Electrochemical systems for converting solar energy

Photoelectrochemical currents and potential distribution at the semiconductor/electrolyte interface for an electrochemical semiconductor solar energy converter have been analysed. Reactions involving minority and majority charge carriers in semiconductors and intermediate stages of electrocatalytic reactions involving electronic surface states were taken into account. The efficiency of semiconductor electrodes exposed to concentrated sunlight has been studied, and ways of increasing the photoconverter efficiency by the chemical modifications of the electrode surface have been considered for gallium arsenide and A^IIB^VI-type compounds. Characteristics of the cells of solar batteries are given.     

Energy from Waste: A Wholly Acceptable Waste-management Solution

This paper briefly reviews the “waste management hierarchy” and why it should be treated as a checklist and not a piece of unquestioning dogma. The role of energy from waste (EfW) is examined in depth to show that it is a rigorous and environmentally sound waste-management option which complements other components of the waste-management hierarchy and assists resource conservation.     

1 kWe sodium borohydride hydrogen generation system: Part I: Experimental study

A 1 kW_e hydrogen generation system using hydrolysis of sodium borohydride (NaBH₄) has been designed and built. The effects of flow rate, fuel concentration, inlet temperature and operating pressure on chemical conversion have been systematically investigated. A 10-point thermocouple profile probe was used to measure the temperature distribution inside the catalyst bed. Chemical conversion was also qualitatively evaluated via the temperature profile. For the present adiabatic reactor, a large temperature gradient at the outlet implies low conversion, while a small temperature gradient at the outlet implies high conversion. In order to obtain accurate measurements of hydrogen flow rate, water vapor carried in the product stream was removed by a custom hydrogen conditioning station. Using 15% concentration NaBH₄ aqueous solution, this system generated hydrogen up to 20 SLPM with a reasonably high chemical conversion (95%). Discharge products from using NaBH₄ concentrations above 15% crystallized upon cooling to room temperature. Such products would be difficult to remove from the discharge tank in a practical setting. Considering the practical difficulties in heating the discharge product to prevent crystallization, the highest usable concentrations would likely fall in the range of 10–15%. The resulting maximum material gravimetric density is 3.1 wt% of hydrogen and falls short of the DOE on-board hydrogen storage system target of 6 wt% for year 2010.     

1 kWe sodium borohydride hydrogen generation system: Part II: Reactor modeling

Sodium borohydride (NaBH₄) hydrogen storage systems offer many advantages for hydrogen storage applications. The physical processes inside a NaBH₄ packed bed reactor involve multi-component and multi-phase flow and multi-mode heat and mass transfer. These processes are also coupled with reaction kinetics. To guide reactor design and optimization, a reactor model involving all of these processes is desired. A one-dimensional numerical model in conjunction with the assumption of homogeneous catalysis is developed in this study. Two submodels have been created to simulate non-isothermal water evaporation processes and pressure drop of two-phase flow through the porous medium. The diffusion coefficient of liquid inside the porous catalyst pellets and the mass transfer coefficient of water vapor are estimated by fitting experimental data at one specified condition and have been verified at other conditions. The predicted temperature profiles, fuel conversion, relative humidity and pressure drops match experimental data reasonably well.     

Univer Project. A grid connected photovoltaic system of at Jaén University. Overview and performance analysis

Nowadays, grid connected photovoltaic (PV) systems are very popular in industrialized countries and can even be considered as the most promising PV application. The integration of these systems into urban buildings offers a large potential for cost reduction and can further increase the overall value of urban architecture. According to available statistics, by the end of 2002, more than 1.3 GWp of PV power was installed in industrialized countries world wide, which represents 70–85% of the total world capacity [J. Ohno, Progress in Photovoltaics: Research and Applications (2001) 471. [1]]. During recent years, a great number of European projects in the PV sector have been carried out in Spain. The Univer Project—UNIversidad VERde—is one of these European projects. It consists of four grid connected PV systems of fully integrated into the Jaén University buildings, in order to provide the University Campus with more than 8% of its electricity needs, i.e. 210 MWh/year.The aim of this paper is to present a general overview of the Univer Project and the performance analysis of its PV systems during their first phase of operation.     

Fatty acid methyl ester synthesis catalyzed by solid superacid catalyst /ZrO2–TiO2/La

A new type of solid superacid catalyst with the composition of /ZrO₂–TiO₂ loaded with lanthanum was prepared by precipitation and impregnation. The catalytic performance for the synthesis of fatty acid methyl ester from fatty acid and methanol was investigated. The influences of preparation conditions on catalyst performance were studied, the optimum results of which showed that amount of La(NO₃)₃ was 0.1 wt.%, the concentration of H₂SO₄ for impregnation was 0.5 mol l⁻¹ and calcination temperature was 550 °C. In addition, the effects of reaction parameters on esterification efficiency were also studied. With the catalyst amount of 5 wt.%, methanol amount of 1 ml/g fatty acid (FA) and reaction duration of 5 h at 60 °C, the conversion ratio could reach above 95%. The catalyst recycled without any treatments could exhibit high activity with the conversion efficiency of above 90% after being reused five times.     

A novel flow battery—A lead-acid battery based on an electrolyte with soluble lead(II): V. Studies of the lead negative electrode

The structure of lead deposits (approximately 1 mm thick) formed in conditions likely to be met at the negative electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. The quality of the lead deposit could be improved by appropriate additives and the preferred additive was shown to be the hexadecyltrimethylammonium cation, C₁₆H₃₃(CH₃)₃N⁺, at a concentration of 5 mM. In the presence of this additive, thick layers with acceptable uniformity could be formed over a range of current densities (20–80 mA cm⁻²) and solution compositions. While electrolyte compositions with lead(II) concentrations in the range 0.1–1.5 M and methanesulfonic acid concentrations in the range 0–2.4 M have been investigated, the best quality deposits are formed at lower concentrations of both species. Surprisingly, the acid concentration was more important than the lead(II) concentration; hence a possible initial electrolyte composition is 1.2 M Pb(II) + 5 mM C₁₆H₃₃(CH₃)₃N⁺ without added acid.     

Sustainable development benefits of clean development mechanism projects: A new methodology for sustainability assessment based on text analysis of the project design documents submitted for validation

The clean development mechanism (CDM) is part of the global carbon market developing rapidly in response to global warming. It has the twin objective to achieve sustainable development (SD) in host countries and assist Annex-1 countries in achieving their emission reduction targets in a cost-efficient manner. However, research has shown that trade-offs between the two objectives exist in favour of cost-efficient emission reductions and that left to the market forces, the CDM does not significantly contribute to sustainable development. The main argument of the paper is the need for an international standard for sustainability assessment—additional to national definitions—to counter weaknesses in the existing system of sustainability approval by designated national authorities in host countries. The article develops a new methodology, i.e. a taxonomy for sustainability assessment based on text analysis of the 744 project design documents (PDDs) submitted for validation by 3 May 2006. Through analysis of the SD benefits of all CDM projects at aggregated levels, the strengths and limitations of the taxonomy are explored. The main policy implication of the research is to propose the taxonomy as the basis of an international verification protocol for designated operational entities (DOEs) for reporting, monitoring and verifying that potential SD benefits described in the PDDs are actually realized.     

A novel flow battery—A lead-acid battery based on an electrolyte with soluble lead(II): Part VI. Studies of the lead dioxide positive electrode

The structure of thick lead dioxide deposits (approximately 1 mm) formed in conditions likely to be met at the positive electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. Compact and well adherent layers are possible with current densities >100 mA cm⁻² in electrolytes containing 0.1–1.5 M lead(II) and methanesulfonic acid concentrations in the range 0–2.4 M; the solutions also contained 5 mM hexadecyltrimethylammonium cation, C₁₆H₃₃(CH₃)₃N⁺. From the viewpoint of the layer properties, the limitation is stress within the deposit leading to cracking and lifting away from the substrate; the stress appears highest at high acid concentration and high current density. There are, however, other factors limiting the maximum current density for lead dioxide deposition, namely oxygen evolution and the overpotential associated with the deposition of lead dioxide. A strategy for operating the soluble lead-acid flow battery is proposed.