The components of a system of photovoltaic panels for the production of electricity
We distinguish 2 types of components of a photovoltaic system:
mandatory
• photovoltaic panels
• inverter
• electric circuit
• counter
optional
• accumulators
Photovoltaic panels
Photovoltaic panels convert solar radiation into electricity with a certain efficiency.
There are different types of photovoltaic panel construction technologies:
mono-crystalline (high efficiency in case of direct solar radiation);
poly-crystalline (best price-performance ratio);
amorphous (high efficiency in the case of indirect solar radiation, requires a larger area for the same installed power).
Important features:
installed power (measured in Wp);
physical characteristics (length, width, thickness, mass);
efficiency (measured in %, represents the percentage of solar energy converted into electricity, relative to the total solar energy available on the panel surface).
The performance of photovoltaic panels is influenced by:
Orientation – an orientation to the South or an East-West orientation is preferable.
Tilt – an optimal angle would be latitude minus 10 grd (34-35 grd for Romania). An angle that is too small can lead to snow deposition and diminishes the ability to produce power. Because Romania is located in the middle area of the northern hemisphere, the optimal angle at which the panels should be in relation to the position of the sun is influenced by the seasons.
Shading caused by other construction elements or trees, with a significant reduction in the performance of the panels.
Temperature – a high temperature implies a significant decrease in performance.
inverter
The inverter transforms the energy produced by the photovoltaic panels (direct current) into usable energy for the consumer, i.e. the energy network (alternating current). The inverter converts direct current (DC) of 12 V into alternating current (AC) of 230 V.
Types of Inverters
On-grid, connected to the national grid, which take over its parameters and transform the photovoltaic direct current into alternating current, with the same parameters as the national grid. This type of inverter is used for systems without storage.
Off-grid, used when there is no national grid in the respective area and which must use a storage system.
Hybrids, which combine the characteristics of the first 2 types.
The performance of the photovoltaic system is determined by 2 factors:
Inverter type. A reduced efficiency of the inverter can cause significant performance losses of the PV system.
The existence of a storage system. In the case of solutions that also include storage, the inverter will charge the batteries, i.e. it will make a conversion from the direct current of the storage to alternating current for use.
Important parameters:
rated input power (measured in Wp or kWp);
photovoltaic voltage range (measured in V, direct current voltage);
rated output power (measured in Wp or kWp);
mains output parameters: nominal voltage, nominal current, nominal frequency (measured in V, A, respectively Hz);
physical characteristics (length, height, thickness, mass)
The components of an Inverter:
The role of the micro-controller is to control the on and off signals, so as to ensure a continuous flow of electric current and prevent overvoltage. The microcontroller also has the role of controlling the safety systems of the inverter or controlling PWM, i.e. the technique used to vary the transported voltage in a controlled manner.
The bipolar junction transistor has the role of regulating electrical signals. The transistor allows the amplification or transmission of electrical energy flow, and its closing and opening process can be switching, when the switching fronts are sudden, or analog, when a linear mode of operation is used. It is called bipolar because the conduction is carried out by two types of electric charge carriers: electrons (-) and holes (+).
The electric bridge H consists of 2 bridge arms, each of which is made of two power transistors, connected in series and equipped with discharge diodes in parallel. The purpose of the H-bridge is to allow a voltage to be applied to a load in any direction. The four component switches of the H-bridge operate alternately, with the role of successively applying a positive (+) or negative (-) voltage to the inverter.
The field effect transistor (unipolar) has the role of controlling the intensity of the electric current in a circuit. The device is composed of 3 terminals, respectively:
● Source: the electrode from where the electric charges start;
● Drain: an electrode to which electrical charges are directed;
● Gate: the electrode that determines the behavior of the device and that maintains the information even if the inverter is disconnected from the voltage source.
Transformer.
The direct current converted by the inverter has a low voltage, and therefore to obtain the voltage of 220 V, necessary for the use of electrical appliances, the device is equipped with a transformer, which brings the converted voltage to the values necessary for the practical use of electricity.
The electrical circuit
The electric circuit represents the wiring between the photovoltaic panels and the inverter, between the inverter and the batteries, between the inverter and the electrical panel, respectively to the necessary protections. Incorrect sizing can lead to performance degradation.
The wiring between the photovoltaic panels and the inverter is done using special cables, called "solar cables".
The grouping of photovoltaic panels in strings (series wiring) will have to take into account the parameters of the inverter (current, voltage), as well as the wiring between the inverter and the batteries or the wiring between the inverter and the electrical panel or the necessary protections.
Shorter electrical routes are recommended
It is important to properly size the cabling, depending on the lengths of the routes.
Electricity meter
The electricity meter accurately determines the amount of electricity passing through a measurement point. In the case of the classic meter, the sense of electricity measured is from the national energy system (SEN) to the consumer.
In the case of a double-way meter, both the energy consumed and the energy produced are counted.
Types: To be a prosumer you need a smart two-way meter, the so-called "smart-meter", which can be accessed from a distance to evaluate both the monthly/annual consumption and to check the operating parameters of the electricity network or to realize consumption/production trends in order to improve this system.
The replacement of the classic meter with a double-way one is done by the distribution operator and is carried out as a result of the issuance of the connection certificate.
It is read by the distribution operator and the information is transmitted to the supplier with whom a sales contract is concluded.
In the case of systems that also have accumulators, the existence of a secondary meter is recommended.
In the case of the financing program carried out by the Environment Agency, a second meter is installed in front of the meter at the delimitation point.
batteries
The role of batteries in a photovoltaic system is to store the energy produced so that it can be used when needed.
For a storage system, the following parameters are important that determine the capacity, respectively the lifetime of the batteries:
Number of charge/discharge cycles;
DoD (Depth of Discharge), i.e. the percentage of battery capacity that can be used without affecting battery life;
The ambient temperature of the space where the batteries are stored.
To be able to use the storage component of the photovoltaic system, a hybrid inverter is required. If one opts for a system without batteries and in the following years some accumulators are also purchased, such an inverter is recommended from the beginning. Its cost is approximately 400 euros higher.