Nominal voltage is the electrical potential difference for which an electrical installation or equipment is designed. It represents the ideal value with which an electrical system operates under normal conditions.
In the case of electrical appliances, the nominal voltage is the value that must not be exceeded during normal operation. It is called "nominal" because it is the reference value that characterizes the equipment, although the actual voltage may vary depending on the operating conditions.
Difference between nominal voltage and actual voltage
Actual tension can be affected by several key factors:
Variations in system load
As devices are connected or disconnected in an electrical system, the current demand fluctuates. These variations can cause changes in the actual voltage, especially in poorly regulated power grids.
Voltage drops in cables or connections
When current flows through a conductor, part of the energy is dissipated in the form of heat due to the electrical resistance of the material. This causes a decrease in voltage at the load end, a phenomenon that is more pronounced in long installations or with cables of inadequate cross-section.
Fluctuations in power generation
In large-scale power systems, power generation is not always constant. Factors such as variability in renewable sources (solar, wind), failures in generating plants or changes in demand can cause fluctuations in the grid voltage.
Nominal voltage in photovoltaic systems
In photovoltaic systems, nominal voltage is a key parameter that defines the design and operation of the electrical system. It refers to the voltage at which solar panels, batteries and inverters operate, and varies depending on the system configuration and its specific application.
Solar panels
Each solar panel has a nominal voltage, which is typically in the range of 12V, 24V or 48V in residential and commercial installations. This value represents the approximate voltage that the panel generates under standard test conditions (STC).
However, actual voltage may vary depending on factors such as solar radiation and temperature.
Battery banks
Systems incorporating energy storage use battery banks with standard nominal voltages of 12V, 24V or 48V. A higher nominal voltage in the battery bank allows the current required for the same power to be reduced, reducing losses in the cables and improving system efficiency.
Power Inverters
The inverter is the device that converts the direct current (DC) generated by the panels into alternating current (AC) for use in the electrical grid.
Its nominal voltage must match that of the system to which it is connected, both at the input (panels or batteries) and at the output (230V domestic network in Europe or 120V in the USA).
Importance of nominal voltage in system design
The choice of nominal voltage in a photovoltaic system impacts several aspects:
- Efficiency: 48V systems are usually more efficient than 12V systems , as they require less current for the same power, reducing losses.
- Compatibility: All system components (panels, batteries, charge controllers and inverters) must be designed for the same nominal voltage.
- Safety and cost: Higher voltages mean lower currents, which allows for the use of thinner wires and reduces overheating, but may also require stricter safety regulations.
Nominal voltage in different electrical systems
The nominal voltage varies depending on the type of current used in the electrical system:
Alternating current (AC)
It is used in high, medium and low voltage power distribution networks, and is the standard for supplying electricity to homes, industries and businesses. Its main advantage is the ease with which it can be transformed to different voltage levels, allowing efficient transmission over long distances.
Direct current (DC)
It is found in batteries, electronic devices, and small appliances. It is also used in industrial applications such as electric traction systems and renewable energy storage (e.g. solar panels and backup batteries). Although long-distance DC transmission is less common, it is used in high-voltage power lines in specific projects due to its lower energy loss compared to AC in certain cases.
Nominal voltage in cables
In the case of electrical cables, the nominal voltage indicates the maximum voltage for which they have been designed and determines the required insulation levels. It is normally expressed as Uo/U , where:
- Uo is the nominal voltage between a conductor and ground.
- U is the nominal voltage between conductors.
Electrical potential difference
Potential difference ( or voltage) is the energy required to move an electric charge from one point to another. It is measured in volts (V) and is influenced by:
- The total load on the system.
-
The distance between the measurement points.
-
The resistances present in the circuit.
Voltage can be measured with a voltmeter , and within the International System of Units (SI) , its unit is the volt (V) .
Do not confuse with the nominal current
Rated voltage is the voltage at which an electrical device or installation has been designed to operate safely, while rated current is the maximum amount of current a device can handle without overheating or being damaged.
On the one hand, the nominal voltage is measured in volts (V) and depends on the electrical system to which the equipment is connected, while the nominal current is measured in amperes (A) and is determined by the connected load and the capacity of the conductors.
Both parameters are related to electrical power by the formula P = V × I, but they perform different functions in the design and protection of electrical systems.
Table with examples of typical nominal voltages
| Application | Type of current | Nominal voltage |
|---|---|---|
| Home power grid | AC | 230V (Europe) / 120V (USA) |
| High voltage lines | AC | 110 kV - 400 kV |
| Car batteries | DC | 12V |
| Consumer Electronics | DC | 5V (USB), 19V (laptop chargers) |
| Photovoltaic systems | DC | 12V, 24V, 48V |