An electric generator is a device designed to produce electricity from a different form of energy.

The different forms of energy, which are transformed into electricity, are usually mechanical energy, chemical energy, photovoltaic energy or directly thermal energy.

Depending on their characteristics, there are several types of electric generators. The analysis of these generators is not limited only to the generators used in photovoltaic solar energy, but we will make a brief review of all types of electric generators.

## Photovoltaic generators

Photovoltaic generators use photovoltaic solar panels to generate electricity. Each solar panel is composed of an array of photovoltaic cells. The photovoltaic cells are responsible for generating electricity thanks to the photovoltaic effect.

Photovoltaic panels are capable of converting light directly into electricity.

Use is (as is obvious) more convenient in areas with good light radiation.

## Electric Induction Generators

These electric induction generators are based on the induction of electric current in a circuit due to Faraday's law and are the most important in terms of electricity production.

This category includes mainly the dynamo, for the production of direct current, and the alternator, capable of generating alternating current.

## Electrochemical Generators

When the flow of electrons is produced by an oxidation-reduction reaction, there is an electrochemical generator. The most common are batteries and fuel cells.

## Radioisotope Generators

Generation in the radioisotope thermoelectric generator is based on the decomposition of radioactive isotopes; radioactive decomposition produces emission of particles and heat. The production of electricity can be obtained directly from the displacement of electrically charged particles, or indirectly from the heat produced by caries.

## Differential thermal generators

The production of electricity is obtained from a temperature difference for the Seebeck effect, the system can exploit, although with modest yields, any thermal gradient.

## Piezoelectricity Generators

Piezoelectric generators exploit the property of particular crystals to produce a potential difference if they are subjected to compression. The phenomenon is exploited in some types of kitchen lighters, but its use has been studied to generate electricity in general, derived from pressure thrusts.

## Ideal electric generation

In the theoretical study of electrical phenomena and circuits, generators are generally considered ideal. An ideal generator can produce any voltage and current without limit and has no internal resistance. The value of current or voltage generated is independent of the applied load.

Actually, there are no ideal generators, since any device has its intrinsic internal resistance, it is also capable of generating voltage and current only within certain limits.

An actual voltage generator can be represented as an ideal voltage generator with serialized internal resistance, while the actual current generator can be represented as an ideal current generator with parallel internal resistance.

In theory, if a circuit comprising an ideal current generator is opened, the output voltage should rise to infinity. However, in the real generators there is a voltage limit value above which the current drops to zero. From the theoretical point of view, in the theoretical representation of the real generator, the current output of the ideal generator closes on the internal resistance.

## Generation in current or voltage

The electrical generation can be carried out in such a way as to establish the electrical voltage (potential difference at the ends of the conductors) or the electric current (current in the conductor). So, conceptually, there are two types of electric generators:

- Voltage generator
- Current generator

The voltage generator produces a defined and constant voltage (or otherwise a predetermined trend as a function of time). The variation of the load applied implies a variation of the current leaving the generator in accordance with the provisions of Ohm's law. On the other hand, the current generator maintains an electric current, and when the load varies, the voltage leaving the generator varies so that, due to Ohm's law, the current remains at the correct value.

## Other types of generators

The technologies capable of generating energy are many, but in general the energy produced is lower and the cost of energy produced by different systems is higher than what can be obtained from electrodynamic generators, which is why applications of Other types of technologies are limited. This type of generators are only for some niche sectors.