In electricity, the rated voltage of an electrical device is the voltage that must not be exceeded in normal operation. The nominal adjective is because that tension usually serves to characterize the device, to name it. The nominal value indicates the theoretical or ideal value of anything that can be quantified, as opposed to the real value, which is what is obtained in a given measurement.
Another definition of rated voltage: The rated voltage is the specific potential difference for which a device or installation is designed.
As it is a nominal value it implies that the voltage can vary due to different circumstances during the operation.
Difference in electrical potential
The difference in electrical potential, or electrical voltage, is equivalent to the energy (or work) necessary to separate electrical charges of opposite sign. The voltage increases the more they grow: total charge, distance and intercurrent resistance forces (resistances) between charges.
In physics, the difference in electrical potential, or voltage, is defined as the difference between the electric potential of two points in space. It is the difference between the potential electric energy that has a charge in the two points due to the presence of an electric field, divided by the value of the charge itself. In stationary conditions, it is equal to the work done to move a unit load across the field from one point to another, changing sign.
The difference in the electrical potential is measured with a voltmeter, usually integrated in an electric tester. Within the International System of Units, the unit of measurement of the electric potential difference is the volt (V).
Analogy of the rated voltage with hydraulic circuits
In an electric circuit supplied by an ideal voltage generator, the difference in electrical potential between the two poles of the generator is equal to the electromotive force. If we consider a real generator, the voltage at the ends of the generator is lower due to the potential drop in relation to the internal resistance of the generator.
The energy supplied by the generator can be dissipated in the circuit in different ways, for example through resistive loads or overvoltages, in case there are electrochemical cells present.
When making an analogy with a hydraulic circuit, the potential difference can be associated with the pressure difference generated in a closed tube filled with liquid with the ends placed at different heights: the difference between two points of the electric circuit corresponds to the difference of pressure between two points of the hydraulic circuit.
The potential difference between the poles of the electric generator can be seen as the difference in height of the tanks of the analog hydraulic circuit and the dissipation of electrical energy as a consequence of the friction of the liquid with the internal walls of the tube. Finally, the intensity of the electric current flowing in the conductor can be put in analogy with the flow velocity of the liquid in the tube.
In this analogy, since water flow can perform a job by sliding from a point of high pressure to a point of low pressure, for example, when operating a turbine, the charges that move between two points with different potential constitute a current electrical, which can feed, for example, an electric motor or in any case provide power in other ways.
Nominal voltage and solar energy
Within photovoltaic solar energy, photovoltaic panels are very sensitive to changes in temperature. The performance of a photovoltaic plate decreases with increasing temperature. The photovoltaic cells are dark colored and oriented towards the Sun, which favors the increase in temperature.
To be able to charge a battery, there must be a potential difference, that is, the panel must offer a certain intensity at a certain voltage (always higher than that of the battery) so that the current can pass to the battery.
The first solar panels in the history of solar energy that were manufactured were called self-regulating, they had a smaller number of photovoltaic cells and therefore their maximum voltage never came to overcharge a battery and did not need the use of charge regulators. But they had the disadvantage that in certain countries where it was very hot they did not get to correctly charge the batteries.
The manufacturers of solar panels for battery charge use, concluded that a panel to charge a battery with a nominal voltage of 12 volts, should have a Voc. (open circuit voltage) that is, when measuring the voltage of a panel in vacuum, between 21 and 22 volts more or less and its Vmax, (maximum working voltage) should be above 17 volts. This way although a charge regulator is needed, to be able to manage this energy, when a battery is charged it ensures that the battery charge will always be correct.
A photovoltaic panel manufactured specifically for charging batteries can also be used in network connections and yet a panel manufactured specifically for connection to a network, will not normally be valid for an insulated installation, where batteries need to be charged.