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Abstract Wind energy development is booming worldwide with Germany and the United States being forerunners in installed capacity. Based on a review of relevant laws and regulations, policy, siting, and permitting documents, academic literature, and expert interviews, the paper compares the permit and environmental impact assessment (IA) policies and regulations pertaining to wind energy projects in both countries. The focus is on the potential of IAs in supporting an environmentally conscious development of wind power generation. This includes the analysis of IA regulations on the project level, strategic level impact assessment and planning processes, opportunities for public involvement and transparency of processes, and the clarity and predictability of the IA provisions. The findings suggest certain variations between both countries' permit and IA processes for wind energy projects and further research needs, inter alia on the actual effects of strategic assessment of wind development on subsequent permitting.

The adoption of solar photovoltaic (PV) technologies has expanded rapidly in recent years, leading to suggestions that this growth, which occurred mostly in high-latitude countries with often low levels of sunshine, may have come at an unnecessarily high price. However, the factors influencing the cost of solar PV, and the subsidies required to sustain its uptake, include more than just the level of sunshine. While cross-country differences in technology costs are hard to ascertain, it is possible to account for the cost of capital on a country-by-country basis. In this paper, we therefore map the cost of solar PV globally, accounting for differences in both the solar resource and the financing cost in order to calculate the levelized cost of electricity (LCOE) from solar PV systems in 143 countries. In contrast to the work of other researchers who typically treat financing costs as uniform across countries, our results suggest that the LCOE of solar PV systems in northern countries may in fact be lower than in equatorial countries, and high latitude countries may thus not have been an unwise location to subsidize the adoption of solar PV technologies in the past. Our results further suggest that efforts to expand PV installation in equatorial developing countries may benefit greatly from policies designed to make low cost finance more widely available, which underlines on-going efforts to “de-risk” low carbon investments.

This study follows a multi-disciplinary approach to implementing an Energy Community (ECs) in Vega de Valcarce, a rural community in Spain. ECs are entities that encompass collective actions of citizens and other actors towards the open, democratic governance of renewable energy sources; ECs can take various technical and organisational forms. This study developed and evaluated socially accepted, technically optimal and feasible options for the implementation of the EC at Vega de Valcarce. We conducted a participatory multi-criteria analysis incorporating the results of mixed-integer linear programming for energy system optimisation and regulatory analysis of ECs under Spanish law. Our study showed that the main objectives of local stakeholders are the reduction of the energy bill and emissions. The limited liability company fulfilled legal and regulatory restrictions the best by implementing a bigger-sized EC. We summarise the key challenges of implementing an EC in a rural context, mainly legal and financial, and conclude with recommendations on how to overcome these. While contributing to understanding the roll-out of ECs in Spain and Europe, our research aims to provide a structured approach for the uptake of renewable energy in rural areas.

Abstract Thermal energy storage (TES) using phase change materials (PCMs) is being widely considered as one of the alternative solutions for effective use of solar energy. This paper presents a multi-objective optimisation strategy for TES systems using PCMs for solar air systems, in which two performance indicators of average heat transfer effectiveness and effective PCM charging time were used as the conflicting objectives. The influence of the key design variables on the performance of an air-based PCM TES system was first experimentally investigated using Taguchi method, and the results were used to develop two performance models for optimisation. A genetic algorithm was used to search for an optimal Pareto front and a multi-criteria decision-making process was employed to determine the compromise optimal solutions. The results showed that the average heat transfer effectiveness of the PCM TES system can be improved from 44.25 to 59.29% while the effective PCM charging time increased from 4.53 to 6.11 h when using the solutions identified by the proposed strategy with the weighting factors of 0.5/0.5 for both objectives, in comparison to a baseline case. A further comparison showed that the optimal design identified by the proposed strategy outperformed the two designs identified using Taguchi method.

Abstract The wave energy flux distribution in the Bohai Sea during wintertime is re-evaluated based on SWAN with the added sea-ice effect, which is derived from an ice-ocean coupled model, FVCOM. Simulated wave parameters and ice cover agree well with the measured wave data and the MODIS images of sea-ice cover, respectively. The results indicate that the decrease of wave energy flux is mainly caused by the formed ice which leads to the reduction of the effective wind fetch and transferred momentum from air to the ocean surface. The numerical results in a typical winter from 2011 to 2012 show that, due to the presence of sea ice, the average wave energy fluxes can be decreased by up to 80% in Liaodong Bay, while up to 50% in Bohai Bay and Laizhou Bay. Under the extreme winter-weather conditions, more pronounced reduction of wave energy flux caused by ice is observed. The findings also imply that in the design of wave energy converters (WECs) and their deployed locations in the Bohai Sea, even the likely ice-free areas in winter time, the effect of other ice-covered regions on the decrease of wave energy flux as a result of decrease in wind fetch should be considered.

Abstract This paper proposes a Nonlinear Model Predictive Controller (NMPC) for pitch control of Horizontal-Axis Wind Turbines (HAWTs) in Region 3 to avoid flutter aero-elastic instability. First, an aero-elastic HAWT rotor model was derived based on extended Hamilton’s principle using the coupled flap-wise and torsional motions of each blade. As for the aerodynamic loading, expressions for lift and pitching moment are obtained based on modifications of Theodorsen’s fixed wing strip theory for a rotating HAWT blade. The model is spatially discretized using the Assumed Modes Method with the first three flap-wise and two torsional mode shapes for the fixed cantilevered blade under free loading. This was applied to the 5-MW NREL (National Renewable Energy Laboratory) reference HAWT. The time-domain response under aerodynamic loading of the developed model was compared to FAST (Fatigue, Aerodynamics, Structure and Turbulence) aero-servo-elastic HAWT simulator. Then, an NMPC pitch controller was designed using the developed model for prediction. This was compared to another NMPC pitch controller which used a lumped-mass drive-train model as a prediction model and to the baseline gain-scheduled PI pitch controller.