Concentration of sunlight onto photo voltaic cells is desired since the concentrating mirrors and lenses are less expensive than the photovoltaic material. Consider the solar photovoltaic cell of Problem 7.18. A 100 mm x 100 mm photovoltaic cell is irradiated with concentrated solar energy. Since the concentrating lens is glass, it absorbs 10% of the irradiation instead of the top surface of the solar cell, as in Problem 7.18. The remaining irradiation is reflected from the system (7%) or is absorbed in the silicon semiconductor material of the photovoltaic cell (83%). The photo voltaic cell is cooled by air directed parallel to its top and bottom surfaces. The air temperature and velocity are 25°C and 5 m/s, respectively, and the bottom surface is coated with a high-emissivity paint, εb = 0,95,

(a) Determine the electric power produced by the photovoltaic cell and the silicon temperature for a square concentrating lens with Llens = 400 mm, which focuses the irradiation falling on the lens to the smaller area of the photovoltaic cell. Assume the concentrating lens temperature is 25°C and does not interfere with boundary layer development over the photovoltaic cell's top surface. The top and bottom boundary layers are both tripped to turbulent conditions at the leading edge of the photovoltaic material.

(b) Determine the electric power output of the photovoltaic cell and the silicon temperature over the range 100 mm

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Solar irradiation, G - Lens Air Focusing 4= 5 m/s T- 25°C lens Tr = 25°C Concentrated irradiation, G. Photovoltaic cell L= 100 mm E See Problem 7.18 Tur = 25°C