Earth has lately been suffering from unforeseen catastrophic phenomena related to the consequences of the greenhouse effect. It is therefore essential not only that sustainability criteria be incorporated into the everyday lifestyle, but also that energy-saving procedures be enhanced. According to the number of wind farms installed annually, wind energy is among the most promising sustainable-energy sources. Taking into account the last statement for energy-saving methods, it is essential to value the contribution of wind energy not only in eliminating CO2 emissions when producing electricity from wind, but also in assessing the total environmental impact associated with the entire lifetime of all the processes related with this energy-production chain. In order to quantify such environmental impacts, life-cycle analysis (LCA) is performed. As a matter of fact, there are a very limited number of studies devoted to LCA of onshore wind-energy-converter supporting towers—a fact that constitutes a first-class opportunity to perform high-end research. In the present work, the life-cycle performance of two types of tall onshore wind-turbine towers has been investigated: a lattice tower and a tubular one. For comparison reasons, both tower configurations have been designed to sustain the same loads, although they have been manufactured by different production methods, different amounts of material were used and different mounting procedures have been applied; all the aforementioned items diversify in their overall life-cycle performance as well as their performance in all LCA phases examined separately. The life-cycle performance of the two different wind-turbine-tower systems is calculated with the use of efficient open LCA software and valuable conclusions have been drawn when combining structural and LCA results in terms of comparing alternative configurations of the supporting systems for wind-energy converters.
Increased contemporary energy needs have led to multiple investments on wind power plants and structural improvements are considered necessary for the construction of taller, more robust and more economical structures. Tubular steel wind turbine towers that are the prevailing structural configuration, demand welding of circular subparts to construct the tower structure. These circumferential welds between tower subparts and between the tower and the connecting flanges are proved to be prone to fatigue failure, since cracks are observed in these areas of already constructed wind towers. The aim of the present work is to enlighten weld design procedures of wind turbine tower welds using damage accumulation methods. For the purposes of the comparative study, two towers of same height differing in shell thickness distribution are taken into account. The towers are compared numerically and analytically following two methods of calculating fatigue loads for structures; the first is an analytical method proposed in design codes and the second is by using artificial loading histories produced by the National Renewable Energy Laboratory software. In both methods, shell thickness is proved to be a decisive factor for the fatigue life of the structure and it is often a challenge to design an economic structure with sufficient fatigue life. From the comparison of the tower's welds fatigue life, useful outcomes have been found on the precision of the methods compared and the relation of fatigue life and material used for construction.
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Renewable energy is expected to experience epic growth in the coming decade, which is reflected in the record new installations since 2010. Wind energy, in particular, has proved its leading role among sustainable energy production means, by the accelerating rise in total installed capacity and by its consistently increasing trend. Taking a closer look at the history of wind power development, it is obvious that it has always been a matter of engineering taller turbines with longer blades. An increase in the tower height means an increase in the material used, thereby, impacting the initial construction cost and the total energy consumed. In the present study, a numerical investigation is carried out in order to actively compare conventional cylindrical shell towers with lattice towers in terms of material use, robustness and environmental impact. Lattice structures are proved to be equivalently competitive to conventional cylindrical solutions since they can be designed to be robust enough while being a much lighter tower in terms of material use. With detailed design, lattice wind turbine towers can constitute the new generation of wind turbine towers.
Tubular steel towers are the most common supporting structure of wind converters. The towers' foundation covers an important part of the initial cost and its configuration depends heavily on the type of subsoil. Onshore structures are founded on spread footing foundations or pile foundations with the first being the commonest. In these spread footing foundations, the tower is either embedded in the concrete foundation slab or the tower bottom flange is anchored to the concrete by means of pretensioned bolts. This anchoring of the steel tower on the concrete foundation is very rarely analyzed separately and recent failures due to inadequate design have alerted the wind industry towards the solution of the problem. For the purposes of the analytical and numerical approaches, two alternative types of foundation dimensioning are investigated. The tower properties of the two configurations are the same, providing the same loading and material data. The analytical study of the foundation anchoring is performed with the use of the equivalent ring method and the numerical verification of the two foundation solutions is performed with the use of a detailed micro model. The same micro model is used for the calculation of the fatigue life of the tower bottom joint following the damage accumulation method. In both foundation solutions, the total cross sectional area of the anchor bolts is proved to be the decisive factor for the selection of bolt size and number. The size of the tower bottom diameter plays also an important role on the maximum number and size of bolts used. Both analytical and numerical results are in good agreement and valuable outcomes are emerging from the comparative study on the foundation dimensioning of contemporary structures.
Wind energy is the most promising sustainable energy source as one can conclude from the recent boost of wind farms installed globally. It is rather important to investigate the total environmental impacts of wind energy, not only taking into account the zero CO2 emissions when producing electricity from wind but also assessing the total environmental burdens and resources requirement associated with the entire lifetime of all the processes related with the energy chain. In order to quantify the environmental impacts of wind energy life cycle analysis (LCA) is performed. Life cycle analysis of tall onshore wind turbine towers is not very thoroughly investigated in literature, which is a first class opportunity to perform high-end research. More specifically in this work, studies examining the life cycle performance of two types of onshore wind turbine towers are investigated; lattice and tubular. The definition of life cycle analysis and the steps applied for its implementation are also discussed. For Wind Energy LCA five phases are usually taken into consideration: manufacturing and construction, onsite erection and assembling, transportation, operation and finally dismantling. At the first steps of the present investigation, a typical system boundary is taken into account and a literature review summary describing the main conclusions from LCA studies on onshore wind turbine towers are presented. From recent LCA results on onshore wind turbines, the manufacturing stage is proved to have the greatest environmental impact, while recycling (that is used as a preferred scenario instead of reuse in the dismantling phase) is proved to act in the most favourable way. In the present study, two wind turbine towers of the same size and same energy production capacity are investigated and compared. Both structural systems, the tubular and the lattice one are proved robust enough and the total material used for their production is calculated in previous work of the research group. The two systems have different production methods, different amounts of material used and different mounting procedures which diversifies their lifecycle performance as a total and their performance in all LCA phases examined separately. Open LCA software was used to assess the lifecycle performance of the two different wind turbine tower types and very important conclusions were derived. After having performed the structural analysis of the two tower types, the LCA analysis completes the series of criteria that have to be taken into account when deciding between the two tower configurations towards more robust, more economical and more sustainable wind energy structures.
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