Overview of solar energy and the working principle of solar cells

Overview of solar energy and the working principle of solar cells

Overview of solar energy

Solar energy generally refers to the radiant energy of sunlight, which mainly comes from the nuclear fusion reaction inside the sun. These energies travel in all directions through space in the form of electromagnetic waves. The energy received by the earth’s atmosphere accounts for only 2.2 billion parts of the total solar radiation energy, up to 173000tw, that is, the energy radiated by the sun to the earth per second is equivalent to 5 million tons of coal, about hundreds of thousands of times the power generation in the world. China is rich in solar energy resources and has superior conditions for the development of solar energy applications. According to the annual sunshine time and the total annual radiation received by each square meter of the ground, the national solar energy resources can be divided into 5 types of regions. Among them, the first, second, and third category areas have more than 2000 hours of sunshine throughout the year, which are areas with rich or relatively abundant solar energy resources and have good solar energy resource utilization conditions. Especially Tibet, Qinghai, Gansu, Ningxia, Xinjiang, etc., are extremely rich in solar energy resources. For the fourth and fifth types of regions, although the solar energy resource conditions are relatively poor, some of them also have the value of solar energy development and utilization.

The application of solar energy has a long history, and solar power generation technology can be divided into two main categories: one type is solar photovoltaic power generation technology, which uses solar cells to directly convert light energy into electrical energy; the other is the solar thermal power generation technology, which collects solar energy through heat collection equipment to heat water to generate water vapor, and then push the turbine generator set to do work to generate electricity. The following will introduce solar photovoltaic power generation technology.

The working principle of solar cells

Solar photovoltaic power generation technology is a technology that uses the photovoltaic effect of semiconductor materials to directly convert light energy into electrical energy. The core component is the solar cell, which is mainly made of semiconductor silicon (the conductivity of the semiconductor is between the insulator and the conductor), which is essentially a large PN junction. When the semiconductor material receives light, it absorbs light energy, excites electrons and holes, which are separated from each other under the action of the electric field in the PN junction, and finally converge at both ends of the PN junction to form an electromotive force externally, that is, the photovoltaic effect. Solar cells are also referred to as photovoltaic cells.

Figure 1 shows the working principle of a solar cell. When sunlight illuminates the PN junction, the excited electrons move freely to the N-type semiconductor; the positively charged holes gather in the P-type semiconductor to generate an electromotive force (the left end is positive and the right end is negative). If an external closed loop is connected, current will flow. A photovoltaic cell module is formed by encapsulating and protecting several photovoltaic cells in series and parallel, and then combining multiple photovoltaic cell modules into a photovoltaic array with a certain power capacity as needed, and combining with energy storage, inverter, controller and other devices to form a photovoltaic power generation system.

Overview of solar energy and the working principle of solar cells
Figure 1 – The working principle of solar cells