- Details
- Category: Articles
A Monolithic Concrete Platform for Floating Offshore Wind Turbines
A novel concept of a floating platform for supporting wind turbines (named WindCrete) has been developed at the Universitat Politècnica de Catalunya (UPC) in order to substantially reduce the capital expenditure or CAPEX for floating offshore wind turbines. The concept is based on a monolithic full concrete structure, including the tower and the floater, which also allows a significant reduction of the operating expense, or OPEX. The basics of the concept are presented in this article, including the advantages of concrete in the marine environment, the main dimensions and the hydrostatic and hydrodynamic properties of WindCrete.
By Climent Molins and Alexis Campos, Universitat Politècnica de Catalunya, Spain
WindCrete consists of a monolithic concrete floating spar buoy and includes both the tower and the floater built in a continuous single piece. This offers a significant cost reduction during the construction and the structure is virtually free of maintenance during its service life (50 or more years). The main hydrostatic and hydrodynamic properties have been checked and validated through experiments in a wave flume, and coupled aero-servo-elastic-hydrodynamic analyses were used to check WindCrete’s structural integrity. Accurate material cost estimations for the platform, including all its internal steel reinforcements, were also performed. A cost comparison with a steel equivalent platform design highlights a material cost reduction larger than 60% in the case of the full concrete design. For the preliminary design, the NREL 5MW was used as the reference wind turbine (see Figure 1).
- Details
- Category: Articles
Effective Reduction Using a Low-Speed Coupling Made of Advanced Composites
Poor drive-train reliability is still one of the main hurdles to get over in order to achieve a more competitive cost for wind energy. Many surveys confirm that gearbox failure rates are moderate compared to other components but, once a failure occurs, it leads to the highest downtime and a considerable loss of energy production. According to the results of investigations carried out by GL Garrad Hassan regarding the relative cost of energy, the reduction of gearbox failures rates by 50% would save revenue losses by almost 40% compared to the initial capital cost of the gearbox. Joint investigations by the National Renewable Energy Laboratory (NREL) and Alstom, with the target of improved drive-train reliability, have shown that non-torque loads (bending moments) can significantly affect the reliability of the gearbox. Non-torque loads are caused by aerodynamic loads, rotor overhung weight and drive-train weight, and occur independently of the drive-train concept. Low-speed couplings are pictured as a potential remedy for new drive-train layouts to solve the problem ‘outside the gearbox’.
By Alexander Kari, Geislinger GmbH, Austria
This article explains how a composite low-speed coupling reduces non-torque loads and improves the drive-train’s dynamic behaviour significantly. At the same time, the coupling does not add unnecessary weight, maintenance or complexity to the wind turbine. This is a somewhat new approach for wind drive-trains – but a potential remedy to increase robustness.
- Details
- Category: Articles
Could It Change the Game for Renewables?
What if reliable and cheap wind energy could be generated, stored and distributed straight out of a box? EnerKíte GmbH from Germany has developed a novel technology to harness the stronger and steadier winds at higher altitudes. At average to fair onshore wind conditions the kite-based wind power plants – or airborne wind energy converters – allow for capacity factors way above 70% while aiming to keep the cost of electricity below 5 euro-cents per kilowatt-hour. The combination of stronger winds at higher altitudes and the low design wind speeds of 7.5m/s enable capacity factors higher than offshore power plants at a lower cost. Distributed generation, storage and hybridisation with other renewables could all help towards 100% renewable scenarios.
By Alexander Bormann, CEO, EnerKite, Germany
The portable EnerKíte container, bearing the fully automated kite (wing), a launching and landing mast, a generator winch and integrated battery storage, is ready for use quickly. The principle of the EnerKíte is quite simple (see Figure 1). The kite flies a figure-of-eight shape in cross-winds using the currents above the boundary layer to unfurl the tether lines with optimal force and speed (phase 1). The tether lines are let out and power a generator winch on the ground. Unlike conventional wind turbines, only the ultra-light wing is placed at altitudes of 200 to 300 m (Figures 2 and 3). Once the tethers are fully unrolled, the recovery phase (phase 2) begins.
- Details
- Category: Articles
Getting Ready for the Future
Within a few years there are not likely to be many places in the world with traditional mega or micro electricity grids. As use of renewables such as wind and especially photovoltaics increases, sometimes to more than 100%, and the energy supplies are linked to grids worldwide, there will be a need to add storage and smart control systems to enable switches between renewable energies and other fuels such as diesel. However, most traditionally manufactured small and medium wind turbines cannot cope with smart grids.
By Frits Ogg, Renewable Energy Consultant, The Netherlands
As most commercial developers in wind tend to sell and use wind turbines of a megawatt or more (MW wind turbines) because these turbines give the fastest and/or largest return on investment, there is a lack of development of small and medium sized wind turbines. MW wind turbines only serve the highly populated areas in the world that have a strong grid. Over 90% of the world is rural and has a weak or island grid. For technical reasons and because of grid capacity there is usually a maximum of 300kW for feeding in electricity from wind turbines on these grids.
- Details
- Category: Articles
Anemometry Technology to Measure the Wind in Front of the Rotor
The ROMO Wind iSpin system uses proven ultrasonic technology to measure wind where it first hits the turbine – directly at the spinner. In this way, it is able to measure parameters at the nacelle which until now have been difficult or impossible to measure accurately. Operators gather exact information on the wind conditions in front of the rotor including wind speed, yaw alignment, flow inclination, turbulence, rotor position and temperature. This enables them to check whether their turbines are aligned for the best possible yield. At the same time, the data allows for optimised wind farm management and load reduction, which prolongs the total life of the turbines.
By Harald Hohlen, ROMO Wind Deutschland GmbH, Germany
Unfortunately, most wind turbine measurement equipment in use today is unable to properly measure the wind hitting the turbine. This industry-wide, fundamental wind measurement problem is caused by the fact that the wind turbine’s own wind measurement equipment when located on the nacelle behind the rotor is heavily affected by rotor turbulence and other unpredictable wind conditions. The problem results in inaccurate and imprecise wind speed and wind direction measurements on the wind turbine and, as a consequence, in reduced yaw alignment capabilities. ROMO Wind’s spinner anemometry technology iSpin, which was developed at DTU and improved by ROMO Wind using actual field experience, measures wind quantities like wind speed, yaw misalignment and flow inclination at the spinner in front of the wind turbine rotor, where the wind conditions are more predictable. As a result, iSpin is an ideal tool to measure yaw misalignment and further wind quantities relevant for wind turbine performance measurements.
- Details
- Category: Articles
The Integrated Urban Green Wind Energy Solution
PowerNEST is a new sustainable energy generation system for the tops of buildings. IBIS Power and Pontis Engineering have joined forces to get PowerNEST to a state where it is ready to enter the European market. The consortium has received a Horizon 2020 SME Phase II grant from the EC and is now fully operational and ready to realise the first demonstration in the Netherlands within a few months. The initial stage of the overall European project consists of installing 25 units within 2 years, therefore gaining sufficient knowledge to develop a standardised mass production design and establish a distribution network. The EU independent review committee awarded a score of 14.35 out of 15.00 to the project with all aspects graded as ‘excellent’.
By Anna Blanch Vergés and Dr Alexander B. Suma, IBIS Power, The Netherlands
PowerNEST is a roof-mounted system designed to use the wind that collides with a building’s façade, capturing and accelerating it towards a centralised turbine to generate electricity (Figure 1). This system is especially designed to generate energy in the urban environment where most of the energy is used.
- Details
- Category: Articles
A Few Potential Design Alternatives and System-level Reassessment
In recent years, increasing evidence of failures has been reported from spherical roller main bearings used in three-point mounting (TPM) drivetrains of wind turbines. One of the leading causes has been micropitting, a failure mode that is possibly overlooked by design, selection and life-prediction tools. It remains to be seen if retrofitting problematic spherical roller bearings (SRBs) with improved bearing design solutions can improve their durability. Questions to ask might be: ‘Are the operating conditions of the main bearing well understood?’ and ‘Are the failures caused by deficient design practice or other unidentified external sources within the system?’ These questions fundamentally challenge the underlying design basis and encourage the need for a system analysis approach that is currently being undertaken by researchers from the National Renewable Energy Laboratory (NREL). Specifically, this article discusses a few potential design alternatives and system-level reassessment to circumvent micropitting in main bearings used in TPM drivetrains.
By Latha Sethuraman, Yi Guo and Shuangwen Sheng, National Wind Technology Center, National Renewable Energy Laboratory, USA
Conditions Leading to Micropitting
Most common main shaft arrangements for TPM drivetrains in wind turbines rated 1.5–2MW employ SRBs. These bearings exhibit a high tolerance to system deflection and misalignment but limited tolerance to thrust loads (in most bearing designs the axial loads cannot exceed 10‒38% of their two-row radial reaction). Preliminary studies by the authors [ref. 1] were carried out using a system analysis approach for a representative TPM wind turbine with a 230/600 series SRB (having a design axial load limit that is 22% of the radial loads). Modelling results (see Figure 1) showed that this design limit is exceeded for a majority of the turbine’s operating conditions.
