A method for estimating direct normal solar irradiation from satellite data for a tropical environment

In order to investigate a potential use of concentrating solar power technologies and select an optimum site for these technologies, it is necessary to obtain information on the geographical distribution of direct normal solar irradiation over an area of interest. In this work, we have developed a method for estimating direct normal irradiation from satellite data for a tropical environment. The method starts with the estimation of global irradiation on a horizontal surface from MTSAT-1R satellite data and other ground-based ancillary data. Then a satellite-based diffuse fraction model was developed and used to estimate the diffuse component of the satellite-derived global irradiation. Based on this estimated global and diffuse irradiation and the solar radiation incident angle, the direct normal irradiation was finally calculated. To evaluate its performance, the method was used to estimate the monthly average hourly direct normal irradiation at seven pyrheliometer stations in Thailand. It was found that values of monthly average hourly direct normal irradiation from the measurements and those estimated from the proposed method are in reasonable agreement, with a root mean square difference of 16% and a mean bias of −1.6%, with respect to mean measured values. After the validation, this method was used to estimate the monthly average hourly direct normal irradiation over Thailand by using MTSAT-1R satellite data for the period from June 2005 to December 2008. Results from the calculation were displayed as hourly and yearly irradiation maps. These maps reveal that the direct normal irradiation in Thailand was strongly affected by the tropical monsoons and local topography of the country.     

A comparison of methods for estimating hourly diffuse solar radiation from global solar radiation

Four methods of estimating hourly diffuse irradiation from hourly global irradiation are compared, using global and diffuse irradiation data from the Australian Bureau of Meteorology for five widely separated Australian locations. A development of one of these methods with constants derived from the data for each place is found to perform best when judged on a criterion of absolute error, and this performance in maintained when constants averaged over the five locations are used. The derived constants are also given for all other Australian locations for which both global and diffuse data are available, and a method is suggested for deriving suitable values of the constants for places situated between 20° and 45° S for which only global radiation data are available. A previously reported dependence of the proportion of diffuse radiation on latitude is demonstrated.     

Comparison of methods for generating typical meteorological year using meteorological data from a tropical environment

This paper presents the comparison of methods for generating typical meteorological year (TMY) data set using a 10-year period of meteorological data from four stations in a tropical environment of Thailand. These methods are the Sadia National Laboratory method, the Danish method and the Festa and Ratto method. In investigating their performance, these methods were employed to generate TMYs for each station. For all parameters of the TMYs and the stations, statistical test indicates that there is no significant difference between the 10-year average values of these parameters and the corresponding average values from TMY generated from each method. The TMY obtained from each method was also used as input data to simulate two solar water heating systems and two photovoltaic systems with different sizes at the four stations by using the TRNSYS simulation program. Solar fractions and electrical output calculated using TMYs are in good agreement with those computed employing the 10-year period hourly meteorological data. It is concluded that the performance of the three methods has no significant difference for all stations under this investigation. Due to its simplicity, the method of Sandia National Laboratories is recommended for the generation of TMY for this tropical environment. The TMYs developed in this work can be used for solar energy and energy conservation applications at the four locations in Thailand.     

A comparison of innovation policy in the smart grid industry across the pacific: China and the USA

Utilities are increasing their investment in smart grid technologies because of the rising demand for electricity, the aging transmission and distribution infrastructure in developed countries and the need for real-time visibility of energy supply and demand to optimize service reliability and cost. Government policies are contributing to this rising investment in the smart grid in many countries around the globe. Using Rothwell and Zegveld's innovation policy framework as a starting point, this paper compares innovation policy in smart grids across the Pacific; specifically, China and the USA. This research describes the policy tools used by both countries and presents results that indicate national preferences for innovation policy that differ in the ways in which they are linked with the state of the power system. China has preferred to use “supply-side policy,” which focuses on “public enterprise, scientific and technical development and legal regulation.” The USA has preferred to use “environmental-side policy,” which focuses on “scientific and technical development, financial, political and public enterprise.” This paper also describes in detail a number of innovation policies being pursued in the smart grid industry in both China and the USA.     

A comparison of spectral irradiance profiles for two nigerian cities using the spectral 2 computer code

The spectral profiles of two Nigerian cities were studied using SERI's SPECTRAL 2 computer code to reveal the nature of the irradiance reaching the ground at the two locations. The spectral profiles show a high diffuse content in the Lagos area even for a clear day and a lower diffuse content and high beam content for Sokoto. The implications of these to photovoltaic systems have been discussed and the conclusions are firstly, PV systems mounted in the fixed tilt position would be practicable in Lagos because the available and usable solar energy inthe global solar spectrum is larger than in the direct solar spectrum due to the high diffuse content. A tracking system would not be very efficient due to the high diffuse content. Secondly, PV systems in the fixed and tracking modes would work well in Sokoto since the global total and the beam irradiance are high. A tracking device would be more efficient here than in Lagos.     

Overall efficiency comparison between the fueling methods of SAEJ2601 using dynamic simulations

This study concerns MC Formula and the table-based protocol hydrogen fueling methods described in SAE J2601 2016 edition fueling protocols for light duty gaseous hydrogen surface vehicles. It considers the overall efficiency and performance of the two methods. This is achieved by dynamic simulations, using the Dymola hydrogen fueling station library. The MC formula and table-based methods are implemented in the library and different simulations are performed, to evaluate the performance of the two different fueling methods under various conditions. The efficiency is evaluated according to; fueling time, State of Charge levels and total energy consumption. The MC formula is up to 26% faster. The state of charge levels are similar between the table-based and MC formula. The energy consumption for the MC formula is up to 6.9% higher than for the table-based method. Comparing consecutive fuelings without recharging the station, the table-based method is able to fill 7 vehicles and the MC formula 5 vehicles.     

A comparison of the divided-bar and QTM methods of measuring thermal conductivity

Reliable determinations of thermal conductivity (K) are essential for any evaluation of terrestrial heat flow. In an extension and confirmation of an earlier study (Sass, 1984a), operational requirements of the relatively new and easy-to-use and maintain QTM (Quick Thermal Conductivity Meter) technique are compared and contrasted with those of the well established divided-bar method. Analysis of QTM experimental data leads to several recommendations: most importantly, (a) at least 5–6 measurements per sample for isotropic rocks (twice as many for anisotropic rocks)–limiting sample processing to no more than 2 per hour—and (b) slab dimensions of at least 20 × 50 × 70 mm (if K < 3 W/mK) to 30 × 70 × 70 mm (if K > 5 W/mK). For saturated specimens, experimental uncertainty (±5%) and reproducibility (±5%) are greater than for the divided-bar apparatus (±4 and ±2%, respectively).Conductivity measurements obtained with the two techniques for 15 dry and water-saturated samples ranging in conductivity from 0.6 to 5.4 W/mK have been compared. For saturated samples, agreement is excellent, with divided-bar values on average several percent greater than QTM values; this discrepancy is most probably related to the different conductivity standards used with the two types of apparatus. Systematic differences of 10–20% arising at conductivities greater than 5 W/mK require further study. For dry samples, divided-bar values are 10% greater on average than QTM values; this difference is attributable to the application in the divided-bar method of an axial load, the principal effect of which is to close low-conductivity air-filled cracks. The need for establishing a uniform international conductivity reference standard is emphasized.     

A comparison of methods to estimate daily global solar irradiation from other climatic variables on the Canadian prairies

Historic estimates of daily global solar irradiation are often required for climatic impact studies. Regression equations with daily global solar irradiation, H, as the dependent variable and other climatic variables as the independent variables provide a practical way to estimate H at locations where it is not measured. They may also have potential to estimate H before 1953, the year of the first routine H measurements in Canada. This study compares several regression equations for calculating H on the Canadian prairies.Simple linear regression with daily bright sunshine duration as the dependent variable accounted for 90% of the variation of H in summer and 75% of the variation of H in winter. Linear regression with the daily air temperature range as the dependent variable accounted for 45% of the variation of H in summer and only 6% of the variation of H in winter. Linear regression with precipitation status (wet or dry) as the dependent variable accounted for only 35% of the summer-time variation in H, but stratifying other regression analyses into wet and dry days reduced their root-mean-squared errors. For periods with sufficiently dense bright sunshine observations (i.e. after 1960), however, H was more accurately estimated from spatially interpolated bright sunshine duration than from locally observed air temperature range or precipitation status.The daily air temperature range and precipitation status may have utility for estimating H for periods before 1953, when they are the only widely available climatic data on the Canadian prairies. Between 1953 and 1989, a period of large climatic variation, the regression coefficients did not vary significantly between contrasting years with cool-wet, intermediate and warm-dry summers. They should apply equally well earlier in the century.     

Chemical looping gasification for hydrogen production: A comparison of two unique processes simulated using ASPEN Plus

The research compares the simulations of two chemical looping gasification (CLG) types using the ASPEN Plus simulation software for the production of H₂. The simulated biomass type was poultry litter (PL). The first CLG type used in situ CO₂ capture utilizing a CaO sorbent, coupled with steam utilization for tar reforming, allowing for the production of a CO₂-rich stream for sequestration. Near-total sorbent recovery and recycle was achieved via the CO₂ desorption process. The second type utilized iron-based oxygen carriers in reduction–oxidation cycles to achieve 99.8% Fe₃O₄ carrier recovery and higher syngas yields. Temperature and pressure sensitivity analyses were conducted on the main reactors to determine optimal operating conditions. The optimal temperatures ranged from 500 to 1250 °C depending on the simulation and reactor type. Atmospheric pressure proved optimal in all cases except for the reducer and oxidizer in the iron-based CLG type, which operated at high pressure. This CLG simulation generated the most syngas in absolute terms (2.54 versus 0.79 kmol/kmol PL), while the CO₂ capture simulation generated much more H₂-rich syngas (92.45 mol-% compared to 62.94 mol-% H₂).     

A technique to map monthly average global illuminance from satellite data in the tropics using a simple semi-empirical model

This paper presents a technique to map monthly average hourly global illuminance from satellite data. A semi-empirical model relating monthly average global illuminance to cloud index, precipitable water, total ozone column (TOC), aerosol optical depth (AOD) and air mass was developed. Data for the cloud index, AOD and TOC were obtained from the visible imagery data of MTSAT-1R, MODIS/Terra and OMI/Aura satellites respectively, while precipitable water was extracted from NCEP/NCAR reanalysis database. The model was formulated using global illuminance measured at four stations in Thailand for a four-year period and validated with an independent one-year data set. Values of monthly average hourly global illuminance calculated from the model and those obtained from the measurements were in good agreement, with a root mean square difference (RMSD) and mean bias difference (MBD) of 8.1% and −0.8%, respectively. The model was used to calculate monthly average hourly global illuminance over Thailand and the results were displayed as illuminance maps. The maps reveal diurnal and seasonal effects mainly in response to solar zenith angle changes and cloud cover related to the southwest and northeast monsoons.     

Measuring the environmental load of household consumption using some methods based on input–output energy analysis: A comparison of methods and a discussion of results

A proper analysis (an evaluation) of the environmental load of consumption is important in the context of sustainable development. Presently, different methods are used to calculate the environmental load of household consumption, mainly in energy and or greenhouse gas emission terms. These methods are all based on input–output energy analysis, but use different data sources and produce different results. In this article, we discern and describe three methods used to calculate the total energy requirements of households, and we discuss the main results produced with these methods. All three methods are applied to the Netherlands in order to compare differences and similarities in the results. We found that the total energy requirement calculated with all three methods was almost the same, with differences less than 4%, however each method provides results at a different level. Basic energy input–output analysis generates total requirements and requirements per consumption category, and is therefore suitable for describing and explaining the effect of household consumption. The hybrid method combining energy input–output analysis with process analysis generates requirements per consumption item and therefore offers opportunities to search for options of change of household consumption patterns to more sustainable consumption.     

A comparison of the accuracy of building energy analysis in Bahrain using data from different weather periods

Weather data are important in building design and energy analysis. In Bahrain, the weather data currently used are based on far past climatic information. Climate variability during the last few decades has raised concern over the ability of these data to provide accurate results when analysing the energy performance of buildings. This study discusses issues related to climate variability and evaluates its impact on the performance of weather data used in building simulation. An evaluation was performed using two methods: firstly, a comparison of measured climatic elements and secondly, a comparison of the thermal performance of two statistically based weather data files. With respect to their impact on typical Bahraini building thermal systems, the comparison was carried out between simulation results and the actual energy consumption of two case studies. This paper shows a 14.5% difference between simulation results based on far past data and present electricity consumption and concludes that the prediction of present and future performance based on recent updated data gives better results.     

A method for the determination of the global solar radiation from meteorological satellite data

A statistical method is presented for the determination of the global solar radiation at ground level. It makes use of data from the meteorological satellites, which provide extensive coverage as well as adequante ground resolution. In the first step, a reference map of ground albedo is deduced from the time-sequence of satellite images. Then, by comparing the satellite data with the computed albedo map, a cloud coverage index is determined for each ground point of 5 km × 5 km. This index is linearly correlated to the atmospheric transiission factor. The regression parameters are estimated using a training set provided by ground pyranometers. Tests for two different time periods show a good agreement between the actual and model-derived hourly global radiation.     

A comparison of models and methods for simulating the microwave heating of moist foodstuffs

We study the problem of heating a one-dimensional approximation to a slab-sided moist foodstuff in a microwave oven, allowing for a phase change and drying. We initially investigate the accuracy of the Lambert law of exponential decay of the applied electric field into the foodstuff and derive an approximation for the field comprising the exponential decay term and an oscillatory component. We then show that the temperature of the foodstuff is given, to a good approximation, by only considering the heating effects of the exponentially decaying field. We then study the effects of drying. This process changes the dielectric properties of the material, which leads to changes in the field. However, these lead to smaller changes in the moisture content. A fast and accurate numerical method is derived which relies on smoothing the phase transition.     

A geospatial method for estimating the levelised cost of hydrogen production from offshore wind

This paper describes the development of a general-purpose geospatial model for assessing the economic viability of hydrogen production from offshore wind power. A key feature of the model is that it uses the offshore project's location characteristics (distance to port, water depth, distance to gas grid injection point). Learning rates are used to predict the cost of the wind farm's components and electrolyser stack replacement. The notional wind farm used in the paper has a capacity of 510 MW. The model is implemented in a geographic information system which is used to create maps of levelised cost of hydrogen from offshore wind in Irish waters. LCOH values in 2030 spatially vary by over 50% depending on location. The geographically distributed LCOH results are summarised in a multivariate production function which is a simple and rapid tool for generating preliminary LCOH estimates based on simple site input variables.     

Interannual variability of the summer wind energy over China: A comparison of multiple datasets

Because of the increase in the nation's need for wind energy, the impacts of climate change on wind energy have been investigated. In addition to long‐term changes, wind energy also shows robust interannual variations, but little effort has been devoted to understanding the underlying mechanisms. In this study, the impact of El Niño on the summer mean wind power density (WPD) over China is investigated. The abilities of five sets of reanalysis data in measuring the interannual variability of the WPD over China are assessed. Encouraging results are seen for all reanalysis datasets, with the MERRA and ERA‐Interim datasets showing the best performance. The relationship between El Niño and the following summer WPD is identified over China. During El Niño decaying year summers, the WPD over south of the Yangtze River valley increases, whereas the WPD over north of the Yangtze River valley decreases. The WPD changes are dominated by an anomalous anticyclone located in the northwestern Pacific. The anticyclone leads to strong southerly winds in southern China and thereby enhances the WPD. In regions north of the Yangtze River valley, the low surface pressure gradient causes a reduction in wind speed and thereby a weak WPD. Because the year‐by‐year variation in El Niño‐Southern Oscillation (ENSO) is highly predictable, our results shed light on the seasonal prediction of wind power over China.     

A comparison of approximate methods for estimation of the creep relaxation of a curved pipe

The relaxation of stress in a linear, thin shell model of a curved pipe constrained to have a fixed rotation and expanding inelastically due to creep is represented by an equation of evolution in time. Using finite differences this continuous system is reduced to a finite set of initial value problems which are numerically integrated using a second order Runge-Kutta method. Thus the relaxation of the resultant in-plane bending moment can be deduced. Results are compared with two simple approximate methods with important repercussions on high temperature pipework design.     

A comparison of test methods for the measurement of hydrogen sensor response and recovery times

Response time is a critically important property of hydrogen safety sensors. Recovery times are less important from a safety perspective, but are often quoted as an indication of the speed of operation of a sensor. However, the measured values depend highly on the method used to evaluate them. The purpose of this work is to assess the suitability of different methods, both flow and diffusion-based, for the measurement of sensor response and recovery times. Four methods have been tested in terms of their repeatability and practicality of execution, as well as the accuracy of their results compared to the manufacturer’s specifications. It was found that each method has its own advantages and limitations, which are discussed herein. For the measurement of response times, a diffusion-based method was found to give the shortest and most precise values and is therefore recommended. However, the flow-based method was found to be the most convenient experimentally and is the only method that is suitable for the measurement of recovery times over a wide concentration range.     

A review and comparison of different methods to determine the series resistance of solar cells

This work presents a review of five different methods to determine the lumped series resistance R_S of solar cells and an experimental investigation of these to find the most reliable and robust method(s) for cell characterization under operating conditions. The methods under consideration are: fitting of the two-diode equation function to a dark IV-curve, comparison of a one-sun with a dark IV-curve, comparison of a Suns-V_OC with a one-sun IV-curve, comparison of two or more IV-curves measured at different illumination intensities, and computation of the area under a one-sun IV-curve. Firstly, for a quantitative evaluation, all series resistance values were plotted against the fill factor FF of the corresponding cell. The accuracy of the methods is quantified using a wide range of solar cells. Secondly, the robustness of the methods in the presence of other FF-limitations such as shunts is also explored. The results and the interpretation of a first analysis of small 2×2 cm² solar cells of the integration method led to a successful improvement of this method, which was proven by a second measurement. All the conducted investigations led us to the conclusion that of these five methods under consideration, the illumination intensity variation, the comparison of a Suns-V_OC with a one-sun IV-curve, and the modified comparison of a one-sun IV-curve with a dark IV-curve method are the most reliable and robust ways to determine the series resistance under operating conditions.