Efficiency of light energy conversion to hydrogen by the photosynthetic bacterium Rhodobacter sphaeroides

A photosynthetic bacterium, Rhodobacter sphaeroides 8703, was found to produce hydrogen at a high rate. Efficiency of solar energy conversion to hydrogen by the bacterium was estimated using a xenon lamp and a xenon lamp-based solar simulator as light sources. The maximum efficiencies were 7.9 and 6.2% under illumination by the xenon lamp at 50 Wm⁻² and by the solar simulator at 75 Wm⁻², respectively.     

The microalga Chlamydomonas reinhardtii CW-15 as a solar cell for hydrogen peroxide photoproduction: Comparison between free and immobilized cells and thylakoids for energy conversion efficiency

Immobilized cells and thylakoid vesicles of the microalga Chlamydomonas reinhardtii CW-15 have been developed as a solar cell because of their capabilities of producing hydrogen peroxide. This compound is an efficient and clean fuel used for rocket propulsion, motors and for heating. Hydrogen peroxide is produced by the photosystem in a catalyst cycle in which a redox mediator (methyl viologen) is reduced by electrons obtained from water by the photosynthetic apparatus of the microalga and it is re-oxidized by the oxygen dissolved in the solution. The photoproduction has been investigated using a discontinuous system with whole cells, or thylakoid vesicles, free or immobilized on alginate. The stimulation by azide as an inhibitor of catalase has also been analyzed. Under determined optimum conditions, the photoproduction by Ca-alginate entrapped cells, with a rate of 33 μmol H₂O₂/mg Chl.h, was maintained for several hours with an energy conversion efficiency of 0.25%.     

The turnover times and pool sizes of photosynthetic hydrogen production by green algae

An investigation of the turnover times of photobiological production of hydrogen gas by green algae indicate that the photoreactions associated with molecular hydrogen production have promising properties for solar energy conversion and storage. Our results indicate that (a) the intrinsic kinetic rate capability of the hydrogen photoapparatus in green algae can keep pace with the incidence rate of light quanta, even in full sunlight; (b) the photogenerated electrons for hydrogen production probably lie in the mainstream of the electron transport chain of photosynthesis.These results have been obtained by performing the first measurements on the turnover times and pool sizes of photosynthetic hydrogen production. For the three species of green algae studied, the turnover times range from 0.1 to 3 ms. The turnover time for photosynthetic hydrogen production is, therefore, comparable to that for oxygen production.Rapid multiple flash experiments have been performed which indicate that the immediate source of reductant for photosynthetic hydrogen production is derived from a pool of 5–20 equivalents, depending on the alga. This pool is probably the plastoquinone pool linking the two photosystems of photosynthesis.     

太阳能制氢技术及其进展

阐述了光解水制氢的原理,介绍了光解水制氢技术的现状,分析了目前光解水制氢技术存在的问题以及提高光解水效率的有效途径,指出了利用光热化学循环进行光解水制氢的新途径.     

太阳能热化学制氢技术研究进展

总结了目前国内外太阳能制氢方法的研究现状,经过分析比较,确定太阳能热化学制氢具有极大的潜在发展空间.同时详细介绍了该方法的最新进展,对该方法研究中存在的问题提出了合理的改进建议.     

On the potential of solar energy conversion into hydrogen and/or other fuels

Solar energy, when used together with water for the production of hydrogen, forms an inexhaustible source of transportable primary energy. Hydrogen is also a potential means of storing solar energy. In this paper the thermodynamic and energetic conditions for the splitting of water are established. The different water decomposition techniques are discussed.Electrolysis. Electrolysis is a proven and convenient way of producing hydrogen. If the very high temperature electrolysis (80–1000°C) development is successful, heat-assisted electrolysis with electric efficiencies of 100% and more looks attractive in connection with thermo-mechanical helio-electricity conversion.Thermal conversion. Highest temperature (≈ 3000°C) direct decomposition (thermolysis) is thermodynamically interesting, but is, for the time being, technologically not feasible. Use of thermochemical cycles is mainly a question of economics and of adaptation to the high temperatures, attainable with solar concentrating devices.Quantum conversion. The thermodynamic potential of light makes quantum conversion highly attractive, requiring much basic research, though.Bioconversion. Biosystems are already operating in nature but with low and lowest efficiencies. With successful R & D to increase efficiencies, bio-energy systems seem to become a convenient way of fuel production.Economics are considered when it seems reasonable to do so, otherwise educated guesses are made as to the economics of the different decomposition techniques and their implications for the possible large-scale hydrogen production by solar energy.Some considerations are made on the influence of large-scale solar power plants on the climate.     

Improving conversion efficiency of solar energy to electricity in cyanobacterial PEMFC by high levels of photo-H2 production

In this study, we described an efficient electrical power generating system containing cyanobacterial photo-H₂ production and custom-built proton exchange membrane fuel cell (PEMFC). The filamentous N₂-fixing cyanobacterium Anabaena cylindrica was used as the photo-H₂ producer. A photosynthesis inhibitor-diuron (DCMU) was used for the enhancement of photo-H₂ production in the culture under argon gas. For the first time, a total of 1.0 μM DCMU was found to be the most effective treatment, as this produced 3.6 fold higher levels of H₂ in microalgae. By measuring polarization curve, the gas mixture collected from the culture was proven to be an effective fuel for electrical generation through a custom-built PEMFC. When the PEMFC was directly combined with the culture tube, the cells generated as much as 843 mV during a 5-day incubation due to the efficient conversion of solar energy to H₂ by A. cylindrica. Light energy conversion efficiency (LCE) for both solar energy to H₂ and solar energy to electricity were also determined. The LCE for the cyanobacterial conversion of solar energy to H₂ reached a peak at four days with a maximal value of 2.05% and an average value of 1.70% ± 0.17. The corresponding LCE for the conversion of solar energy to electricity in this system was 1.13% at peak and 0.94% ± 0.09 on average.     

Reactivity of CeO2-based ceramics for solar hydrogen production via a two-step water-splitting cycle with concentrated solar energy

Ce_0.9M_0.1O_2−δ ceramics (M = Mg, Ca, Sr, Sc, Y, Dy, Zr and Hf) were synthesized by a polymerized complex method. X-ray powder diffraction (XRD) patterns indicate that solid solutions with a fluorite structure were formed after the synthesis, and this structure was retained after redox cycles. An analysis of the redox cycles using a direct gas mass spectrometer (DGMS) suggests that the reactivity of CeO₂-based ceramics in the O₂-releasing step could be enhanced by doping the ceramics with cations with a higher valence and a smaller effective ionic radius. The investigation of two-step water-splitting cycles indicates that the amount of H₂ evolved in the H₂-generation step is dominated by the amount of O₂ (Ce³⁺) evolved in the O₂-releasing step. Electrochemical impedance spectroscopy (EIS) investigations show that the higher bulk conductivity of CeO₂-based ceramics at intermediate temperatures could promote reactivity by enhancing the molar ratio of H₂–O₂ that is evolved during the two-step water-splitting cycles. The highest reactivity, both in the redox and in the two-step water-splitting cycles, is exhibited by Ce_0.9Hf_0.1O₂.     

Application of ANOVA method to study solar energy for hydrogen production

This study is directed to specifically clear on the data's parametric effect on the hydrogen production utilizing the sun based energy through the water electrolysis. The Analysis of Variance (ANOVA) technique is used to check and verify on the potentials of other factual demonstrative devices with respect to the real and anticipated quality, the reaction in the middle of residuals and the anticipated 3-D surface and shape plot investigation. The database of the created model was created in view of the profound study to be carried out. A factual model was produced and an exploratory acceptance of the investigation of polynomials was set up by applying the Response Surface Methodology (RSM). The factual investigation of the informative parameters and the resulting reactions demonstrated that the proposed model and the analytical results would appropriately indicate an anticipated predominant fit.     

An assessment of electrolytic hydrogen production by means of photovoltaic energy conversion

Photovoltaic-powered electrolysis is studied by using an analytical system-simulation model. Available experimental results are compared with the results of the analytical simulation and, further, the computational model is used to establish a model-driven electrolysis experiment. The input for the analytical model includes real weather data recorded on an annual basis at two different locations. The results include information on the system efficiency, power-matching conditions, annual system output and a cost evaluation of the solar hydrogen product.     

Light shade bands for the improvement of solar hydrogen production efficiency by Rhodobacter sphaeroides RV

At mid-day, the sunlight provides excessive energy for photo-hydrogen production by photosynthetic bacteria. Conversion efficiency from light energy to hydrogen decreased under high illumination. To overcome this problem, we examined a method to spatial dispersion of the high illumination. The new photobioreactor using the light shade bands set on the surface of the reactor was developed for efficient hydrogen production. Spatial dispersion gave remarkable effect on conversion efficiency under the excessive light condition. Indoors, the 1.0 cm width of light shade bands gave the best conversion efficiency (2.1%). Actual use of the sunlight, the 1.5 cm width of light shade bands provided the best conversion efficiency (1.4%). Light inhibition was successfully suppressed by the light shade bands in both experiments. The dispersed light energy could be used for other energy conversion device as solar cells.     

Evaluation of conversion efficiency of light to hydrogen energy by Anabaena variabilis

Cyanobacteria provide an efficient system for producing _H2${\mathrm{H}}_2$ from water using solar energy. The energy conversion efficiency can be defined by the ratio of _H2${\mathrm{H}}_2$ produced to the light energy absorbed. An IR and opalescent plate method was used to measure the light energy absorbed. Since cyanobacteria absorb light in the visible range but not in the infrared range, the net amount of light energy absorbed by the cells can be estimated by measuring the IR and visible light intensities transmitted through the biochamber. A rectangular biochamber was used for measuring the conversion efficiency from light energy to _H2${\mathrm{H}}_2$ energy. A quantum meter and radiometer were used to measure the light intensity transmitted through the chamber. Anabaena variabilis was cultured in a BG11 medium with 3.6 mM NaNO₃${}_3$ and the light intensity was 40–50 μmol/m²/s$\mathrm{\mu }\mathrm{mol}/{\mathrm{m}}^2/\mathrm{s}$ in the growth phase and 120–140 μmol/m²/s$\mathrm{\mu }\mathrm{mol}/{\mathrm{m}}^2/\mathrm{s}$ in the _H2${\mathrm{H}}_2$ production phase. The maximum _H2${\mathrm{H}}_2$ production was 50 ml for 40 h and cell density was 1.2 g/l. The _H2${\mathrm{H}}_2$ production rate was 4.1 ml _H2/g${\mathrm{H}}_2/\mathrm{g}$ dry cell weight/h. Based on the light absorbed in the _H2${\mathrm{H}}_2$ production phase, the energy conversion efficiency from light to _H2${\mathrm{H}}_2$ was 1.5% on average and 3.9% at the maximum. Based on the light energy absorbed in the cell growth and _H2${\mathrm{H}}_2$ production phases, the energy conversion efficiency was 1.1% on average.     

Combination of dark- and photo-fermentation to enhance hydrogen production and energy conversion efficiency

In this study, we investigated a two-phase process of combining the dark- and photo-fermentation methods to reutilize the residual solution derived from dark fermentation and increase the hydrogen yield (HY) from glucose. In dark fermentation, an orthogonal experimental design was used to optimize the culture medium for Clostridium butyricum (C. butyricum). The optimal culture medium composition was determined as glucose 20 g/l, NaCl 3 g/l, MgCl₂ 0.1 g/l, FeCl₂ 0.1 g/l, K₂HPO₄ 2.5 g/l, l-cysteine 0.5 g/l, vitamin solution 10 ml/l, and trace element solution 10 ml/l. In this method, the maximum HY increased from 1.59 to 1.72 mol H₂/mol glucose and hydrogen production rate (HPR) from 86.8 to 100 ml H₂/l/h. The metabolite byproducts from dark fermentation, mostly containing acetate and butyrate, were inoculated with Rhodopseudomonas palustris (R. palustris) and reutilized to produce hydrogen in photo-fermentation. In photo-fermentation, the maximum HY was 4.16 mol H₂/mol glucose, and the maximum removal ratios of acetate and butyrate were 92.3% and 99.8%, respectively. Combining dark fermentation and photo-fermentation caused a dramatic increase of HY from 1.59 to 5.48 mol H₂/mol glucose. The conversion efficiency of heat value in dark fermentation surged from 13.3% to 46.0% in the two-phase system.     

Multi-objective optimization of a hydrogen production through the HyS process powered by solar energy in different scenarios

Thermochemical or hybrid cycles powered by concentrated solar energy are a very promising way to produce an effective clean hydrogen through the water splitting, in terms of greenhouse gas (GHG) emissions and power production sustainability. SOL2HY2 is an European project focused on this goal. It deepens the so-called HyS process in a closed or partially open version using a proper SO₂ depolarized electrolyser, and moreover, it investigates key materials and process solutions, along the entire production chain. However, the identification of the best solution to obtain a suitable hydrogen in terms of cost, efficiency, availability of energy and material, sharing of renewable energy source, continuity of operation in different locations and plant sizes, poses many challenges in terms of flexibility and complexity of the system. In fact, it involves various chemical equipment, different solar and thermal storage technologies, and variable operative conditions with different reaction temperatures and mixture concentrations. Hence it arises the importance to have a tool for the investigation of this system.In this paper, data analysis and multi-objective techniques are used to study and optimize the process under consideration. Several mathematical methods have been exploited to make the best use of the available data, such as Design of Experiments techniques, meta-modeling strategies and genetic algorithms. All these methods have been implemented in the open source environments Scilab and R.     

Pretreatment of Miscanthus for hydrogen production by Thermotoga elfii

Pretreatment methods for the production of fermentable substrates from Miscanthus, a lignocellulosic biomass, were investigated. Results demonstrated an inverse relationship between lignin content and the efficiency of enzymatic hydrolysis of polysaccharides. High delignification values were obtained by the combination of mechanical, i.e. extrusion or milling, and chemical pretreatment (sodium hydroxide). An optimized process consisted of a one-step extrusion-NaOH pretreatment at moderate temperature (70°C). A mass balance of this process in combination with enzymatic hydrolysis showed the following: pretreatment resulted in 77% delignification, a cellulose yield of more than 95% and 44% hydrolysis of hemicellulose. After enzymatic hydrolysis 69% and 38% of the initial cellulose and hemicellulose fraction, respectively, was converted into glucose, xylose and arabinose. Of the initial biomass, 33% was converted into monosaccharides. Normal growth of Thermotoga elfii on hydrolysate was observed and high amounts of hydrogen were produced.     

Techno-economic analysis of a hybrid energy system for CCHP and hydrogen production based on solar energy

A typical problem in Northeast China is that a large amount of surplus electricity has arisen owing to the serious photovoltaic power curtailment phenomenon. To effectively utilize the excess photovoltaic power, a hybrid energy system is proposed that uses surplus electricity to produce hydrogen in this paper. It combines solar energy, hydrogen production system, and Combined Cooling Heating and Power (CCHP) system to realize cooling, heating, power, and hydrogen generation. The system supplies energy for three public buildings in Dalian City, Liaoning Province, China, and the system configuration with the lowest unit energy cost (0.0615$/kWh) was obtained via optimization. Two comparison strategies were used to evaluate the hybrid energy system in terms of unit energy cost, annual total cost, fossil energy consumption, and carbon dioxide emissions. Subsequently, the annual total energy supply, typical daily loads, and cost of the optimized system were analyzed. In conclusion, the system is feasible for small area public buildings, and provides a solution to solve the phenomenon of photovoltaic power curtailment.     

On the study of hydrogen production from water using solar thermal energy

Theoretical thermal efficiency of hydrogen production by one-step water splitting utilizing solar heat at high temperatures is calculated. Carnot efficiency is assumed for the conversion of effective work input, and the solar collection efficiency is considered for the total energy input. The overall efficiency shows its maximum in the range of temperature between 1500 and 2700 K depending upon the solar concentration ratio and the method of product separation. The technical feasibility of direct splitting method is discussed on the basis of those calculated results.     

NADPH fluorescence as an indicator of hydrogen production in the green algae Chlamydomonas reinhardtii

This study investigated cellular Nicotinamide Adenine Dinucleotide Phosphate (NADPH) fluorescence as a potential indicator of biohydrogen production in Chlamydomonas reinhardtii and a β-NADPH standard. NADPH fluorescence profiles of cultures grown in TAP-S (Tris-acetate phosphate minus sulphur) media, TAP (Tris-acetate phosphate) media and TAP + 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) were subsequently compared. Hydrogen production induced from sulphur depletion was found to correlate directly (r = 0.941) with NADPH over the ten day period. The addition of leachate was used to increase hydrogen yields, and subsequently increased the NADPH concentration by 50%–70%. A direct correlation was observed (r = 0.929) between NADPH and hydrogen when the leachate supplemented media was used. As NADPH is the terminal electron acceptor in the photosynthetic chain, results show that NADPH has a pivotal role in hydrogen production as a carrier molecule. Under sulphur depletion, cellular NADPH fluorescence can be used as an indicator of hydrogen production.     

Theoretical upper limit to the conversion efficiency of solar energy

The theoretical maximum useful work obtainable from solar energy has been calculated taking account of its directional character. The method employed is the calculation of the availability of a thermodynamic system containing such energy in an environment corresponding to the earth's surface. The corresponding efficiency is where T_o is the ambient temperature, T_s the equivalent solar temperature and δ the half angle of the cone subtended by the sun's disc.     

Screening of water-splitting thermochemical cycles potentially attractive for hydrogen production by concentrated solar energy

Hydrogen, a promising and clean energy carrier, could potentially replace the use of fossil fuels in the transportation sector. Currently, no environmentally attractive, large-scale, low-cost and high-efficiency hydrogen production process is available for commercialization. Solar-driven water-splitting thermochemical cycles may constitute one of the ultimate options for CO₂-free production of hydrogen. The method is environmentally friendly since it uses only water and solar energy. First, the potentially attractive thermochemical cycles must be identified based on a set of criteria. To reach this goal, a database that contains 280 referenced cycles was established. Then, the selection and evaluation of the promising cycles was performed in the temperature range of 900–2000 °C, suitable to the use of concentrated solar energy. About 30 cycles selected for further investigations are presented in this paper. The principles and basis for a thermodynamic evaluation of the cycles are also given.