A simple method for partitioning total solar radiation into diffuse/direct components in the United States

Solar radiation is a major sustainable and clean energy resource, and use of solar radiation is expected to increase. The utilization efficiency of solar energy varies with the relative proportions of the direct and diffuse components that compose total solar radiation and with the slope and aspect of the irradiated surface. The purpose of this paper is to develop a simple method for estimating diffuse and direct solar radiation at sites with observation of only total solar radiation. An existing model for estimating diffuse radiation, i.e., a linear relationship between the diffuse fraction (the ratio of diffuse radiation to total solar radiation) and the clearness index (the ratio of total solar radiation to extraterrestrial radiation), is applied to 7 sites across the continental United States with observations of diffuse and total radiation. The linear model shows good monthly performance. The model parameters (slope and interception) show a strong seasonal pattern that exhibits small variation across the 7 sites; therefore, the average values of the two monthly parameters may be used for estimating diffuse radiation for other locations with observations of total radiation.     

Prediction of diffuse solar radiation using satellite data

In the project of the solar systems, the values of the solar radiation of a region must be known. The global solar radiation measurements are performed by the Turkish Meteorological Service in Turkey, while the diffuse solar radiation measurements are unavailable. In this study, some new models for predicting the monthly average daily diffuse solar radiation on a horizontal surface for Erzincan, Turkey are developed using satellite data. The evaluation of the models is carried out with the statistical analysis methods of mean bias error (MBE), root mean square error (RMSE) and correlation coefficient (r). The results are proved that the correlation equations obtained in here can be used to forecast diffuse solar radiation reasonably well.     

Comparative assessment of solar photovoltaic panels based on metal-derived hazardous waste,resource depletion,and toxicity potentials

Solar photovoltaic (PV) cells are used to resolve energy security and climate change problems. Although PV panels have long physical lifetimes, they would be eventually replaced by new ones with higher energy efficiency and then changed to waste. Depending on the types of PV cells, waste PV panels have different environmental impact potentials due to different contents of substances. This study assesses and compares hazardous waste, resource depletion, and toxicity potentials from metals in three types of PV modules (i.e., polycrystalline silicon (Si), amorphous Si, and CIGS (copper/indium/gallium/di-selenite) PVs) on per-watt electricity generation basis. Hazardous waste potentials are examined by using metal leachability tests, and resource depletion and toxicity potentials are evaluated by using life cycle impact assessment methods. The polycrystalline Si and CIGS PVs have hazardous waste potentials due to lead (Pb) and cadmium/selenium, respectively, whereas the amorphous Si PV does not. The polycrystalline Si PV has the highest resource depletion potential due primarily to silver; the CIGS PV has the next highest due primarily to selenium; and the amorphous Si PV had the lowest, which is derived primarily from tin and copper. For toxicity potentials, overall the amorphous Si PV had lower potentials, derived primarily from barium/copper/nickel/zinc, than the polycrystalline Si and CIGS PVs of which the toxicity potentials were primarily form copper/lead/nickel/silver and copper/mercury/molybdenum/nickel/silver, respectively. Therefore, waste polycrystalline Si and CIGS PV panels should be recycled and managed with priority, and PV technology development needs to be directed to amorphous Si PV from the material perspective.     

Renewable electricity policies,heterogeneity, and cost effectiveness

Renewable electricity policies promote investment in renewable electricity generators and have become increasingly common around the world. Because of intermittency and the composition of other generators in the power system, the value of certain renewable – particularly wind and solar – varies across locations and technologies. This paper investigates the implications of this heterogeneity for the cost effectiveness of renewable electricity policies. A simple model of the power system shows that renewable electricity policies cause different investment mixes. Policies also differ according to their effect on electricity prices, and both factors cause the cost effectiveness to vary across policies. We use a detailed, long-run planning model that accounts for intermittency on an hourly basis to compare the cost effectiveness for a range of policies and alternative parameter assumptions. The differences in cost effectiveness are economically significant, where broader policies, such as an emissions price, outperform renewable electricity policies.     

Evaluation of the potential of harvesting heat energy from asphalt pavements

The potential of harvesting heat energy from asphalt pavement using a piping network with fluid flowing through it needs to be evaluated before spending a significant amount of time on planning details of design and construction. The key factors involved in this evaluation include the temperature of the pavement at the depth at which the system is being considered, as well as the temperature of the fluid used for harvesting the heat energy. Costs include those required for the system such as pumps and pipes, and cost of energy required for pumping. Taking all of the factors into consideration, a macro-enabled spreadsheet has been developed that allows the user to input air temperature data as well as pipe location and cost parameters. The end results are data on flow rate versus yearly savings and payback period. From these data, a user can easily determine whether the payback period is reasonable or not and could also evaluate the effect of the different parameters on the payback period. Examples of the results of analysis for different cities in four different parts of the USA and Singapore and Chennai, India, are presented. The payback period shows a good relationship with the latitude of the location – the period increases with an increase in latitude. The public domain location from where the spreadsheet can be downloaded is provided.     

太阳光下Fenton氧化-混凝法深度处理垃圾渗滤液试验研究

针对经生物处理后难以进一步生物降解的垃圾渗滤液,提出采用太阳光下Fenton氧化-混凝法进行深度处理.比较了直接混凝法、太阳光下Fenton氧化法及其联合处理技术对垃圾渗滤液COD_(Cr)的处理效果.结果表明,垃圾渗滤液进行直接混凝处理的效果不理想.COD_(Cr)的去除率仅为17.8%;太阳光可有效地催化Fenton试剂对垃圾渗滤液COD_(Cr)的去除效果,但要其COD_(Cr)低于国家二级排放标准则需消耗H_2O_2的浓度大于600 mmol/L.导致其处理成本较高;而采用太阳光下Fenton氧化-混凝联合处理技术.垃圾渗滤液低于国家二级排放标准只需投加H_2O_2的浓度为170 mmol/L,比单纯采用太阳光下Fenton 氧化法处理垃圾渗滤液可节约H_2O_2用量2.53倍以上.     

Performance study on evacuated tubular collector coupled solar still in West Texas climate

Experimental study was performed on a single basin active solar distillation system augmented with a solar collector using evacuated solar tubes. Field tests were conducted over several days under the climatic conditions of West Texas to evaluate the effect evacuated solar tubes have on the daily distillate yield rate. To investigate the feasibility of the solar tubes, active and passive solar stills with and without exterior insulation were examined. The maximum daily production rate for the active distillation system using evacuated solar tubes and the passive distillation system was 3.6 and 1.4 kg/m²day, respectively. The results showed the augmentation of the still with evacuated solar tubes increased its production capacity by a factor of 2.63. It also increased the maximum temperature of the water in the still basin by at least 20 °C. Economic analysis shows that it is feasible to use evacuated tubular collector coupled solar still as an alternative means for reclaiming water in farmlands with a payback period of approximately 6 years.     

Indirect forced solar drying of banana slices: phenomenological explanation of non-isotropic shrinkage and color changes kinetics

Solar drying technology is a noteworthy technique as it uses the renewable solar energy. In this study, thin slices of banana were dried by using an indirect forced solar dryer at air mass flow rates of 0.016, 0.041, and 0.082 kg s^?1. In order to assess the kinetics of shrinkage and color changes, image processing technique was applied for determining area, volume, density, total color difference and browning index. Shrinkage factor of the samples was less than 1 during drying indicating non-isotropic shrinkage with contraction of inner voids. Furthermore, product shrinkage showed two descending drying steps in which the volume change was more than the evaporated water volume in the first step and equal to that in the second step. The dimensionless evaporated water volume with respect to the dimensionless volume difference of the product also revealed that two steps of volume change existed during drying separated at critical moisture ratio 0.23. The area and volume changes were only related to the product moisture content and were independent of the air mass flow rate, and hence air temperature. In contrary to the browning index, the total color difference was not influenced by air mass flow rate and the least change in browning index occurred at mass flow rate of 0.041 kg s^?1.     

Canopy slope effect on the performance of the solar chimney power plant

Solar chimney power plants constitute an impressive construction by its size and its output seems low for its dimensions. Although many works have been carried out on the subject, there is still much scientific and technical improvement to be done. In the present work, we consider the modeling of turbulent flow under the effect of natural convection within a solar chimney power plant (SCPP) by performing numerical simulation using the Saturne Code coupled with Syrthes code. The objective of the study is the analysis of the collector cover slope influence on the performance of the SCPP in two cases. In the first case, the storage system considered is composed solely of the ground under the collector. For the second case, the storage system is made, in addition to the ground, of a 10 cm thick tub filled with water, covering the entire surface of the collector. The concept of minimizing the entropy production is also studied with the objective of optimizing the geometric configuration as well as the effect of the collector cover slope on the efficiency of SCPP. The boundary conditions are defined according to the meteorological data for a typical day available on the site of Adrar, Algeria. The results allow us to focus on the storage system influence on the SCPP performance and the duration of its operation after sunset. This leads to the improvement of the global efficiency of the SCPP. Results show the positive impact of the extra storage media use and the configuration which improves the velocity at the chimney entrance.