In simple terms, the heat (or electrical energy) generated from light is known as solar energy. Primarily, there are two forms of solar energy — solar thermal conversion, which implies the conversion of sunlight into heat, and photovoltaic conversion, which implies the conversion of sunlight into electricity.
We’ve all been parts of experiments where we used to light up a paper using a magnifying glass, by focusing the sunlight onto a spot. This is precisely the method used for solar thermal conversion to produce energy; only the scale at which the process is done is huge, and hence the amount of energy produced is also considerable. Although solar energy harnessed through this method is being used in several interesting applications, it has to be admitted that the major focus of research has been to improve the methods of photovoltaic conversion, as electricity is much more useful as a form of energy than heat. To harvest solar energy various equipment is required — solar photovoltaic cells, solar concentrators, solar thermal panels and oven, apart from batteries to store the energy.
Fundamentals of Generating Solar Energy
The principle use of solar energy is in the form of photovoltaic effect. A photovoltaic cell converts light energy to electricity. When light rays fall on these cells, the electrons in the cell get excited and create a potential difference. Thus, electricity is generated and the power is harnessed through wires attached to the cell.
Solar energy is harnessed by using solar panels. These panels are made of small cells, arranged in an assembly. Solar panels are made up of silicon, a semiconductor material known for transmitting electricity. When light is absorbed by the cells comprising the panel, the light generates electrons and there is a potential difference between N type emitter and P type base which generates electricity.
A solar panel is well circuited to trap the generated electricity. The current which is generated is in the form of Direct Current (DC). Routine use home appliances can never utilize DC for their functioning. These home appliances use only Alternate Current (AC) to function. Now, the DC has to be converted into AC for further utilization. It is done by using an inverter.
The efficiency of solar panels suffers when electrons in the solar panel do not receive sufficient sunlight. When the solar panel does not get sufficient energy, the heat generation process worsens. This is one of the reasons why such panels operate better in tropical and sub-tropical regions. The efficiency of solar energy may suffer when the cell is not working to the fullest which means some electrons are lost in the process. The release of heat by electrons can interfere with the components of the panel.
Earlier, large silicon crystals were used to produce electricity once they came in contact with sunlight. This is possible because the electrons in the silicon begin to move when exposed to sunlight, and hence, heat is generated. The silicon is responsible for turning the light absorbed into electricity. The process may be simple, but silicon crystals are expensive. With advancement in technology, newer and cheaper crystals are being introduced. For instance, copper, indium, gallium and selenide are some of the alternatives used. This thin film solar technology converts light into electricity.
Use of reflectors and mirrors
Reflectors and mirrors are used to centralize the sun’s rays so that extreme heat is generated. The sunlight is focused on a container filled with liquid, mostly water. This liquid is heated to extremely high temperature to produce steam and this steam is used to turn turbine. With the help of the turning turbine, electricity is generated. An absorber converts sunlight into heat. An absorber can be a surface painted in black, or ceramic material. It can collect 95% of the sun’s rays.
The term photovoltaic is a combination of a Greek word phos and Voltaic, the name of an Italian physicist. It simply means generating electrical energy on exposure to light. The photovoltaic cell consists of panels made of two different materials. One layer is positive and the other is negative. When this cell is exposed to sunlight it generates electricity. Solar cells are combined to result in solar panels. More solar panels interlinked together can generate more power. So, one can scale up the process of photovoltaic conversion to create a lot energy in the form of electricity, which is produced by exciting the electrons in the solar cell. This electricity is on direct current and has to be converted into alternate current. In the conversion process, a small amount of energy is lost. But once the conversion is done, it is ready for household use.
Solar Concentrators and Solar Oven
A solar concentrator is a concentration of mirrors. Here, curved mirrors are used to focus the sunlight on a particular point. At this focal point, a solar photovoltaic cell or stirling engine is used. Solar concentrators range over several sizes. Some can be as small in size as a satellite dish, whereas others can cover acres of land. A solar tower is placed at the center of such a huge installation, and huge amount of electricity is produced.
Solar ovens are curved reflective surfaces similar to solar concentrators. In such an assembly, a container for food is placed in the middle so that the concentrated energy can be made to cook the contained food. In this manner, one can cook food without burning wood or fossil fuels! This process can be used to sterilize water as well. It is the simplest method to cook food using solar energy.
Active and Passive Solar Energy
There are two types of solar energy that can be used to generate electricity — active and passive. Active solar energy focuses on solar panels and photovoltaic cells and they are used to produce electricity. Depending on certain aspects, the output can be determined. The generation is linked with the number of cells in the panel. Thermal solar energy is a form of active solar power that uses thermal energy to heat water at home. There are certain devices that circulate and pump water to keep the water warm.
Passive solar energy is used to run mechanical devices. In cold countries, it is a popular practice to make passive use of solar energy. South facing windows are specifically designed with special materials so as to absorb a lot of sunlight, which further lends warmth to the house’s interiors.