由于单晶硅电池片和多晶硅电池片前期生产工艺的不同，使它们从外观到电性能都有一些区别。从外观上看：单晶硅电池片四个角呈圆弧状，表面没有花纹;多晶硅电池片四个角为方角，表面有类似冰花一样的花纹。

对于使用者来说，单晶硅电池和多晶硅电池是没有太大区别的。单晶硅电池和多晶硅电池的寿命和稳定性都很好。虽然单晶硅电池的平均转换效率比多晶硅电池的平均转换效率高l%左右，但是由于单晶硅太阳能电池只能做成准正方形(其4个角是圆弧)，当组成太阳能电池元件时就有一部分面积填不满，而多晶硅太阳能电池是正方形，不存在这个问题，因此对于太阳能电池元件的效率来讲几乎是一样的。另外，由于两种太阳能电池材料的制造工艺不一样，多晶硅太阳能电池制造过程中消耗的能量要比单晶硅太阳能电池少30%左右，所以多晶硅太阳能电池占全球太阳能电池总产量的份额越来越大，制造成本也将大大小于单晶硅电池，所以使用多晶硅太阳能电池将更节能、更环保。

9、逆变器的概念

逆变是针对整流而言的，整流器把交流电能变换成直流电能的过程称为整流。那么把直流电能变换成交流电能的过程就称为逆变了，把完成逆变功能的电路称为逆变电路，把实现逆变过程的装置称为逆变器。

在太阳能光伏发电系统中为什么一定要采用光伏逆变器呢?目前我国发电系统主要是直流系统，即将太阳能电池发出的电给蓄电池充电，而蓄电池直接给负载供电，如我国西北地方使用较多的太阳照明系统以及远离电网的微波站供电系统均为直流系统。此类系统结构简单，成本低廉，但由于负载直流电压的不同(如12V、24V、48V等)，很难实现系统的标准化和相容性。特别是家用电器，如日光灯、电视机、电冰箱、电风扇和大多数动力机械都是利用交流电工作的，即大多数为交流负载，所以利用直流电力供电的光伏电源，很难作为商品进入市场。太阳能光伏系统设置逆变器的目的就是将直流电转换为交流电，便于满足大多数使用者负载的需要。

此外，如果电力线受到破坏或被迫关闭，逆变器就要停止向用电设备或电网供电。如果电力线电压偏低或欠压，或出现较大的扰动时，要采用一种用于“非孤岛”逆变器的传感器来传感这种情况。当出现这种情况时，逆变器将自动地关闭向电网供电，或把电力传输到其他地方，从而防止它成为电力发电的“孤岛”。所谓孤岛效应，即电网出现故障后，并联在电网上的光伏并网发电系统依旧可以工作，处于独立运行状态。

Because of the different pre-production technology of monocrystalline silicon cell sheet and polycrystalline silicon cell sheet, there are some differences between them from appearance to electrical properties.   From the appearance: the four corners of the monocrystalline silicon cell are arc shaped, no surface pattern;   The four corners of the polycrystalline silicon cell are square, and the surface has a pattern similar to ice flowers.  

 

 

 

To the user, there is not much difference between a monocrystalline silicon cell and a polycrystalline silicon cell.  Monocrystalline silicon cells and polycrystalline silicon cells have good life and stability.  Although the average conversion efficiency of monocrystalline cells better than the average conversion efficiency of polysilicon batteries around l %, but because of monocrystalline silicon solar cell can only be made quasi square (the four Angle is arc), when the solar battery components are part of an area of fill, and polycrystalline silicon solar cell is a square, there is no this problem,  So it's almost the same for the efficiency of the solar cell components.  In addition, due to the manufacturing process of two kinds of solar cell materials, polycrystalline silicon solar cell manufacturing process consumes less energy than monocrystalline silicon solar cell is about 30%, so the polycrystalline silicon solar cells account for a growing share of the total global solar cell production, the manufacturing cost will be much smaller than that of single crystal silicon cell,  So using polysilicon solar cells will be more energy efficient and environmentally friendly.  

 

9. The concept of inverter  

 

 

 

Inverter is for rectification, the rectifier to convert AC electric energy into DC electric energy process called rectification.  So the process of DC energy into AC energy is called the inverter, the completion of the inverter function of the circuit called the inverter circuit, the realization of the inverter process device called the inverter.  

 

 

 

Why must the photovoltaic inverter be used in the solar photovoltaic power generation system?  At present, the power generation system in our country is mainly a DC system, which is to charge battery with the electricity produced by the solar cells, and supply power to the battery directly. As the solar lighting system which is widely used in the northwest of our country and the microwave station power supply system are all DC system.  This kind of system has simple structure and low cost, but it is difficult to realize the standardization and compatibility of the system due to the different DC voltages of the load (such as 12V, 24V, 48V, etc.).  Especially household appliances, such as fluorescent lamps, television sets, refrigerators, electric fans and most power machinery are the use of alternating current work, that is, most of the AC load, so the use of DC power supply of photovoltaic power, it is difficult to enter the market as a commodity.  The purpose of setting inverter in solar photovoltaic system is to convert direct current to alternating current, which is convenient to meet the needs of most users.  

 

 

 

In addition, if the power line is damaged or forced to shut down, the inverter stops supplying power to the electrical equipment or grid.  If the power line voltage is low or undervoltage, or there is a large disturbance, use a sensor for "non-island" inverter to sense this situation.   When this happens, the inverter will automatically turn off its power supply to the grid or transmit it elsewhere, preventing it from becoming an "island" of electricity generation.   The so-called island effect means that the grid-connected photovoltaic power generation system connected in parallel to the grid can still work and operate independently after the grid fails.