1. Principles of Solar Photovoltaic Power Generation

光生伏打效应在液体和固体物质中都会发生，但是只有固体（尤其是半导体PN结器件）在太阳光照射下的光电转换效率较高。利用光生伏打效应原理制成晶体硅太阳能电池，可将太阳的光能直接转换成为电能。太阳能光伏发电的能量转换器是太阳能电池，又称光伏电池，是太阳能光伏发电系统的基础和核心器件。太阳能转换成为电能的过程主要包括3个步骤：

Photovoltaic effect can occur in both liquid and solid materials, but only solid (especially semiconductor PN junction devices) have higher Solar-cell efficiency under sunlight. The crystalline silicon solar cell is made by using the principle of Photovoltaic effect, which can directly convert the solar energy into electric energy. The energy converter of solar photovoltaic power generation is solar cells, also known as photovoltaic cells, which are the foundation and core components of solar photovoltaic power generation systems. The process of converting solar energy into electrical energy mainly includes three steps:

(1)太阳能电池吸收一定能量的光子后，半导体内产生电子一空穴对，称为“光生载流子”，两者的电极性相反，电子带负电，空穴带正电。

(1) After solar cells absorb photons of a certain amount of energy, electron hole pairs are generated in semiconductors, known as "photo generated charge carriers". The polarity of the two is opposite, with electrons negatively charged and holes positively charged.

(2)电极性相反的光生载流子被半导体PN结所产生的静电场分离开。

(2) Photogenerated charge carriers with opposite polarity are separated by the electrostatic field generated by the semiconductor PN junction.

(3)光生载流电子和空穴分别被太阳能电池的正、负极收集，并在外电路中产生电流，从而获得电能。

(3) Photogenerated current carrying electrons and holes are collected by the positive and negative electrodes of the solar cell, respectively, and generate current in the external circuit to obtain electrical energy.

太阳能光伏发电原理如下图所示。当光线照射太阳能电池表面时，一部分光子被硅材料吸收，光子的能量传递给硅原子，使电子发生跃迁，成为自由电子，在PN结两侧集聚形成电位差。当外部电路接通时，在该电压的作用下，将会有电流流过外部电路产生一定的输出功率。这个过程的实质是光子能量转换成电能的过程。

The principle of solar photovoltaic power generation is shown in the following figure. When light shines on the surface of a solar cell, a portion of photons are absorbed by the silicon material, and the energy of the photons is transferred to the silicon atoms, causing electrons to undergo transitions and become free electrons, which gather on both sides of the PN junction to form a potential difference. When the external circuit is connected, under the action of this voltage, a current will flow through the external circuit to generate a certain output power. The essence of this process is the process of converting photon energy into electrical energy.

在太阳能发电系统中，系统的总效率η由太阳能电池组件的光电转换效率、控制器效率、蓄电池效率、逆变器效率及负载的效率等决定。目前，太阳能电池的光电转换效率只有17%左右。因此，提高太阳能电池组件的光电转换效率、降低太阳能光伏发电系统的单位功率造价，是太阳能光伏发电产业化的重点和难点。自太阳能电池问世以来，晶体硅作为主要材料保持着统治地位。目前对硅太阳能电池转换效率的研究，主要围绕着加大吸能面（如采用双面电池减小反射）、运用吸杂技术和钝化工艺提高硅太阳能电池的转换效率、电池超薄型化等方面。

In a solar power generation system, the overall efficiency of the system η It is determined by the Solar-cell efficiency of solar cell module, controller efficiency, battery efficiency, inverter efficiency and load efficiency. At present, the Solar-cell efficiency of solar cells is only about 17%. Therefore, improving the Solar-cell efficiency of solar cell modules and reducing the unit power cost of solar photovoltaic power generation system are the key and difficult points of the industrialization of solar photovoltaic power generation. Since the advent of solar cells, crystalline silicon has maintained a dominant position as the main material. At present, research on the conversion efficiency of silicon solar cells mainly focuses on increasing the energy absorbing surface (such as using double-sided cells to reduce reflection), using impurity absorption technology and passivation process to improve the conversion efficiency of silicon solar cells, and making the cells ultra-thin.

目前，太阳能光伏发电系统主要应用于以下3个大的方面。

Currently, solar photovoltaic power generation systems are mainly applied in the following three major areas.

(1)为无电场合提供电源，主要为广大无电地区居民生活生产提供电力，为微波中继站和移动电话基站提供电源等。

(1) To provide power for electric field free integration, mainly for the daily life and production of residents in areas without electricity, as well as for microwave relay stations and mobile phone base stations.

(2)太阳能日用电子产品，如各类太阳能充电器、太阳能路灯和太阳能草坪灯等。

(2) Solar daily electronic products, such as various solar chargers, solar street lights, and solar lawn lights.

(3)并网发电，即接入电网。我国光伏并网发电已经很成熟了，从2013年开始，出台了一系列的光伏发电促进政策，鼓励有条件的地区工商业和户用、公共建筑等建设光伏发电设施。

(3) Grid connected power generation, i.e. connected to the national power grid. China's photovoltaic grid connected power generation has become very mature. Since 2013, the country has introduced a series of policies to promote photovoltaic power generation, encouraging the construction of photovoltaic power generation facilities for businesses, households, public buildings, and other areas where conditions permit.

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