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The development of photovoltaics (PV)-powered vehicles are expected to contribute to reduce CO2 emission of vehicles and create a clean energy society. This paper presents the impact of high-efficiency solar cell modules on reduction in CO2 emission, charging cost reduction for electric vehicles, and reducing storage capacity of PV-powered electric vehicles. In this paper, the effects of solar cell module efficiency upon driving distance of PV-powered vehicles are also shown. Especially, the potential of Si tandem solar cells for PV-powered vehicle applications is discussed. This paper presents that the III-V/Si 3-junction solar cell modules with an efficiency of more than 37% have the potential of longer driving distance of 30 km/day average and more than 50 km/day on a clear day compared to an average 16 km/day driving by vehicles powered by 20% efficiency Si solar cell modules.

Development of high-efficiency solar cell modules and new application fields such as PV (Photovoltaics)-powered vehicles are significant for the further development of PV and the creation of new clean energy infrastructure based on PV. In this paper, analytical results for impact of high-efficiency solar cell modules on increasing driving distance, reducing CO 2 emission and saving charging cost of electric vehicles by PV-powered vehicles. Because the Si tandem solar cells are expected to have significant potential for PV-powered vehicle applications, potentials of high-efficiency and driving distance are also analyzed. The III-V/Si 3-junction solar cell modules have potential of driving distance of 30 km/day average and more than 50 km/day on a clear day.

The performance of CPV is sensitive to the spectrum change. Several previous works have been published on the sensitivity of multi-junction cells to airmass variations as well as works on band gap tuning and optimization of multi-junction stacks under concentrated radiation in various locations. Such a variety of atmospheric conditions, airmass as well as climate (quality of direct sunlight) are dynamic and cannot be controlled by the product design. All we can do is to customize the design by locations (not capable of dynamic variation) or inventing a robust device configuration against a dynamic change of atmospheric conditions (also effective to regional variation). Enhancing a luminescent coupling is useful to suppress the spectrum mismatching loss inherent to outdoor CPV installation. The configuration of the solar cell with 100 % of the recycling of the surplus photon energy for compensating spectrum mismatching is called an SMJ solar cell (super-multi-junction solar cell). The advantage of the SMJ solar cells in non-concentrating fixed sloped angle installation was intensively analyzed in the previous works. However, that of CPV was only investigated under the combination of the worst-case atmospheric parameter distributions, and not under the realistic spectrum variations, so that the calculation result was too extreme. This paper intended to fill the missing stone, by updating a previous result on CPV modeled under the combination of the worst-case variations of atmospheric conditions in the worst locations for CPV, by the realistic fluctuation pattern of meteorological parameters and climate using the intensive analysis that was done to the non-concentration installation (fixed installation). The SMJ was also confirmed valid to CPV under the dynamic fluctuation of the direct solar resources. Different from the non-concentrating operation, the normal CPV was found raising annual average outdoor efficiency under realistic atmospheric conditions simulated by the regional states in Miyazaki, Japan, up to six-junctions. This analysis also implies the bandgap design guideline for the robustness of the spectrum variation, trying to place the bandgap energy of the some of the sub-cells close to the water-absorption band (1.3 eV, 1.1 eV, and 0.89 eV).

The highest efficiency solar cell won in the efficiency race does not always give the most excellent annual energy yield in the real world solar condition that the spectrum is ever-changing. The study of the radiative coupling of the concentrator solar cells implied that the efficiency could increase by the recycle of the radiative recombination generated by the surplus current in upper junction. Such configuration of the multi-junction cells is often called by a super-multi-junction cell. We expanded it to non-concentrating installation. It was shown that this super-multi-junction cell configuration was found robust and can keep almost the same to the maximum potential efficiency (50 % in realistic spectrum fluctuation) up to 10 junctions by a Monte Carlo method. The super-multi-junction cell is also robust of the bandgap engineering of each junction. Therefore, the future multi-junction may not be needed to tune the bandgap for matching the standard solar spectrum, as well as relying upon artificial technologies like ELO, wafer-bonding, mechanical-stacking, and reverse-growth, but merely uses up-right and lattice-matching growth technologies. Although we have two challenging techniques; one is the optical cap layer that may be the directional photon coupling layer in the application of the photonics technologies, and another is the high-quality epitaxial growth with almost 100 % of the radiative efficiency.

Concentrator photovoltaic (CPV) system is promising as the next generation PV using ultrahigh efficiency multi-junction solar cells. In the CPV, optics concentrate sunlight, thereby reducing the area occupied by solar cells and reducing cost. In this study, we analyzed the two CPV systems installed in University of Miyazaki in a long-term outdoor operation. One is composed of the lattice-matched type of the most common triple-junction solar cell, and the other is composed of the lattice-mismatched type. As a result, the performance was different from each other with respect to the module temperature.

Hall mobility measurements of ${n}$- and $p$-type Si substrate under the concentrated sunlight irradiation were carried out to discuss the effect of large amount of carrier generation. The Hall mobility decreased Linearly with increasing the sunlight concentration. It was also found that these decrease could prevent by using a sample with high doping concentration. From the comparison with the calculation, we concluded that the reduction of Hall mobility was due to increase of the photo-generated carriers (both hole and electron). Calculation of Hall mobility as a function of impurity doping concentration demonstrated that a suitable doping concentration for solar cell use was considered to be $10^{16}\mathrm {c}\mathrm {m}^{-3}$ in both ${n}$- and $p$-type Si substrate from viewpoint of Hall mobility under 16-suns concentrated irradiation.

To analyze the impact of a direct spectral distribution of the solar spectrum on the outdoor performance of concentrator photovoltaic (CPV) systems, an index for the direct spectral distribution is needed. Average photon energy (APE), the average energy of a photon in the direct solar spectrum, is one of these indexes. In this contribution, the uniqueness of APE to the direct solar spectral distribution is statistically analyzed to assure that an APE value uniquely yields the shape of a direct solar radiation spectrum. The results have exhibited the uniqueness of the direct normal solar spectrum with each APE value, in which the standard deviations are quite small. Short-circuit current density of the InGaP/InGaAs/Ge triple-junction solar cell in the CPV system is additionally calculated using the direct spectral irradiance with different APE values. It is revealed that APE is a useful index to describe the direct spectral distribution to evaluate the outdoor performance of the CPV systems.

An accurate and quick performance measurement of PV modules and cells are very important. Non-contact measurements of PV characteristics without interruption of the operation of the PV system are desired. A high accuracy electrostatic voltmeter was used for the non-contact measurement of voltage of solar cell in a module structure. The values of the voltage measured with the voltage tester and electric potential measured with the electrostatic voltmeter agreed well. The noncontact electrostatic voltmeter can measure the voltage of solar cell in the module structure with a margin of error within 0.01 V.

Temperature characteristic analysis of the triple-junction solar cell was carried out using circuit simulator under concentration conditions. The temperature exponent of saturation current density for each single-junction solar cell was derived. Extracted temperature exponents were used in the equivalent circuit model for the triple-junction solar cell, and the calculations of solar cell performance were carried out at various temperatures and concentration ratios. The calculation results agreed well with the measured results.

Using an equivalent circuit model, the output characteristics of a bifacial photovoltaic solar module under various shaded conditions of the back side of the module were analyzed in detail. From the dark current-voltage (I-V) characteristics of bifacial photovoltaic solar cell, the diode parameters were extracted. The extracted diode parameters were applied to the equivalent circuit model for the bifacial photovoltaic solar module, and the solar-module performance was calculated. There was good agreement between the measured and calculated IV characteristics of the bifacial photovoltaic solar module under various shaded conditions.

When installing concentrator photovoltaic (CPV) systems in desert areas, we must consider the impact of sandstorms on the Fresnel lens in CPV modules. CPV systems are much more sensitive to sandstorms than flat-panel PV systems because they can only use the direct beam component of sunlight. In this study, the transmittance of a PMMA substrate after sandblasting was evaluated and the influence of sandblasting on the output of a CPV system was assessed. The transmittance of PMMA decreased with an increase in the momentum of blown sand. The conversion efficiency of a CPV module was determined by equivalent circuit calculation. The conversion efficiency decreased with increasing momentum. The coefficient of degradation was 0.17 point per unit momentum.

SiC was prepared from Shirasu volcanic ash using solar furnace. The solar furnace is composed by two parts; Fresnel lens and reacting furnace. Fresnel lens is used to concentrate sunlight onto the reacting furnace where the sample was put on. The sample was made from the mixture of SiO2 formed using Shirasu volcanic ash and graphite, and placed in the carbon crucible inside the reacting furnace. By using light of sun concentrated with Fresnel lens, the sample was irradiated for 15 minutes and the furnace was left until it cooled down to room temperature. Both irradiated and cooling processes were done under Ar atmosphere. After the experiment, the sample was evaluated by XRD and Raman spectroscopy and the result indicated that β-SiC was formed.

The output characteristics of concentrator photovoltaic (CPV) system were analyzed in the data period of a year from November 2010 to October 2011. Characteristics of CPV are more sensitive to environmental factors as compared to flat-plate PV system. Especially, solar spectrum distribution has considerable influence on the output of CPV because CPV uses multi-junction solar cells. In this study, we analyzed the influence of environmental factors using average photon energy (APE) and temperature of solar cell (Tcell). Most frequent condition during operation was APE = 1.87 ± 0.005 eV and Tcell = 65 ± 2.5 °C. Performance ratio at the most frequent condition was 83.9%. These results indicated the importance of the understanding of the behavior of the outdoor performance and the accurate data of environmental conditions where the PV systems were installed.

The most common method for solar cell installation is the inclining mounting method, this method can also be used with the bifacial solar cell. For the installation, its important to understand the properties of light which is entering the back surface of the bifacial solar cell. In this study, we measured the incidence light of the back surface of bifacial solar cell and compared its output power to the common single-surface solar cell to investigate the optimal condition for its installation in terms of (1) tilt angle, (2) height, (3) optimal region and (4) ground surface condition where the panel should be installed.

An anti-soiling layer was coated on the surface of polymethylmethacrylate (PMMA), which is the primary material of Fresnel lenses for concentrator photovoltaics. The layer was prepared by coating the photocatalytic surface layer with modified WO 3 and partially hydrolyzed tetraethyl orthosilicate. When sand was discharged onto the PMMA samples, the mass of adherent sand was more than 0.010 g for the sample without the coating and approximately 0.005 g for the sample with the coating. The electrostatic potential of the sample without the coating increased with increasing amount of incident sand, reaching a maximum value of 0.25 kV. On the other hand, the electrostatic potential of the sample with the coating was suppressed to 0.10 kV. The presence of electrostatic charges on the surface of the samples was a main factor for the adhesion of sand, and it could be suppressed by the anti-soiling photocatalytic layer.

We organized a project of solar cells in University of Miyazaki in order to develop the technologies for solar cells. We have four kinds PV module systems, such as hybrid Si Thin film (1 kW), Poly-Si (50 kW), CIS (100 kW) and CPV (14 kW×2). Their total is 179 kW. These take appoximately 5% of total electricity of the university.

If the optical collector surfaces in concentrator photovoltaic (CPV) systems are soiled, a significant proportion of sunlight is scattered and definitively lost because the scattered rays cannot be focused onto the solar cell. In this study, we studied the influence of soiling on poly-methyl methacrylate (PMMA) substrates with and without super-hydrophilicity anti-soiling layer. After 5 months, the reduction rate of transmittance for the sample without anti-soiling coat was 7.1%. In contrast, that for the sample with anti-soiling coat could be suppressed to 4.2%. Moreover, the relationship between wind speed and accumulation of dust was discussed.

The anti-soiling layer was coated on the surface of Fresnel lens for concentrator photovoltaic. The anti-soiling layer was prepared by coating the acrylic urethane capping layer, the inorganic/organic nanograded intermediate layer, and the photocatalytic surface layer including modified WO3 and partial hydrolyzed tetraethyl orthosilicate. The adherent sand for the sample without coating was 0.023 g and that for the sample with coating was 0.008 g. The adhesion of sand was suppressed owing to the effect of the anti-soiling coating. The electrostatic potential for the sample without coating was 0.23 kV, and the value was much higher than that for the sample with coating. The electrostatic charge at the surface of sample was suppressed with the anti-soiling coating.

We estimated the annual mean conversion efficiency of partially static concentrator (PSC) module. The PSC module consistes of static concentrator, small III-V top solar cell and large Si bottom solar cell. The large Si bottom solar cell absorbes the solar power that is not collected by the III-V top soler cell. The mean optical efficiency decreased with the increase of concentration ratio. The decreasing ratio of mean optical efficiency between 1X to 4X was 49.9%. By using PSC module structure, it was possible to boost the annually mean conversion efficiency. The decreasing ratio of annually mean conversion efficiency between 1X to 4X was 21.5%. The acceptance angle of conversion efficiency was larger than that of optical efficiency. The PSC module structure also improved acceptance angle of the conversion efficiency.

III-V on Si cell is one of the most promising candidates of the low-cost and high-efficiency solar cell beyond the limit of Si cells. However, it is likely that the cost of III-V cell will keep greater than that of Si cells. The partial concentrator technology was invented to concentrate the sunlight onto smaller III-V cells on the Si cell with the increased acceptance angle for static concentrator operation. The partial concentrator allows on-axis optical loss but expands the apparent acceptance angle often beyond the thermodynamic limit. The spilled light will be saved and collected by the bottom Si cell. It is not just placing the Si cell around the concentrated III-V cell, but its design philosophy is “partially” collecting the sunlight to the III-V cell to expand the acceptance. Depending on the values of cost parameters, the cost of the partial CPV module becomes minimum at 4 x – 10 x of concentration onto the top III-V cell, meaning that the area of expensive III-V cell can be saved to 1/4 – 1/10. ...

A thermal radiation layer was coated on the aluminum chassis of a concentrator photovoltaic (CPV) module. The temperature of the solar cell in the CPV module with the thermal radiation coating was approximately 10 °C lower than that of the module without the thermal radiation coating. The uniformity of the temperature distribution in the CPV module was considerably improved. The thermal radiation coating acted not only as a thermal radiation layer but also as a thermal conduction layer. The open-circuit voltage of the CPV module with thermal radiation coating was 0.5 V higher than that of the module without the coating during the period evaluated. The conversion efficiency of the CPV module with thermal radiation coating was 0.5% higher than that of the module without the coating.

In this paper, we optimized the basic aspherical lens for automobile using optical method. Since the panel is installed in horizontal, the distribution of incident angle that is important to concentrator optics design needs to be newly defined. By optimization of lens structure, the optical efficiency increased to 46.7%.

For the purpose of designing the high efficient static solar concentrator on automobile, we discuss the way to increase the aperture area. The 2-dimensional (2D) single and double refraction models based on the Snell's law are prepared under the conditions of random azimuth and large off-angle of the incident ray. We find that the center height of the lens is a key parameter to increase the aperture size. For lens array systems, the optimum center height is determined by the upper limit which is required to suppress the shadowing loss at the adjacent lenses. We demonstrate the ray tracing of the 2D lens model.

The impact of sandblasting on Fresnel lenses for concentrator photovoltaic (CPV) modules must be carefully considered when CPV systems are installed in desert areas. In this study, the transmittance after sandblasting of acrylic polymethylmethacrylate (PMMA) and glass substrates was evaluated, and their durability was assessed. The transmittance decreased as the momentum of the blown sand increased. The conversion efficiency of the CPV modules was estimated using equivalent circuit calculations, and the influence of sandblasting on the output of the CPV modules was quantitatively predicted. The coefficients of degradation for the PMMA and glass CPV modules were 0.17 and 0.08 points per unit of momentum, respectively. The durability of the CPV module with the glass Fresnel lens is approximately twice that with the PMMA lens.

For the development of concentrator photovoltaic (CPV) module realizing high efficiency, it is necessary to achieve the high efficiency optical system including Fresnel lens and homogenizer. For the improvement of optical systems, it is very important to understand the contribution of the light irradiated to a localized position on the Fresnel lens. The light beam induced current (LBIC) system was constructed to evaluate the focusing characteristic of the CPV module. We locally irradiated a light from solar simulator to the CPV mini-module and measured the generation current, and the localized characteristics were represented by two-dimensional mappings. Moreover, we evaluated the influence of tracking error by changing the irradiation angle. In the case of tracking errors, the peak of generated current was shifted and the current was decreased. In the case of tracking error of 1.0 o, the total generated current was reduced 12%, in comparison with the normal irradiance.

Under the concentration conditions, it is important to optimize the design of electrodes and cell structures, because the high density energy is emitted to the cell and photocurrent with high density is generated by each subcell of multi-junction solar cell. The in-plane distributions of power consumption due to the each resistance component were calculated by using total 3D simulator. In the case of optical design without homogenizer, local power consumptions due to the electrode resistance were observed at a part of cell. On the other hand, in the case of optical design with homogenizer, the power consumption was considerably reduced. This technique can be applied to the structural optimization of solar cells for concentration.

A 3-dimensional (3D) simulation for a concentrator photovoltaic (CPV) module using a triple-junction solar cell was developed. By connecting ray-trace simulation for an optics model and 3D equivalent circuit simulation for a triple-junction solar cell, the operating characteristics of a CPV module were calculated. By using the 3D simulation, we considered the influence of tracking error on the CPV module. It was found that maximum output power was not correlated with optical efficiency of the optics system and was strongly dependent on fill factor. We can use this total 3D simulation for the evaluation and optimization of CPV modules.

We discussed the outdoor operation of a fixed flat sub module with an InGaP/GaAs/InGaAs inverted metamorphic triple-junction solar cell (IMM module) for the first time in the world. The global solar spectrum distribution was assessed using the average photon energy (APE) and spectral matching ratio (SMR) indexes in this study. The conversion efficiency of the IMM module was more than 30% and was markedly affected by APE rather than by module temperature under real environmental conditions. markedly increased in the high APE region. In the case of APE of more than 1.60 eV, the photocurrent of the bottom subcell decreased owing to the blue-rich spectrum, which limited the short-circuit current. The absorption region of the bottom subcell overlapped with the water absorption region in the solar spectrum; therefore, environmental conditions such as water precipitation greatly affected the output of the current-matching inverted triple-junction solar cell.

We have fabricated thin-film solar cells using polycrystalline silicon (poly-Si) films formed by flash lamp annealing (FLA) of 4.5-µm-thick amorphous Si (a-Si) films deposited on Cr-coated glass substrates. High-pressure water-vapor annealing (HPWVA) is effective to improve the minority carrier lifetime of poly-Si films up to 10 µs long. Diode and solar cell characteristics can be seen only in the solar cells formed using poly-Si films after HPWVA, indicating the need for defect termination. The actual solar cell operation demonstrated indicates feasibility of using poly-Si films formed through FLA on glass substrates as a thin-film solar cell material.

Temperature characteristics of an InGaP/InGaAs/Ge triple-junction solar cell were analyzed in detail using an equivalent circuit calculation. The current–voltage (I–V) characteristics of single-junction solar cells (InGaP, InGaAs, Ge solar cells) were measured at various temperatures. Fitting of I–V curves between measured and calculated data was carried out, and the diode parameters and temperature exponents of the single-junction solar cells were extracted. The parameters for each single-junction solar cell were used in the equivalent circuit model for the triple-junction solar cell, and calculations of solar cell performance were carried out. Measured and calculated results of the I–V characteristics at various temperatures agreed well.

Antireflection nanostructure was formed by simple wet chemical etching using catalysis of silver (Ag) nanoparticle. Single nano-sized Ag particle dispersion solution was coated onto Si(1 0 0) substrate with polished surface. Then, the samples were soaked in an aqueous etching solution of hydrofluoric acid and hydrogen peroxide. The surface of 9-min-etched Si substrate appeared black, and the reflectivity was reduced to below 5% throughout the entire spectrum from 200 to 1000 nm owing to the formed nanostructure. The absorption was significantly increased after the formation of antireflection structure with 9 min etching, and the conversion efficiency of solar cell with antireflection structure increased from 8.25 to 10.0% owing to the increase of short-circuit current.

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y 2 O 3 content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.

For applications of stand-alone systems including an electric vehicle (EV) power station, a tracking system with low power consumption will be demanded. One possible solution to save idling power is intermittent tracking, for example, tracking in every 30 minutes. To achieve this, a new CPV module was designed. With the combination of an advanced feed-forward tracking control, the 30 minutes of intermittent tracking may be possible by 100 x of geometrical concentration (the projected lens area by the cell aperture area with alignment margin).

We tried to repair the surface of damaged poly-methyl methacrylate and glass using a simple coating and evaluated the transmittance of direct component of light. We coated a repairing material on the damaged surface of the sample. After the first sandblasting, the transmittance and the calculated conversion efficiency of CPV decreased due to the damage derived by the sandblasting. However, after the first coating, they made a recovery due to the effect of the repairing coating. In the second step (sandblasting and coating), the recovery was also observed. Instead of replacement of damaged lens or module, the coating can bring the performance back into the improved condition.

We proposed a modified 3-diode equivalent circuit model for analysis of multicrystalline silicon (Mc-Si) solar cells. By using this equivalent circuit model, we can precisely evaluate the characteristics of Mc-Si solar cells taking the influence of grain boundaries and large leakage current through the peripheries into consideration and extract electrical properties. The calculated value of current-voltage characteristics for small size (3 mm×3 mm) Mc-Si solar cells using this model completely agreed with the measured value at various cell temperatures. Moreover, the calculated open-circuit voltage ( V oc ) obtained by extracted parameters and measured V oc agreed well.

We investigated the multireflection effect on the formation of a periodic surface structure produced by a linearly polarized Nd:YAG laser beam of 532 nm on an Si film deposited on a glass substrate, as well as on heating rate in the film, compared with an excimer laser beam. From the theoretical calculation results, it was found that the formation of the periodic surface structure and heating rate strongly depended on film thickness or that they were influenced by the multireflection effect. The thickness most effective for forming the periodic surface structure and heating rate was about 60 nm. Furthermore, we attempted to verify the calculation results by carrying out an experiment in which we checked whether the periodic structure was formed on the surface of the melting-crystallized Si films. As a result, the thickness range for producing the periodic surface structure was found to be from 50 to 70 nm, which were larger than the theoretical values of 40 to 60 nm.

Effects of hydrogen plasma treatment on minority carrier diffusion length and recombination velocity at grain boundaries in polycrystalline silicon solar cells have been evaluated by the scanned laser-beam-induced current technique. We have successfully evaluated the two-dimensional minority carrier diffusion length. On the basis of the evaluated diffusion length, the recombination velocity at the grain boundaries was obtained. The recombination velocity was improved by the hydrogen plasma treatment from 15,000—20,000 to 5000—10,000 cm/s. It was quantitatively confirmed that the hydrogen plasma treatment is very effective in both grains and grain boundaries.

We tried to repair the surface of damaged polymethyl methacrylate and glass using a simple coating and evaluated the transmittance of direct component of light. We coated a repairing material on the surface of the sample. After the 1st sandblasting, the transmittance and the calculated conversion efficiency of CPV decreased due to the damage derived by the sand. However, after the 1st coating, they made a recovery due to the effect of the repairing coating. In the second steps (sandblasting and coating), the recovery was also observed. Instead of replacement of damaged lens or module, the coating can bring the performance back into good condition.

Output characteristics of tracking type concentrator photovoltaic (CPV) system, multi-crystalline silicon (mc-Si) PV system, and CIGS PV system were analyzed in the data period of a year from August 2013 to July 2014. In this study, we analyzed the influence of environmental factors using average photon energy (APE) and temperature of solar cell (Tcell). The characteristics of 14 kW CPV system, 50 kW multi-crystalline silicon PV system, 60 kW CIGS PV system were evaluated and compared. As a result, the output performance of CPV was highest between the three systems at the most frequent conditions of outdoor environment.

The temperature dependences of the electrical characteristics of InGaP/InGaAs/Ge triple-junction solar cells under concentration were evaluated. For these solar cells, conversion efficiency ( η ) decreased with increasing temperature, and increased with increasing concentration ratio owing to an increase in open-circuit voltage. The decrease in η with increasing temperature decreases with increasing concentration ratio. Moreover, the annual output of a concentrator system with a high-efficiency triple-junction cell was estimated utilizing the experimental solar cell's characteristics obtained in this study and field-test meteorological data collected for 1 year at the Nara Institute of Science and Technology, and compared with that of a nonconcentration flat-plate system.

The series resistance of an InGaP/InGaAs/Ge triple-junction solar cell was evaluated in detail. Series resistance components such as electrode resistance, tunnel junction resistance and lateral resistance between electrodes were estimated separately. The characteristics of the triple-junction solar cell under concentrated light were evaluated by equivalent circuit calculation with a simulation program with integrated circuit emphasis (SPICE). By equivalent circuit calculation, the optimization of cell designs was performed, focusing on series resistance and cell current in order to realize high-efficiency concentrator cells.

Temperature characteristics of the open-circuit voltage (Voc) were investigated in the temperature range from 30°C to 240°C for the InGaP/InGaAs/Ge triple-junction cells. Also, single-junction cells that had the similar structure to the subcells in the triple-junction cells were studied. In the high-temperature range (from 170°C to 240°C), the temperature coefficients of Voc of the InGaP/InGaAs/Ge triple-junction solar cell (dVoc/dT) were different from those in the low-temperature range (from 30°C to 100°C). This is because photo-voltage from the Ge subcell becomes almost 0 V in the high-temperature range. It was found that the open-circuit voltage of a Ge single-junction cell reduced to almost 0 V temperatures over 120°C under 1 sun condition.

Field-test data from a 50 kW photovoltaic (PV) system installed at The Nara Institute of Science and Technology (NAIST) were analyzed in detail. We found that the PV system operated in a wide temperature range and was strongly affected by the temperature coefficient of conversion efficiency when the module temperature became high. The temperature coefficient dependence of the system performance was analyzed in order to estimate the annual output of the system in an actual operating environment. As a result, it was found that the annual output energy of the PV system increased about 1% by an improvement of 0.1%/°C in the temperature coefficient. This result indicates that it is very important to consider the temperature characteristics in solar cell development.

SiC was formed using volcanic ash as starting material and concentrated sunlight as energy resource. The solar furnace was composed of two parts: Fresnel lens and reacting furnace. The reacting furnace was composed of a cylindrical vacuum chamber and quartz glass plate functioning to guide the concentrated sunlight into the furnace and was placed at the focal point of the Fresnel lens. The sample was made from the mixture of silica formed from volcanic ash and graphite and placed in the carbon crucible inside the reacting furnace. The temperature in the carbon crucible reached more than 1500°C. After the reaction using concentrated light,β-SiC was formed. The weight % of formed SiC was 90.5%.

In this study, we propose a new concentrator photovoltaic (CPV) system design with a large-acceptance-angle lens, which tracks the sun on the basis of a new 30-min intermittent tracking method that does not require a special high-precision CPV tracking system. This will reduce costs, because a large percentage of the cost of a typical CPV system comes from the expensive accurate tracking system. The present system had a concentration ratio of 111 and an acceptance angle of 4.5°. We conducted an experiment to evaluate the thermal and electrical performances of the system in an outdoor test site in Miyazaki, Japan. The experimental results were compared with optical, thermal, and electrical simulation results. The simulated results showed good agreement with the experimental ones.

We propose a novel production method to fabricate high-efficiency thin-film poly-Si solar cells using flash lamp annealing (FLA) for crystallization of micrometer-order-thick p-i-n amorphous silicon (a-Si) structure, prepared by catalytic chemical vapor deposition (Cat-CVD, Hot-Wire CVD) on low-temperature glass substrates and following high-pressure water vapor annealing for defect passivation. The FLA enables us to crystallize a-Si films with only one pulse of less than 10 ms duration, and use of Cat-CVD provides a-Si cost-effectively because of high deposition rate of a-Si over 10 nm/s. Secondary ion mass spectroscopy (SIMS) profiles reveal that diffusion of dopants in p- or n-type layers is sufficiently suppressed after FLA, indicating possibility of simultaneous crystallization of p-i-n stacked a-Si films. High-pressure water vapor annealing (HPWVA) enhances the minority carrier lifetime of the poly-Si up to about 10 μs and drastically improves diode properties of the p-i-n poly-Si structure. No light-induced degradation is observed in the solar cell property of the poly-Si solar cell after 24-hour 1-sun light soaking.

Recently, submicron structures or nano structures have been used for fluidic, electronic, optic, and mechanical devices in various fields. Most of these fine structures are fabricated by conventional lithographic process, and they require complicated steps including masking and molding. Therefore, there is much demand for fabrication techniques for fine structures without lithographic process for faster and cheaper manufacture. It has been reported that linearly polarized laser irradiation induces spatially periodic fine structures on the surfaces of semiconductors, 1–4) metals, 5–7) and polymers. 8,9) The formation of these laser-induced periodic surface structures (LIPSS) means that laser irradiation produces a periodic temperature distribution on the surface of the irradiated

Under the concentration conditions, it is important to manage the operating temperature of a concentrator photovoltaic (CPV) module, because a high-density solar energy enters into the solar cell. The estimation of operating temperature and mechanical stress is important for the solution of failure mechanisms. We estimated the operating temperature and thermal stress of the CPV module using structural mechanics simulation. In the case of the non-uniform light condition, inhomogeneous temperature distribution was generated in the solar cell and the highest thermal stress at the center of the finger electrode was observed. In the case of uniform light condition, the maximum temperature and thermal stress were suppressed. The developed model can be applied to the design optimization of CPV module which achieves low operating temperature and low thermal stress.