Solar photovoltaic panels are the new, greener alternative to other energy generators as they do not pollute the environment and do not emit greenhouse gases into the atmosphere while operating. Over the years significant progress has been made in the technology of production of both photovoltaic modules and batteries for solar energy storage. They are becoming more affordable and effective as a result of which their demand is growing dramatically. Solar energy saves households and businesses hundreds of thousands of levs from electricity bills on an annual basis.

Principle of operation of the solar panels 

A typical solar panel consists of individual solar cells, each made of layers of silicon, phosphorus and boron. The top layer provides a positive charge, the phosphor layer provides a negative charge and the silicon wafer acts as a semiconductor. When solar photons hit the surface of the panel, it emits electrons through the silicon sandwich into the electric field generated by the solar cells. This leads to the formation of a directional current which is then harnessed to usable power. This process is called the photovoltaic effect which is why solar panels are also known as photovoltaic panels or PV panels.A typical solar panel contains 60, 72 or 90 individual solar cells.

This phenomenon was discovered by the French physicist Antoine Becquerel in 1839. As per his scientific claims it is based on the behaviour of semiconductor materials when they are hit by sunlight. When photons of light come into contact with these semiconductors they transfer their energy to the electrons and this generates an electrical voltage. Silicon is the most widely used semiconductor material. 

Types of photovoltaic panels

First generation (highest class) solar panels

• Monocrystalline panels

Monocrystalline solar panels are the most popular panels used mainly in rooftop solar installations. They are made of the purest silicon (single-crystal silicon) by the method of the Polish physicist Jan Czochralski - a process in which a single silicon crystal called an ingot is formed. It is cut into thin silicon wafers which are then used in solar modules. In the manufacturing process the ends of each silicon cell are cut for higher efficiency. Thus, the uniform dark color, rounded edges and white rhombuses between each cell become a hallmark of the mini-crystal solar panel. 

In terms of efficiency, these panels have the highest efficiency - up to 20%. Another advantage is that their performance is almost unaffected by high temperatures and other weather conditions. Although their price is the highest compared to the others, they also have the longest service life - about 25 years.

• Polycrystalline panels

They are easier to distinguish from the rest in appearance: they have a lighter color, inhomogeneous and unevenly colored surface and their edges are not cut. They are produced by melting raw silicon which is a faster and significantly cheaper process than that used for single crystal panels. This contributes both to their lower final price and to their significantly lower efficiency - up to 15%. Also, they are affected to a greater extent by high temperatures and have lower spatial efficiency. 

Second generation photovoltaic panels

• Thin-film panels

Thin-film panels are manufactured by placing one or more thin layers of semiconductor photovoltaic material on a substrate (bearing surface). This material can be silicon, cadmium or copper, respectively the panel is called:

• thin-layer amorphous solar panel
• cadmium telluride photovoltaic panel
• CIGS photovoltaic panel

Unlike single-crystal and polycrystalline solar panels, thin-film panels are thinner and more flexible. This is because the cells in them are approximately 350 times thinner than those used in single-crystal and polycrystalline solar panels. Their main disadvantage is that they take up much more space, have a shorter service life and are therefore extremely unsuitable for residential installations. On the other hand, they are a relatively good and far more budget-friendly alternative to single-crystal and polycrystalline photovoltaic panels.

• Amorphous silicon panels

They are the best developed version of thin-film panels. In their manufacture three-layer technology with a thickness of 1 micrometer (one millionth of a meter) is used. This thickness is possible because amorphous silicon has the ability to absorb light to a much higher degree than crystalline silicon. With only 7% efficiency, amorphous silicon panels are less efficient than those with crystalline silicon which has an efficiency ratio of about 18% but the advantage is the fact that A-Si solar panels are relatively low cost.

Third generation photovoltaic panels

• Biohybrid solar panels

This type of solar cell is still being studied and the idea for the new solar energy technology originated at Vanderbilt University, USA. In the last few decades there have been numerous experiments with biohybrid electrodes using some biocomponents of the photosynthetic apparatus to convert sunlight into electricity. They are based on the use of a revolutionary new method for the use of photosynthetic protein complexes as devices for collecting light and converting it into electricity. At this stage however, its development is at the level of laboratory research. 

• Cadmium telluride photovoltaic panels

Of all the technologies for producing solar energy this one has the lowest possible carbon footprint. It also requires the least amount of water to produce. Another major advantage is the extremely low production cost. The only disadvantage of using cadmium telluride is the fact that it can be toxic, if swallowed or inhaled. In Europe this is one of the biggest barriers to overcoming as many people have fears and concerns about the wider use of the technology behind this type of solar panel.

• Concentrated photovoltaic cells (CVP and HCVP)

They generate electricity just like conventional photovoltaic systems, registering an efficiency factor of up to 41% - the highest ever among all photovoltaic systems. This type of solar panel consists of curved mirror surfaces, lenses. Sometimes they even use built-in cooling systems to increase productivity. CVP panels can only be most effective, if they are facing the sun at a perfect angle. For this purpose a solar tracker is used inside the solar panel with the help of which it slowly changes its position, following the sun.