Preparation of solar grade silicon from optical fibers wastes with thermal plasmas

In this paper, we investigated a new way to recycle silica optical fiber wastes for feedstock supply of solar grade silicon (SOG-Si) on the basis of harmless treatment of hazardous wastes, which will provide an alternative route for silicon production processes compared to the conventional silicon supply for photovoltaic industry. Silicon was prepared in hydrogen–argon thermal plasma systems designed by authors and analyzed via X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, laser Raman spectroscopy and chemical analysis. Only the elements of silicon and oxygen in the production were detected, which suggests that this method is a promising way to prepare high-purity silicon at low cost for feedstock supply of SOG-Si although the content of metallic silicon was above 17 wt% at present.     

NEDO's solar energy program

The New Energy and Industrial Technology Development Organization (NEDO) is the main agency implementing research and development on solar energy technology in Japan. NEDO has also some projects and programs for international cooperation and domestic dissemination. These activities are reviewed in this report.     

New sunshine project and new trend of PV R&D program in Japan

The development and application of new energy resources seems to promise significant effects in tackling the problems of reassembling Japan's feeble energy supply structure and of the damages done to global environment by acid rain, carbon dioxide and its offspring known as greenhouse effect. Now, the development of new energy is promoted under the ‘New Sunshine Program” started in 1993, following “Sunshine Project” started in 1974. As a result of technical development and legislative supports, the introduction and dissemination of photovoltaic (PV) power generation has been promoted recently. To promote new energy introduction in Japan including PV power generation, a “Basic Guidelines for New Energy Introduction” was decided upon in a December 1994 Cabinet meeting. In the “Guidelines” a policy was formulated whereby the introductory targets for PV power generation were set at 400MW in 2000 and 4,600MW in 2010. The state, local public bodies, and the private sector are cooperatively to promote accelerated introduction.Since its founding in October 1980, NEDO (New Energy and Industrial Technology Development Organization) has, as the central organization in Japan for development of new energy including PV power generation, strived to meet this obligation, with assistance from various spheres. The thesis is outline of the “New Sunshine Program” and Japan's contribution in the technological development and dissemination of PV power generation being made on the initiative of NEDO.     

Measurements, analyses and evaluation of residential PV systems by Japanese monitoring program

This paper is about measurements, analyses and evaluation of residential PV systems in the Japanese Monitoring Program, on which JQA was subsidized by NEDO (New Energy Development and Industrial Technology Organization) that is currently proceeding [NSS R&D] from FY1997 to FY 2000.The aim of this investigation refers, through the data evaluation and analyses, to obtain knowledge required for optimizing design of PV systems, such as system performance, characteristics and regional dependency under practical operation and to develop the system evaluation technology on the design parameter method.     

a-Si/mc-Si hybrid solar cell using silicon sheet substrate

A hybrid junction solar cell with amorphous silicon (a-Si) and multicrystalline silicon (mc-Si) was fabricated using a mc-Si sheet substrate, which is produced directly from molten silicon using a novel rotational solidification method. The efficiency of 11.6% was obtained for the hybrid junction cell, while 10.2% for the single junction cell made of a mc-Si sheet substrate, which confirmed that the hybrid structure is effective to improve the solar cell property made of a mc-Si substrate. With introducing light trapping structure, the efficiency was improved to be 12.0%. Moreover, the possibility of Jsc improvement was investigated using the advanced light trapping structure. Jsc of 15.6 mA/cm² was obtained and it was confirmed that the hybrid junction is a promising structure.     

Measurement of stress on blade of NEDO's 500 kW prototype wind turbine

Among the components used in a wind turbine the blade is the most damageable component for fatigue caused by atmospheric turbulence. Therefor it is necessary to understand the stresses which are occurring on the operating wind turbine blade. We installed a prototype 500 kW wind turbine developed by the NEDO (New Energy and industrial technology Development Organization) in Tappi Wind Park where is very complex terrain, to study its performance, reliability and durability. Some measurements and data analysis of the blade stress have been done. In this paper, some results of the stress measurement are presented.     

Hot dry rock geothermal energy in Japan: Developments by Miti and Nedo

For the last ten years, MITI and NEDO have been supporting field work in Japan aimed at developing techniques of HDR reservoir creation. Early work was performed at 300 m depth at Yakedake and, more recently, two existing 1800 m boreholes have been acquired at Hijiori; the bottom hole temperature on this site exceeds 250°C. Plans are in hand for hydraulic fracturing aimed at reservoir creation.     

PVTEC photovoltaic activity and its integrations to buildings

For dissemination and promotion of photovoltaic power generation systems, it is important to reduce power generation cost because the cost is very expensive compared with conventional power generation methods. The cost of building materials integrated PV modules can be at least partially offsetted by replacing building materials with PV modules, so PV modules integrated with building are extremely effective for cost reduction. In addition, the reduction of installing cost can be expected. PVTEC has started the research and development of new type PV modules integrated with building materials under contract with the New Energy and Industrial Technology Development Organization (NEDO) as a four-year project from fiscal 1993.     

Crystalline Si solar cells based on solar grade silicon materials

A new method named Chemical Physics (CP) method was developed to produce solar grade silicon feedstock at a company in China. In this paper the characteristic of the solar grade silicon made by CP method was analysed. The results show that the purity of solar grade silicon is above 5 N and most of impurities are below 0.0001 wt.%. Crystalline silicon solar cells were prepared using solar grade silicon wafers based on CP method. Average efficiency of the solar cells is about 15.05%, and the highest efficiency is 15.60% under AM1.5 illumination conditions. The light-induced degradation of the solar cells was examined. Degradation by up to 15% of the initial efficiency of the solar cells is detected. The solar cell results and light-induced characteristic show that the solar cells based on CP methods have desired performance and thus have the potential for large scale production.     

Safety design of compressed hydrogen trailers with composite cylinders

Compressed hydrogen is delivered by trailers in steel cylinders at 19.6 MPa in Japan. Kawasaki Heavy Industries, Ltd. developed two compressed hydrogen trailers with composite cylinders in collaboration with JX Nippon Oil in a project of the New Energy and Industrial Technology Development Organization (NEDO).The first trailer, which was the first hydrogen trailer with composite cylinder in Japan, has 35 MPa cylinders and the second trailer has 45 MPa cylinders. These trailers have been operated transporting hydrogen and feedstock to hydrogen refueling stations without the accident. This paper describes the safety design, including compliance with regulations, the influence of vibrations, and safety verification in case of a collision.     

Development of hot dry rock technology at the Hijiori test site

Since 1985, the New Energy and Industrial Technology Development Organization (NEDO) has conducted a Hot Dry Rock project at the Hijiori test site, Yamagata prefecture. The objective of this project is to develop and test technologies such as borehole logging, hydraulic fracturing, fracture mapping and reservoir evaluation, which are essential for the development of a Hot Dry Rock power generation system. In 1991, heat was successfully extracted from a shallow reservoir at a depth of 1800 m for three months using one injection well (SKG-2) and three production wells (HDR-1, HDR-2 and HDR-3). About 80% of the injected water was recovered from these production wells. The thermal output of hot water and steam reached about 8 MW. Since 1992, a deep reservoir at a depth of 2200 m has been developed. In 1995 and 1996, heat extraction tests were conducted using one injection well (HDR-1) and two production wells (HDR-2 and HDR-3). A long-term circulation test, lasting about two years, is planned to evaluate the reservoir, starting in 2000.     

Practical values of various parameters for PV system design

In order to reasonably design a PV system, it is important to use appropriate parameter values. Few papers, however, describe design parameters that are defined systematically. The authors have been entrusted by the New Energy and Industrial Technology Development Organization (NEDO) with research and development of PV system evaluation since 1990 in order to establish optimum design and operation methods of various kinds of PV systems which are expected to be put into commercial use in the future.In this research, which is based on the data obtained from test facilities which were constructed at Hamamatsu site, various design parameters were calculated and reported as primary values provisionally estimated. This paper presents practical values of various parameters for PV system design as a table, revised with design parameter values studied later on. In particular, cell temperature factor was studied in view of regional differences and module mounting.The authors will confirm reasonable design of PV system by using such various design parameter values.     

An evaluation on the life cycle of photovoltaic energy system considering production energy of off-grade silicon

In this study, single-crystalline silicon (c-Si) photovoltaic (PV) cells and residential PV systems using off-grade silicon supplied from semiconductor industries were evaluated from a life cycle point of view. Energy payback time (EPT) of the residential PV system with the c-Si PV cells made of the off-grade silicon was estimated at 15.5 years and indirect CO₂ emission per unit electrical output was calculated at 91 g-C/kWh even in the worst case. These figures were more than those of the polycrystalline-Si and the amorphous-Si PV cells to be used in the near future, but the EPT was shorter than its lifetime and the indirect CO₂ emissions were less than the recent average CO₂ emissions per kWh from the utilities in Japan. The recycling of the c-Si PV cells should be discussed for the reason of the effective use of energy and silicon material.     

Development and performance test of smart power conditioner for value-added PV application

It is a disadvantage that PV power generation is only useful for clear daytime. However, a new 24 hours of application in an extended area can be added by active utilization of potential ability of PV power conditioner. For this purpose, a new multi-functional power conditioner was developed, which has a smoothing function to reduce PV output variation and load fluctuation, and also has additional function to compensate harmonics current and reactive power caused by customer's load.As a result of indoor testing, a reduction rate of around for harmonics current and reactive power were achieved. In addition, the reduction rate around for smoothing of PV output variation and load fluctuation were verified.The work was promoted by NEDO as part of the New Sunshine Project in Japan.     

Electrical/electronic effects of titanium and iron impurities in EFG and FZ solar cell silicon: SPV/EBIC analysis

In this paper results on surface photovoltage (SPV) and electron beam induced conductivity (EBIC) studies of edge-defined film-fed growth (EFG) and floating zone (FZ) silicon solar cell materials (both p-type) are presented. A systematic comparison based on minority carrier diffusion length and carrier recombination is made between: (i) samples contaminated with Ti and/or Fe, (ii) samples gettered by phosphorous diffusion, and (iii) as-received samples. Deep level transient spectroscopy (DLTS) measurements, together with the iron-boron (FeB) pairing kinetics [1] have successfully been used to detect the presence of Fe in the samples. Even though this process is effective in revealing Fe impurities in p-type FZ silicon it is evidently not suitable for Fe identification in p-type EFG silicon. Ti, like Fe, is found to be a prominent lifetime-limiting metallic impurity in both EFG and FZ silicon. Phosphorous diffusion is proven to be an effective external gettering technique for fast-diffusing impurities such as Fe, but not for Ti.     

Molecular dynamics simulation of amorphous silicon with Tersoff potential

We have performed molecular dynamics simulation of amorphous silicon (a-Si) by rapid quenching, with empirical interatomic potential (Tersoff potential) as a first step toward hydrogenated amorphous silicon film growth simulations. The numerical results on structural properties showed fairly good agreement with experimental data or numerical results from ab-initio molecular dynamics in other groups. In our a-Si sample, the average coordination is 4.2 and approximately 18% of the atoms have a coordination number of 5. In addition, visualization of the a-Si sample by computer graphics made it possible to see that there are some microcavities in the sample, which was predicted in experimental data.     

Oxygen in Czochralski silicon used for solar cells

Compared to the Czochralski (CZ) silicon used in microelectronic industry (M-CZ Si), the annealing behavior of oxygen in the CZ silicon used for solar cells (S-CZ Si) was investigated by means of FTIR and SEM. It was found that the oxygen concentration in S-CZ Si crystal was lower than in the M-CZ Si crystal. During single-step annealing in the temperature range of 800–1100°C, the oxygen in S-CZ Si was hard to precipitate, even if the material contained higher carbon concentrations. After pre-annealing at 750°C, many more oxygen precipitates were formed. The amount and density of the oxygen precipitates were almost the same as in M-CZ Si annealed in single step. It is considered that oxygen has no significant influence on the efficiency of solar cells made from Cz silicon if it is annealed only by a single step in the range of 800–1100°C.     

颗粒硅带多晶硅薄膜太阳电池的研制

以工业硅粉为原料制备出颗粒硅带（SSP），对颗粒硅带表面形态进行了分析。以SSP为衬底，采用快速热化学气相沉积（RTCVD）法生长多晶硅薄膜，并以此制作出效率为2．93％的颗粒硅带多晶硅薄膜太阳电池，这在国内属首先。并报道了对以SSP为衬底的多晶硅薄膜太阳电池的初步研究结果，同时讨论了该类电源的结构、工艺特点和改进措施。     

Chemical treatment of crystalline silicon solar cells as a method of recovering pure silicon from photovoltaic modules

Photovoltaic technology is used worldwide to provide reliable and cost-effective electricity for industrial, commercial, residential and community applications. The average lifetime of PV modules can be expected to be more than 25 years. The disposal of PV systems will become a problem in view of the continually increasing production of PV modules. These can be recycled for about the same cost as their disposal.Photovoltaic modules in crystalline silicon solar cells are made from the following elements, in order of mass: glass, aluminium frame, EVA copolymer transparent hermetising layer, photovoltaic cells, installation box, Tedlar^® protective foil and assembly bolts. From an economic point of view, taking into account the price and supply level, pure silicon, which can be recycled from PV cells, is the most valuable construction material used.Recovering pure silicon from damaged or end-of-life PV modules can lead to economic and environmental benefits. Because of the high quality requirement for the recovered silicon, chemical processing is the most important stage of the recycling process. The chemical treatment conditions need to be precisely adjusted in order to achieve the required purity level of the recovered silicon. For PV systems based on crystalline silicon, a series of etching processes was carried out as follows: etching of electric connectors, anti-reflective coating and n-p junction. The chemistry of etching solutions was individually adjusted for the different silicon cell types. Efforts were made to formulate a universal composition for the etching solution. The principal task at this point was to optimise the etching temperature, time and alkali concentration in such a way that only as much silicon was removed as necessary.     

New processes for the production of solar-grade polycrystalline silicon: A review

The global energy consumption is predicted to grow dramatically every year. Higher energy prices and public awareness for the global warming problem have opened up the market for solar cells. The generation of electricity with solar cells is considered to be one of the key technologies of the new century. The impressive growth is mainly based on solar cells made from polycrystalline silicon. This paper reviews the recent advances in chemical and metallurgical routes for photovoltaic (PV) silicon production.