The photovoltaic system is based on the ability of certain materials to convert light directly into electricity. Although the basic physical principle has been known for a long time, the technical development of solar cells is far from over, and further improvements can be expected in the future.
The principle
Semiconductors owe their name to the property to behave both like an electrical conductor and like a non-conductor. In a solar cell, the non-conductive material becomes a conductor because the electrons are released from the non-conductive crystal compound through the absorption of a photon. The kinetic energy that they absorb forms the electricity generated. The energy of the photon must lie in a material-dependent interval that is precisely limited. Photons with too much or too little energy do not contribute to the generation of electricity. "The energy of a photon is directly proportional to its frequency". Therefore, it means that the usable part of the light spectrum is limited.
The search for new materials to replace the silicon most commonly used today is intensively pursued worldwide. The focus is on two properties that these new materials should have. First, the usable part of the light spectrum should be as large as possible. Second, the so-called recombination rate should be as low as possible. It indicates how quickly the electrons spontaneously fall back from the conductive to the non-conductive state. The still low efficiency of organic photovoltaics is related to the fact that this recombination rate is comparatively high in organic semiconductors.
The inverter
A solar cell generates direct current, which must be converted into the alternating current before being used or fed into the grid. Usually, only one inverter is installed, which converts the electricity from all photovoltaic modules. It is also possible to use a separate inverter for each solar module in the system. In principle, this divides the photovoltaic system into many small systems that work independently of one another. The solar cell has the great advantage that a defective or in the shadow of a module does not affect the others, which is otherwise the case. However, the costs are significantly higher, and the cabling is considerably more complicated. There are also compromise solutions between the two, in which some modules share an inverter.
Grid-connected systems
Almost all photovoltaic systems are connected to the power grid. Island systems without contact with the general power grid are significantly more common in countries where photovoltaics supply villages with electricity that are not connected to the public power supply. The connection to the power grid causes problems because the grid somehow has to compensate for the fluctuating output of photovoltaics. Today stand-alone systems only make sense where the electricity generated can be used immediately. Practical electricity storage can change that in the future.
Photovoltaics still has enormous potential for improvement. The production of silicon is highly energy-intensive and therefore expensive. The first goal is to develop cheaper materials that offer at least the same performance. In addition, the possible uses of photovoltaic systems can be broadened considerably if efficient electricity storage systems are available. @via sciencedirect.
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