were developed and tested.{/access}
- Category: Articles
Fluid Dynamics Optimisation of an Innovative Aerogenerator: PAULA
During recent years, the enormous increase in wind energy exploitation has highlighted the need for innovative conversion technologies able to concentrate power production in the areas with both a good wind potential and plenty of space availability. With these requirements in mind, many interesting solutions have been developed for offshore wind turbines, but currently there are very few innovative proposals for the utilisation of the potential of high-altitude winds.
By F. Castellani, University of Perugia, M. Marchionni, University of Calabria and P. Boldrin, ‘Under The Etruscan Sun’ project, Italy
During recent years, the enormous increase in wind energy exploitation has highlighted the need for innovative conversion technologies able to concentrate power production in the areas with both a good wind potential and plenty of space availability. With these requirements in mind, many interesting solutions have been developed for offshore wind turbines, but currently there are very few innovative proposals for the utilisation of the potential of high-altitude winds.By F. Castellani, University of Perugia, M. Marchionni, University of Calabria and P. Boldrin, ‘Under The Etruscan Sun’ project, Italy
- Category: Articles
Techniques to Put Your Data to Work for You
Wind plants generate enormous amounts of data which, if utilised properly, can provide significant insight for operational improvements, resulting in more proactive plant management, and a better return on investments. In order to effectively and efficiently utilise the plant data, it becomes necessary to employ a variety of analysis techniques. These techniques could be simple signal comparisons or the calculation of advanced key performance indicators. In either case, the end goal remains the same: to give plant operators tools and techniques which will utilise the data currently available at a wind plant to optimise plant performance.
By Paul Legac, Applications Engineer, AWS Truepower, USA
Wind plants generate enormous amounts of data which, if utilised properly, can provide significant insight for operational improvements, resulting in more proactive plant management, and a better return on investments. In order to effectively and efficiently utilise the plant data, it becomes necessary to employ a variety of analysis techniques. These techniques could be simple signal comparisons or the calculation of advanced key performance indicators. In either case, the end goal remains the same: to give plant operators tools and techniques which will utilise the data currently available at a wind plant to optimise plant performance.By Paul Legac, Applications Engineer, AWS Truepower, USA
- Category: Articles
The Advantages of a Square Rigged Sail Design
Currently, the most common method for harnessing wind energy has been to use horizontal-axis wind turbines. However, they have certain inherent disadvantages. Vertical-axis wind turbines overcome some of these disadvantages but many designs introduce problems of their own. After summarising the disadvantages and advantages of past and current designs of both horizontal and vertical-axis turbines, the author introduces the idea of a square rigged sail wind turbine, which he feels has greater utility than previous designs.
By Jon Howard, Research Specialist, H Energy Innovations, USA
Description of 'Prior Art'
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}Wind power has been a source of energy for centuries; however, there have always been distinctly different approaches as to how to extract that energy. In particular, there have been both horizontal-axis and vertical-axis wind turbines. In these modern times, the most common method for harnessing wind energy has been to use a horizontal-axis wind turbine. While horizontal-axis wind turbines have been promoted as being the more efficient type compared to other methods, they present several disadvantages. For instance, horizontal-axis wind turbines have to be turned into the wind to start functioning. Also, they have a relatively high cut-in wind speed for operation and a low cut-out wind speed. This allows for only a relatively narrow window of operation, beyond which they are prone to damage. Another problem associated with the horizontal-axis design is that they optimally require a near gale force wind to produce power. Further, horizontal-axis wind turbines can be extremely high above a ground surface, making it difficult for technicians to perform repairs. Due to such heights, technicians are often exposed to grave risks as they provide maintenance in adverse weather conditions.
Alternatives to Traditional Designs
Vertical-axis wind turbines change the axis of rotation of the turbine. These offer an alternative to the traditional wind turbine. The vertical-axis wind turbines improve the safety of servicing and maintenance duties because services are performed much closer to the ground. In the 1920s, a French inventor by the name of Georges Jean Marie Darrieus designed a vertical-axis wind turbine that has been referred to as the ‘Darrieus design’ or ‘eggbeater’. The Darrieus design uses a series of sails that are fixed at a set angle and arranged symmetrically around a vertical axis. The symmetry of the sails provides a very effective means of generating a rotational force to the vertical shaft axis. These types of vertical-axis wind turbines are used today on tall buildings to utilise the high wind velocity found at higher altitudes. Unfortunately, sail fatigue, which causes premature failure of the system, is a common problem associated with the Darrieus design.
As an alternative to the Darrieus design, the US Patent No. 4,449,053, issued to Kutcher, shows a vertical-axis wind turbine that uses vertically positioned rotor blades. Blades are connected both at the top and bottom of a vertically extending rotor tube. While the Kutcher design reduces sail fatigue, the vertically positioned rotor blades do not easily capture wind at all angles, thereby reducing their effectiveness.
Other Vertical-Axis Designs
Another variation is the Giromill Cycloturbine, shown in US Patent No. 7,315,093, issued to Graham. The Giromill Cycloturbine has sails mounted such that the sails can rotate around an axis. The design of the Cycloturbine allows the sails to be pitched such that the sails are always at an angle relative to the wind. A main advantage to this design is that the torque generated remains almost constant over a fairly wide angle. Therefore, a Cycloturbine with three or four sails has a fairly constant torque. Predetermining the range of angles, the torque approaches a possible maximum torque, wherein the system generates more power. The system also has the advantage of being able to self start by pitching the down-wind moving sails flat to the wind to generate drag and start the turbine spinning at a low speed. One drawback to this design is that the sail pitching mechanism is complex and generally heavy, and a wind direction sensor must be added to the design in order to properly pitch the sails.
Current Designs
Currently, the commercial application of wind energy harnessing is primarily, if not exclusively, horizontal-axis wind turbines, even though vertical-axis wind turbines avoid most of the disadvantages inherent in the horizontal-axis design. For example, vertical-axis wind turbines are omni-directional and have a lower cut-in wind speed and higher cut-out speed, thus making the window of operation wider. Also, vertical-axis wind turbines can have components that need servicing located at the bottom end of the structure making access more convenient. Vertical-axis wind turbines also allow for lower-ratio gearboxes, which are less expensive and more efficient than the gearboxes needed to operate horizontal-axis wind turbines, Further, vertical-axis wind turbines are able to operate at a higher wind speed and at lower risk of suffering wind damage. Finally, vertical-axis wind turbines are more suited to a simpler design and construction.
Thus, there is a continuing need for a vertical-axis wind turbine that captures the inherent advantages of the vertical-axis design, yet improves upon the drawbacks of existing vertical-axis designs.
Summary of Findings
The conclusion that was drawn from studying previous designs in this field was that an improved version, without the drawbacks of the previous models, could be created by using reinforced square rigged sails fixed at a 90 degree angle, at the tip of parallel and horizontal yardarms. Such a design is described below.
Square Rigged Sail Wind Turbine
The suggested new wind turbine is a vertical axis turbine designed to generate electricity at both onshore and offshore locations. The turbine is driven by a square rigged sail conformation that can include one or more stacked sail assemblies. Each sail assembly includes a main shaft having a vertical axis of rotation, with each successive sail assembly in the stack sharing the main shaft. Each sail assembly includes one or more yardarms that extend horizontally from the main shaft. The sails are attached to the yardarms such that the main shaft is central and positioned between the sails.
From the top down in the blue diagram (figure 1), the second and fourth sail assemblies are obscured showing two sails only for each. Also, the entire rear vertical column, the vertical main shaft axis, and corner bracing on the lower three sail assemblies are obscured in this diagram.
Biography of the Author
Since 2007, Jon Howard has been a research specialist, for H Energy Innovations, in
southern California, USA, where extensive studies have been conducted in wind energy. Mr Howard’s research on wind energy development and studies in meteorology and the environment has led him to create a vertical-axis wind turbine with greater utility advantage than the previous designs.{/access}
Currently, the most common method for harnessing wind energy has been to use horizontal-axis wind turbines. However, they have certain inherent disadvantages. Vertical-axis wind turbines overcome some of these disadvantages but many designs introduce problems of their own. After summarising the disadvantages and advantages of past and current designs of both horizontal and vertical-axis turbines, the author introduces the idea of a square rigged sail wind turbine, which he feels has greater utility than previous designs.By Jon Howard, Research Specialist, H Energy Innovations, USA
Description of 'Prior Art'
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}Wind power has been a source of energy for centuries; however, there have always been distinctly different approaches as to how to extract that energy. In particular, there have been both horizontal-axis and vertical-axis wind turbines. In these modern times, the most common method for harnessing wind energy has been to use a horizontal-axis wind turbine. While horizontal-axis wind turbines have been promoted as being the more efficient type compared to other methods, they present several disadvantages. For instance, horizontal-axis wind turbines have to be turned into the wind to start functioning. Also, they have a relatively high cut-in wind speed for operation and a low cut-out wind speed. This allows for only a relatively narrow window of operation, beyond which they are prone to damage. Another problem associated with the horizontal-axis design is that they optimally require a near gale force wind to produce power. Further, horizontal-axis wind turbines can be extremely high above a ground surface, making it difficult for technicians to perform repairs. Due to such heights, technicians are often exposed to grave risks as they provide maintenance in adverse weather conditions.
Alternatives to Traditional Designs
Vertical-axis wind turbines change the axis of rotation of the turbine. These offer an alternative to the traditional wind turbine. The vertical-axis wind turbines improve the safety of servicing and maintenance duties because services are performed much closer to the ground. In the 1920s, a French inventor by the name of Georges Jean Marie Darrieus designed a vertical-axis wind turbine that has been referred to as the ‘Darrieus design’ or ‘eggbeater’. The Darrieus design uses a series of sails that are fixed at a set angle and arranged symmetrically around a vertical axis. The symmetry of the sails provides a very effective means of generating a rotational force to the vertical shaft axis. These types of vertical-axis wind turbines are used today on tall buildings to utilise the high wind velocity found at higher altitudes. Unfortunately, sail fatigue, which causes premature failure of the system, is a common problem associated with the Darrieus design.
As an alternative to the Darrieus design, the US Patent No. 4,449,053, issued to Kutcher, shows a vertical-axis wind turbine that uses vertically positioned rotor blades. Blades are connected both at the top and bottom of a vertically extending rotor tube. While the Kutcher design reduces sail fatigue, the vertically positioned rotor blades do not easily capture wind at all angles, thereby reducing their effectiveness.
Other Vertical-Axis Designs
Another variation is the Giromill Cycloturbine, shown in US Patent No. 7,315,093, issued to Graham. The Giromill Cycloturbine has sails mounted such that the sails can rotate around an axis. The design of the Cycloturbine allows the sails to be pitched such that the sails are always at an angle relative to the wind. A main advantage to this design is that the torque generated remains almost constant over a fairly wide angle. Therefore, a Cycloturbine with three or four sails has a fairly constant torque. Predetermining the range of angles, the torque approaches a possible maximum torque, wherein the system generates more power. The system also has the advantage of being able to self start by pitching the down-wind moving sails flat to the wind to generate drag and start the turbine spinning at a low speed. One drawback to this design is that the sail pitching mechanism is complex and generally heavy, and a wind direction sensor must be added to the design in order to properly pitch the sails.
Current Designs
Currently, the commercial application of wind energy harnessing is primarily, if not exclusively, horizontal-axis wind turbines, even though vertical-axis wind turbines avoid most of the disadvantages inherent in the horizontal-axis design. For example, vertical-axis wind turbines are omni-directional and have a lower cut-in wind speed and higher cut-out speed, thus making the window of operation wider. Also, vertical-axis wind turbines can have components that need servicing located at the bottom end of the structure making access more convenient. Vertical-axis wind turbines also allow for lower-ratio gearboxes, which are less expensive and more efficient than the gearboxes needed to operate horizontal-axis wind turbines, Further, vertical-axis wind turbines are able to operate at a higher wind speed and at lower risk of suffering wind damage. Finally, vertical-axis wind turbines are more suited to a simpler design and construction.
Thus, there is a continuing need for a vertical-axis wind turbine that captures the inherent advantages of the vertical-axis design, yet improves upon the drawbacks of existing vertical-axis designs.
Summary of Findings
The conclusion that was drawn from studying previous designs in this field was that an improved version, without the drawbacks of the previous models, could be created by using reinforced square rigged sails fixed at a 90 degree angle, at the tip of parallel and horizontal yardarms. Such a design is described below.
Square Rigged Sail Wind Turbine
The suggested new wind turbine is a vertical axis turbine designed to generate electricity at both onshore and offshore locations. The turbine is driven by a square rigged sail conformation that can include one or more stacked sail assemblies. Each sail assembly includes a main shaft having a vertical axis of rotation, with each successive sail assembly in the stack sharing the main shaft. Each sail assembly includes one or more yardarms that extend horizontally from the main shaft. The sails are attached to the yardarms such that the main shaft is central and positioned between the sails.
From the top down in the blue diagram (figure 1), the second and fourth sail assemblies are obscured showing two sails only for each. Also, the entire rear vertical column, the vertical main shaft axis, and corner bracing on the lower three sail assemblies are obscured in this diagram.
Biography of the Author
Since 2007, Jon Howard has been a research specialist, for H Energy Innovations, in
southern California, USA, where extensive studies have been conducted in wind energy. Mr Howard’s research on wind energy development and studies in meteorology and the environment has led him to create a vertical-axis wind turbine with greater utility advantage than the previous designs.{/access}
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