“NEDO PV Challenges” was established in 2014, as new strategy for research and development of PV in Japan. It aims for “strategy for support to the society after popularization”, instead of the conventional “strategy for popularization”. It shows 5 challenges that are “LCOE reduction”, “Enhanced reliability”, “Cancellation of siting restriction”, “Establishment of recycling system” and “Creation of high added value businesses”. The target of “LCOE reduction” is 7JPY/kWh in 2030 and NEDO promotes the various research and development of PV. As a result of development, achievement of the world’s highest efficient module, etc. has produced many results. Such results will lead to the creation of solar power system market in various areas different from conventional areas, such as transportation sector.

The silicon solar cell occupies most of the photovoltaic market 60 years after the first solar cell was invented in 1954. The improvement of the conversion efficiency was made for long period by the enormous effort of many people. In this review, the structural change of the silicon solar cells and the progress of the efficiency are explained from the viewpoint of the surface passivation technologies that affect to the open circuit voltage and the temperature coefficient of output power. The development trend is also discussed. The cost reduction of silicon solar modules is significant with increasing the production volume, so that the electricity by the photovoltaic power generation came to account for several percent of the world electricity. Some new types of applications are introduced and the further effort for spreading photovoltaics is explained.

CIS-based thin-film PV technology is one of the PV technologies which is competitive against the market-dominant polycrystalline-Si PV technology on the performance. Currently Solar Frontier K.K. is the only company which had transferred their R&D results successfully to the commercialization stage and moved to the annual production capacity up to 1 GW/year by 2011. CIS-based thin-film PV technology of Solar Frontier K.K. has a device design completely different from both conventional crystalline Si PV technologies by using a Pb-free solder and CdTe thin-film PV technology by applying a Cd-free device structure. Solar Frontier K.K. has developed the “versatile” PV recycle process applicable to all types of PV modules like crystalline Si and CIS-based thin-film PV modules. The strong point of Solar Frontier K.K. is that they understand the product life cycle management covering from the selection of raw materials to make their CIS-based thin-film PV technology no impact to the environment to no industrialized-waste disposal through the developed PV recycle process applicable to the end-of-life PV modules which enables to collect possibly and mostly all of valuables from the PV modules Such concept for their production will be a “21st-century style” production.

The current research status of compound semiconductor multiple junction photovoltaic cells having the highest energy conversion efficiencies among solar cells of all kinds, is reviewed together with their application to concentrator photovoltaics. The sunlight concentration and tracking are beneficial to construct solar power generation systems with the best energy efficiencies in principle. However, the cost of optics and mechanics are still high and there is significant discrepancy between cell efficiency and system efficiency. Further research is needed to increase the overall performance as the power generation system.

In order to surpass the theoretical Shockley-Queisser limit of energy conversion efficiency of single-junction solar cells as well as to lower the cost, advanced concepts and new materials are emerging. By placing a dense array of quantum dots in the active region of a pin solar cell, which consequently leads to formation of a superlattice miniband or intermediate-band, the solar cell efficiency could reach 63% under full sunlight concentration. Recent status and future research opportunities are reviewed.

Organometal halide solar cells have gathered wide interests from the photovoltaics research fields. This newcomer established a category as “perovskite solar cells” in the solar cell classifications, such as “Solar cell efficiency tables” or NREL chart. The power conversion efficiency over 22% was achieved within a few years from its advent. In this review article, publications about perovskite solar cells were comprehensively summarized along their “submitted date”, to record the course of the progress of perovskite solar cells. At the first stage, perovskite solar cells were established as nano-structured solar cells. The efficiency up to 15% attracted the researchers in dye-sensitized solar cells and organic thin-film solar cells. After the appearance of planar hetero-junction type solar cells, the power generation mechanism of perovskite solar cells has been argued. Rapid progress of perovskite solar cell studies reached a report of 19.3% efficiency published on August, 2014. Around that time, several issues arose, such as I-V hysteresis, chloride contents. Although there were several severe comments about these issues, the developments of perovskite solar cells progressed steadily, then efficiencies over 20% were reported. At present, the highest efficiency in published papers is 21.8% of mesoscopic perovskite solar cells. Such history is summarized in this review.

The power conversion efficiencies (PCEs) of organic photovoltaics (OPVs) have continued to grow over the past several years. The most widely used active layer for OPVs, the so-called bulk heterojunction (BHJ) layer, is based on the blending of electron-accepting and electron-donating materials. BHJ structures based on polymer donors and fullerene acceptors have significantly increased the performance of OPVs, now exhibiting PCEs of 11～12% under standard illumination conditions. A simple estimation indicates that the developments of novel low-bandgap conjugated polymers for BHJ OPVs will contribute to significant improvements in the PCE up to 15% in the future. Other topics such as developments of non-fullerene accepting materials and inorganic nanoparticle accepting materials with high permittivity are also introduced for further increasing PCEs.

Recently, photovoltaic (PV) power generation has attracted much attention with the background of environmental and energy issues such as global warming and exhaustion of fossil fuels. In Japan, PV has been spread rapidly and widely with aggressive support from the feed-in tariffs. The installed capacity of PV has reached about 36 GW at the end of September in 2016. On the other hand, PV systems need to be connected to a power grid in order to securely utilize solar power because the PV output drastically fluctuates in accordance with weather conditions. This results in various problems such as degradation of power quality in a power system. Furthermore, cost reduction and maintenance requirement of PV become increasingly visible as serious issues for PV to play a role in future power system. In this review, current situation and latest trends of PV in Japan are surveyed from the viewpoint of system technologies, and their future perspectives are also mentioned.

Recent developments in an inert gas plasma MHD (closed cycle MHD) electrical power generation are described after a brief introduction of current research activities on MHD energy conversion technology and its application. As for an inert gas plasma MHD generator with seeding, a lot of fruitful knowledge has been accumulated and a road map of the development of high performance generator has been almost established. A seed free inert gas plasma MHD generator under development has a potential of breakthrough for realization of an innovative MHD electrical power generation, where a pre-ionization of inert gas at the generator inlet with a small consumption of MHD power output itself is the key.

Energy supply is very important to support sustainable economic growth in Japan. Particularly increase efficiency of electric power generation in order to reduce energy resource consumption and to reduce global warming becomes more important after the Great East Japan Earthquake in 2011 because most of nuclear power plants have been shut down. Generally, to increase efficiency of electric power generation in thermal plants, increase operating temperature is essential from the view point of thermodynamics. Therefore, we have to introduce Magnetohydrodynamic (MHD) generator which can be operated over 2000 [K] temperature regime as next to gas turbine/steam turbine combined cycle. We are proposing capacitive-coupled power extraction type MHD generator where electrodes are located outside of a generator channel to improve durability of metal electrodes. In this study, experimental demonstration was carried out with capacitive-coupled MHD generator driven with inductive-coupled plasma source with AC applied magnetic field. AC electric power was successfully extracted from this type of an MHD generator. Also effectiveness of compensation of loading factor by inserting inductor in output circuit was shown by the present experiments.

This review presents the recent progress in liquid metal magnetohydrodynamic (LMMHD) power generation. Since the liquid metal is opaque, the experimental measurements are difficult. The development of computational fluid dynamics enables to analyze the complex LMMHD flow phenomena with coupling fluid dynamics and electromagnetics. Increase in magnetic flux density augments the Lorentz force and suppresses turbulence fluctuations. However, localized high magnetic flux density leads to the side wall jets where turbulence transition takes places. In the viewpoint of the simple configuration without complex rotation parts, LMMHD power generation is examined to apply to new energy sources lately. The LMMHD power generation system utilizing ocean wave energy is introduced and the effects of shape loss, working fluid and wave period on the electrical efficiency and output power are exhibited. It is found that this system is suitable for the long period ocean wave, and high magnetic flux density curbs the deteriorations of electrical efficiency and output power.

A magnetohydrodynamic(MHD) generator, which has no hot, highly stressed moving parts, directory transforms the enthalpy of electrically conductive fluid into electric power based on the Faraday electromotive effect. The MHD generator can utilize a high temperature gas condition which quickly destroys turbine, and therefore a power plant using the MHD generator is expected to achieve a higher thermal efficiency than that of conventional gas/steam turbine power plants. In the paper, the basic concept of disk-shaped nonequilibrium MHD generator using thermally non-equilibrium noble gas plasma is described briefly, and then MHD numerical simulation to predict the performances of large-scale, disk-shaped non-equilibrium MHD generators is explained together with the description of the governing equations of magneto-plasma-dynamics based on a two-temperature model. Results of the MHD numerical simulation indicates that the non-equilibrium MHD generators employing strong magnetic field such as 10 T could achieve the performance required for the practical use.