Photovoltaic materials convert sunlight directly

Chapter 12, Problem 12.31

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Photovoltaic materials convert sunlight directly toelectric power. Some of the photons that are incidentupon the material displace electrons that are in turncollected to create an electric current. The overall effi-ciency of a photovoltaic panel, , is the ratio of elec-trical energy produced to the energy content of theincident radiation. The efficiency depends primarilyon two properties of the photovoltaic material, (i) theband gap, which identifies the energy states of photonshaving the potential to be converted to electric current,and (ii) the interband gap conversion efficiency, bg,which is the fraction of the total energy of photons within the band gap that is converted to electricity.Therefore, ?bgFbgwhere Fbgis the fraction of thephoton energy incident on the surface within the bandgap. Photons that are either outside the materialsband gap or within the band gap but not converted toelectrical energy are either reflected from the panel orabsorbed and converted to thermal energy.Consider a photovoltaic material with a band gapof 1.1B1.8 eV, where Bis the energy state of aphoton. The wavelength is related to the energy stateof a photon by the relationship ??1240 eV?nm/B.The incident solar irradiation approximates that of ablackbody at 5800 K and GS?1000 W/m2.(a) Determine the wavelength range of solar irradia-tion corresponding to the band gap.(b) Determine the overall efficiency of the photo- voltaic material if the interband gap efficiency isbg?0.50.(c) If half of the incident photons that are not con-verted to electricity are absorbed and converted tothermal energy, determine the heat absorption perunit surface area of the panel.