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1、太阳能热光伏发电系统研究与仿真外文翻译 Introduction11 Photovoltaic Energy Conversion12 solar Cells and Solar Energy Conversion13 solar Cell Applications References 11PHOTOVOLTAIC ENERGY CONVERSION Photovoltaic energy conversion is the direct production of electrical energy in the form of current and voltage from elect
2、romagnetic ie lightincluding infrared visible and ultraviolet energy The basic four steps needed for photovoltaic energy conversion are 1 a light absorption process which causes a transition in a material the absorber from ground state to an excited state the conversion of the excited state into at
3、least a free negative and free positive-charge carriers pair and 3 discriminating transport mechanism which causes the resulting free negative-charge carriers to move in one direction to a con- tact that we will call the cathode and the resulting free positive- charge carriers to move in another dir
4、ection to a contact that we will call the anode The energetic photogenerated negative-charge carriers arriving at the cathode result in electrons which travel through an external path an electric circuit While traveling this path they lose their energy doing something useful at an electrical load an
5、d finally they return to the anode of the cell At the anode every one of the returning electrons completes the fourth step of photovoltaic energy conversion which is closing the circle by 4 combining with an arriving positive-charge carrier thereby returning the absorber to the ground state In some
6、materials the excited state may be a photogenerated free electron-free hole pair In such a situation step 1 and step 2 coalesce In some materials the excited state may be an exciton In which case steps 1 and 2 are distinctA study of the various man-made photovoltaic devices that carry out these four
7、 steps is the subject of this text Our main interest is photovoltaic devices that can efficiently convert the energy in sunlight into usable electrical energy Such devices are termed solar cells or solar photovoltaic devices Photovoltaic devices can be designed to be effective for electromagnetic sp
8、ectra other than sunlight For example devices can be designed to convert radiated heat infrared light into usable electrical energy These are termed thermal photovoltaic devices There are also devices which directly convert light into chemical energy In these the photogenerated excited state is used
9、 to drive chemical reactions rather than to drive electrons through an electric circuit One example is the class of devices used for photolysis While our emphasis is on solar cells for producing electrical energy photolysis is briefly discussed later in the book 12 SOLAR CELLS AND SOLAR ENERGY CONVE
10、RSION The energy supply for a solar cell is photons coming from the sun This input is distributed in ways that depend on variables like latitude time of day and atmospheric conditions over different wavelengths the various distributions that are possible called solar spectra The product of this ligh
11、t energy input in the case of a solar cell is usable electrical energy in the form of current and voltage Some common standard energy supplies from the sun which are available at or on the earth are plot- ted against wavelength in Wnm spectra in Figure 1l A An alternative photons-snm spectrum is see
12、n in Figure 11BThe spectra in Figure 11A give the power impinging per area in a band of wavelengths 1 nm wide the bandwitdth centered on each wavelength In this figure the AM0 spectrum is based on ASTM standard E 490FIGURE 11 Solar energy spectra a Data expressed in watts per per nm bandwidth for AM
13、O from Ref 1 with permission and for AM l5G and AW15D spectra from Ref2 with permission b The AM l5G data expressed in terms of impinging photons per second per cm2 per 20 nm bandwidthand is used for satellite applications The AM15G spectrum based on ASTM standard G173 is for terrestrial application
14、s and includes direct and diffuse light It integrates to 1000 Wthe AM15D spectrumalso based on G173 is for terrestrial applications but includes direct light only It integrates to 888 W The spectrum in Figure 1l B has been obtained from the AM15G spectrum of Figure 1l A by converting power to photon
15、s per second per cm2 and by using a bandwidth of 20nm Photon spectra exemplified by that in Figure 1l B are more convenient for solar cell assessments because optimally one photon translates into one free electron-free hole pair via steps 1 and 2 of the four steps needed for photovoltaic energy conv
16、ersionStandard spectra are needed in solar cell research development and marketing because the actual spectrum impinging on a cell in operation can vary due to weather season time of day and location Having standard spectra allows the experimental solar cell performance of one device to be compared to that of other dev
