Performance Study of Wind Turbine Generators

It is well known that the wind power has definitely certain impact on the grid power. Issues associated with the integration of wind power into the utility grid are interface issues, operational issues and planning issues. Interface issues include harmonics, reactive power consumption, voltage regulation and frequency control. Operational issues are intermittent power generation, operating reserve requirements, unit commitment and economic despatch. And planning issues are concerned with intermittent wind resources compared to conventional power resources. An important question, when connecting the wind turbine generators to the utility grid, is how much the power / voltage quality will be influenced, since the power production by wind turbines is intermittent, quantity wise as well as quality wise. This paper is focused on the on comparison between the constant speed wind turbines and variable speed wind turbines, reactive power consumption and harmonics generated by both wind turbines. Total harmonic distortion is calculated by the application of C++ software and a comparison is done between the generators with respect to the harmonics. It is observed that constant speed wind turbine generates low order harmonics and variable speed turbine generates high order harmonics. On the basis of results, some solutions are suggested to improve the wind power quality and to reduce reactive power consumption. It seems that variable speed wind turbines with electronic interface are better with respect to the utility grid point of view.

Studies of Heat Pumps Using Direct Expansion Type Solar Collectors

A photovoltaic and thermal hybrid panel which was made of an aluminum roll -bond panel with a photovoltaic module on the surface was developed recently for use as an evaporator of a heat pump for residential hot water supply and room heating.1) Pressure loss of the refrigerant at the evaporator was large. Therefore, in the present study, shapes of the inlet and the outlet of the panel were modified to reduce pressure loss; also, thermal performance of the heat pump which adopted three evaporator panels connected in series was examined. Total area of the panels was about 1.9 m2 and the rated capacity of the compressor was 250 W. These modifications reduced pressure loss and improved thermal performance. The effect of the location of the feeler bulb on performance of the heat pump was also examined. It was inferred that the feeler bulb fixed on the tube at the outlet of the evaporator should be as close as possible to the evaporator outlet.

Improved Alignment Technique for Dish Concentrators

Parabolic dish concentrators have shown significant promise of generating competitive electric energy for grid and off-grid applications. The efficiency of a dish-electric system is strongly affected by the quality of the concentrator optics. Most parabolic systems consist of a number of facets mounted to a support structure in an approximate parabolic arrangement, where the individual facets have spherical or parabolic optical shapes. The individual facets must be accurately aligned because improper alignment can compromise performance or create hot spots that can reduce receiver life. A number of techniques have been used over the years to align concentrator facets. In the Advanced Dish Development System (ADDS) project, a color look-back alignment approach that accurately aligns facets (mirror panels) and in addition indicates quantitative information about the focal length was developed. Key factors influencing the alignment, some of which had very large effects on the quality of the alignment, were also identified. The influence of some of the key factors was characterized with a flux mapping system on the second-generation ADDS concentrator. Some of these factors also affect other alignment approaches. The approach was also successfully applied to two other concentrators with differing facet arrangements. Finally, we have extended the method to a 2-f approach that eliminates the need for a distant line-of-sight to the dish and permits alignment at near vertical dish attitudes. In this paper, we outline the color look-back alignment approach, discuss the key alignment factors and their effect on flux distribution, and discuss extensions to non-gore dishes. A companion paper discusses the 2-f color alignment approach in detail.

Performance Assessment and Prediction of a PV Array Installed Vertically on Building Walls

This paper predicts relationship between array performance and surrounding ambient including installation conditions for PV array installed on building walls. A PV system assumed for calculation is a PV array installed on the north, south, east and west walls of a building which was constructed as a NEDO field-test project. In the case of performance simulation for the actual PV system, calculated performance generally agrees with real measured data. Based on them, produced electrical energy is simulated as a function of ground albedo, array tilt angle and space between the PV array and the wall for installation. In addition, shading effect on produced electrical energy is also estimated by assuming some neighboring buildings. Effect of sub-array installation on different walls on DC power output is also estimated.

Numerical Study on the CZ Silicon Melt Convection for High Efficient Solar Cell

Conversion efficiency of solar cell is strongly affected by quality of substrate and the quality of substrate is influenced by melt convection if the substrate crystal is grown by melt growth technique. Therefore, melt convection control techniques are important to produce a high quality single crystal. In this paper, we have proposed a high frequency magnetic field applied CZ method and investigated the effect of high frequency magnetic field on silicon melt convection. The result reveals that the high frequency magnetic fields affect the tendency of the melt convection: until certain intensity of the high frequency magnetic field, the melt convection is suppressed and above such intensity of the high frequency magnetic field, the melt convection intensity is enhanced. This result indicates that the melt convection can be controlled by the high frequency magnetic field and the high quality silicon single crystals will be grown by this method.

Thermal Performance of Unvented Attics in Hot-Dry Climates: Results From Building America

As unvented attics have become a more common design feature implemented by Building America partners in hot-dry climates of the United States, more attention has been focused on how this approach affects heating and cooling energy consumption. By eliminating the ridge and eave vents that circulate outside air through the attic in most new houses and by moving the insulation from the attic floor to the underside of the roof, an unvented attic becomes a semiconditioned space, creating a more benign environment for space conditioning ducts. An energy trade-off is made, however, because the additional surface area (and perhaps reduced insulation thickness) increases the building loss coefficient. Other advantages and disadvantages, unrelated to energy, must also be considered. This paper addresses the energy-related effects of unvented attics in hot-dry climates based on field testing and analysis conducted by the National Renewable Energy Laboratory.

Efficient Optical Couplings for Fiber-Distributed Solar Lighting

Optical couplings in large core optical waveguides have many similarities with those in conventional optical fibers but pose some unconventional challenges as well. The larger geometry, looser manufacturing tolerances and reduced dimensional stability compound the problems associated with making low-loss couplings in large core waveguides. The individual factors contributing to coupling losses are discussed to develop an understanding of the extant loss mechanisms. Individual methods and materials employed to mitigate the impact of each of the dominant loss mechanisms are discussed in detail. A combination of endface geometry control, axial alignment constraint and refractive index matching are employed to produce highly efficient optical couplings in large core waveguides. The combination of these elements has significantly reduced the insertion losses due to connector couplings. Prior to implementing the current methods losses of 15% and greater were common but these have been reduced to 2%–5% with the current methods.

Technical Training for Women in the PV Field

Over the past decade, more women have become interested in renewable energy, particularly photovoltaics, but a suitable training environment is difficult to find. Approximately five years ago, Solar Energy International (SEI) started offering classes for women only. The premise is that a women only class provides a friendly atmosphere for women to ask basic questions, take time working with tools and concepts, and practice hands-on activities in a supportive environment. Sandia National Labs has assisted SEI by providing technical content and hands-on instruction. The classes are split between the classroom and the field. This paper will provide an overview of the technical training, safety and the importance of the National Electrical Code® (NEC)®, and accomplishments of the students beyond these classes.

A Dynamic Response of a Module/Array Simulator Using I-V Magnifier Circuit of a PN Photo-Sensor

Basic characteristics and dynamic response of a 30W module/array simulator using PV I-V magnifier circuit was studied. It was confirmed that each gain of voltage and current was independently adjustable using feedback control of current signal. Simulator circuit output power is controlled by LED irradiation light which works as an irradiation of sun light to real PV modules. Maximum power of the circuit depends on maximum power of the power amplifier used in the circuit. A photo-current of pn photo-sensor was some micro ampere hence the current gain of the simulator needed more than 50dB. The voltage gain was not more than 3dB because a multi junction pn photo-sensor was used. To control the simulator circuit by personal computer, an LED driver circuit was added. A fill factor was also easily changeable by change of shunt resistor connected with pn photo-sensor in parallel. A dynamic response of short circuit current was measured and confirmed that the circuit has enough response ability to apply the MPPT evaluation. A grand line of each module is isolated, hence any topology of connections is available. This circuit simplifies the control system and makes it easy to handle multi simulator units by one personal computer. This system is suitable for the evaluation of multi inverter system.

Convective Heat Transfer Analysis of Open Cell Metal Foam for Solar Air Heaters

A one-dimensional heat transfer model for open-cell metal foam is presented. Three aluminum foams having different areas, relative densities, ligament diameters, and number of pores per inch were analyzed. The effective thermal conductivity and the heat transfer increased with the number of pores per inch. The effective thermal conductivity of the foams can be up to four times higher than that of solid aluminum. The resulting improvement in heat transfer can be as high as 50 percent. The maximum heat transfer for the aluminum foams occurs at a pore Reynolds number of 52. The heat transfer, in addition, becomes insensitive to the flow regime for pore Reynolds numbers beyond 200.