Global oil reserve is estimated to last for only 40-50 years. Natural gas, uranium and coal reserves also have their limitation. Solar energy is inexhaustible and its utilization process generates no pollution. Solar energy emitted from nuclear fusion becomes approximately 1.2x1014 kW when it reaches earth surface after a trip of 150 million km and atmospheric absorbance. Amazingly, one hour of this energy irradiation on earth can provide the human energy need throughout the year. Therefore, we should not ask “why solar?”, but “why NOT solar?”.
How does solar cell work?
The principle for solar cell to generate power is to convert light energy of solar irradiation into electrical energy. When solar light is irradiated on solar cell, photon energy can excite electrons in semiconductor material to produce electron-hole pairs. The electron-hole pairs are subject to the internal electric field formed by P-N or P-i-N structure in solar cell and driven to separate. Therefore, electrons move to the negative electrode while the holes move to the positive electrode. Conducting wire connects the positive electrode, the negative electrode and the load in series to form a circuit. As a result, electric current is generated to supply external load. This is the fundamental operation principle for solar cell.
Loss processes in a standard solar cell
(1) non-absorption of below band gap photons
(2) lattice thermalisation loss
(3) and (4) junction and contact voltage losses
(5) recombination loss.
What’s the benefit to environment?
The 2008 annual power consumption is about 1.7x1013 kWh. Under the condition that each degree of power generation has 0.58 kg CO2 emission on average, there is about 1010 tons CO2 emission due to power generation. Compared to 1,000 g CO2 emission per degree of power generation by coal burning or oil burning power plant, solar power generation only has about 100 g CO2 emission per degree of power. It greatly reduces CO2 emission and effectively lowers greenhouse effect. It follows the trend as an environment-friendly and low-pollution power generation method.