All the energy that man used, except nuclear and geothermal energy, comes from the sun. The price of crude oil and natural gas is greater than ever. In order to reduce dependence on fossil fuels, many countries are oriented towards alternative energy sources, especially solar energy. Solar panels absorb the sun’s energy and convert into electricity or thermal energy for space heating. The working principle of solar cells is based on the photoelectric effect.
Advantages of photovoltaic conversion are many. Solar cells directly convert solar energy (without movable mechanical components), no environmental pollution, low maintenance, service life of twenty to thirty years, and so on. The disadvantages are: their work depends on the amount of solar radiation; power density (W/m2) is relatively low and high initial price. Fortunately, their price keeps falling and the repayment period is quite short.
The working principle of solar cells and solar panels
When the photovoltaic cells absorb solar radiation, photovoltaic effect leads to the production of the electromotive force at the ends of the cells. Thus, the solar cells become a source of electricity. Every solar cell is composed of a plurality of diodes. The cells can be connected together in series and in parallel to produce the corresponding voltage. Thirty-six cells connected in series can provide voltage of 12 volts. In this way we obtain a solar cell module in which the cells are fixed and protected from adverse weather conditions.
The modules are placed one next to another in photovoltaic flat plate collectors. Collectors make photovoltaic system together with other necessary elements (inverters, controllers, batteries, tanks and pipes). Solar panels are a fundamental part of every solar system.
Silicon is generally used for the production of solar cells (90% of the world’s solar panels). In addition to silicon, it is used: germanium (Ge), indium phosphide (InP), gallium arsenide (GaAs), cadmium sulfide (CdS) and others. Today, solar cells usually based on: mono-crystalline, polycrystalline and amorphous silicon; gallium arsenide (GaAs) and copper-sulfide.
Design and types of solar collectors
Production technology of solar panels is very advanced in recent ten years. There are various types of solar collectors on the market, but they all can be divided into two groups according to the design:
- Flat plate collectors (classic solar collectors) – They have a degree of exploiting solar energy 50-80%. The collector is covered with solar glass which makes it resistant to breakage. They can be placed on the hip/ flat roof or on the ground.
- Evacuated tube collectors (vacuum tube collectors) – Consist of many vacuum tubes and they have a high level of solar energy absorption. Each tube can be individually replaced without discharging the system.
Also, solar panels can be divided according to the material from which they are made:
- Monocrystalline panels
- Polycrystalline silicon (Multi-silicon) panels
- Amorphous solar collectors
- Cadmium telluride panels
- Gallium arsenide
The use of solar panels
The solar collectors are installed in a variety of systems for the following purposes:
- Space heating
- Water heating
- Production of electrical energy
- Irrigation solar systems
- Additions to other systems
Their use is increasing in households and industries all over the world. Solar panels replace many electrical systems and have a positive impact on the environment.