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15 th International Photovoltaic Science & Engineering Conference (PVSEC-15) Shanghai China 2005 10-1 176 The Multi Solar Window Eng. Ami Elazari MBA Millennium Electric T.O.U. Ltd., P.O. Box 12346, Herzelia Industrial Zone 46733 Israel Phone : 972-9-9588071, Fax : 972-9-9588075, E-Mail : Info@millenniumsolar.com Abstract: The main objective of this project is the development and integration of new photovoltaic solar panels to deliver electric power, hot water and/or hot air for heating or adsorption cooling purposes. These panels will be further integrated in the building, as windows giving it a good, aesthetic impression together with the glass surfaces that form the panels. This solution will directly answer the need to improve the low performance of the photovoltaic BIPV panels. In order to achieve this objective, listed below are the scientific and technological objectives that will be the essence of this project: Development of a new generation of high efficiency, cost effective solar window panels, capable of producing with the same collector three different types of utilities: electricity, hot water and hot air, both usable also for air conditioning. Increasing the electrical efficiency of the photovoltaic cells by innovative cell cooling methods. Development of a CFD model to determine optimal design and flow pattern for cooling of the PV cells. Integration of this SOLAR WINDOW concept in a test building. Analysis and evaluation of their operating performance. Key Words: Photovoltaic, BIPV, solar window, building-integrated. 1 State of the Art and Innovation Nowadays, conventional solar systems are normally constructed for the generation of only one type of energy, either thermal solar energy or electric solar energy. This leads to a few problems and disadvantages like: z Larger installation areas needed, if there is a demand for thermal and electrical energy. z Higher acquisition costs, because of a more panels needed and longer installation times. z Reduced efficiency of photovoltaic systems due to high temperatures in the panels. The current photovoltaic generators in use need to palliate the low performance that does not go usually beyond 10% or 15%, because in these types of facilities the heat is not taken advantage of in an appropriate way, leading to a loss of approximately 34% of the incident energy. The performance of these systems diminishes quickly as the temperature of the collector increases, having important losses as soon as the temperature of the cells is between 40°C ~45°C. The solar panels available on the market have an average production of between 120 and 150 W/m2 of maximum power for the required temperatures. As far as hot water is concerned, profitability has been more than shown. With this process, a better use of solar energy is made in the most logical way without cost, as the sun does the heating. The same happens with the hot air. If these three methods are integrated (photovoltaic energy, hot water and hot air production), there will be a significant improvement, which will be followed by economical benefits for the end users of the system. Some companies have already developed solar collectors that produce within the same unit, photovoltaic energy and hot air, but so far, there is no collector available in the market able to generate the three types of energy at the same time with same collecting surface or at high electrical efficiencies. Millennium has a stand-alone system already developed, and 29 integrated solar units of this nature have been installed in houses with very good results in energy efficiency. However, so far none of these units has been integrated in building facades. The photovoltaic cells diminish their performance when the operation temperature increases. If the photovoltaic cell is refrigerated by air and/or water, it makes possible to obtain appropriate temperatures for the good functioning of the photovoltaic system. In this way it seeks to take advantage of the heat that gets lost with the object of heating water and air (together with the solar radiation), which can be used as energy contribution to the home. The installation of the SOLAR WINDOW should be done in such a way that it provides the right amount of electricity, hot water and hot air. It should be fitted with batteries for the storage of energy or feed direct to the electric grid and as it has been the practise to date for systems of photovoltaic panels. To the actual state of the art, they do not exist, therefore, the durable surface glass must: z effectively oppose the solar irradiation in the summer, demolishing the relative consequent heating of the building; z maximize the collection of solar radiation in winter, exploiting this phenomenon to naturally heat the environment consequently demolishing the energy consumption of the plant; z possession of a neutral coloration that would avoid to the occupants to perceive the colors of the external environment as unnatural and distorted, with serious reductions of the comfort visual and consequent reflex on their productivity. The SOLAR WINDOW and its integration in the building contrarily to the systems above described introduce the following advantages: z it allows to maximize the collection of solar radiation in whatever season of the year, storing therefore "free" energy for then redistributes it according to the specific requirements of the user; z the surplus of produced warm water can be used for the winter heating of the environment through ceiling panels, (ceiling radiant panels with operating temperature of around 35°C ~40°C and therefore compatible with those produced by the solar panel); this system maximizes the efficiency of the heating plant and also reduces his costs and it doesn't behavemovements of air masses so that minimizes the diffusion of dusts and fine pollutants, reducing therefore the phenomena of indoor pollution. The use of such system of heating (and cooling) makes the use of Solar Window 177 particularly useful for air conditioning of clean environments as the hospitals. z In summer times, the system can supply cold for air conditioning of buildings, either via “pumping” out hot air or by using adsorption-cooling systems, operated with hot water coming from cooling the PV cells. Fig.1 Design study for a new generation of solar window panels 2 Scientific and Technological Con- clusions Scientific and technological Conclusions: z The development of a new generation of high efficiency, cost effective solar window panels, capable of producing with the same collector three different types of utilities (see Fig.2): electricity, hot water and hot air, both usable also for air conditioning. Fig.2 Design study for SOLAR WINDOW integration in building facades z Increasing the electrical efficiency of the photovoltaic cells by innovative cell cooling methods z Development of a model to determine optimal design and flow pattern for cooling of the PV cells. z Integration of this SOLAR WINDOW concept in a test building. z Analysis and evaluation of their operating performance. z Optimisation of the preliminary design of the entire solar system based on the CFD and practical test reresults. z Development of an optimised automatic control system for the SOLAR WINDOW system with special regard to the demand of the different utilities. The measurable technological objectives that the SOLAR WINDOW system achieve, based on the experience of the already operating stand-alone systems, are shown in the following table. Tab.1 Comparative Energy Output of a A regular solar thermal water heating system DHW, and Stand-alone photovoltaic system ENERGY OUTPUT POTENTIAL Regular solar thermal water heating system DHW (kcal) Stand-alone photovoltaic system, Wp SOLAR WINDOW kcal and Wp Thermal Energy 12000 - 5000 + 8000 kcal Space + water Electricity - 450 Wp 550 Wp Total Daily Output 14 kWh hot water 1.5-2.5 kWh electricity 15 kWh space + water 4 kWh electricity 15,4 kWh hot water 4,2-7 kWh electricity 27,7 kWh space+water Therefore the proposed SOLAR WINDOW concept improves the effectiveness of renewable energy utilisation in buildings. In addition to the scientific and technological objectives, from an environmental point of view, the proposed project also aims to: z contribute to a substantial reduction of fossil fuels consumption in buildings. z contribute to the EU objectives for the reduction of global greenhouse gases, in particular CO2, as utilisation of surface near geothermal energy is emission free. z achieve a substantial reduction of the EU’s fossil energy imports and dependency. z promote sustainability by supporting an ecologically favourable technology. z Contribute to the EU goal of a 12% share of renewable energies by the year 2010 have a significant impact on the accomplishment of the requirements mentioned in the European Directive 2002/91/EC (Energy performance of buildings), which is one of the latest measures of the European Parliament to reduce energy consumption in the Member States. 3 List of References and Related Literature Refrencet: [1] Bazilian, M. D., Leenders, F., Van Der Ree, B. G. C., and Prasad, D., 2001, "Photovoltaic cogeneration in the built environment", Solar energy, Vol. 71, pp 57-69. [2] Becker, R., 1995, "Computational Model for Analysis of Dynamic Thermal Performance of a Hybrid Slab-Collector System with Passive Discharge". Solar Energy Journal, Vol. 55, No. 6, pp. 419-433, 1995. [3] Becker, R., 1995, “Hybrid Systems in Intelligent Buildings”, Proceedings of the 1st. Intelligent Buildings International Congress, Feb. 1995, Stier Group, Tel-Aviv, ISRAEL, pp. 229-240. [4] Benemann, J., Chehab, O., Schaar-Gabriel, E., 2001, "building integrated PV modules", Solar Energy Materials & Solar Cells 67 (2001) 345-354.