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Development of high-efficiency solar cell modules and new application fields are significant for the further development of photovoltaics (PV) and creation of new clean energy infrastructure based on PV. Especially, development of PV-powered EV applications is desirable and very important for this end. This paper shows analytical results for efficiency potential of various solar cells for choosing candidates of high-efficiency solar cell modules for automobile applications. As a result of analysis, Si tandem solar cells are thought to be some of their candidates. This paper also overviews efficiency potential and recent activities of various Si tandem solar cells such as III-V/Si, II-VI/Si, chalcopyrite/Si, perovskite/Si and nanowire/Si tandem solar cells. The III-V/Si tandem solar cells are expected to have a high potential for various applications because of high efficiency with efficiencies of more than 36% for 2-junction and 42 % for 3-junction tandem solar cells under 1-sun AM1.5 G, lightweight and low-cost potential. Recent results for our 28.2 % efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si 3-junction solar cell are also presented. Approaches to automobile application by using III-V/Si tandem solar cells and static low concentration are presented.

Development of highly-efficient photovoltaic (PV) modules and expanding its application fields are significant for the further development of PV technologies and realization of innovative green energy infrastructure based on PV. Especially, development of solar-powered vehicles as a new application is highly desired and very important for this end. This paper presents the impact of PV cell/module conversion efficiency on reduction in CO2 emission and increase in driving range of the electric based vehicles. Our studies show that the utilization of a highly-efficient (higher than 30%) PV module enables the solar-powered vehicle to drive 30 km/day without charging in the case of light weight cars with electric mileage of 17 km/kWh under solar irradiation of 3.7 kWh/m2/day, which means that the majority of the family cars in Japan can run only by the sunlight without supplying fossil fuels. Thus, it is essential to develop high-efficiency as well as low-cost solar cells and modules for automotive applications. The analytical results developed by the authors for conversion efficiency potential of various solar cells for choosing candidates of the PV modules for automotive applications are shown. Then we overview the conversion efficiency potential and recent progress of various Si tandem solar cells, such as III-V/Si, II-VI/Si, chalcopyrite/Si, and perovskite/Si tandem solar cells. The III-V/Si tandem solar cells are expected to have a high potential for various applications because of its high conversion efficiency of larger than 36% for dual-junction and 42% for triple-junction solar cells under 1-sun AM1.5 G illumination, lightweight and low-cost potentials. The analysis shows that III-V based multi-junction and Si based tandem solar cells are considered to be promising candidates for the automotive application. Finally, we report recent results for our 28.2% efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si triple-junction solar cell. In addition, new approaches which are suitable for automotive applications by using III-V triple-junction, and static low concentrator PV modules are also presented.

Equivalent circuit network simulation is widely used in modeling solar cells in three dimensions. However, the computational time and numerical instability increases dramatically when the number of circuit element increases. This problem is exacerbated by increasing the number of junctions in the solar cells. We propose a downsampling algorithm to reduce the time complexity but retain reasonable accuracy within the appropriate parameter space of multi-junction solar cells. We also publish a full-featured software that implements this algorithm and the full circuit network simulation along with this paper.

This paper describes the design and evaluation of a III–V/Si partial concentrator photovoltaic (CPV) module with a stacked structure comprising a highly transparent CPV module and a Si cell, which aims to maximize the power generation from global normal irradiation (GNI) by harvesting not only direct, but diffuse sunlight as well. The module structure was designed by considering the optical and heat transfer characteristics, and its performance was evaluated by outdoor and indoor tests using a prototype submodule with a geometrical concentration ratio of 100×. The submodule achieves diffuse sunlight transmission of over 80%, thus generating more power from diffuse sunlight. Under clear-sky condition, the submodule with a single-sided Si cell exhibits the maximum GNI-based module efficiency of 30.7%. The submodule with a bifacial Si cell further improves the power generation and tolerance to tracking error angle for various sunlight conditions.

Efficiency potential of crystalline Si solar cells is analyzed by considering external radiative efficiency (ERE), voltage, and fill factor losses. Crystalline Si solar cells have an efficiency potential of more than 28.5% by realizing ERE of 20% from about 5% and normalized resistance of less than 0.05 from around 0.1. Nonradiative recombination losses in single-crystalline and multicrystalline Si solar cells are also discussed. Especially, nonrecombination and resistance losses in multicrystalline Si solar cells are shown to be higher than those of single-crystalline cells. Importance of further improvement of minority-carrier lifetime in crystalline Si solar cells is suggested for further improvement of crystalline Si solar cells. High efficiency of more than 28.5% will be realized by realizing high minority-carrier lifetime of more than 30 ms. Key issues for those ends are reduction in carbon concentration of less than 1 × 1014 cm−3, oxygen precipitated and dislocations even in single-crystalline Si solar cells, and reduction in dislocation density of less than 3 × 103 cm−2 in multicrystalline Si solar cells.

This paper overviews photovoltaic R&D projects in Japan. Recently, world-record and second highest efficiencies of various types of solar cells have been demonstrated under the New Energy and Industrial Technology Development Organization Project: 44.4% (under concentration) and 37.9% (under 1 sun) InGaP/GaAs/InGaAs inverted metamorphic 3-junction solar cells by Sharp, 26.7% single crystalline Si heterojunction back-contact solar cell by Kaneka, 22.3% copper indium gallium selenide solar cell by Solar Frontier, a-Si/μc-Si/μc-Si thin-film triple-junction solar cell with stabilized efficiency of 14.0% by AIST, 11.9% dye-sensitized solar cell by Sharp, and 11.2% organic solar cell by Toshiba. This paper also presents efficiency potential of high-efficiency and next-generation solar cells analyzed by considering external radiative efficiency, open-circuit voltage loss, and fill factor loss. Efficiency potential of crystalline Si, GaAs, III-V compound 3-junction and 5-junction, CIGSe, CdTe, CZTS(Se), multiquantum well, and quantum dot and perovskite solar cells is shown to be 28.5%, 29.7%, 40%, 43%, 26.5%, 26.5%, 20%, 25.8%, and 24.9% under 1 sun, respectively.

Bandgap optimization of the tandem cells has been calculated by many scientists under the standard air-mass 1.5 spectrum or the site-specific conditions using statistics of meteorological observations and spectrum data. Calculation of the optimized bandgap combination at the specific site required many annually-observed atmospheric parameters. It is not realistic, because most of the installation site does not have detailed annual spectrum information. This paper has two purposes. One is to quantitatively understand the impact of the variance of the atmospheric conditions to the bandgap optimization design. Another is to propose the practical method to take the spectrum information of the specific site by even in a single day’s measurement. For evaluating the impact of the atmospheric conditions, both the best and the worst distributions were taken from the measurement data. With including other meteorological and geographical data variance, the dataset of the annual spectrum with different sun-height was generated and distribution of the calculated optimized bandgap combination was examined. The optimum bandgaps varied by aerosol depth, water precipitation, latitude, and seasonal sunshine duration change as it was expected. It was also found that the optimization of the bandgaps combination at the specific site, considering ever-changing spectrum, may be determined by the matching condition to the sun height at the culmination on the winter solstice, because the distributions of optimum bandgap combinations were much closed to those of annual integration, in spite of the fact that they were calculated by a single time (single date) of the measurement. Different from AM1.5 the sun height can be taken two times a day throughout a year.

The present status of R&D for various types of solar cells is presented by overviewing research and development projects for solar cells in Japan as the PV R&D Project Leader of the New Energy and Industrial Technology Development Organization (NEDO) and the Japan Science and Technology Agency (JST). Developments of high-efficiency solar cells such as 44.4% (under concentration) and 37.9% (under 1-sun) InGaP/GaAs/InGaAs 3-junction solar cells by Sharp, 26.6% crystalline Si heterojunction back-contact (HBC) solar cells by Kaneka, 22.3% CIGS solar cells by Solar Frontier have been demonstrated under the NEDO PV R&D Project. 15.0% efficiency has also been attained with 1 cm2 perovskite solar cell by NIMS under the JST Project. This article also presents analytical results for efficiency potential of high-efficiency solar cells based on external radiative efficiency (ERE), open-circuit voltage loss and fill factor loss. Crystalline Si solar cells, GaAs, III–V compound 3-junction and 5-junction, CIGSe, and CdTe solar cells have efficiency potential of 28.5%, 29.7%, 42%, 43%, 26.5%, and 26.5% under 1-sun condition, respectively, by improvements in ERE.

The impact to the optical environment result from shading of PV panels becomes concerned. This paper describes how to calculate illumination level on the land around tracking PV (both isolated and arrayed) panel. The land under the flat-plate PV is dark by shading, but the influence from the tracking PV is not very significant, typically half in average. This is because shadow by tracking panel moves. The shading influence is further decreased with the increase of pedestal height. With this advantage, tracking PV can be combined with agriculture as a double use of the land.

We demonstrated a static (non-tracking) low concentration photovoltaic module that employs a new design paradigm that mixes two different types of the lens arrays. This design approach brings the annual optical collection efficiency closer to the theoretical upper limit but with high manufac-turability and scalability, because this design paradigm give more degree of freedom to optimize the overall efficiencies. We demonstrated that the module with the hybrid lens array is 2-%(absolute) more efficient than its single lens array counterparts at on-axis illumination. Also, the good match of the modeled and experimental incident-angle dependent module efficiency confirms the robustness of our fabrication process, showing the promise of achieving high annual collection efficiency of this module.

Solar panels used for EV charging stations and car-roof PV are often partially shaded and lead to substantial energy loss. It is known that this mismatching loss can be reduced by increasing the number of parallel strings. First, a probability model was developed using a one-year solar irradiance monitoring around the car body in 5 directions. The developed model successfully matched to the measured solar resource in each direction and succeeded to quantify the probability of the partial shading on the car. Another related issue of the inherent mismatching loss of the car-roof PV is non-uniform illumination caused by the curved shape of the panel. This can also be modeled by ray-tracing simulation. Then, we calculated the PV output affected by mismatching due to various sunlight patterns and partial shade patterns by Monte Carlo method. It was found that the average efficiency asymptotically approached 1 - 1 / N (N is the number of strings). We also examined the relationship between partial shade quantity and power generation loss in a 30 kW solar system array and verified the above model.

Micro CPV is a promising technology for reducing high-precision assembly cost while making use of the high efficiency of CPV. However, the requirement of the installation and tracking accuracy remains the same. A production method is often taken to manufacture small size modules with high accuracy, high homogeneity, low cost, and to compile them. There is a concern that the performance of the large-area panel may deteriorate due to accuracy in the assembly. A micro-Kohler concentrator optics was designed suitable to the micro CPV modules, and the designed acceptance angle (90 % power point) reached 1.8 degrees with the 500 x axially symmetrical (truncated to square) primary plano-convex lens.

Curved photovoltaic, typically using flexible one receives different irradiation from the sunlight. The energy yield is often overestimated by ignoring local cosine loss and other losses related to the curvature of the PV surface. Although the formula to some extent varies by the type of the curved surface, it is modeled by the curve-correction factor from the flat-plate conditions. The curve correction factor is calculated either geometrical calculation or the numerical ray-tracing simulation. In these proceedings, the one by Monte Carlo method (Ray-tracing simulation) is discussed. First, the incident angle the sunlight affected by the orientation (random orientation if necessary), shading by surrounding structures (randomly distributed), climate pattern, and both direct and diffused sunlight from a regional database, was calculated. Second, the absorbed flux onto the curved module surface was calculated using random rays by the above distribution of the sunlight. Third, the regional influences onto the energy generation of the curved PV panel were discussed. The energy yield of the curved PV drops significantly by the increase of the curvature and incident angle distribution affected by latitude, climate pattern, and shading environment.

Micro CPV is a promising technology for reducing high-precision assembly cost while making use of the high efficiency of CPV. A production method is often taken to manufacture small size modules with high accuracy, high homogeneity, low cost, and to compile them. There is a concern that the performance of the large-area panel may deteriorate due to accuracy in the assembly. We did the Monte Carlo analysis for simulate assemble error. It could successfully define inspection conditions and tolerance control thresholds with consideration of the worst-case of the tracking errors. With proper but reasonable inspections (component acceptance and alignment accuracy test), it is possible to collect micro-CPV units to a reasonable-size of the CPV panel keeping more than 90 % of the output even with the worst-case installation and tracking errors. This approach can be expanded to the analysis of impact by the partial shading of the lens that has a significant impact on the performance of CPV.

Although photovoltaics (PV) are expected to contribute as major electricity and energy source, there are some important issues such as continuous development of PV R&D and creation of new markets to be developed. This paper emphasizes acceleration of PV system installations in Japan in order to overcome difficulty of increasing nuclear energy. This paper also presents importance of high-efficiency, low cost and highly reliable solar cells and modules by overviewing efficiency potential of various solar cells including Si tandem solar cells. Our approaches to automobile application by using high-efficiency and low-cost solar cell modules are presented.

Dome-shaped Fresnel lenses were developed with a new design algorithm. The lens was defined as the integration of pentagon prisms. This method is flexible and generates a dome-shaped Fresnel lens suitable for high concentration by keeping the thickness approximately equal in the entire region of the lens so that the lens becomes mechanically robust with the minimum amount of materials.

Shading loss of a multitracker concentrator photovoltaic (CPV) system can be predicted, and for doing this, geometrical optimization will be useful. The optimum allocation for infinite land will be either rectangular allocation parallel to the N–S and E–W axis or checkerboard allocation. We solve an optimization problem with the introduction of nondimensional parameters in geometry, namely, optimum conditions as a function of space factor and panel aspect ratio. The type of optimum allocation pattern and its aspect ratio depend on latitude, climate pattern, aspect ratio of panels, and space factor. Our calculation results show that, in general, checkerboard allocation is preferred for locations with higher latitude, higher sun irradiation in summer, higher space factor, and horizontally longer rectangular solar panels.

The paper presents a quantitative approach to the investigation and comparison of the material qualities of III-V on silicon (III-V/Si) solar cells by using external radiative efficiencies. We use this analysis to predict the limiting efficiencies and evaluate the criteria of material quality in order to achieve high efficiency III-V/Si solar cells. This result yields several implications for the design of high efficiency III-V/Si solar cells.

The efficiency potential of chalcopyrite and kesterite solar cells including CIGSe (CuInGaSe2), CIGS (CuInGaS2), CZTS (Cu2ZnSnS4) and CZTSSe [Cu2ZnSn(S,Se )4] solar cells is discussed based on external radiative efficiency (ERE), open-circuit voltage loss, fill factor loss, non-radiative recombination and resistance loss. CIGSe cells achieve efficiency potential of 26.8% and 27.5% by improving the ERE from around 1% to 10% and 20%, respectively. CIGS and CZTS(Se) cells achieve the efficiency potential of 25% and 22%, respectively, by improvement in ERE from around 1 × 10−4% to 3%–5%. The effects of non-radiative recombination and resistance loss upon the properties of wide-bandgap CIGSe, CIGS and CZTS(Se) cells are discussed. In the case of wide-bandgap CIGSe cells, lattice mismatching between the buffer layer and CIGSe active layer and deep-level defects are thought to originate from non-radiative recombination loss. CIGS and CZTS(Se) cells are shown to have lower ERE and higher resistance loss compared to that of CIGSe cells.

It is well known that CPV is sensitive to the spectrum change, and its high-performance is often discouraged by the spectrum mismatching loss by the seasonal change of the atmospheric parameters. We found multiple methods could improve the robustness to the spectrum sensitivity, including enhancing luminescence coupling and fine-tuning to the bottom-bandgap matched to local atmospheric conditions (water absorption).It is well known that CPV is sensitive to the spectrum change, and its high-performance is often discouraged by the spectrum mismatching loss by the seasonal change of the atmospheric parameters. We found multiple methods could improve the robustness to the spectrum sensitivity, including enhancing luminescence coupling and fine-tuning to the bottom-bandgap matched to local atmospheric conditions (water absorption).

We demonstrated a static (non-tracking) low concentration photovoltaic module that employs a new design paradigm that mixes two different types of the lens arrays. This design approach brings the annual optical collection efficiency closer to the theoretical upper limit but with high manufacturability and scalability, because this design paradigm gives more degree of freedom to optimize the overall efficiencies. We demonstrated that the module with the hybrid lens array is 2-%(absolute) more efficient than its single lens array counterparts at on-axis illumination. Also, the good match of the modeled and experimental incident-angle dependent module efficiency confirms the robustness of our fabrication process, showing the promise of achieving high annual collection efficiency of this module.

This paper describes the design and evaluation of a low-concentration static III-V/Si partial CPV module that aims to maximize the power generation in the limited car-rooftop area by harvesting full global sunlight. The concentrator lens was designed considering the incident angle dependence of annual global irradiance on the car-rooftop (horizontal flat) surface. The fundamental characteristics were investigated by optical simulation and indoor test using a prototype submodule with a geometrical concentration ratio of 3.5×. The designed lens can collect 46.6% and 36.4% of the annual solar irradiation onto triple-junction and Si cells, respectively, achieving the annual electricity yield which is equivalent to ˜30% efficiency flat PV module.

We propose a new design paradigm of static low concentration photovoltaics for III-V or silicon solar cells. Although static/non-tracking low concentrator optics has been studied extensively, most of these designs are either difficult to implement or low optical efficiency. In this work, we present a design that uses lens array that mixes two different optics, giving more degrees of freedom to optimize the optics and the size of solar cells. This design approach brings the optical efficiency closer to the theoretical upper limit while maintaining manufacturability and scalability. Although the design example presented in this work is aimed to mount on sloped surface, this can be also applied to the building integrated photovoltaics or on car-roof.

Fluctuation of the atmospheric parameters substantially impact to the energy yield of multi-junction cells. The calculation considering the variation of atmospheric parameters showed a dramatic decline of the annual energy yield from the cells with more than five junctions. Partially Radiativecoupling multi-junction solar cells were proposed, and optimization work was done. The top and the bottom junctions have lower bandgap for buffering to the mismatching and collecting a full range of the sunlight by robust energy conversion, and the annual energy substantially increases even by five or six junctions.

Multi-junction cells have high efficiency but their performance ratio was less than the conventional single junction cell. One of the issues is lower outdoor performance in the outdoor operation conditions due to spectrum mismatch influenced by fluctuation of sun-height and atmospheric parameters. In this study, to predict the energy yield at an arbitrary point, firstly, we estimated the range of atmospheric parameter fluctuation that determines the spectrum from Bird’s spectrum model using the DNI spectrum measured at University of Miyazaki. Furthermore, we examined the uncertainty of the outdoor performance of CPV system using the DNI spectrum resynthesized from the Monte Carlo method. As a result, when considering the atmospheric parameters, calculated values approached to the measured values and the uncertainty of outdoor performance was confirmed.

This paper discusses the potential of the power conversion efficiency of solar cells from various materials considering external radiative efficiency, open-circuit voltage loss. The possibility of the power conversion efficiency is summarized in the 1st chapter. The examined cells are Silicon, III-V, CIS, CdTe, Organic, Dye-sensitized and Perovskite. The 2nd and successive chapters discuss the potential of the multijunction cells. The power conversion efficiency can be raised by using multi-junction structure. However, fluctuation of the atmospheric parameters substantially impacts the energy yield. The calculation considering the variation of atmospheric parameters showed a dramatic decline of the annual energy yield from the cells with more than five junctions. Super-multijunction solar cells were proposed, and optimization work was done. The top and the bottom junctions have lower bandgap for buffering to the mismatching and collecting a full range of the sunlight by robust energy conversion, and the annual energy substantially increases even by five or six junctions.

The properties of the acceptor states in GaAsN grown by chemical beam epitaxy (CBE) are studied by analyzing their charges based on the Poole–Frenkel model. Deep level transient spectroscopy (DLTS) shows two acceptor levels at 0.11 and 0.19 eV above the valence band maximum. The emission rates of carriers from these states are enhanced with increasing the electric field during the DLTS measurement, which indicates that the energies required for the emission are decreased. By analyzing this field-enhanced emission process, the polarizabilities of the levels at 0.11 and 0.19 eV are found to be −1 (±0.1) and −2 (±0.1), respectively. In addition, these states have almost the same concentration. Therefore, we conclude that they originate from the same defect, acting as a double acceptor in GaAsN film grown by CBE.

The N–H related acceptor defects in GaAsN grown by chemical beam epitaxy (CBE) are studied by hydrogen isotopes, H and D. When the films are grown by a conventional arsenic source, deep level transient spectroscopy (DLTS) reveals two energy levels at 0.11 and 0.19 eV above the valence band. These levels were considered to act as a double acceptor in the literature. When the films are grown by a deuterated arsenic source, new signals appear in DLTS spectra at 0.15 and 0.23 eV. This indicates that the new signals are originated from D-related defects. The energy differences between 0.15 and 0.11 eV, and that between 0.23 and 0.19 eV are same (0.04 eV). Although these energy levels become deeper with increasing the growth temperature, the energy differences are almost constant independent of the growth condition. In addition, the intensity ratios of the peaks at 0.15 (0.23) eV to that at 0.11 (0.19) eV have a good correlation with the isotopic concentration ratio of D to H in the grown films. Therefore, we conclude that the energy differences and intensity ratios of the DLTS peaks occur due to the structural change from N–H to N−D in the same type of defect, and that this acceptor is an N–H related defect.

The measurement of the atmospheric parameters by fitting to the measured spectrum was used to analyze the uncertainty of the energy generation of CPV. It was found the fluctuation of the atmospheric parameters substantially impact to the energy yield of multi-junction cells. The calculation considering the variation of atmospheric parameters showed a dramatic decline of the annual energy yield from the cells with more than five junctions. Optimized multijunction solar cells using luminescent coupling for an adjuster of the spectrum mismatching was proposed and analyzed. The top and the bottom junctions have lower bandgap for buffering to the mismatching and collecting a full range of the sunlight by robust energy conversion, and the annual energy substantially increases even by five or six junctions. The advanced modeling of the multi-junction cells considering the sensitivity of the atmospheric parameters and the degree of luminescent coupling is useful to the accurate prediction of the solar power in the smart control to the car-roof PV.

This paper presents current status and future direction of Photovoltaic (PV) electric power system installations in the world. This article also overviews PV R&D activities in Japan as the PV R&D Project Leader of NEDO and JST. Present status of various solar cells efficiencies under NEDO and JST PV R&D projects are presented: 44.4% for concentrator III-V compound 3-junction solar cell, 37.9% for 1-sun III-V compound 3-junctiion cell, 26.7% for single-crystal Si cell, 22.3% for CIGS cell, and 14.0% for a-Si based 3-junction cell. Efficiency potential of various solar cells is also discussed. Prospects of PV and our recent approaches towards the creation of “Mobility Society by using Solar Energy” are discussed.

Calculation of the optimized bandgap combination at the specific site required many annually-observed atmospheric parameters. For evaluating the impact of the atmospheric conditions, both the best and the worst distributions were taken from the measurement data. It was found that the optimization of the bandgaps combination considering ever-changing spectrum, may be determined by the matching condition to the sun height at the culmination on the winter solstice. Considering influence on the annual energy yield of the CPV multi-junction cell, the best number of junction was 3 and more than 4 junctions was not better for the annual energy yield.

The cost reduction potential of concentrator photovoltaics (CPV) by adding a silicon backplane solar cell is quantified. Using a backplane solar cell module in a CPV system to absorb the diffused sunlight has been proposed and demonstrated as a way to fully utilize the global solar spectrum instead of just direct normal incidence. However, it is not clear that whether the energy price of this system can ultimately be competitive with the state-of-the-art CPV or flat-panel silicon PV system. In this paper, we analyzed the energy yields and the cost of the III-V/Si hybrid CPV system to find its limiting cost reduction potential. Our results suggest that it is unlikely that the energy price of CPV can be dramatically reduced simply by introducing the backplane silicon module into the the state-of-the-art CPV system. One should completely reconsider the designs of CPV components and leverage the unique properties of the III-V/Si hybrid CPV system to make this concept succeed.

We announced a open source solar cell modeling and analysis toolkit written in Python. The standard off-the-shelf solar cell simulation software is often difficult to modify or reuse some of its functionality into new solar cell models. In this software package, we wrap the solar cell simulations into individual modules and application programming interfaces to make them very user-friendly. This library contains a wide range of functions to do the heavy-lifting, error-prone jobs of modeling solar cells, such as unit conversions and arithmetic operations of spectrum data, absorption-emission reciprocity or solving the I-Vs of multi-junction cells. This allows the users to rapidly adapt and build their own models with these modularized and verified components. Source codes, detailed documentation and examples can be found in https://kanhua.github.io/pypvcell.

Combining Si PV module technology with an efficient III- V CPVs top PV into a tandem device is an attractive approach to enhance the efficiency of PV modules. Here, a method called III- V/Si hybrid configurations for enhancing the Si module efficiency is placing III- V static CPVs at the edge gap of each Si wafer rather than stacking in the top of Si. The prototype PV module shows the enhancement of efficiency. The cost evaluations of the III- V lSi hybrid configurations compared with Si module is discussed under various presumed cost ratio of 111-V/Si PVs.

CPV went off the market mainly due to problems of trackers. We are trying to solve the tracking issue. Step 1. Control of the mating module by imperfection of tackers: We have developed a Monte Carlo model of the behavior of CPV module and system with assemble errors. Step 2. Advanced CPV module for rough tracking: We have succeeded in demonstrating 100 x and 28.5% CPV module tracking every 30 minutes. Step 3. No tracking: We have developed a modern design method that enables ultra-wide acceptance by advanced asymmetrical optics.

A CAD/CAM friendly design based on a Monte Carlo method was developed to give the optimized axially-asymmetrical lens profile suitable to the grid arrangement with given site conditions such as horizontal plane, and sloped surface in the southern direction. Such CPV panel selectively collects the sunlight from high incident angle and has the substantially wide acceptance half angle with sacrifice of the optical loss in the normal region. The optimization using asymmetrical function successfully adjusted the lens profile for the grid arrangement. With the use of optimized axially-asymmetrical lens, it is not always necessary to rely on honeycomb arrangement.

This paper describes the design and evaluation of a partial concentration III-V/Si module that aims to maximize the power generation from global normal irradiation by harvesting not only direct sunlight but also diffuse sunlight. The module structure was designed by optical and thermal analysis, and the fundamental characteristics were investigated by performing outdoor and indoor tests using a prototype mini-module with a geometrical concentration ratio of 100X. Experimental results show that the mini-module achieves enhanced diffuse sunlight transmission of 82 % and generates more power from diffuse sunlight than the previous prototype reported by the authors. The tolerance to tracking error was also confirmed, which may contribute to mitigate the requirement of tracking accuracy.