The photo-voltaic effect can be described easily for a p-n junction in a semi-conductor material. In a piece of a pure intrinsic semi-conductor such as silicon there are no free electron at absolute zero,since each valance electron of material atom is tied in chemical bond.If this piece of the silicon is doped with phosphorus or arsenic, there will be the ex-cess of electrons leading to a n-type semicon-ductor. Similarly if another piece of the sili-con is doped with boron , there will be a deficiency of electrons leading to a p- type semiconductor. If these two pieces of silicon are connected , a p-n junction is obtained . In tendency will be for the free electron of n-side to flow to the p-side, and the holes of the p-side will tends to flow to the n-region to compensate for their respective deficiencies. Thus a built-in potential barrier is formed.
When light strike on the p-n junction photo-ns with energy above that required to break the covalent bonds will create an electron hole pair. The hole is formed in the valance band,or an electron is added to the conduct-ion band. For a photon in a visible range the diffusion length i.e. average distance which the carrier diffuse before they recombine, has the magnitude of a micron. Those charge carriers that are within a diffusion length of the potential barrier will be trapp-ed by the barriers and caused to flow across it in an attempt to reduce their energy. Therefore a potential energy between the layer is formed and it is used to force the electrons through an external circuit.
The solar photo-voltaic cells convert incident solar light energy directly to direct current electrical energy. Power delivered depends on intensity of sun light and the load resista-nce. several solar cells can be connected in series on parallel to get desired the voltage, current and power. Solar cells connected in parallel form a module, and the modules are connected in series,parallel ,series-parallel configuration to form a solar PV panel. Solar PV panels are installed outdoors so as to the receive maximum sun light during tha day and thoughtout the year. Solar PV panels are usually fixed type as they à simple ,cheap and maintenance free.
Since solar PV panels deliver DC electrical power only during favourable conditions of sun light, energy storage batteries as used to supply power during nights and the cloudy weather. For feeding loads t 50 Hz AC supply , DC power supplied by the solar PV panel is converted by means of static inverters to the single phase or three phase. Power conditio-ning unit provided for improving AC wave-form, regulating the voltage, inverting DC to AC and protective control, and monitoring functions.
Kya baat h
ReplyDelete