The energy of the sun comes from nuclear fusion inside the sun. According to a rough estimate, the total energy flow of the sun radiating to the universe in all directions is 4×10^26 J/s. Among them, the light and heat delivered to the earth is 25 billion calories per minute (2.5×10^18 cal/min), which is roughly equivalent to the energy generated by burning 400 million tons when converted into coal energy. In a single year (calculated according to 365 days), the energy radiated by the sun to the earth's surface is equivalent to tens of thousands of times of the energy provided by the existing human energy sources in the same year [1]. Therefore, the sun is the source of the earth's energy, and the specific conditions such as the size and spectral distribution of the energy that can be received on the ground are the direct basis for our future use of solar energy.
How solar cells work
Photovoltaic power generation, in the simplest terms, is that when a semiconductor device with a special structure is illuminated by light, a DC voltage (or current) will be generated; when the illumination stops, the voltage (or current) will disappear immediately. A solar cell is a semiconductor device that uses the photovoltaic effect to generate power output. On a low-doped n-type semiconductor substrate, a shallow junction p-type emission layer is formed by boron (B) diffusion to form a pn junction, and then a metal gate and an anti-reflection film are prepared on this layer to increase the penetration rate into the cell. Incident light and efficiently collect current. When sunlight hits a solar cell, photons with sufficient energy excite the electrons in it, creating electron-hole pairs. They are separated from each other under the action of the electric field of the space charge, the electrons move to the positively charged N region, and the holes move to the negatively charged P region. In a steady state, the external circuit presents an open-circuit voltage. If a load is connected to the external circuit, the solar cell will output current and do work to the external circuit.
The source of earth's energy - the sun
