Evaluation of conventional and high-performance routine solar radiation measurements for improved solar resource, climatological trends, and radiative modeling

The solar renewable energy community depends on radiometric measurements and instrumentation for data to design and monitor solar energy systems, and develop and validate solar radiation models. This contribution evaluates the impact of instrument uncertainties contributing to data inaccuracies and their effect on short-term and long-term measurement series, and on radiation model validation studies. For the latter part, transposition (horizontal-to-tilt) models are used as an example. Confirming previous studies, it is found that a widely used pyranometer strongly underestimates diffuse and global radiation, particularly in winter, unless appropriate corrective measures are taken. Other types of measurement problems are also discussed, such as those involved in the indirect determination of direct or diffuse irradiance, and in shadowband correction methods. The sensitivity of the predictions from transposition models to inaccuracies in input radiation data is demonstrated. Caution is therefore issued to the whole community regarding drawing detailed conclusions about solar radiation data without due attention to the data quality issues only recently identified.     

A method to calibrate a solar pyranometer for measuring reference diffuse irradiance

Accurate pyranometer calibrations, traceable to internationally recognized standards, are critical for solar irradiance measurements. One calibration method is the component summation, where the pyranometers are calibrated outdoors under clear sky conditions, and the reference global solar irradiance is calculated as the sum of two reference components, the diffuse and subtended beam solar irradiances. The beam component is measured with pyrheliometers traceable to the World Radiometric Reference, while there is no internationally recognized reference for the diffuse component. In the absence of such a reference, we present a method to consistently calibrate pyranometers for measuring the diffuse component with an estimated uncertainty of ±(3% of reading+1 W/m²). The method is based on using a modified shade/unshade method, and pyranometers with less than 1 W/m² thermal offset errors. We evaluated the consistency of our method by calibrating three pyranometers four times. Calibration results show that the responsivity change is within ±0.52% for the three pyranometers. We also evaluated the effect of calibrating pyranometers unshaded, then using them shaded to measure diffuse irradiance. We calibrated three unshaded pyranometers using the component summation method. Their outdoor measurements of clear sky diffuse irradiance, from sunrise to sundown, showed that the three calibrated pyranometers can be used to measure the diffuse irradiance to within ±1.4 W/m² variation from the reference irradiance.     

Analysis of uncertainties in gas uptake measurements using the gravimetric method

A full analysis of the uncertainties in the calculation of the amount of gas absorbed or desorbed by a sample using the gravimetric technique has been made. The gravimetric technique provides a near direct measurement of the uptake of gas by continuously measuring the weight of the sample plus absorbed gas and is frequently used to characterise the uptake of hydrogen in potential hydrogen storage materials. These calculations provide the capability to determine the uncertainty in the final gas uptake measurement given knowledge of the measurement uncertainties. Uptake of hydrogen gas on activated carbon has been modelled to allow individual constants such as the buoyancy volumes as well as measurement uncertainties to be changed while determining the effect on the uptake uncertainty. The measurement uncertainties critical to minimising the overall uptake uncertainty have been identified and a comparison with another popular gas uptake method, the Sieverts technique, has been made.     

Analysis of the uncertainties in gas uptake measurements using the Sieverts method

An analysis of the uncertainties in the calculation of the amount of gas absorbed or desorbed by a sample has been made for the manometric or Sieverts technique, commonly used for the determination of hydrogen uptake on potential hydrogen storage materials. The analytical derivations provide a means to calculate the uncertainty in each step of a hydrogen absorption isotherm. In addition, a Sieverts system is modelled to allow a detailed investigation of the effect of volumes and other parameters as well as the relative impact of the different measurement uncertainties. Reliable uncertainty estimates are especially important for authoritative measurements of gas uptake by carbons and other nanostructured materials used for hydrogen storage.     

A global model for residential energy use: Uncertainty in calibration to regional data

Uncertainties in energy demand modelling allow for the development of different models, but also leave room for different calibrations of a single model. We apply an automated model calibration procedure to analyse calibration uncertainty of residential sector energy use modelling in the TIMER 2.0 global energy model. This model simulates energy use on the basis of changes in useful energy intensity, technology development (AEEI) and price responses (PIEEI). We find that different implementations of these factors yield behavioural model results. Model calibration uncertainty is identified as influential source for variation in future projections: amounting 30% to 100% around the best estimate. Energy modellers should systematically account for this and communicate calibration uncertainty ranges.     

A sonic method for building air-leakage measurements

The objective of this research is to obtain a correlation between air and sound leakages through slits. Audible sound, in the frequency range from 160 to 8000 Hz, is provided and sound pressure levels on both sides of the considered slit are detected by microphones, so that sound transmission losses can be obtained. Simultaneously, the air leakage through the slit under an inside-outside pressure difference of 50 Pa is also measured. Two different slits are used, one of which is rectangular of narrow width (0·05–1·00 mm), and the other is of the same section but with bent portions of the passage, as might be encountered in building constructions.The results show the correlation which represents graphically different curves for the source sound frequencies: ∼ 2000 Hz is found favourable for the intended purpose.     

A method for estimating monthly global solar radiation

In this paper a method is followed for estimating monthly totals of global solar radiation from a combination of calculations of monthly cloudless global solar radiation, surface meteorological observations, and empirical formulae relating sunshine duration to global solar radiation. The percent deviation of calculated from observed values is not negligible, but is much less than errors obtained by using extraterrestrial solar radiation totals. In case of values of monthly global solar radiation which are estimated for other regions, the resulted possible errors should be determined again. Some techniques leading to adaptation of the regression equations for other areas are argued.     

A two-point method for turbulent pipe flow measurements

A method for turbulent pipe flow measurements using velocities at two radial positions is presented. The method is insensitive to the Reynolds number and surface roughness; therefore, it is suitable for use in pipe systems subjected to slow variations in flow and pipe surface conditions. Applied to three independent data sources, the method shows significant improvement in average accuracy in comparison with a single-point method and a log-linear method.     

A fuzzy levelised energy cost method for renewable energy technology assessment

Renewable energy project development is highly complex and success is by no means guaranteed. Decisions are often made with approximate or uncertain information yet the current methods employed by decision-makers do not necessarily accommodate this. Levelised energy costs (LEC) are one such commonly applied measure utilised within the energy industry to assess the viability of potential projects and inform policy. The research proposes a method for achieving this by enhancing the traditional discounting LEC measure with fuzzy set theory. Furthermore, the research develops the fuzzy LEC (F-LEC) methodology to incorporate the cost of financing a project from debt and equity sources. Applied to an example bioenergy project, the research demonstrates the benefit of incorporating fuzziness for project viability, optimal capital structure and key variable sensitivity analysis decision-making. The proposed method contributes by incorporating uncertain and approximate information to the widely utilised LEC measure and by being applicable to a wide range of energy project viability decisions.     

A method for contact angle measurements under flow conditions

In this paper at first, a review of methods for measurements of the contact angle is presented. Following the review for contact angle measurements is developed method based on Langmuir approach. The method is aimed to be use in measurements the contact angle and rivulet’s width under vertical flows as well as for the cases when rivulet does not flow down vertically along a vertical plane.     

A web service for controlling the quality of measurements of global solar irradiation

The control of the quality of irradiation data is often a prerequisite to their further processing. Though data are usually controlled by meteorological offices, the sources are so numerous that the user often faces time-series of measurements containing questionable values. As customers of irradiation data, we established our own procedures to screen time-series of measurements. Since this problem of quality control is of concern to many researchers and engineers and since it is often a lengthy and tedious task, we decided to make this screening procedure available to everyone as a web service. This service is the purpose of this paper. The objective is not to perform a precise and fine control, an objective out of reach without details on the site and instruments, but to perform a likelihood control of the data and to check their plausibility. This is achieved by comparing observations with some expectations based upon the extraterrestrial irradiation and a simulation of the irradiation for clear skies. This service is available to everyone on the Web site www.helioclim.net. It offers a very convenient means to check time-series of irradiation: data are input in a HTML page by a copy and paste procedure and the return is also a HTML page that can be analyzed in detail for the data flagged as suspicious.     

Methods for probabilistic modeling of concentrating solar power plants

Probabilistic modeling of concentrating solar power technologies provides important information regarding uncertainties and sensitivities not available from deterministic models. Benefits of using probabilistic models include quantification of uncertainties inherent in the system and characterization of their impact on system performance and economics. This paper presents the tools necessary to conduct probabilistic modeling of concentrating solar technologies. The probabilistic method begins with the identification of uncertain variables and the assignment of appropriate distributions for those variables. Those parameters are then sampled using a stratified method (Latin Hypercube Sampling) to ensure complete and representative sampling from each distribution. Models of performance, reliability, and/or cost are then simulated multiple times using the sampled set of parameters. The results yield a cumulative distribution function that can be analyzed to quantify the probability of achieving a particular metric (e.g., net energy output or levelized energy cost) and to rank the importance of the uncertain input parameters.     

Daily global solar radiation modeling for Gran Canaria Island

The main aim of this paper is the daily global solar radiation modeling with different estimation models for the island of Gran Canaria (Spain). The errors of those ones will be studied and, moreover, the results will be compared with a solar radiation numerical model previously developed and validated. We have tested five different models starting from the Ångström linear model. Logarithmic, exponential, cubic models, and an exponential-linear composed model have been developed. The best results were obtained with the composed model. The development of these models will allow getting accurate results far from the measurements stations.     

A new stochastic approach to transient heat conduction modeling with uncertainty

We present a generalized polynomial chaos algorithm for the solution of transient heat conduction subject to uncertain inputs, i.e. random heat conductivity and capacity. The stochastic input and solution are represented spectrally by the orthogonal polynomial functionals from the Askey scheme, as a generalization of the original polynomial chaos idea of Wiener [Am. J. Math. 60 (1938) 897]. A Galerkin projection in random space is applied to derive the equations in the weak form. The resulting set of deterministic equations is subsequently discretized by the spectral/hp element method in physical space and integrated in time. Numerical examples are given and the convergence of the chaos expansion is demonstrated for a model problem.     

A grouping-based global harmony search algorithm for modeling of proton exchange membrane fuel cell

In recent years, accurate identification of voltage versus current (V-I) characteristics of proton exchange membrane fuel cell (PEMFC) has attracted significant attention in the literature. However, the main drawback in accurate modeling is the lack of information about the precise values of the model parameters. In this paper, in order to overcome this drawback a grouping-based global harmony search algorithm, named GGHS, is proposed for parameter identification issue. The proposed algorithm attempts to provide an efficient way in which a new harmony can be properly improvised. In order to study the capability of the proposed algorithm, the results obtained by GGHS are compared with those obtained by two versions of harmony search (HS) algorithms, three versions of particle swarm optimization (PSO) algorithms, as well as seeker optimization algorithm (SOA). Simulation results accentuate the superiority of the GGHS over the other methods.     

A comprehensive modeling method for proton exchange membrane electrolyzer development

Hydrogen attracts significant interests as an effective energy carrier that can be derived from renewable sources. Hydrogen production using a proton-exchange membrane (PEM) electrolyzer can efficiently convert renewable power via water splitting in wide scales—from large, centralized generation to on-site production. Mathematical models with multiple scales and fidelities facilitate the continuing improvements of PEM electrolyzer development to improve performance, cost, and reliability. The model scopes and methods are presented in this paper, which also introduces a comprehensive PEM electrolysis modeling tool based on computational fluid dynamics (CFD) software, ANSYS/Fluent. The modeling tool incorporates electrochemical model of a PEM electrolysis cell to simulate the performance of coupled thermal-fluid, species transport, and electrochemical processes in a product-scale cell or stack by leveraging the powerful meshing generation and CFD solver of ANSYS/Fluent. The thermal-fluid modeling includes liquid water/gas two-phase flow and simulates a PEM electrolysis cell by using Fluent user-defined functions as add-on modules accounting for PEM-specific species transport and electrochemical processes. The modeling outcomes expediate PEM electrolyzer scaling up from basic material development and laboratory testing.     

Production functions for climate policy modeling: An empirical analysis

Quantitative models for climate policy modeling differ in the production structure used and in the sizes of the elasticities of substitution. The empirical foundation for both is generally lacking. This paper estimates the parameters of 2-level CES production functions with capital, labour and energy as inputs, and is the first to systematically compare all nesting structures. Using industry-level data from 12 OECD countries, we find that the nesting structure where capital and labour are combined first, fits the data best, but for most countries and industries we cannot reject that all three inputs can be put into one single nest. These two nesting structures are used by most climate models. However, while several climate policy models use a Cobb–Douglas function for (part of the) production function, we reject elasticities equal to one, in favour of considerably smaller values. Finally we find evidence for factor-specific technological change. With lower elasticities and with factor-specific technological change, some climate policy models may find a bigger effect of endogenous technological change on mitigating the costs of climate policy.     

电控发动机开发装置的研制

在为发动机配装电控系统时,需要优化电控单元中的控制数据,以使发动机发挥出最佳性能。为此需要在发动机工作时实时在线读取和修改电控单元中的控制数据,并要求对数据的修改不得影响发动机正常运转。为实现上述功能研制了电控发动机开发装置。该装置使用了单片机和双端口ＲＡＭ,并且通过光纤与微机进行串行通讯,具有参数修改,状态监视、参数采集等功能。装置结构紧凑,操作简单,抗干扰能力强,适合发动机台试验和整车试验的恶     

A new parameter extraction method for accurate modeling of PEM fuel cells

In this paper, a new parameter extraction method for accurate modeling of proton exchange membrane (PEM) fuel cell systems is presented. The main difficulty in obtaining an accurate PEM fuel cell dynamical model is the lack of manufacturer information about the exact values of the parameters needed for the model. In order to obtain a realistic dynamic model of the PEM system, the electrochemical considerations of the system are incorporated into the model. Although many models have been reported in the literature, the parameter extraction issue has been neglected. However, model parameters must be precisely identified in order to obtain accurate simulation results. The main contribution of the present work is the application of the simulated annealing (SA) optimization algorithm as a method for identification of PEM fuel cell model parameter identification. The major advantage of SA is its ability to avoid becoming trapped in local minimum, as well as its flexibility and robustness. The parameter extraction and performance validation are carried out by comparing experimental and simulated results. The good agreement observed confirms the usefulness of the proposed extraction approach together with adopted PEM fuel cell model as an efficient tool to help design of power fuel cell power systems. Copyright © 2009 John Wiley & Sons, Ltd.