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This paper provides a simplified analysis tool to assess the energy saving potential of daylighting for commercial buildings through skylights. Specifically, the impact of daylighting is investigated for various fenestration opening sizes, glazing types, control strategies, and geographic locations. A top floor of a prototypical office building has been considered in the analysis. The results obtained for the office building can be applied to other types of buildings such as retails stores, schools, and warehouses. Based on the simulation analysis results, it was determined that skylight to floor ratio more than 0.3 does not affect significantly the lighting energy savings. An optimum value of skylight to floor area ratio was found to be 0.2 to minimize the annual total building energy use.

An analytical method has been developed for the determination of average ground reflectivites for solar collectors and has been successfully applied to 12 representative winter landscapes. This method allows consideration of a wide variety of landscapes, independent of season, and rests on an analytical basis not existing in previous methods. An average ground reflectivity of 0.6 to 0.7 is accurate for most rural landscapes in winter where snow cover is predominant. (WDM)

The 1 MW Saguaro solar parabolic trough power plant began operation in December 2005. The plant will initially operate without an energy storage system. However, recent studies predict a thermocline-type storage should be the most cost-effective storage concept for solar parabolic troughs power plants. If such a system can be successfully demonstrated at Saguaro, future trough plants will likely adopt this storage technology. A thermocline storage system for Saguaro has been proposed by Department of Energy (DOE) laboratories and the solar industry. In this paper, the time-dependent performance of the proposed storage system was evaluated with a new model of the plant based on the TRNSYS simulation system. Results indicate that the proposed system should work well at Saguaro. The paper describes the TRNSYS model and the engineering insights gleaned from annual performance simulations of the plant.

Energy efficiency, vehicle weight, driving range, and fuel economy are compared among fuel cell vehicles (FCV) with different types of fuel storage and battery-powered electric vehicles. Three options for onboard fuel storage are examined and compared in order to evaluate the most energy efficient option of storing fuel in fuel cell vehicles: compressed hydrogen gas storage, metal hydride storage, and onboard reformer of methanol. Solar energy is considered the primary source for fair comparison of efficiencies for true zero emission vehicles. Component efficiencies are from the literature. The battery powered electric vehicle has the highest efficiency of conversion from solar energy for a driving range of 300 miles. Among the fuel cell vehicles, the most efficient is the vehicle with onboard compressed hydrogen storage. The compressed gas FCV is also the leader in four other categories: vehicle weight for a given range, driving range for a given weight, efficiency starting with fossil fuels, and miles per gallon equivalent (about equal to a hybrid electric) on urban and highway driving cycles.

A solar thermal power project that makes use of a compact linear Fresnel reflector array to concentrate solar radiation onto a stationary absorber cavity suspended above the array has been proposed. The cavity is trapezoidal in cross-section. The upper surface of the cavity is a flat plate absorber with steam tubes running behind it. The lower surface is a glass window that allows solar radiation, focused by the mirror array, to enter the cavity. Heat loss from the absorber occurs via a complex interaction between radiation, convection and conduction within the cavity, and then from the cavity to the surroundings. This paper describes the experimental techniques used to investigate the heat losses from the absorber, and the flow visualization technique used to capture the flow patterns within the cavity. It then goes on to compare the experimental results with predictions obtained from a model developed using FLUENT, a commercially available computational fluid dynamics package. Excellent agreement is achieved between the flow patterns observed in the experiment and those predicted by the computational model. Reasonable agreement between the experimentally determined heat losses and those predicted by the computational model are also shown to exist.

Abstract Here, we present research addressing one of the main challenges facing the efficient production of solar energy in arid regions where solar insolation is at its highest, but where the significant challenges of pervasive dust, sand storms and insufficient rain can dramatically alter the feasibility of harvesting solar energy. In this study, the impact of dust on the light transmittance through low iron glass was assessed for different periods of time. Additionally, different cleaning mechanisms were briefly reviewed including the promising technique of dry cleaning using robotic systems. This paper explores the effect of dry cleaning for the removal of dust particles settled down on glass and the impact of brushing on the transmission of the glass. It was demonstrated that dry cleaning using Nylon brushes does not have a significant, permanent effect on the optical characteristics of the glass surface, even when the brush is used to clean a dusty surface. Significantly, the process of brushing dusty samples does improve transmittance over the un-brushed state. However, the cleaning efficiency of the nylon brushes is not as high as cleaning using water and delicate wipers. The glass samples showed some changes in the surface of the glass after brushing, however, this was shown not to have a permanent effect on the optical characteristics of the glass after the simulated equivalent of 20 years of cleaning. Therefore, the data presented in this paper demonstrates the need for careful testing in the development and assessment of dry cleaning dust mitigation solutions. It also offers an indication of the technology’s positive potential and elucidates some of the most important obstacles that need to be overcome.

Abstract A fast scheme for estimation of the instantaneous direct solar irradiance (DSI) at the Earth’s surface is developed based on detailed radiative transfer calculations for the full range of atmospheric conditions. The parameterisation is divided into the components for clear sky and overcast conditions. For the clear sky condition, the effects of absorption due to water vapour, carbon dioxide and ozone on the DSI are explicitly treated. The effects of Rayleigh scattering, aerosols are also treated on a physical basis. Based on the clear sky results, the transmittances due to effects of clouds are determined for both liquid and ice clouds. The results are parameterised in terms of cloud visible optical depth. The input variables required for determination of DSI include precipitable water, column ozone amount, CO2 mixing ratio, aerosol optical depth, cloud visible optical depth, surface pressure and solar zenith angle. These variables are all available in numerical weather prediction (NWP) forecast models or can be obtained from satellite observations. Therefore, the scheme can be used to determine the DSI using NWP model products or satellite data. The scheme has been tested using the observations obtained at three stations of the US Department of Energy Atmospheric Radiation Measurements (ARM) program. The relative mean bias differences under clear-sky and all-sky conditions are better than 3.2% and 5.1%, respectively. The correlation coefficients between modelled results and observations are all greater than 0.99. The sampling errors of DSI due to the use of 3-hourly or 1-hourly low frequency in radiation calculations in NWP models are evaluated using the fast scheme and ARM observational data. It is found that these errors can be greater than 800 W m−2 for many cases where sky condition changes from clear to overcast. Application of the current scheme can reduce these errors to less than 100 W m−2.

Abstract Fenestration attachments are anticipated to produce significant reductions in building energy use because they can be deployed quickly at low-cost. New software tools enable users to assess the building energy impacts of optically complex fenestration systems (CFS) such as shades, Venetian blinds, or daylighting systems. However, such tools require users to provide bi-directional scattering distribution function (BSDF) data that describe the solar-optical performance of the CFS. A free, open-source Radiance tool genBSDF enables users to generate BSDF data for arbitrary CFS. Prior to genBSDF, BSDF data for arbitrary fenestration systems could only be produced using either expensive software or with expensive equipment. genBSDF outputs CFS data in the Window 6 XML file format and so can be used with CFS-enabled software tools to model multi-layered window systems composed of glazing and shading layers. We explain the basis and use of the genBSDF tool and validate the tool by comparing results for four different cases to BSDF data produced via alternate methods. This validation demonstrates that BSDFs created with genBSDF are comparable to BSDFs generated analytically using TracePro and by measurement with a scanning goniophotometer. This tool is expected to support accelerated adoption of fenestration attachments and daylighting technologies.