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The Severn Estuary has the world's second largest tide range and a barrage across the estuary, located just seawards of Cardiff in Wales and Weston in the South West England, has been proposed for over half a century, with the objective of extracting large amounts of tidal energy. A Severn Barrage, as previously proposed by the Severn Tidal Power Group (STPG), would be the largest renewable energy project for tidal power generation in the world, if built as proposed, and would generate approximately 5% of the UK's electricity needs. However, concerns have been raised over the environmental impacts of such a barrage, including potential increase in flood risk, loss of intertidal habitats etc. In addressing the challenges of maximizing the energy output and minimizing the environmental impacts of such a barrage, this research study has focused on using a Continental Shelf model, based on the modified Environmental Fluid Dynamics Code (EFDC) with a barrage operation module (EFDC_B), to investigate both the far and near field hydrodynamic impacts of a barrage for different operating scenarios. Three scenarios have been considered to simulate the Severn Barrage, operating via two-way generation and using different combinations of turbines and sluices. The first scenario consisted of 216 turbines and 166 sluices installed along the barrage; the second consisted of 382 turbines with no sluices; and the third consisted of 764 turbines and no sluices. The specification of the sluice gates and turbines are the same for all scenarios. The model results indicate that the third scenario has the best mitigating effects for the far-field and near-field flood risks caused by a barrage and produces the most similar results of minimum water depth and maximum velocity distributions to those obtained from simulating the natural conditions of the estuary, i.e. the current conditions. The results also show that the flow patterns around the barrage are closest to those for the existing natural conditions with minimal slight changes in the estuary. Thus, the results clearly indicate that the environmental impacts of a Severn Barrage can be minimized if the barrage is operated for two-way generation and under the third scenario. Although it appears that the energy output for the third scenario is less than that obtained for the other two scenarios, if very low head (VLH) turbines are used, then the third scenario could generate more energy as more turbines could be cited along the barrage structure. Therefore, the study shows that a Severn Barrage, operating in two-way generation and with 764 turbines (ideally VLH turbines), would be the best option to meet the needs of maximizing the energy output, but having a minimal impact on environmental changes in the estuary and far-field.

Abstract This work focuses on the selection and development of high-pressure Ti-Mn based alloy for a domestic 2-stage Metal Hydride Hydrogen Compressor (MHHC) capable of compressing hydrogen from 15 bar to over 350 bar with a maximum operating temperature of 130 °C. Thermodynamic, kinetics and hydrogen storage characteristics of Ti-Mn based alloy were shown to be very sensitive to the alloy's composition. Stability of the hydride phase could be significantly reduced by increasing the Mn content of the alloy and contracting the C14 Laves phase unit cell volume, therefore meeting the required thermodynamic for the target MHHC. The structure and hydrogen capacity of the alloy remained almost constant even after 1000 hydrogen absorption and desorption cycles at room temperature. A significant reduction in the hydrogen absorption plateau slope of the modified high-pressure alloy was achieved by increasing the C14 Laves phase proportion. As a result, effective improvement in the hydrogen sorption kinetics of the modified alloy was observed with most of the hydrogen ab/desorbed in less than 5 min. Although compositional modification showed to be beneficial for lowering the hydrogen absorption plateau slope in high-pressure alloys, the level of hysteresis seemed to be mainly dominated by the alloys thermodynamic.

Fluctuating loads on tidal turbines are important for fatigue analysis and there is limited information or simulation available for full-scale conditions. Here, CFD simulations have been performed for a geometry-resolved full-scale tidal-stream turbine and compared with experimental data from a 1 MW machine deployed at the EMEC test site. Initially, Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulations (LES) were performed using an inflow mean velocity profile representative of the site but low inflow turbulence. Mean blade pressures were similar for the two types of turbulence closure and yielded mean power coefficients comparable with measurements. Then, to simulate the effect of turbulence on loads, LES with synthetic turbulence prescribed at inlet was employed. For these simulations, inflow profiles of mean velocity, Reynolds stresses and length scales were determined from a precursor channel-flow simulation, with additional factoring of stresses and length scales to match hub-height conditions measured on site. Fluctuations in thrust, power and blade bending moment arise cyclically from onset mean velocity shear and the blocking effect of the support tower and over continuous spectral ranges from blade-generated turbulence, approach-flow turbulence and waves. LES simulations with realistic inflow turbulence satisfactorily reproduced the relative spectral distribution of blade bending moments in low-wave conditions.

Abstract This paper describes a low cost method for mass-production of parabolic surfaces with fibreglass. Cavities produced with plastic conduits, covered with fibreglass at the back of the collector surface, provide reinforcement in the longitudinal and transverse directions, to increase rigidity. This produces a low-cost high-rigidity structure that is an accurate copy of the mould. The accuracy of the parabolic surface depends on the accuracy of the mould. The details of the mould production and the procedure for producing the parabolic surface are presented. The total thickness of the fibreglass is 4mm (mean value). The inside surface where the reflector is fixed is manufactured to a high degree of surface finish. The cost of the surface is US$ 30 per square metre of aperture area for 90° rim angle. The standard deviation of the distribution of the parabolic surface errors is found equal to 4.7 mrad which indicates a very accurate surface. The deflection of the surface to a force corresponding to a wind velocity of 90 MPH is well within reasonable limits.

Abstract Currently, renewable energy is rapidly developing across the world in response to technical, economic and environmental developments, as well as political and social initiatives. On the other hand, excessive penetration of distributed generation (DG) systems into electrical networks may lead to various problems and operational limit violations, such as over and under voltages, excessive line losses, overloading of transformers and feeders, protection failure and high harmonic distortion levels exceeding the limits of international standards. These problems occur when the system exceeds its hosting capacity (HC) limit. The HC is a transactive approach that provides a way for the distribution network to be integrated with different types of energy systems. Accordingly, HC assessment and enhancements become an essential target for both distribution system operators and DG investors. This paper provides, for the first time, a systematic and extensive overview of the HC research, developments, assessment techniques and enhancement technologies. The paper consists of four HC principal sections: historical developments, performance limits, perceptions and enhancement techniques. Besides, practical experiences of system operators, energy markets and outcomes gained from real case studies are presented and discussed. It was concluded that success in integrating more distributed generation hinges on accurate hosting capacity assessment.