A simple analytical treatment of edge-illuminated VMJ silicon solar cells

The series connected silicon vertical multi-junctions (VMJs) solar cells have been suggested as means for ensuring high voltage high efficiency solar cells. This study includes a review of some previously published work concerning the edge-illuminated VMJs solar cells. We introduce a simple one-dimensional analysis to study the high voltage series connected silicon VMJs solar cells. The cell, under study, consists of 40 VMJs. Each junction (unit cell) has dimensions of 250 μm × 0.78 cm × 500 μm. We calculate the short circuit current, the open circuit voltage and the efficiency for an ideal cell, having perfect carrier collection at short circuit conditions, and for real cells. An optimization with respect to the base doping, the emitter doping, the surface recombination velocity and the number of junctions is done for the real cell. A conversion efficiency of 20% has been calculated under AM1.5 light spectrum for real cells having a base doping of 10¹⁶ cm⁻³ and an emitter doping of 10¹⁷ cm⁻³.     

Hydrogen production by biomass gasification in supercritical or subcritical water with Raney-Ni and other catalysts

Gasification of peanut shell, sawdust and straw in supercritical or subcritical water has been studied in a batch reactor with the presence of a series of Raney-Ni and its mixture with ZnCl₂ or Ca(OH)₂. The main gas products were hydrogen, methane, carbon dioxide, and a small amount of carbon monoxide. Different types of Raney-Ni, containing different metal components such as Fe, Mo or Cr, have different influences on the gasification yield and hydrogen selectivity. The catalysis effect can be improved obviously by adding ZnCl₂ or Ca(OH)₂. Increasing the reaction temperature or adding ZnCl₂ and Ca(OH)₂ could improve the mass of H₂ in gas products and reduce the mass of CH₄ and CO₂ at the same time. The possible mechanism is that ZnCl₂ can decompose the biomass particle by accelerating cellulose hydrolyzation in high-temperature water, increasing more specific surface to admit catalysts, while Ca(OH)₂ can absorb CO₂ to produce CaCO₃ deposit, which can drop out from the reactant system, and which will drive the reaction to get more hydrogen. With respect to the biomass conversion to gas product and selectivity of H₂ at low temperature, the series of Raney-Ni has shown many advantages over other catalysts; thus, this kind of catalyst has great potential to be utilized in the hydrogen industry for the gasification of biomass.     

Singlet methylene removal by saturated and unsaturated hydrocarbons

The technique of laser flash phyotolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene, ¹CH₂ (ã¹A₁), with various saturated and unsaturated hydrocarbons. The removal rate constants for CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆, C₂H₂, CH₂CCH₂, and C₆H₆ were found to be in excellent agreement with previously reported results. Removal rate constants were also measured for n-C₄H₁₀, i-C₄H₁₀, n-C₅H₁₂, c-C₃H₆, c-C₆H₁₂, 1-C₄H₈, cis-2-C₄H₈, trans-2-C₄H₈, and 1-C₄H₆, and determined to be (3.17 ± 0.15), (2.53 ± 0.11), (3.35 ± 0.24), (1.63 ± 0.08), (3.77 ± 0.21), (3.80 ± 0.20), (3.67 ± 0.16), (3.43 ± 0.16) and (4.05 ± 0.18) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, respectively. This series of hydrocarbons forms the basis of a larger series of compounds containing a wide variety of organic functional groups. The removal rate constants are reported here, both as a series within its own right, and as a reference point for future work.     

The solar heating system with seasonal storage at the Solar-Campus Jülich

The Solar-Campus Jülich is an area of 14 ha in the north of the existing University of Applied Sciences. Three independent partners are constructing low energy buildings on this site (heating demand 144 MJ m⁻² a⁻¹). To date (June 2000) an auditorium with a library has been completed as well as an additional laboratory building. The Students’ Association Aachen has erected 23 houses with accommodation for 136 students. The houses are arranged in five rows, each of them demonstrating different kinds of modern energy-saving technologies for heating and ventilation. The energy utility in Jülich intends to build industrial buildings and move their complete organisation from southern Jülich to the Solar-Campus. A solar district heating concept, with seasonal storage, is planned to cover about 50–60% of the heating demand of all the buildings. The paper gives details of the design of the pyramidal seasonal storage tank including cost analysis. The top cover of the 2500 m³ tank will be constructed of several insulated floating pontoons, which are connected to each other, so that it is possible to walk on it. The 1200 m² of collectors are distributed over the different buildings and coupled to the underground storage tank by either a 2-, 3- or 4-pipe distribution network. Due to the low energy demand, the overall energy consumption will be low (2124 GJ a⁻¹). The heating cost consequently will be high: 0.17 DM/kWh with a conventional gas-based system, and 0.54 DM/kWh with the solar system including seasonal storage.     

A proton-conducting solid state H2S-O2 fuel cell. 1. anode catalysts, and operation at atmospheric pressure and 20–90°C

A stable solid state H₂S--O₂ fuel cell has been developed and operated at 1 atm and 20-90°C. A series of anode catalysts has been examined using Nafion^® as a common proton conducting membrane; those containing Pd and Pt were found to be effective using H₂ or H₂S as the anode feed gas, but MoS₂--C catalysts were effective for use of H₂S but not for H₂. The highest potential attained using H₂S and Pd/C catalyst was 722 mV (theory: 1140 mV). When H₂S was used as anode feed the potential decreased up to 35% over 24 h as sulfur was deposited on the anode. The efficiency of the cell increased with temperature up to 90°C.     

Electrochemical behaviour of amorphous V2O5(-P2O5) cathodes for lithium secondary batteries

The electrochemical behaviour of amorphous vanadium oxides (a-V₂O₅ and a-V₂O₅-P₂O₅) cathodes in lithium cells has been investigated. The reversibility of the cathodes is superior to that Of c-V₂O₅ and the cathodes can operate for> 300 cycles. The relationship between cathode composition and cycle performance has been determined, and P₂O₅, as a network-former, has been found not to harm the reversibility of cathodes. The degradation in capacity with cycling of the Li/a-V₂O₅(-P₂O₅) system is due to deterioration of the anode, i.e., an increased polarization on discharge.     

Design and installation of solar photovoltaic powered water pumping system at Usmanu Danfodiyo University, Sokoto

The paper presents the outcome of the powering of a conventional a.c. type water pump by photovoltaic (pv) solar modules which were 28 in number connected 7 in series giving a total of 4 parallel strings. An assesment of the system, which provides water to the University Mechanical Workshop and a nearby village, shows that the system has been operating continously since October 1993 and on average 20 m³ of water is pumped daily at average solar radiation level of 5kWh/m²/day.     

Conversion of straw and similar agricultural wastes

Mainly the economic aspects prevent a far more extensive use of biomass, including straw as a fuel in energy supply.

During the latest years several straw fired plants have been put in operation, especially in Denmark, and they have demonstrated that both district heating and combined heat and power (CHP) production based on straw are technically possible.

However, experience has shown that a very precise research and development effort is necessary before the straw fired plants are competitive to traditional plants fired with fossil fuels, as to operational safety and economy.

The R & D activities ought first and foremost to aim at: 1) Reduction of costs connected to all processes from harvest to energy production, 2) wider know-how of the firing and combustion technical characteristics of straw, and 3) environmental conditions, including emissions and ash depositing problems.     

AC Impedance of Li(Ni1/3Co1/3Mn1/3)O2/graphite cell as UPS

以Li（Ni_1/3Co_1/3Mn_1/3）O₂/graphite动力电池为研究对象,在模拟备用电源工况下对动力电池进行交流阻抗测试。通过建立等效电路来研究欧姆阻抗R_s、电荷传递阻抗R_ct和扩散阻抗CPE_W随不同搁置时间、荷电状态（state of charge,SOC）的变化规律,研究Li（Ni_1/3Co_1/3Mn_1/3）O₂/graphite动力电池在备用电源工况下,容量和阻抗的变化趋势。结果表明：随着搁置时间的增加,电池容量衰减1.7%左右。随着搁置时间的增加,不同SOC下的欧姆阻抗R_s具有相同的变化趋势,电荷传递阻抗明显增加。随着SOC的降低,由双电层产生的电荷传递阻抗在逐渐增加。在SOC=0%时,扩散阻抗随搁置时间的增加而增加,在SOC=100%、50%的扩散阻抗有细微的增加。容量衰退和阻抗结果显示出Li（Ni_1/3Co_1/3Mn_1/3）O₂/graphite动力电池可以很好地在备用电源工况上使用。     

The chemistry of sodium with sulfur in flames

An experimental and analytical program of sodium/sulfur chemistry has been conducted in a series of fuel rich and lean H₂/O₂/N₂ flames, with and without added sulfur, and covering a wide range of temperatures and stoichiometries. Fluorescence measurements of OH and Na profiles together with sodium line reversal temperature profiles provided a broad data base for kinetic modeling. Analysis indicated NaSO₂ to be the only significant sodium/sulfur product formed in the lean flames. NaOS is dominant in the rich flames, coupled with small contributions from NaSO₂, NaSH, NaS and NaS₂. A bond dissociation energy of D₀(Na---SO₂) = 197 ± 20 kJ mol⁻¹ is derived. Calculations indicate that the linear or triangular structures for NaOS both co-exist in approximately equal proportions in flames. Analyses based on results developed in the study show that Na₂SO₄ formation is kinetically limited and cannot be a significant gas phase flame product at sodium levels much below 100 ppm. Na₂SO₄ induced corrosion in combustion systems must result from heterogeneously formed Na₂SO₄.     

A robust H∞ power system stabilizer with noadverse effect on shaft torsional modes

The H^∞ optimal control theory has been used to design a robust power system stabilizer (PSS) to improve transient and dynamic stabilities of a turbogenerator connected to an infinite busbar. It is demonstrated that the effects of disturbances in the machine output can be minimized and sufficient closed-loop stability margins (robustness) can be obtained to tolerate variations in the loop transfer functions, such as those which might arise from unmodeled low-damped high-frequency modes of oscillations. The resulting controller would effectively enhance the synchronizing and damping torques of the machine without the risk of exciting the shaft torsional modes. This is in marked contrast with the unstable performance of linear quadratic (LQ) optimal controllers under similar conditions. The H^∞ design methodology also ensures a satisfactory performance of the PSS under a wide range of system operating conditions     

Mg2NiH: A new hydride phase in the Mg2Ni---H2 system

A new hydride phase apart from Mg₂NiH₄ has been identified in the Mg₂Ni---H₂ system by pressure-composition-temperature relationships, thermal analyses and X-ray diffraction measurements. The new phase has an approximate composition Mg₂NiH and is considered to be the intermediate phase in the Mg₂Ni---H₂ reaction. The additional hydride phase, Mg₂NiH (named as β-hydride) and the full hydride phase, Mg₂NiH₄ (named as γ-hydride) have been shown to crystallize in monoclinic structure. The β-phase (Mg₂NiH) also exhibits a phase transition from monoclinic to cubic structure similar to the γ-phase (Mg₂NiH₄).     

High temperature solar heated seasonal storage system for low temperature heating of buildings

A preliminary study of a solar-heated low-temperature space-heating system with seasonal storage in the ground has been performed. The system performance has been evaluated using the simulation models TRNSYS and MINSUN together with the ground storage module DST. The study implies an economically feasible design for a total annual heat demand of about 2500 MWh. The main objective was to perform a study on Anneberg, a planned residential area of 90 single-family houses with 1080 MWh total heat demand. The suggested heating system with a solar fraction of 60% includes 3000 m² of solar collectors but electrical heaters to produce peak heating. The floor heating system was designed for 30°C supply temperature. The temperature of the seasonal storage unit, a borehole array in crystalline rock of 60,000 m³, varies between 30 and 45°C over the year. The total annual heating costs, which include all costs (including capital, energy, maintenance etc.) associated with the heating system, were investigated for three different systems: solar heating (1000 SEK MWh⁻¹), small-scale district heating (1100 SEK MWh⁻¹) and individual ground-coupled heat pumps (920 SEK MWh⁻¹). The heat loss from the Anneberg storage system was 42% of the collected solar energy. This heat loss would be reduced in a larger storage system, so a case where the size of the proposed solar heating system was enlarged by a factor of three was also investigated. The total annual cost of the solar heating system was reduced by about 20% to about 800 SEK MWh⁻¹, which is lower than the best conventional alternative.     

Polythiophene-based supercapacitors

Polythiophene (Pth) and polyparafluorophenylthiophene (PFPT) have been chemically synthesized for use as active materials in supercapacitor electrodes. Electrochemical characterization has been performed by cyclic voltammetry and an electrode study has been achieved to get the maximum capacity out of the polymers and give good cyclability. Specific capacity values of 7 mAh g⁻¹ and 40 mAh g⁻¹ were obtained for PFPT and polythiophene, respectively. Supercapacitors have been built to characterize this type of system. Energy storage levels of 260 F g⁻¹ were obtained with Pth and 110 F g⁻¹ with PFPT.     

Experimental analysis and evaluation of a vacuum enclosed concentrated solar thermoelectric generator coupled with a spectrally selective absorber coating

Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present study, we have experimentally analysed steady-state temperature variation of a spectrally selective solar absorber coating (α?=?0.954, ε?=?0.13) with variation in solar irradiation flux (concentration ratios?=?39, 50 and 65) using Fresnel lens and vacuum enclosure pressure (200?mbar to 900?mbar in steps of 100?mbar). It is observed that the experimental results so obtained go hand in hand with a COMSOL simulation model of the set-up. Further, we have carried out performance analysis of a solar thermoelectric generator (STEG) set-up enclosed in vacuum conditions equipped with Fresnel lens and absorber set-up coupled to Bi₂Te₃ thermoelectric module array electrically connected in series. The results depict a maximum power output of 0.91?W and a peak efficiency of 2.21% at a hot-side temperature of 642?K.     

On the computer simulation of the P–C isotherms of ZrFe2 type hydrogen storage materials

This paper deals with computer simulation of the P–C isotherms of some ZrFe₂ type (Zr(Fe_1−xCr_x)₂, Zr_1−xTi_xFe_1.4Cr_0.6, Zr_1−2xMm_xTi_xFe_1.4Cr_0.6 : x00.4) of hydrogen storage materials. A feasible mathematical model has been developed to simulate the P–C isotherms. The randomized variables in the model applied for simulating the P–C isotherms of the above-mentioned ZrFe₂ type hydrogen storage materials correspond to change in enthalpy (ΔH) and entropy (ΔS) of hydride formation. Several ZrFe₂ type materials as in above have been synthesized and their P–C isotherms, enthalpy and entropy change has been evaluated experimentally in order to have input data for simulation. A special software was developed to simulate the P–C isotherms using the said model. A close match between the experimentally observed and simulated P–C isotherms for the above said ZrFe₂ type alloys has been obtained.     

多种能源联合运行控制系统的设计与应用

  [目的]  由于风电、光伏、小水电、煤层气发电等多种间歇性能源具备波动性、随机性等特点,大规模接入电网后将给电网的安全稳定运行及控制带来很大的影响,而传统的电网运行控制系统不能完全适应对大规模间歇性能源的运行控制,因此需要开展含间歇性能源控制系统的研究,以实现对间歇性能源的运行控制。  [方法]  针对间歇性能源的特点,设计了多种能源联合运行控制系统的系统架构、关键应用技术,为间歇性能源的运行控制提供技术系统的支撑。  [结果]  所设计的多种能源联合运行控制系统实现了间歇性能源参与电网的运行控制,提高了系统应对间歇性能源波动的能力。  [结论]  系统已在贵州电网获得落地应用,验证了其对间歇性能源运行控制的可行性。     

The effect of doping rare-earth chloride dopant on the dehydrogenation properties of NaAlH4 and its catalytic mechanism

A series of rare-earth chlorides has been adopted to catalyze dehydrogenation reaction of NaAlH₄. X-ray diffraction analysis and isothermal dehydrogenation measurement have proved that these chlorides enhance the dehydrogenation kinetics and lower the decomposition temperature of NaAlH₄. The catalytic effect from high to low is in following order: SmCl₃>CeCl₃>TiCl₃>NdCl₃>GdCl₃>LaCl₃>ErCl₃. In order to reveal the catalytic mechanism of the rare-earth chlorides on dehydrogenation reactions, systems doped with LaCl₃ were investigated under different milling and dehydrogenation conditions. It has been proposed that the La cation reacts with hydrogen, which was released from NaAlH₄, and then forms some sort of La–Al alloys. This process improves the performance of NaAlH₄ dehydrogenation at a relatively low temperature. In the present research, the catalytic effect of La₂O₃ has also been investigated. Results show that La₂O₃ also have a catalytic effect on the dehydrogenation of NaAlH₄, but the effect is less obvious than that of the rare-earth chlorides.     

Hydrogen storage capability of carbon nanotube Be@C120

PM3 (RHF) type semiempirical quantum chemical calculations have been carried out on (nH₂+Be)@C₁₂₀ systems where C₁₂₀ is a capped tube and n15. The results indicate that all these systems are stable but endothermic in nature. (7H₂+Be)@C₁₂₀ system has the lowest heat of formation value.     

Forced convection burnout for water in rod bundles at high pressures

Burnout data from several new 12-rod test sections are presented. The influence of power distribution, minimum wall-to-rod separation, and mass flux is investigated. The gross behavior of these test sections has been re-analysed by two computer programs which allow the determination of local coolant conditions in an internally connected, boiling bundle as was used in this study.

The rods were 0.440 in in diameter and wrapped with 0.22 in O.D. hypodermic needle tubing on a 6 in pitch. Burnout data were obtained at 1200 psia and at mass fluxes from 1–5 × 10⁶ lb/h ft². Differences between the heat generation rates in the two interior rods and the remaining ten peripheral rods were 1:1, 1.55:1, and 2.64:1. The minimum wall-to-rod separation was 0.022 in in four test sections and approximately 0.032 in in a fifth test section.

The gross and local behavior of the test sections are compared to tubular data. Such a comparison indicates that a cold wall effect exists in the peripheral channels whereas the local behavior in the interior channels agrees closely with the tubular data.