The measurement of photosynthetically active radiation

In crop ecology, the two most popular definitions of photosynthetically active radiation are the irradiance (radiant power flux density) in the waveband 400 to 700 nm, and the quantum flux density in the same waveband. Instruments calibrated in either of these two units are available. Calculations show that the quantum flux measurement is less subject to the systematic error caused by the spectral response not matching the action spectrum for photosynthesis in an “average crop plant” (11) than is the irradiance measurement. The range of errors is ±6 and ±16 per cent, respectively, for the 9 natural and artificial light sources examined. The imperfections of the instruments themselves are not included.     

Luminous efficacy of direct solar radiation for all sky types

Three models for the luminous efficacy of direct solar radiation on a horizontal surface, valid for all sky conditions, have been developed in the present work, and two of them are proposed. In all the models a function for the direct luminous efficacy for all sky conditions relative to the direct luminous efficacy for clear skies is obtained, using the function for the direct luminous efficacy for clear skies given in a previous work, and the brightness index as a new independent variable. One of the two models is obtained by fitting the values of the relative luminous efficacy as a function of the brightness index. The other proposed model is developed by obtaining in the first place models for direct illuminance and direct irradiance, both relative to the corresponding clear sky models, and then finding the ratio between the relative direct illuminance and irradiance models. Statistical assessment of the direct illuminance values estimated with the proposed models gives similar values for the MBE and the RMSE. However, the model obtained from illuminance and irradiance models is mathematically coherent.     

Luminous flux and luminous efficacy of black-body radiation: an analytical approximation

Analytical expressions for calculation of luminous flux and luminous efficacy corresponding to a given radiant flux with black-body spectrum are presented. The results are directly applicable to extraterrestrial solar radiant flux and likewise to any other light source with a spectral distribution roughly equal to a black-body spectrum.     

On the complexity of radiation models for PV energy production calculation

Several authors have analysed the changes of the probability density function of the solar radiation with different time resolutions. Some others have approached to study the significance of these changes when produced energy calculations are attempted. We have undertaken different transformations to four Spanish databases in order to clarify the interrelationship between radiation models and produced energy estimations. Our contribution is straightforward: the complexity of a solar radiation model needed for yearly energy calculations, is very low. Twelve values of monthly mean of solar radiation are enough to estimate energy with errors below 3%. Time resolutions better than hourly samples do not improve significantly the result of energy estimations.     

REST2: High-performance solar radiation model for cloudless-sky irradiance, illuminance, and photosynthetically active radiation – Validation with a benchmark dataset

REST2, a high-performance model to predict cloudless-sky broadband irradiance, illuminance and photosynthetically active radiation (PAR) from atmospheric data, is presented. Its derivation uses the same two-band scheme as in the previous CPCR2 model, but with numerous improvements. Great attention is devoted to precisely account for the effect of aerosols, in particular.Detailed research-class measurements from Billings, OK are used to assess the performance of the model for the prediction of direct, diffuse and global broadband irradiance. These measurements were made in May 2003 during a sophisticated radiative closure experiment, which involved the best radiometric instrumentation currently available and many ancillary instruments. As a whole, these exceptional measurements constitute the only known modern benchmark dataset made specifically to test the intrinsic performance of radiation models. Using this dataset as reference, it is shown that REST2 performs better than CPCR2 for irradiance, illuminance or PAR predictions. The availability of the turbidity data required by REST2 or other similar models is also discussed, as well as the effect that turbidity has on each component of broadband irradiance, PAR irradiance and illuminance, and on the diffuse/global PAR ratio.     

Lumped-parameter models for low-temperature geothermal fields and their application

The behavior of low-temperature geothermal reservoirs under exploitation is simulated using analytical lumped-parameter models. These models consider the effects of fluid production and reinjection, as well as natural recharge, on the pressures (or water levels) of low-temperature, liquid-dominated geothermal systems. The computed responses for constant production/injection flow rates are given in the form of analytical expressions. Variable flow rate cases are modeled, based on the Duhamel's principle. Reservoir parameters are obtained by applying a weighted nonlinear least-squares estimation technique in which measured field data are history matched to the corresponding model response. By using history-matched models, the future performance of the reservoir can be predicted for different production/injection scenarios in order to optimize the management of a given geothermal system.We demonstrate the applicability of the models by simulating measured data from the Laugarnes geothermal field in Iceland, and the Balcova–Narlidere field in Turkey.     

Luminous efficacy of daylight under different sky conditions

Dalighting is recognised as an important and useful strategy in terms of energy-efficient building design in hot climates. However, daylighting is always accompanied by unwanted solar heat gain, particularly during the cooling season. To achieve and evaluate daylighting design, solar radiation and outdoor illuminance data are needed. In 1991, a measuring station was installed at the City University of Hong Kong to measure global and diffuse solar radiation and outdoor illuminance. The measured data are analysed, and empirical models to determine luminous efficacy under different sky conditions are developed and presented. Implications for energy efficiency in building designs are discussed.     

Kinetic models for hydrogen sorption and their application to the H2-M system

Several kinetic models for the H₂-M system have been proposed and the corresponding rate equations developed. The solutions of these rate equations were compared to the experimental data for certain H₂-metal systems. These models can successfully explain the absorption/desorption kinetics of some H₂-M systems. Detailed discussions regarding the limitation of the kinetic model are also presented.     

Solar radiation calculation methodology for building exterior surfaces

The present article shows a new methodology of calculation of the direct, diffuse and reflected incident solar radiation, in all type of surfaces, either in open urban environments or inside buildings. This methodology is applicable in problems related to solar access (space heating in buildings, shadowing of open spaces), solar gains (space cooling in buildings), and daylighting. Solar radiation is the most important contribution to the surface and volumetric energy balance during the daytime. Particularly, solar radiation is the main contributor to heat gains in buildings, especially in residential buildings, where internal gains are very low. Utilization of daylight in buildings may result in significant savings in electricity consumption for lighting while creating a higher quality indoor environment. Additional energy savings may also be realized during cooling season, when reduction of internal heat gains due to electric lighting results in a corresponding reduction of cooling energy consumption.The analysis of the existing calculation methods and proposed in the scientific bibliography for the calculation of the solar radiation in problems of solar access in winter, solar gains in summer, and daylighting, takes us to the necessity of outlining a new and complete methodology. This new methodology is applicable to all these problems with a great accuracy and calculation speed.     

Estimating atmospheric ozone for solar radiation models

Absorption of incoming solar radiation by atmospheric ozone, while only a small part of total depletion of the solar beam, can contribute up to 20 per cent or more to the absorption taking place. Good methods exist to estimate absorption by ozone, but these methods require values for ozone amounts present in the beam path. An empirical, mathematical model has been developed that shows close agreement with observed annual ozone contents over North America. Only latitude, longitude, and day of the year are needed as inputs to obtain ozone-depth estimates from the model. The model can be adjusted to provide similar accuracy for most of the world. Seasonal variations are also built into the model.     

Estimation of Luminous efficacy of daylight and exterior illuminance for composite climate of Indore city in Mid Western India

Daylighting is one of the basic components of passive solar building design and its estimation is essential. In India there are a few available data of measured illuminance as in many regions of the world. The Indian climate is generally clear with overcast conditions prevailing through the months of June to September, which provides good potential to daylighting in buildings. Therefore, an analytical model that would encompass the weather conditions of Indore was selected. Hourly exterior horizontal and slope daylight availability has been estimated for Indore using daylight modeling techniques based on solar radiation data.     

气体热辐射机理的研究与热辐射特性的计算

从对气体热辐射的微观机理的研究出发，利用谐振子模型对气体燃烧产物的热辐射特性进行了研究与计算，结果表明：气体的热辐射波谱取决于气体分子的固有振动频率、等离子体频率、阻尼系数以及气层厚度，提高压力、气层厚度和降低温度可以有效地改善气体热辐射的选择性。     

Dynamic fuel cell models and their application in hardware in the loop simulation

Currently, fuel cell technology plays an important role in the development of alternative energy converters for mobile, portable and stationary applications. With the help of physical based models of fuel cell systems and appropriate test benches it is possible to design different applications and investigate their stationary and dynamic behaviour. The polymer electrolyte membrane (PEM) fuel cell system model includes gas humidifier, air and hydrogen supply, current converter and a detailed stack model incorporating the physical characteristics of the different layers. In particular, the use of these models together with hardware in the loop (HIL) capable test stands helps to decrease the costs and accelerate the development of fuel cell systems. The interface program provides fast data exchange between the test bench and the physical model of the fuel cell or any other systems in real time. So the flexibility and efficiency of the test bench increase fundamentally, because it is possible to replace real components with their mathematical models.     

Electrochemical behavior of polyamides with cyclic disulfide structure and their application to positive active material for lithium secondary battery

Polyamides (DTA-I, DTA-II, and DTA-III) containing cyclic disulfide structure were prepared by condensation between 1,2-dithiane-3,6-dicarboxylic acid (DTA) and alkyl diamine, NH₂–(CH₂)_n–NH₂ (DTA-I; n=4, DTA-II; n=6, DTA-III; n=8) and their application to positive active material for lithium secondary batteries was investigated. Cyclic voltammetry (CV) measurements under slow sweep rate (0.5 mV s⁻¹) with a carbon paste electrode containing the polyamide (DTA-I, DTA-II, or DTA-III) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), 1:1 by volume containing lithium salt, such as LiClO₄). The responses based on the redox of the disulfide bonds in the polyamide were observed.Test cells, Li/PC-DME (1:1. by volume) with 1 mol dm⁻³ LiClO₄/the polyamide cathode, were constructed and their performance was tested under constant current charge/discharge condition. The average capacity of the test cells with the DTA-III cathode was 64.3 Ah kg⁻¹ of cathode (135 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (–CO–(CH₂)₂–S–S–(CH₂)₂–CONH–(CH₂)₈–NH–, GTA-III) was also investigated and the average capacity was 56.8 Ah kg⁻¹ of cathode (100 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (1.76 V)). Cycle efficiency of the test cell with the DTA-III cathode was higher than that with the GTA-III cathode.     

Investigations into the performance of photovoltaics-based active filter configurations and their control schemes under uniform and non-uniform radiation conditions

With their growing popularity as alternative to conventional fuel, photovoltaics(PV) are being increasingly employed for a wide range of applications. Power quality improvement through a PV-fed active filter (PVAF) or inverter is one such application. A PVAF can supply active and reactive power to the grid when solar radiation is available or control the reactive power during periods of low or no radiation. The advantages of PVAF as an independent active source of compensation, reduced transmission losses etc. over a conventional AF have already been highlighted in the literature. However, not much attention has been paid to the effects of the PVAF configuration on its operational performance. Similarly, the effect of control schemes used to control such filters has also not been investigated. Various configurations of PVAF (viz. stringor multiple-string- or centralised-inverter based) are possible depending upon the configuration of the PV array (source). This study compares various PVAF configurations and their control schemes in terms of their ability to compensate reactive power, harmonics and phase-imbalances caused by unbalanced linear and nonlinear loads in a three-phase, four-wire distribution system. Performance parameters such as power output and power quality as described by total harmonic distortion, phase imbalance and neutral conductor current are evaluated under both uniform and non-uniform radiation (e.g. partially shaded) conditions. In particular, results are presented to highlight and compare the effects of partial shading on the control schemes and PVAF configurations. Based on this study, several critical observations and remarks are presented.     

基于MATLAB的太阳辐射资源计算

运用MATLAB软件编程,计算了太阳辐射穿过大气层后到达地面的强度,综合考虑海拔高度、大气透明度系数的影响,建立了太阳辐射强度数学计算模型。模型计算得到的理论数据与用MS4型太阳能资源测试仪测试获得的数据进行了对比分析,相对误差在0.002%～9.981%之间,验证了计算模型的合理性。     

Evaluation and comparison of hourly solar radiation models

In this paper, an attempt has been made to develop a new model to evaluate the hourly solar radiation for composite climate of New Delhi. The comparison of new model for hourly solar radiation has been carried out by using various model proposed by others. The root mean square error (RMSE) and mean bias error (MBE) have been used to compare the accuracy of new and others model. The results show that the ASHRAE and new proposed model estimate hourly solar radiation better for composite climate of New Delhi in comparison to other models. Hourly solar radiation estimated by constants obtained by new model (modified ASHRAE model) for composite climate of India is fairly comparable with measured data. The percentage mean bias error with new constants for New Delhi was found as low as 0.15 and 0% for hourly beam and diffuse radiation, respectively. There is a 1.9–8.5% RMSE between observed and predicted values of beam radiation using new constants for clear days. The statistical analysis has been used for the present study. Copyright © 2008 John Wiley & Sons, Ltd.     

Development of improved solar radiation models for predicting beam transmittance

A pair of enhanced models are presented herein which, while relying only on global irradiation measurements, result in increased predictive power in estimating the hourly beam irradiation. The first model correlates the beam transmittance with clearness index and air mass. The second correlates the beam transmittance with the clearness index and with a new variable based on the temporal variation of the global radiation. The new variable helps describe the sky condition without the need of any further meteorological information. The models were developed using a new surface fitting technique applied to data which were collected at the Solar Total Energy Project in Shenandoah, Georgia (33.4°N, 84.7°W) over a five-year period.