• Energy Research
• Closed Access close
• US close
• ES close
• IT close
• Renewable Energy close

Abstract This paper investigates the performance of a variable ratio gearbox (VRG) used in a small fixed-speed wind turbine with active blades. The major components of the VRG-enabled drivetrain are an automatic-manual gearbox and squirrel cage induction generator that connects directly to the grid. The simplicity of this system may be appealing for applications when cost and reliability are of concern. It is an alternative to variable speed systems, which necessitate a modified generator and power conditioning equipment. During partial load operation the VRG provides a discrete set of rotor speeds. This allows the controller to track the wind speed and to achieve a greater efficiency. This study suggests three VRG ratios are sufficient to improve performance when used with active blades. A case study is presented where the performance is simulated using three different wind data sets. The study suggests that the VRG can improve production between 7 and 8.5% in low wind areas. The design procedure also illustrates a technique for finding the lowest and highest gear ratios needed for VRG design. These ratios allow the system to achieve the lowest cut-in and rated speeds. The approach also has useful implications for the design of a continuously variable transmission.

This paper presents the cooling performance of a water-to-refrigerant type ground heat source heat pump system (GSHP) installed in a school building in Korea. The evaluation of the cooling performance has been conducted under the actual operation of GSHP system in the summer of year 2007. Ten heat pump units with the capacity of 10 HP each were installed in the building. Also, a closed vertical typed-ground heat exchanger with 24 boreholes of 175 m in depth was constructed for the GSHP system. To analyze the cooling performance of the GSHP system, we monitored various operating conditions, including the outdoor temperature, the ground temperature, and the water temperature of inlet and outlet of the ground heat exchanger. Simultaneously, the cooling capacity and the input power were evaluated to determine the cooling performance of the GSHP system. The average cooling coefficient of performance (COP) and overall COP of the GSHP system were found to be ∼8.3 and ∼5.9 at 65% partial load condition, respectively. While the air source heat pump (ASHP) system, which has the same capacity with the GSHP system, was found to have the average COP of ∼3.9 and overall COP of ∼3.4, implying that the GSHP system is more efficient than the ASHP system due to its lower temperature of condenser.

Several standalone photovoltaic systems were installed, between 1983 and 1991, to provide lighting and vaccine refrigeration at health clinics in rural areas of Guyana. This paper reports on the results of a diagnostic survey of these units. This exercise was done in 1994 and it was aimed at assessing the scope and nature of the servicing or rehabilitation works that were necessary to restore the operational levels of the photovoltaic systems.

Abstract Climate responsive strategies contained in traditional native dwellings can provide theoretical basis for the development of sustainable buildings. This study focused on a quantitative analysis of cliff-side cave dwellings located in cold region of China. Field measurements in summer and winter were carried out. Based on the monitoring data, thermal environment of the cave dwelling and thermal characteristics of the adobe massive building envelope were evaluated. Results showed that the cliff-side cave dwelling was well adapted to local environment for its good ability of thermal insulation under the natural conditions. Furthermore, in order to assess the whole annual thermal performance and thermal comfort level, numerical simulations on the cliff-side cave dwelling models was also performed using the software Energyplus. Results showed that 52.50% time of the year was comfortable of the living room. Meanwhile, some technical strategies of making full use of solar energy and natural ventilation was proposed in the end of this paper, which can provide technical support for the regeneration design of traditional residential buildings.

A data-driven approach for maximization of the power produced by wind turbines is presented. The power optimization objective is accomplished by computing optimal control settings of wind turbines using data mining and evolutionary strategy algorithms. Data mining algorithms identify a functional mapping between the power output and controllable and non-controllable variables of a wind turbine. An evolutionary strategy algorithm is applied to determine control settings maximizing the power output of a turbine based on the identified model. Computational studies have demonstrated meaningful opportunities to improve the turbine power output by optimizing blade pitch and yaw angle. It is shown that the pitch angle is an important variable in maximizing energy captured from the wind. Power output can be increased by optimization of the pitch angle. The concepts proposed in this paper are illustrated with industrial wind farm data.

Cost of energy generated from offshore wind is impacted by maintenance cost to a great extent. Cost of maintenance depends primarily on the strategy for performing maintenance. In this paper a maintenance cost model for offshore wind turbine components following multilevel opportunistic preventive maintenance strategy is formulated. In this strategy, opportunity for performing preventive actions on components is taken while a failed component is replaced. Two kinds of preventive actions are considered, preventive replacement and preventive maintenance. In the former, components that undergo that action become as good as new (i.e., the replaced components, are not just as good as new, but are actually new), but in the latter, ages of components are reduced to some degree depending on the level of maintenance action. Total cost associated with maintenance depends on the setting of age groups that determine which component should be preventively maintained and to what degree. Through optimum selection of the number of age groups, cost of maintenance can be minimized. A model is formulated where total maintenance cost is expressed as a function of number of age groups for components. A numerical study is used to illustrate the model. The results show that total cost of maintenance is significantly impacted by number of age groups and age thresholds set for components.