**1. Introduction**

186 Solar Cells – Thin-Film Technologies

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Sept. 2008.

Energy-related concerns about traditional resources include the depletion of fossil fuel, a dramatic increase in oil prices, the global warming effect caused by pollutant emissions from conventional energy resources, and the increase in the energy demand. These concerns have resulted in the recent remarkable growth of renewable energy industries [1-3]. Furthermore, renewable energy has become a significantly important research area for many researchers as well as for governments of many countries as they attempt to ensure the safety, long-term capability, and sustainability of the use of global alternative energy resources [2]. Renewable energy resources include solar, geothermal, wind, biomass, ocean, and hydroelectric energy. [4] In particular, both solar (i.e. photovoltaics) and wind energy are considered to be leading technologies with respect to electrical power generation.

The study of photovoltaics (PV) has been carried out since the 1980s' and is currently the most significant renewable energy resources available. According to the Renewable Energy Policy Network for the 21st Century (REN21), there has been a strong growth in the use of PV of 55 % and the worldwide solar PV electric capacity is expected to increase from 1,000 MW in 2000 to 140,000 MW by 2030 [5]. Moreover, it is forecast by the European Renewable Energy Council that this renewable electric energy could become sufficient to cover the base load and half of the global electricity energy demand by 2040 [6]. Generally in the PV industry, crystalline silicon has generally occupied about 95 % of the market share of materials, while only 5 % of all solar cells use amorphous silicon [7]. However, in order to improve the cost efficiency of solar cells by using less material, the thin-film PV module with amorphous silicon has become an active research and development (R&D) area [8]. In particular, solar cells that use amorphous silicon have the advantage of being able to generate a higher energy output under high temperatures than crystalline silicon solar cells, which are less affected by the temperature increase with respect to performance of electricity output than are the crystalline silicon solar cells. Moreover, installed at the rooftop and on the exterior wall of the building, a thin-film solar cell can be conveniently used as a façade that generates power for the entire building. This system is known as a building integrated photovoltaic system (BIPV). The thin-film solar cell can also provide the advantage of heat insulation and shading when incorporated into a harmonious building design. Therefore, the thin-film solar cell is expected to be a very bright prospect as a new engine for economical growth in the near future. Currently in Korea, many researchers are conducting

Power Output Characteristics of Transparent a-Si BiPV Window Module 189

Fig. 1. Transmittance of PV module depending on the wavelength

Fig. 2. Preparation for single plate of double-glazed PV module using transparent

From the performance evaluation of the heat insulation, the prepared PV module exhibited a 2.64 W/m2-℃ thermal transmittance, as shown in Figure 3. However, it showed an 18 % solar heat gain coefficient (SHGC), which was much lower than that measured for the common double glazed window. WINDOW 6.0 and THERM5.0 (LBNL, USA) were used to analyze the heat insulation of the standard type of double glazed PV module widely used

amorphous silicon (A-Si) thin-film cell.

vigorous research on PV with respect to the application of crystalline silicon solar cells. An example of such research includes the evaluation of the power output of PV modules with respect to the ventilation of the rear side of the module. However, research on the transparent thin-film solar cell as a building façade application including windows and doors is only in its early stages.

Therefore, the objective of this study is to establish building application data for the replacement of conventional building materials with thin-film solar cells. In this study, an evaluation is carried out on the performance of the thin-film solar cell through long-term monitoring of the power output according to the inclined slope (the incidence angle). This is conducted by using a full-scale mock-up model of the thin-film solar cell applied to a double glazed system. In addition, the aim of the application data of the thin-film solar cell is to analyze the effect of both the inclined slope and the azimuth angle on the power output performance by comparing this data with the simulation data for PV modules[9].
