Based on the author's subjectivism that the future energy situation will follow the path near so called ‘hard energy path’, the role of energy technologies for the energy problems is stressed and the natural energy resources are positioned as complementary of fossil and atomic energy. The kinds and amounts of the natural energy resources are reviewed. It is considered to be necessary to generalize the scheme of energy engineering for the assesment of various kinds of energy resources and technologies. Applied physicists are hoped to be more active to do everything. The component technologies such as energy conversion devices of low exergy density, energy storage devices and high efficiency heat exchangers will be key technologies not only for new energies but also for energy-saving.
A review of the present status of researches for the developement of solar battery is presented. Key problems for the improvement of efficiency and cost reduction are discussed. Features of the sunlight spectrum, the quantum-mechanical energy conversion, properties of the output voltage and current, selection and the combination of the junction materials, as well as the system design, are treated.
Photovoltaic systems are well known to be capable of providing electricity from solar energy to a wide variety of applications. However, there are still now lots of problems which have to be solved to be competitive with utilities. The most important among them is how to reduce their costs. This paper gives information about the significant cost reduction methods for single crystal silicon solar cells. It describes the recent topics on the developments and fabrication techniques of low cost silicon sheets as well as of the developments of new processes for economical pn junction formations, electrical interconnections of solar cells and their encapsu-lations.
This paper reviews the performance and problems of silicon solar cells using polycrystalline ingot and sheet crystals. To improve the cell performance, two kinds of studies are performed on the grain-boundary hydrogenation and impurity gettering of crystalline grains.
Present status of the science and technology in the amorphous silicon solar cell has been reviewed. A number of various efforts to improve the cell performances and some current topics in the field are introduced from the viewpoints of both device physics and the fabrication technology. Progress in the amorphous silicon solar cell efficiencies and their technical data are also summerized and discussed.
Compound semiconductor solar cells have near optimum band gap for solar spectrum, and efficiencies in exess of 20% are expected. (GaAI)As/GaAs heterojunction solar cells have an efficiency over 20%. Recent progress of GaAs solar cells is reviewed with emphasis on the development as a concentrator solar cell and the single crystalline thin film technology. Furthermore, the spectral splitting type and the monolithic cascade type solar cells are also reviewed.
Improvement in energy conversion efficiency of solar cells is strongly related with inno-vation of junction structures. In this paper, advances in physics in junction structures of solar cells are reviewed. Photovoltaic characteristics in pn junctions, heterojunctions, Schottky and MIS structures are described. Problems in new junction structures such as MIS structures are elucidated. Physics in junction structures of polycrystalline and amorphous materials are discussed. Importance of junction structures in development of high efficient solar cells is emphasized.
A review of the problems related to composition of solar cell module is presented in the case of silicon cells for practical terrestrial use. Importance of series resistance and a method of making ohmic contact to the surface are outlined. Design consideration of arrays, module structures and materials used to module are reviewed.
This review presents a survey of solar furnaces and their applications. After a brief historical overview, the optics of paraboloidal concentrator, concentration ratio and attainable temperature are theoretically treated. The design and construction of large solar furnaces in the world are introduced in some detail. The application to the high-temperature physics is exemplified by the investigations carried out in the Tohoku University. The applications to the energy conversion and high-temperature industry, expected in future, are described also.
The present status of R & D on solar thermal electric power pilot plants in the world is summarized and especially the 1 MW pilot plants at Nio, Kagawa prefecture are reported in detail. Economy, energy analysis and site selection for solar thermal electric power system in Japan are discussed. The capital cost, especially of collector is high at the moment. In future, the cost will be reduced from one by five to one by eight. The results of energy analysis indicated that the energy inputs for solar thermal electric power system is recovered from 15 to 24 years.
This paper reviews solar selective films, that is, solar selective absorbers and solar selective transparent filters which are necessary for the utilization of solar thermal energy. The optical characteristics required for the solar selective films is described and the notion of the efficiency in the solar selective films is introduced. Many solar selective absorbers and transparent filters which have been proposed and fabricated up to the present are classified according to the mechanisms by which these films work and some examples are shown. The evaluation of the efficiency and the durability of the fabricated solar selective films is described.
Elaborate mechanisms in the early stage of photosynthesis are reviewed in view of utilizing solar photon irradiation for production of organic matter as energy source, The mechanisms reviewed are 1) photosynthetic pigments for capturing a wide range of solar irradiation, and energy transfer of absorbed light energy to the reaction center chlorophyll, 2) charge separation in the reaction center chlorophyll by the transferred energy, 3) electron transport in the thylakoid membrane for further separation of electrons and positive holes for stabilization, and addition of the energies from two photochemical reactions (systems 1 and 2) for reduction of NADP and for oxidation of water, 4) multi-photon reactions (four steps) for oxidation of two molecules of water to evolve one molecule of oxygen, 5) photophosphory-lation for production of ATP by means of the chemical and electrochemical potentials produced by light energy across the thylakoid membrane, and 6) the Calvin-Benson cycle for reduction of CO2 to carbohydrates by NADPH and ATP thus formed. The efficiency in photosynthesis is discussed based on these mechanisms.
Recent advances in studies of photochemical conversion of sunlight are described. The principles of chemical conversion are introduced and four main subjects (photoelectrochemical cells, heterogeneous photocatalytic reactions, electrochemical simulation of photosynthesis, and water splitting reactions with ruthenium complexes) are discussed,
The characteristics on ocean thermal energy and salinity gradient are presented from the points of the formation of each energy source, the potential amounts of the resources, the energy density and the energy quality. The principles of energy conversion from ocean thermal difference and salinity gradient are described. As for Ocean Thermal Energy Conversion (OTEC) the concepts are 1) closed Rankine cycle, 2) open Rankine cycle, 3) thermoelectric conversion and 4) Nitinol Engine. The concepts of the energy conversion from salinity gradient are 1) retarded osmosis power generation, 2) dialytic battery system, 3) mechanochemical energy production and 4) vapor pressure difference conversion. R & D status and the key problem of the energy technologies are briefly introduced. It is concluded that ocean energy sources are being considered as possible contributors to the future energy system and their systems should co-exist with other ocean utilization systems.
A distribution of wave power around Japan is estimated due to visual data of wave height for recent ten years in order to make it clear that wave energy is one of the important alternative clean energy for Japan. The linearized theory of wave power extraction of floating bodies is reviewed. It Includes fluid dynamic forces acting on floating bodies, motions, energy extraction and control of load damping. Lastly the present state of their development and probrems which should be solved for practical use are described.
The utilization of wind power as an energy resource has a very long history. Under the circumstance of energy crisis, the wind is being re-evaluated as an important alternative source of energy on a world-wide scale. First, in this paper, the author estimates the potential of wind power in Japan and then confirmes this value is very large one. Then, presents a current status of the research and development of the wind energy in the world. Finally, he describes the contribution of the applied physics to the field of wind utilization. Especially, discusses the importance of energy density, conditions of the techniques of wind energy conversion, wind energy utilization and “soft energy paths”, and the environ-mental impact of wind energy utilization.
In this paper, the recent developments of the CDE (Concentration Difference Energy) system and engine are reported. This system offers a kind of general methods of energy conversion, storage and utilization of thermal and mechanical energy of alternative resources as solar, oceanic heat and wind power using cyclic change of concentration of solvent in any solutions, which is one of a thereto chemical energy conversion phenomena. The aqueous solution of mixture of CaCl2 and LiCl is selected here as the most suitable solution, and nickel cupper alloy is selected to be the best anti-corrosive material against the above solution. A manned try-wheel CDE car is driven for more than 15 minutes, and 1kw CDE engine is experimented successfully. Many proposals of future application of this CDE system including power recovery from industrial waste heat and power generation from salinity gradient energy resouces are also proposed.