Photovoltaics is on the rise in Germany. In this article, you will learn how a photovoltaic system works and what components it is made of.
How does photovoltaics work?
A photovoltaic system converts sunlight into electrical energy. Solar modules made of solar cells are used for this. The sunlight sets the electrons in the solar cells in motion and generates direct current. This is converted into alternating current by the inverter and made available for the household.
The way a photovoltaic system works is somewhat more complex than described above. A PV system consists of several components that are essential for efficient operation.
Which components are needed for electricity production?
A PV system consists of a few components. The most important are:
- solar modules
- solar cable
- solar meters and feed-in meters
- inverter
Alternatively, a power storage unit and 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 electrical energy. The solar cells are connected in series so that their voltage adds up. A solar module usually consists of 60 or 72 cells or 120 to 144 half cells. They achieve an output of 300 to 400 Wp, although solar modules with over 600 Wp are now available on the market.
Solar cells are mainly made of silicon. Silicon is a semiconductor material with photovoltaic properties. When sunlight hits the solar cell, it excites the electrons. Their movement creates electricity. Two differently doped layers are needed for the solar cell to generate electricity:
- 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;
- The lower silicon layer is p-doped with boron. Boron has one less electron than silicon, which creates a hole;
- The free electrons from the n-doped silicon-phosphorus layer migrate into the p-doped layer and fill the holes. This creates a boundary layer of boron atoms with four electrons. These atoms become stationary because they no longer have any holes;
- Electron migration creates electrical poles. When electrons migrate, the upper layer becomes positively charged and the lower layer negatively charged. Sunlight releases electrons from boron atoms in solar cells. The electrons are attracted to the positive pole and migrate to the upper layer. This process occurs in all solar cells exposed to sunlight.
structure of a solar cell
The excited electrons are discharged from the top solar cell layer. This happens via an electrical conductor, usually a metal grid on the back of the solar module. When the sun shines, more and more electrons are pushed through the metal contacts and guided through the solar cables.
On the bottom of the solar module there is a metal contact that is connected to the solar cables. The electrons flow through the cable and reappear in the lower layer. By remaining in constant motion, they generate an electrical voltage.
solar cable
Solar cables connect the modules of a solar system. They are weatherproof and UV-resistant and transport the electricity between the PV modules. There are various ways to connect or switch these cables. This affects the voltage, the current and the overall performance:
- At the 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 remains the same. At the end, the first and last modules each have a cable that is connected to the inverter. This is the most common type of connection and the one with the fewest cables.
- At the parallel connection negative cables are connected to negative cables and positive cables to positive cables. This increases the current while the module voltage remains the same. In the end, there are still two cables connected to the inverter. The advantage is that the shading of one module has no effect on the power output of the others. The disadvantage is that more cables have to be laid and the installation is more complex.
solar meter
The solar meter measures the total electricity generated by the photovoltaic system. This is crucial for determining the yield generated and the profitability of the PV system. The solar meter is installed on the direct current side, i.e. before the inverter.
inverter
A inverter makes it possible to use the generated solar power in the home. Solar power is direct current, while households and the public grid use alternating current:
- direct current flows constantly in one direction, from negative to positive. The strength of the current remains constant over time;
- At alternating current the flow of electricity changes direction regularly. The frequency, measured in Hertz (Hz), indicates how often this change occurs per second. In Europe, the power grids operate at 50 Hz, which means the direction changes 50 times per second.
PV inverters use sophisticated circuits to generate a sinusoidal wave for electronic devices. The switches open and close power lines rapidly, changing the direction of the current. To achieve a smooth 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 the electrical current and voltage to operate the solar system close to its maximum power point.
electricity storage
Due to the high electricity prices, it is now worthwhile to store the excess electricity instead of feeding it into the grid. electricity storage integrated into the PV system. This allows the self-generated solar power to be used outside of the production times. This in turn increases self-consumption and the profitability of the system.
An electricity storage device consists of a positive electrode (anode), a negative electrode (cathode) and an electrolyte as a conductive liquid. The electrolyte surrounds the two electrodes. If the solar system generates excess electricity, the electrons move through the electrolyte from the cathode to the anode. The anode is fully charged with electrons. At the anode, the electrons react and form atoms. Excess electricity is thus stored in the form of chemical energy.
During the discharge, the atoms migrate back to the cathode. There they are converted back into electrons. The electrons are available as electrical current and are fed into the household circuit.
To make a power storage system particularly worthwhile, combine it with an energy management system.
energy management system
The task an energy manager for PV systems is to increase the self-consumption of solar power in the household and to reduce electricity costs. Energy management identifies and uses energy saving potential. It records and analyses energy flows and sources, develops ideas for improvement, evaluates the economic viability and implements them. Most energy management systems are controlled by an app or software.
consumption meters and feed-in meters
If you connect a PV system to the public power grid, you need a consumption meter and a feed-in meter:
- The feed-in meter measures the electricity fed into the grid;
- The consumption meter measures the electricity consumed in the household.
The consumption meter is usually already in place. The feed-in meter is only installed when the PV system is commissioned, once you have registered the system with the grid operator and it has been approved by them. Nowadays, bidirectional meters are usually installed, which combine the consumption and feed-in meters.
