Energy from sun is free and the sun will continue to shine for billions of years to come. While the solar energy is inexhaustible and renewable, its irradiance is environment-friendly. The solar power system does not emit CO2, which is environmentally damaging. In addition, silicon, the raw material in making solar cells, is the second most abundant element in the earth’s crust. Since the solar industry has been developing and the technology is maturing, the PV power systems are efficient for both commercial and residential use. The price of PV systems is also more affordable now due to recent price cuts.
In contrast, fossil fuels, as our main sources of energy, are depleting. Our high dependence on fossil fuels is inevitably going to push up their prices continuously until they are used up. Fossil fuels are nonrenewable and environmentally damaging. Recent climate change is in part a consequence from the increased CO2 concentration in the atmosphere caused by burning fossil fuels.
Therefore, it is essential for us to seek alternative renewable energy resources for guaranteed energy supply and environmental protection. Solar is the answer.
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Photovoltaic (PV) effect is the conversion of sunlight energy into electricity.
In a PV system, the PV cells exercise this effect. Semi-conducting materials in the PV cell are doped to form P-N structure as an internal electric field. The p-type (positive) silicon has the tendency to give up electrons and acquire holes while the n-type (negative) silicon accepts electrons. When sunlight hit the cell, the photons in light excite some of the electrons in the semiconductors to become electron-hole (negative-positive) pairs. Since there is an internal electric field, these pairs are induced to separate. As a consequence, the electrons move to the negative electrode while the holes move to the positive electrode. A conducting wire connects the negative electrode, the load, and the positive electrode in series to form a circuit. As a result, an electric current is generated to supply the external load. This is how PV effect works in a solar cell.
Depending on the system’s connection to the electricity grid, different components are integrated in a PV system. Generally, all the systems include PV modules, wiring, and the associating construction materials.
- In an off-grid system, additional components include battery banks, a charge controller, an optional backup generator, and an optional inverter. While in the off-grid hybrid system, other renewable energy generators such as the wind turbine are added in addition to the components in the off-grid system.
- In a grid-tie system, additional components include a solar production meter, a switching unit, an export/import meter, an inverter, optional battery banks and the associating charge controller
Solar cells are assembled together to form solar modules. Through PV effect, the solar cells capture sunlight and turn it into direct current (DC) electricity. For off-grid system, the DC can be immediately used for DC loads if there is no inverter or the DC can then be directed to an inverter, which converts DC into alternating current (AC) that is suitable for conventional electric appliances. For the off-grid system, excess energy generated from the PV panels is usually stored in batteries, controlled by the charge controller, for use at night when there is no sunlight. An optional backup power such as diesel generator can be installed if electricity from the batteries run out. For grid-tied system, DC is converted into AC to be used on-site or stored for backup if the system includes battery banks. When there is more demand, power can be drawn from the grid. Excess supply of electricity from the PV panels can also be fed back into the grid. This process of drawing and feeding electricity to the grid is monitored by the solar production meter and the export/import meter.
Solar modules can be arranged into arrays that are large enough to function as power stations converting sunlight into electrical energy for industrial, commercial, and residential use. Solar modules in smaller configuration can be installed on buildings for residential or commercial use. Solar panels can also be used in remote areas where there is a short supply of electricity or where electricity can not be delivered such as in space.