A novel UV-mediated low-temperature sintering of TiO2 for dye-sensitized solar cells

Titania pastes were fired at 450 °C in oxygen to give white titania that was used to prepare dye-sensitized solar cells (DSSC). Titania fired at lower temperature and/or under inert atmosphere have brown stripes and cells made from these stripes had no measurable efficiency. When the titania paste was screen printed and then heated and simultaneously irradiated with UV light, white stripes were obtained. Improved efficiency was noted for PV cells made from pastes heated at lower temperature under irradiation vs. cells made from low-temperature heated paste but without irradiation. UV irradiation appears to facilitate clean oxidation of residual organic materials in the titania precursor pastes. The best cells in our study made with our titania paste treated at 450 °C in oxygen had the following characteristics: efficiency=3.45%; V_oc=630 mV; J_sc=8.5 mA/cm²; and a fill factor=0.64.     

A practical field study of various solar cells on their performance in Malaysia

A practical field study has been carried out with the intention to analyze and compare the performance of various types of commercially available solar panels under Malaysia's weather. Four different types of solar panels, such as mono-crystalline silicon, multi-crystalline silicon, amorphous silicon and copper–indium–diselenide (CIS) solar panels are used for the practical field study. A number of performance related parameters have been collected using data logger over a period of three consecutive days in the hope that this would give some initial information on the real performance of different solar panels. Results show that mono-crystalline silicon and multi-crystalline silicon solar module perform better when they are under hot sun, whereas the CIS and triple junction amorphous silicon solar panel perform better when it is cloudy and has diffused sunshine. Furthermore, the efficiency of crystalline silicon solar panel has been found to drop when the temperature rises higher. This phenomenon does not appear in the CIS and amorphous silicon solar panels, which shows that the performance of CIS and amorphous silicon solar cells are better in terms of power conversion efficiency and overall performance ratio. Better performance of thin film solar cells like amorphous silicon and CIS are observed from the initial results, which draws attention over the selection of solar panels and also may encourage the usage of these in tropical weather like Malaysia.     

Comparison of thermochemical,electrolytic, photoelectrolytic and photochemical solar-to-hydrogen production technologies

Hydrogen produced from solar energy is one of the most promising solar energy technologies that can significantly contribute to a sustainable energy supply in the future. This paper discusses the unique advantages of using solar energy over other forms of energy to produce hydrogen. Then it examines the latest research and development progress of various solar-to-hydrogen production technologies based on thermal, electrical, and photon energy. Comparisons are made to include water splitting methods, solar energy forms, energy efficiency, basic components needed by the processes, and engineering systems, among others. The definitions of overall solar-to-hydrogen production efficiencies and the categorization criteria for various methods are examined and discussed. The examined methods include thermochemical water splitting, water electrolysis, photoelectrochemical, and photochemical methods, among others. It is concluded that large production scales are more suitable for thermochemical cycles in order to minimize the energy losses caused by high temperature requirements or multiple chemical reactions and auxiliary processes. Water electrolysis powered by solar generated electricity is currently more mature than other technologies. The solar-to-electricity conversion efficiency is the main limitation in the improvement of the overall hydrogen production efficiency. By comparison, solar powered electrolysis, photoelectrochemical and photochemical technologies can be more advantageous for hydrogen fueling stations because fewer processes are needed, external power sources can be avoided, and extra hydrogen distribution systems can be avoided as well. The narrow wavelength ranges of photosensitive materials limit the efficiencies of solar photovoltaic panels, photoelectrodes, and photocatalysts, hence limit the solar-to-hydrogen efficiencies of solar based water electrolysis, photoelectrochemical and photochemical technologies. Extension of the working wavelength of the materials is an important future research direction to improve the solar-to-hydrogen efficiency.     

A new method for estimating the longevity and degradation of photovoltaic systems considering weather states

The power output of solar photovoltaic (PV) systems is affected by solar radiation and ambient temperature. The commonly used evaluation techniques usually overlook the four weather states which are clear, cloudy, foggy, and rainy. In this paper, an ovel analytical model of the four weather conditions based on the Markov chain is proposed. The Markov method is well suited to estimate the reliability and availability of systems based on a continuous stochastic process. The proposed method is generic enough to be applied to reliability evaluation of PV systems and even other applications. Further aspects investigated include the new degradation model for reliability predication of PV modules. The results indicate that the PV module degradation over years, failures, and solar radiation must be considered in choosing an efficient PV system with an optimal design to achieve the maximum benefit of the PV system. For each aspect, a method is proposed, and the complete focusing methodology is expounded and validated using simulated point targets. The results also demonstrate the feasibility and applicability of the proposed method for effective modeling of the chronological aspects and stochastic characteristics of solar cells as well as the optimal configuration and sizing of large PV plants in terms of cost and reliability.     

Solar energy—A look into power generation,challenges, and a solar‐powered future

Sun is an inexhaustible source of energy capable of fulfilling all the energy needs of humankind. The energy from the sun can be converted into electricity or used directly. Electricity can be generated from solar energy either directly using photovoltaic (PV) cells or indirectly using concentrated solar power (CSP) technology. Progress has been made to raise the efficiency of the PV solar cells that can now reach up to approximately 34.1% in multi‐junction PV cells. Electricity generation from concentrated solar technologies has a promising future as well, especially the CSP, because of its high capacity, efficiency, and energy storage capability. Solar energy also has direct application in agriculture primarily for water treatment and irrigation. Solar energy is being used to power the vehicles and for domestic purposes such as space heating and cooking. The most exciting possibility for solar energy is satellite power station that will be transmitting electrical energy from the solar panels in space to Earth via microwave beams. Solar energy has a bright future because of the technological advancement in this field and its environment‐friendly nature. The biggest challenge however facing the solar energy future is its unavailability all‐round the year, coupled with its high capital cost and scarcity of the materials for PV cells. These challenges can be met by developing an efficient energy storage system and developing cheap, efficient, and abundant PV solar cells. This article discusses the solar energy system as a whole and provides a comprehensive review on the direct and the indirect ways to produce electricity from solar energy and the direct uses of solar energy. The state‐of‐the‐art procedures being employed for PV characterization and performance rating have been summarized . Moreover, the technical, economic, environmental, and storage‐related challenges are discussed with possible solutions. Furthermore, a comprehensive list of future potential research directions in the field of direct and indirect electricity generation from solar energy is proposed.     

Solution processable quinacridone based materials as acceptor for organic heterojunction solar cells

Two series of novel quinacridone (QA) based materials that combined a strong absorption over a broad range in visible region with good electrical characteristics, which were used as the new electron-accepting materials for organic solar cells, are explored. Unique cyclic compounds 1-6 are synthesized by incorporating electron withdrawing groups (CN, COOH) at carbonyl position of alkyl substituted quinacridones, which lead to the compounds possessing the characteristics of solution-processed and being suitable for photovoltaic applications. Heterojunction solar cells with simple device configuration using these soluble materials as acceptor and effective donor poly (3-hexyl thiophene) (P3HT) were fabricated. The maximum power conversion efficiency (PCE) achieved in the solar cell based on compound 5 is 0.42% under simulated AM 1.5 solar irradiation with J_sc=1.80 mA cm⁻², V_oc=0.50 V and FF=47%. Although the aimed devices just exhibit moderate PCE, our results clearly suggest that the new-type electron-accepting materials different from fullerene have great potential as acceptor in heterojunction solar cell due to many advantages of the QA derivatives such as relatively inexpensive, good electrochemical stability and could be readily modified.     

Optimization of cell to module conversion loss by reducing the resistive losses

Conventional silicon based photovoltaic industries, which convert silicon cells to modules attracted the attention of the researchers due to the cell to module conversion power losses. The conversion power losses are due to the various parameters such as shadow effect, inherent properties of the solar cells, properties of the materials used for fabricating the module etc. Among them, the inherent properties of the solar cells play a major role in module power. The electrical properties of the solar cell such as series resistance and fill factor drive the conversion power losses in the module. By increasing the number of contact points, the losses will be reduced. In this work it is found that by introducing an extra bus bar in metallization pattern leads to a great reduction in conversion losses. The fill factor gain is observed in three bus bar based modules compared to two bus bar based modules because of the contact points per cell increase which lead to low resistance losses. It is obvious that the power gain in three bus bar modules dominates shadowing loss due to an additional bus bar. A systematic approach on minimising the cell to module conversion loss by optimizing the front contact bus bar width has been studied. It is important that beyond the optimum value of bus bar numbers and its width the shadowing loss will dominate over the gain.     

Practical guidelines for grid metallization in photovoltaic solar cell research

During the research stage, many photovoltaic solar cells suffer substantial power loss due to the use of non-optimum top contact grids. The very nature of solar cell research implies that many cell parameters will be in a continual state of change and thus the grid will seldom be truly optimized. However, several things can be done to ensure that a solar cell grid will perform well even if the parameters vary. In this paper, critical parameters for solar cell grid modeling and design are identified and discussed. Particular attention is paid to the manner in which process aspects affect these parameters and the subsequent power loss of the grid. Finally, practical guidelines are presented, the use of which can minimize the effect of process variation.     

Measurements on a PV solar pump equipped with a piston pump with a matching valve

The work on a simple high efficient solar pump equipped with a piston pump with a matching valve, reported at the Solar World Congress in Budapest, has been continued. Quasi-static and dynamic models of the solar pump have been derived with which the operation of the system is simulated. A test rig has been built at ECN in Petten (The Netherlands) to perform some preliminary measurements. These tests show that the piston with a matching valve indeed ensures a good matching of the system components over a wide range of solar insolations. Daily average solar panel maximum power point tracking efficiencies of over 80% were measured. Daily average subsystem efficiencies (solar panel power output to hydraulic power output) measured were about 40%, which is lower than expected. These low efficiencies were caused by substantial power losses in the motor, transmission and pump. The losses can easily be reduced by appropriate design of each component; subsystem efficiencies of 50% should be attainable.     

ANALYTICAL AND GRAPHICAL METHODS OR DETERMINATION OF SOLAR CELL PARAMETERS AND INVESTIGATIONS OF SHADOWING EFFECT

In actual solar cells, the main power loss is due to the effect of the internal series resistance and the shunt resistance of the solar cell. Two methods; mathematical and graphical, were used to determine these two resistances for an Iraqi monocrystalline solar cell (type AI-Mansour). The results show that both of the series resistance (0·09 Ω) and the shunt resistance (210 Ω) can usually be neglected in an array performance evaluation for systems which don't use concentration arrangements

In addition to the series and shunt resistances computations, the analysis of the mismatching among solar cells as well as the power dissipation by shadowed or faulty cells for different module configurations are discussed in detail in this paper. As a result it was found that the maximum number of cells that can be safely series, parallel connected are 50 and 6 cells respectively.     

Proposal of utilization of nuclear spent fuels for gamma cells

Large amounts of nuclear spent fuel are generated in nuclear power plants every year and stored in fuel storage facilities for 20–30 years until reprocessing. However, the spent fuel still has residual energies, such as high-temperature heat energy and high-intensity gamma radioactivity. We have examined the characteristics of solar cells exposed to gamma radiation for the development of gamma cells utilizing nuclear spent fuel. We used a highly intense ⁶⁰Co gamma source as a suitable substitute for spent fuel due to safety concerns and convenience. Two representative types of solar cells, amorphous and crystalline cells, were examined and the current and voltage generated by each type were measured. In general, solar cells are largely insensitive to gamma radiation because the radiation passes through solar cells without imparting all of its energy. In order to enhance the sensitivity to radiation, the solar cells were coupled to CsI(Tl), NaI(Tl) and plastic scintillators. We confirmed the following characteristics: (1) amorphous solar cells coupled to a CsI(Tl) scintillator are able to generate a large amount of electric power, compared to crystal-type solar cells, (2) amorphous cells exhibit a good linear response to high-intensity gamma radiation and generate electric power almost in proportion to the volume of the scintillator used, (3) the generated electric power is independent of the incident angle of the gamma rays and the amount of power is determined only by the volume of the scintillator used. The electric power generated by a single solar cell is very small, but a large amount of electric power can be obtained by arranging many solar cells in stacks and combining their induced current or voltage and by operating the cells all day, as they are not affected by weather conditions. We concluded that gamma cells utilizing the gamma radiation of nuclear spent fuel can be expected to be useful for electric power generation in the near future.     

数字式太阳电池阵列模拟器

阐述了新近发展的以工程用太阳电池数学模型，专用控制软件和电力电子技术为基础的数字太阳电池阵列模拟器。实验表明，该种模拟器性能良好，可以在实验室复现10kWp以下不同功率太阳电池阵列在不同日射强度、环境温度下的特性，并在屏幕上显示出被模拟阵列的I－V及P－V曲线，以闪烁光标显示该阵列在设定日射强度和环境温度下最大功率的位置及其量值，同时也以闪烁光标指标系统的工作点位置，研究操作人员可以清晰地观察到二者之间的差异。该种模拟器可以方便地引导系统研究人员分析系统运行存在的问题，从而使系统工作于最佳状态，它为光伏系统工作者及光伏系统生产厂商提供了系统优化配置的有效手段。     

Platinum nanoparticle decorated rutile titania synthesized by surfactant free hydrothermal method for visible light catalysis for dye degradation and hydrogen production study

Rutile phase of titanium oxide and platinum nanoparticle decorated rutile titania is prepared by a surfactant free hydrothermal process in acidic condition. The pure rutile phase of TiO₂ particle is forms the specific cauliflower morphology. Hydrothermal process in presence of specific acid addition led to the formation of cauli-flower shaped rutile phase of titania. The efficiency and solar assisted photo catalytic ability of these materials are tested for methylene blue degradation as well as hydrogen generation by methanol reforming process. The X-ray diffraction of pattern of pure rutile phase formation is confirmed by reported JCPDS data. The surface physico-chemical property of prepared rutile Titania is further characterized by BET, Raman and SEM analysis. The HR-TEM of the prepared samples show the reduced particle size for rutile titania and studied their morphology in detail. Solar light assisted methylene blue degradation reaction was carrying out to study the catalytic efficiency towards dye degradation and kinetic activity of the same for prepared commercial titania and pure rutile TiO₂. The platinum loaded and photo deposited rutile Titania is further analyzed for hydrogen production reaction by methanol reforming process. The rate of hydrogen evolution on platinum nanoparticle photo deposited on reforming process shows more than 900 μmol/g compared to pristine rutile titania catalysts.     

Transformation of TiO2 nanoparticles to nanotubes by simple solvothermal route and its performance as dye-sensitized solar cell (DSSC) photoanode

Titania nanotubes were synthesized by simple solvothermal method using quasi crystalline TiO₂ nanoparticles as the starting material without using autoclave. In the presence of concentrated NaOH (sodium hydroxide), TiO₂ nanoparticles were transformed into nanotubes. The complete transformation of nanoparticles to nanotubes was witnessed using Field Emission Scanning Electron Microscopy (FESEM) and High-resolution transmission electron microscopy (HRTEM) images and further, the materials were found to be polycrystalline in nature. From the X-ray diffraction pattern and Raman analysis, the TiO₂ nanoparticles were found to exhibit the anatase phase and the nanotubes were found to exhibit the titanate phase. The surface area and pore size distribution were analysed using BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda) analysis. The surface area of the nanotubes was found to be higher compared to the initial nanoparticles and bimodal type pore distributions were observed from the BJH study. The bandgap and defect emissions of the nanotubes and nanoparticles were analysed using UV–Vis absorption and photoluminescence (PL) analysis. The chemical states of the prepared nanoparticles were further characterized using X-ray photoelectron spectroscopy. The Dye-sensitized solar cells (DSSC) were fabricated using the prepared TiO₂ nanostructures as photoanodes and their power conversion efficiencies were analysed.     

Alternative buffers for chalcopyrite solar cells

A literature survey is given of recent developments on alternative buffers in chalcopyrite solar cells. Numerous materials to replace the CdS buffer have been developed. Deposition methods include wet chemical as well as dry processes. Additionally, devices without a buffer are developed. Several approaches have reached maturity and efficiency results equal to CdS reference cells.     

UV light protection through TiO2 blocking layers for inverted organic solar cells

Fully organic solar cells (OSCs) based on polymers and fullerenes have attracted remarkable interest during the last decade and high power conversion efficiencies (PCEs) beyond 8% have been realized. However, air stability of these cells remains poor. The conventional geometry of OSCs utilizes strongly oxidizing metal top contacts like Al or Ca. These metals are easily oxidized in air resulting in rapid decrease of PCE if cells are not perfectly encapsulated. Using a thin electron-selective hole-blocking bottom layer like TiO₂ enables fabrication of solar cells in a so-called inverted geometry. In this geometry, noble metals like Ag or Au can be used as top contacts, which are less sensitive to ambient oxygen. Thus, air-stability of these inverted solar cells is significantly improved. In this study we investigate inverted polythiophene-methanofullerene solar cells. We find significant influence of the TiO₂ layer thickness on light absorption and illumination stability of the solar cells, as well as the trap filling by photoinduced carriers. Even though TiO₂ layers as thick as 500 nm seem not to be detrimental for charge transport, light intensity losses limit the device performance. In turn, illumination stability is better for thicker TiO₂ layers, which can serve as UV filters and protect the photoactive materials from degradation, when compared to thin TiO₂ layers. Considering these different effects we state that a thickness of 100 nm is the optimization of the TiO₂ layer.     

Super high-efficiency multi-junction and concentrator solar cells

III–V compound multi-junction (MJ) (tandem) solar cells have the potential for achieving high conversion efficiencies of over 50% and are promising for space and terrestrial applications.We have proposed AlInP–InGaP double hetero (DH) structure top cell, wide-band gap InGaP DH structure tunnel junction for sub cell interconnection, and lattice-matched InGaAs middle cell. In 2004, we have successfully fabricated world-record efficiency concentrator InGaP/InGaAs/Ge 3-junction solar cells with an efficiency of 37.4% at 200-suns AM1.5 as a result of widening top cell band gap, current matching of sub cells, precise lattice matching of sub cell materials, proposal of InGaP–Ge heteroface bottom cell, and introduction of DH-structure tunnel junction. In addition, we have realized high-efficiency concentrator InGaP/InGaAs/Ge 3-junction solar cell modules (with area of 7000 cm²) with an out-door efficiency of 27% as a result of developing high-efficiency InGaP/InGaAs/Ge 3-junction cells, low optical loss Fresnel lens and homogenizers, and designing low thermal conductivity modules.Future prospects are also presented. We have proposed concentrator III–V compound MJ solar cells as the 3rd-generation solar cells in addition to 1st-generation crystalline Si solar cells and 2nd-generation thin-film solar cells. We are now challenging to develop low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m² for terrestrial applications and high-efficiency, light-weight and low-cost MJ solar cells for space applications.     

Theoretical and experimental investigation of an ammonia–water power and refrigeration thermodynamic cycle

A combined thermal power and cooling cycle proposed by Goswami is under intensive investigation, both theoretically and experimentally. The proposed cycle combines the Rankine and absorption refrigeration cycles, using a binary ammonia–water mixture as the working fluid. This cycle can be used as a bottoming cycle using waste heat from a conventional power cycle or an independent cycle using low temperature sources such as geothermal and solar energy. Initial parametric studies of the cycle showed the potential for the cycle to be optimized for first or second law efficiency, as well as work or cooling output. For a solar heat source, optimization of the second law efficiency is most appropriate, since the spent heat source fluid is recycled through the solar collectors. The optimization results verified that the cycle could be optimized using the generalized reduced gradient method. Theoretical results were extended to include realistic irreversibilities in the cycle, in preparation for the experimental study. An experimental system was constructed to demonstrate the feasibility of the cycle and to compare the experimental results with the theoretical simulation. Results showed that the vapor generation and absorption condensation processes work experimentally. The potential for combined turbine work and refrigeration output was evidenced in operating the system. Analysis of losses showed where improvements could be made, in preparation for further testing over a broader range of operating parameters.     

Polymer-electrolyte water electrolysis

The electricity for the electrolyzer is supplied by a variable electricity supply unit that simulates actual outputs of both series and parallel combinations of solar cells exposed to various solar intensities. An amorphous-silicon solar cell is used as a sensor for the unit The operation was continued for more than 600 days without trouble. The case of direct connection of the solar cell and polymer electrolyte (PE) water electrolyzer is simulated: the test results show that more than 95% of the peak electricity power of the solar battery can be utilized for the electrolyzer over various solar radiation conditions.     

Solar tower power plant in Germany and future perspectives of the development of the technology in Greece and Cyprus

Since the 80s power production with solar thermal power plants has been a way to substitute fossil fuels. By concentrating direct solar radiation from heliostats very high temperatures of a thermal fluid can be reached. The resulting heat is converted to mechanical energy in a steam cycle which generates electricity.High efficiencies and fast start-up are reached by using air as a heat medium, as well as using porous ceramic materials as solar receiver of the concentrated sunlight.In Germany the construction of a 1.5 MW_e solar tower power plant began in 2008. It is operational since December 2008 and started production of electricity in the spring of 2009.In Greece and Cyprus, countries with high solar potential, the development of this competitive solar thermal technology is imperative, since it has already been implemented in other Mediterranean countries.