A photovoltaic system is a set of elements that have the purpose of producing electricity from solar energy. It is a type of renewable energy that captures and processes solar radiation through PV panels.
The different parts of a PV system vary slightly depending on whether they are grid-connected photovoltaic facilities or off-grid systems.
In off-grid solar systems, the energy generated can be stored using solar batteries and charge controllers. In the case of grid-connected solar systems, the electricity generated is supplied to the general electricity grid for distribution.
The main components of a solar panel system are:
1. Solar Panels
Solar panels are an essential part of a photovoltaic system. They are devices that capture solar radiation and are responsible for transforming solar energy into electricity through the photovoltaic effect. This type of solar panel comprises small elements called solar cells.
The PV cell is the part of the PV panel responsible for transforming solar radiation into electrical energy thanks to the photovoltaic effect. The generating power of solar panels is DC electricity that is suitable to store in a battery system. Still, we will usually need a power inverter to use it.
Solar cells are encapsulated in two layers between a front sheet of glass and a back layer of a thermoplastic polymer or other glass sheets. The glass sheet is used when desired to obtain modules with some transparency.
Usually, this set of elements is framed in an anodized aluminum structure to increase resistance and facilitate the anchoring of the solar panel.
Types of Solar Cells
Commonly, solar cells of a solar power system are made of silicon. According to its structure, we can divide them into three subcategories:
Monocrystalline silicon solar cells.
Polycrystalline silicon solar cells with higher conversion efficiencies.
Amorphous silicon cells are the least efficient but least expensive.
2. Power Inverters
The inverter is an electronic device responsible for converting DC to AC in a solar PV system to optimize the electricity supply.
The photovoltaic solar panel of this system provides DC electricity. This current can be transformed into alternating current (AC) through the current inverter and injected into the grid.
The process, simplified, would be as follows:
First, power is generated at low voltages (380-800 V) and in DC.
Then, it is transformed with a power inverter into AC electricity.
In electrical power plants of less than 100 kW, energy is injected directly into the low-voltage grid. And for powers more significant than 100 kW, a transformer is used to raise the energy to medium voltage and is injected into the electrical lines.
3. Solar Trackers
Solar trackers have the mission to orient the position of the PV panels depending on the position of the Sun to increase their performance. Its use is quite common in big solar arrays. The solar tracker comprises one or two electric motors and, usually, a solar sensor to detect the Sun's position and to be able to calculate the optimal tilt of the panel.
Solar trackers can significantly increase solar production, around 30% for the former and an additional 6% for the latter, in places with high direct radiation.
There are several types of solar trackers:
Two-axis solar trackers: the surface of the photovoltaic panel is always perpendicular to the Sun.
Solar trackers on a polar axis: the surface of the solar panel rotates on an axis facing south and tilted at an angle equal to the latitude.
Solar trackers on an azimuthal axis: the surface rotates on a vertical axis, and the angle of the surface is constant and equal to the latitude.
Solar trackers on a horizontal axis: the surface rotates on a horizontal axis and is oriented north-south.
4. Electrical Wiring
Electrical wiring is the part that transports electrical energy from its generation for its subsequent distribution and transport. Therefore, its dimensioning is determined by the most restrictive criterion between the maximum potential difference and the maximum permissible intensity.
The dimensioning of the electrical wiring is much more significant in the case of on-grid solar systems. However, in the case of off-grid systems, it is only necessary to transfer the electrical energy locally, generally to solar batteries.
Solar batteries are a mandatory part of an off-grid solar system. Usually, the energy generated by solar panels is not enough to power your home when needed. This component aims to store energy when it is sunny as chemical energy and keep it ready to be supplied when required.
For the correct operation of these components, a charge controller is also necessary to guarantee an optimal filling of the batteries and thus extend the useful life of the batteries.
Some grid-connected solar systems use batteries because it is more efficient. The advantage is that you don't need over-dimension the set of batteries because you have the grid behind just in case it is insufficient.
6. Charge Controllers
A charge controller is a device that regulates the flow of electricity from a photovoltaic (PV) system to a battery bank or other load. Charge controllers are a vital part of any PV system, as they help to ensure that the batteries are not overcharged and damaged.
Charge controllers are installed between the solar panels and the battery to control the state of charge of the battery.
How Does a Solar Charge Controller Work?
A charge controller works by controlling the amount of power going into a battery and the charging capacity of the battery. It adapts to the operation of the battery but prevents the battery from being overcharged. The battery charge stages work as follows:
Bulk Stage: In this stage, the current supplied to the battery passes with maximum intensity. In this way, the voltage increases rapidly and reaches a power of 12.6 V in general batteries until it reaches the first voltage limit that the battery has. Up to that point, the battery is about 90% charged. At this point, the voltage reached by the battery is around 14.4 V —depending on the battery used— and, although current absorption is drastically reduced, the intensity at which it is supplied continues to be maximum.
Absorption stage: In this case, what happens is that the charging speed decreases until the battery is fully charged. The voltage reached in this stage corresponds to that at the end of the Bulk phase and to the maximum capacity that the battery allows —also known as the absorption limit.
Float stage: What happens at this moment is that the voltage —or voltage— decreases, generally up to 13.5 V. The same happens with the injected current, which is reduced until the battery is complete. It is the last filling period of the battery.
Suppose the solar array generates too much energy that exceeds the energy storage maximum of the battery. In that case, the solar charge controller ensures that power is not injected into the battery, avoiding an overload. This energy is lost by a process known as the Joule effect, which generates heat.
Typically, generators must be adjusted to the parameters of the battery. That is, to the charging capacity, to the voltages with which they work, etc., so less energy is not wasted.