Photovoltaic power generation is on the rise in the United States. This article explains how a photovoltaic system works and what components it consists of.
How does photovoltaic power generation work?
Photovoltaic systems convert sunlight into electrical energy. Solar modules consisting of solar cells are used for this purpose. Sunlight sets electrons in the solar cells in motion and produces direct current. This is converted into alternating current by an inverter and supplied to the home.
The way a photovoltaic system works is a little more complicated than what has been described above. A photovoltaic system consists of several components that are critical to its efficient operation.
What components are needed to generate electricity?
A photovoltaic system consists of only a few components. The most important
*Solar panels
*Solar cables
*Solar meters and feeder meters
*Inverters
Alternatively, a power storage unit and an energy manager are also used. The individual components are described in more detail below.
Solar modules and solar cells
Solar modules contain solar cells that convert sunlight into electricity. The solar cells are connected in series so that their voltages add up. Typically, a solar module consists of 60 or 72 cells or 120 to 144 half-cells. They have an output of 400 to 600 Wp, although there are now solar modules with more than 300 Wp on the market.
Solar cells are primarily made of silicon. Silicon is a semiconductor material with photovoltaic properties. When sunlight hits a solar cell, it excites electrons. Their movement generates electricity. Two differently doped layers are required for solar cells to generate electricity:
1. The top layer is called the n-doped layer. It contains silicon and phosphorus. Silicon has four bound electrons, while phosphorus has five electrons. This extra electron is free in the layer;
2. The lower silicon layer is p-type doped with boron. Boron has one less electron than silicon, forming a hole;
3. The free electrons from the n-doped silicon phosphorus layer migrate to the p-doped layer and fill the holes. This forms a boundary layer of boron atoms with four electrons. These atoms become stationary because they no longer have any holes.
4. Electrons migrate to create electrodes. When electrons migrate, the upper layer becomes positively charged and the lower layer becomes negatively charged. Sunlight releases electrons from boron atoms in the solar cell. The electrons are attracted to the positive electrode and migrate to the upper layer. This process occurs in all solar cells exposed to sunlight.
The excited electrons are released from the upper solar cell layer. This is achieved through an electrical conductor, usually a metal grid on the back of the solar module. As sunlight shines, more and more electrons are pushed through the metal contacts and conducted through the solar cable.
The underside of the solar module has a metal contact that is used to connect to the solar cable. The electrons flow through the cable and re-emerge at the bottom layer. By keeping them moving, they generate voltage.
Solar Cable
Solar cables connect the modules of a solar system. They are weatherproof, UV-resistant and transfer power between photovoltaic modules. There are several ways to connect or switch these cables. This has an impact on the current voltage, amperage and total output:
1. In series connection, the solar modules are connected in series. The positive cable is connected to the negative cable. The voltage of all modules is added together, while the current intensity remains the same. Finally, the first and last modules have a cable connected to the inverter. This is the most common type of circuit and the one with the least cables.
2. When connected in parallel, the negative pole is connected to the negative pole and the positive pole is connected to the positive pole. This increases the current while the module voltage remains unchanged. In the end, there are still two cables connected to the inverter. The advantage is that the shading of one module will not affect the current output of other modules. The disadvantage is that more cables need to be laid and the installation is more complicated.
Solar meter
Solar meters measure the total amount of electricity generated by a PV system. This is important for determining the yield generated and the cost-effectiveness of the PV system. Solar meters are installed on the DC side, before the inverter.
Inverter
A solar inverter makes it possible to use the solar energy generated in the home. Solar energy uses direct current, while homes and the public grid use alternating current:
1. Direct current flows continuously in one direction, from the negative electrode to the positive electrode. The current intensity remains constant over time;
2. When there is alternating current, the current changes direction regularly. Frequency is measured in Hertz (Hz), which indicates how often this change occurs per second. In Europe, the power grid operates at 50 Hz, which means that the direction changes 50 times per second.
Photovoltaic inverters use complex circuits to generate sine waves for electronic devices. Switches quickly open and close the power line, changing the direction of the current. To get a uniform sine wave, the switching frequency is divided into smaller segments with different current strengths.
To monitor and optimize PV systems, modern inverters contain MPPT (Maximum Power Point Tracking). They influence current and voltage in order to operate the solar system close to its maximum power point.
Power storage
Due to high electricity prices, it is now worthwhile to store excess electricity instead of feeding it into the grid. For this purpose, electricity storage systems are integrated into photovoltaic systems. This makes it possible to use self-generated solar energy outside of generation times. This in turn increases self-consumption and the profitability of the system.
The energy storage system consists of a positive electrode (anode), a negative electrode (cathode) and an electrolyte, which is a conductive liquid. The electrolyte surrounds both electrodes. If the solar system generates excess electricity, electrons move from the cathode to the anode through the electrolyte. The anode is filled with electrons. At the anode, the electrons react and form atoms. In this way, the excess electrical energy is stored in the form of chemical energy.
During discharge, the atoms move back to the cathode. There they are converted back into electrons. The electrons can be provided as electric current and fed into household circuits.
To make an energy storage system particularly valuable, combine it with an energy management system.
Energy Management System
The task of a photovoltaic system energy manager is to increase the self-consumption of solar energy in the home and reduce electricity costs. An energy management system identifies and exploits potential energy savings. It records and analyzes energy flows and sources, proposes ideas for improvements, evaluates cost-effectiveness and implements them. Most energy management systems are controlled via apps or software.
Consumption and feed-in meters
If you connect your PV system to the public grid, you will need consumption and feed-in meters:
1. The feed-in meter measures the amount of electricity fed into the grid.
2. The consumption meter measures the amount of electricity consumed by a household.
Consumption meters usually already exist. Feed-in meters are only installed when the PV system is commissioned, after the system has been registered with the grid operator and their approval. Nowadays, bidirectional meters are usually installed, combining consumption and feed-in meters.
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