solar energy 太阳能第8章模块单元

1、A typical bulk silicon PV module used in outdoor remote power applications.Different module structures for different types of solar cellsTypical bulk silicon module materialsSeveral types of Si PV modules由氟塑料、涤纶复合而成的Tedlar(TPT)背膜组成。高真空加热层压工艺及配备经防腐处理铝合金边框、水密接线盒，抗紫外老化和抗风强度达2400Mpa。Cells are laminated

2、between high transmissivity, low-iron, 3mm tempered glass and sheet of tedlar-polyeaster-tedlar (TPT) material by two sheets of ethylene Vinyl acetate (EVA). This protects against moisture penetrating into the module. A versatile junction box provides flexibility of connections A heavy-duty anodized

3、 aluminium frame provides strength and convenient mounting access. For each 18 cells series strings, one bypass diode is installed.The packing density of round and square cellsI-V curve for N cells in series x M cells in parallelShading of one region of a module compared to another is a major cause

4、of mismatch is PV modules.String & block ?Cells connected in parallel. The voltage across the cellCombination is always the same and the total current from the Combination is the sum of the currents in the individual cells.Bypass diodes in paralleled modules.Impact of blocking diodes in parallel

5、 connected modulesA blocking diode is typically used to prevent the module from loading the battery at night by preventing current from flow from the battery through the PV array. With parallel connected modules, each string to be connected in parallel should have its own blocking diode. This not on

6、ly reduces the required current carrying capability of the blocking diode, but also prevents current flowing from one parallel string into a lower-current string and therefore help to minimize mismatch losses arising in parallel connected arrays.lLight reflected from the front surface of the module

7、does not contribute to the electrical power generated. Such light is considered an electrical loss mechanism which needs to be minimized. Neither does reflected light contribute to heating of the PV module. The maximum temperature rise of the module is therefore calculated as the incident power mult

8、iplied by the reflection. lFor typical PV modules with a glass top surface, the reflected light contains about 4% of the incident energy.The module temperature is determined by the equilibrium between heat generated in the PV module by the sun and the conduction, convection and radiative heat loss f

9、rom the module.A is the area of the surface conducting heat;l is the length of the material through which heat must travel;K is the thermal conductivity in units of Wm-1Where Pheat is the heat (power) generated by the PV module; is the thermal resistance of the emitting surface in W-1;T is the tempe

10、rature difference between the two materials in .The heat which is transferred by this process is given by the equation:Where A is the area of contact between the two materials;H is the convection heat transfer co-efficient in units of Wm-2-1, (experimental parameter) T is the temperature difference

11、between the two materials in .The net heat or power lost from the module due to radiation is the difference between the heat emitted from the surroundings to the module and the heat emitted from the PV module to the surroundings, or in mathematical format: Where Tsc is the temperature of the solar c

12、ell;Tamb is the temperature of the ambient surrounding the solar cell; is the emissivity of the surface is the Stafan-Boltzmann constant.The nominal operating cell temperature (NOCT) is defined as the temperature reached by open circuit cells in a module under the conditions as listed below: Irradia

13、nce on cell surface=800W/m2;Air temperature=20;Wind velocity=1m/s;Mounting=open back side.The spacing between cells tries to increase an amount given by:Where G,C , are the expansion coefficients of the glass and the cell respectively;D is the cell width;C is the cell centre to centre distance.Solar

14、 modules must have adequate strength and rigidity to allow normal handling before and during installation.If glass is used for the top surface, it must be tempered, since the central areas of the modules hotter than areas near the frame. This places tension at the edges, and can cause cracking. In a

15、n array, the modules must be able to accommodate some degree of twisting in the mounting structure, as well as to withstand wind induced vibrations and the loads imposed by high winds, snow and ice.Possible module twisting on a distorted mounting frame.Example of PV module degradation or failure. sh

16、own here is the degradation of the ARC of a solar cell caused by water vapor ingress.(1) Shading by a tree;(2) Soiling the front surface;et al.These reductions in power are all reversible provided that the original cause is rectified.A typical solar cell consists of a glass or plastic cover or other encapsulant, an antireflective layer, a front contact t