If you want to convert solar energy into electricity, you need solar modules. The panels are interconnected solar cells and always work according to the same principle. Which solar modules are the right depends on the location, budget, and other factors.
Solar modules or photovoltaic modules are the heart of every photovoltaic system. They contain solar cells connected in parallel or series, generating energy from solar radiation. Solar modules are mostly flat plates, so they are called solar panels. The Low German and Dutch word “panel” means “board.” The corresponding English expression is “solar panel.” In addition to these stable “boards,” there are also flexible modules that can be bent.
How are solar modules constructed?
Thick-film solar modules consist of several solar cells connected to form a string using narrow soldering ribbons. Cross connectors are attached between the strands, which lead the current to the junction boxes.
Two plastic foils, which are firmly connected (laminated) to each other and the solar cells by heating, protect the construction from moisture and aggressive gases. The originally milky-white films become transparent after lamination.
The module has a safety glass pane at the top and is enclosed in a stable aluminum frame for mechanical protection. In this case, one speaks of glass-foil modules. Modules, where a pane of glass also protects the back, are called glass-glass modules. The great advantage of the second glass layer is that the solar cells are located in the so-called neutral fiber and are not mechanically stressed in the event of bending. Wind or snow loads can otherwise break the cells and tear off the cell connectors.
Thin-film solar modules are created by depositing the photovoltaic semiconductor on a carrier layer, usually 1 to 2 mm thick glass. This active layer is only a few micrometers (100ths of a millimeter) thick. In addition, the module is not framed in most cases. These thin-film modules are correspondingly light but also sensitive.
How are solar panels made?
From silicon to solar cells
The basic material of most solar cells is silicon. The semiconductor material is obtained and cleaned in a complex process. So-called ingots (silicon rods) are created and cut into wafers. These thin discs are chemically cleaned again and then doped. Finally, the contacts are printed. In the case of thin-film solar cells, the semiconductor materials are vapor-deposited or sprayed onto a carrier.
From the solar cell to the module
To ensure the cells are working properly, they are checked for functionality. Solar cells that have passed the tests are combined in the “Stringer” to form a series connection, a so-called string.
The glass plates protecting the cells are thoroughly washed before assembly. An EVA film (ethylene vinyl acetate) is positioned on the dry glass, and the strings are on top of that. The strings are then connected with conductor tracks. Next, another EVA film and the back film (glass-film modules) or a rear glass (glass-glass modules) are placed.
The prepared module then goes into a laminator where the foils are fused to the others. At around 150 °C, the film crosslinks, forming a gas and moisture-tight bond that completely encloses the cells.
After cooling down, the module is given an aluminum profile frame. An adhesive tape around the edges of the module assembly ensures that it sits firmly in the frame. Alternatively, liquid glue can be used. The individual parts of the frame are then permanently connected.
A junction box is mounted on the contacts on the back of the module and then glued on. Finally, the conductive parts are soldered or clamped to the module.
Finally, the quality control of the module takes place. In the so-called flash test, the modules are exposed to the flash of a high-performance LED, and a characteristic curve, i.e., the performance data, is recorded. Using an electroluminescence test with a high-resolution camera, cracks and microcracks in the cell can be detected. This test is sometimes carried out after the cells have been soldered into strings.
Hotspots (faults due to local overheating) and other irregularities can also be found using thermal imaging.
Nowadays, of course, the processes are largely automated. The most important steps in production can be seen much better in this video.
What is the performance of solar modules?
The performance of solar modules results from the interconnection of the individual solar cells. In this respect, it depends on the performance of the individual cells and their number. With solar cells connected in series, the weakest cell determines the total output of the module.
Depending on the number of cells used, the size of the module also changes. When selecting solar modules, the individual module’s specified output must be divided by its area to obtain comparable values.
Of course, the module performance also depends on the type of cells used because the materials used determine the efficiency with which solar energy is converted into electrical energy. Monocrystalline solar cells are considered to be particularly powerful. Additional technical modifications can increase efficiency of solar panels. So-called PERC cells, in which the back of the cell is provided with a reflective layer, enabling a higher light yield, have become market-established in recent years. Tandem solar cells, in which different semiconductor materials are layered on top of each other, are also promising. The layers absorb different parts of the light spectrum, resulting in a better yield and significantly higher efficiency. So far, however, the manufacturing process for these solar cells has been too expensive, which is why they are only used in special applications such as satellites.
The performance of the first solar modules was well below 100 Wp, and more are standard. The performance specified by the manufacturer is measured in standardized tests to make comparison possible. These internationally valid standard test conditions (STC) specify, for example, an outside temperature of 25 °C, an exact irradiance, and a defined angle of incidence. Under real conditions on the roof, the performance values of a solar module deviate from the manufacturer’s specifications.
Where are solar modules used?
Solar modules were developed for space travel as early as the late 1950s to supply electricity to satellites. The particularly useful and expensive modules are still used there today.
The oil crisis in the 1970s gave the decisive impetus to manufacturing products for everyday applications. Initially, small electrical devices such as pocket calculators or wristwatches were developed with a few solar cells for power supply. Solar cells were also soon used for signal systems or parking machines. At the same time, photovoltaic systems for the energy supply were set up. For the large-area solar parks, inexpensive thin-film modules were and are primarily used, which are “standing” on a frame.
The idea of a decentralized energy supply, in which each house is equipped with its photovoltaic system, emerged in the 1980s and became increasingly important. The 1,000 Roofs Program (1990) and the 100,000 Roofs Program (1999 – 2003), as well as the Renewable Energy Sources Act (EEG) of 2000, provided a decisive impetus for the practical implementation of this idea in Germany.
Nowadays, solar modules are built and used all over the world. Thanks to falling prices and constant further development of the modules, photovoltaics has now established itself in many places as a pillar of a sustainable, resource-saving energy supply. Germany’s share in covering electricity requirements is currently around 9 percent.
For private applications and small businesses, the solar modules are usually attached to the roof of the house or built into the roof skin (on-roof and in-roof systems). If the area is scarce or already occupied, carports, hall roofs, patio, or parking lot roofs offer additional photovoltaic potential. The facades of buildings are also suitable for installing modules. Floating PV systems on quarry ponds and other bodies of water are also becoming increasingly interesting for commercial use.
So far, it has primarily been the owners of buildings who have been able to use solar power for themselves, while tenants have mostly been left out. In the meantime, however, there are also so-called tenant electricity models, in which the tenants obtain electricity from the roof of their residential building or its physical vicinity. Even the smallest systems for the balcony are experiencing an upswing.
Although most PV systems are tied to a fixed location, mobile applications also exist. For example, the lighter and flexible thin-film modules are often used herein systems on a mobile home or houseboat. On a small scale, solar modules can also be found as solutions for the on-the-go or on textiles. In many places far from the grid, you can use complete solar power kits for homes to build off-grid solar systems.
Buy solar panels: Criteria for a solar panel comparison
Buying solar modules individually generally makes sense if they are required for smaller applications and can be installed by yourself. You can create an overall offer considering the desired system performance and the available roof area to purchase a photovoltaic system. But even if these parameters are fixed, users usually still ask themselves about selecting the specific modules.
Numerous manufacturers offer solar modules and various designs, which sometimes causes considerable differences in acquisition costs. Going for the cheapest modules may be tempting, but it’s not always the best decision. Before you buy solar modules, you should compare the product specifications from different suppliers to make the best possible investment.
What about solar panel testing?
Unlike many other types of products, there are no solar module tests that independent and reputable institutions, such as Stiftung Warentest, carry out. On the one hand, it isn’t easy to adequately reflect the constantly changing market.
On the other hand, a quick solar module test cannot adequately consider two essential quality criteria of solar systems: the longevity and the electricity yield over the entire service life that depends on it.
Where to buy solar panels? In any case, it is advisable to buy solar panels from established companies, also concerning a contact person in case of a guarantee. It is not possible to give a general answer as to which supplier produces the best solar modules since it also depends, among other things, on the respective specialization in a certain technology. What is clear, however, is that German and Chinese manufacturers are leading in solar energy. You regularly bring innovative photovoltaic products onto the market. Customers can rely on the good quality of both solar modules from established Chinese and German producers. They will always suggest their favorites if you choose a particular installation company. Let the experts advise you in detail on the advantages and disadvantages.
Get advice before you buy solar panels
Anyone who buys solar modules makes a significant investment. If you want to make sure that you identify the most suitable solar modules for your specific circumstances, you can use the energy check service of consumer advice centers.
Their energy consultants will come to your home and give you individual recommendations. The consultations are funded by the Federal Ministry of Economics and Climate Protection. The joint inspection and development of a concept costs interested parties only 30 euros. Low-income households even get them for free.
Can I install my solar panels myself?
Solar modules are electrical systems. So the most important question is: Which currents are flowing? Our body resistance is 700 to 1000 ohms, so 50 V is enough to reach life-threatening currents of 50 mA. Typical thick-film modules for roof installation are below this at 30 to 40 V, but a mistake can be fatal even when two modules are connected. Not to forget that the installation is usually done at a great height on the roof. It is, therefore, better to let specialist companies do the installation. Not only is this less dangerous, but you are also insured if damage occurs due to installation errors.
Some homeowners think it’s a good idea to do the scaffolding needed for the solar panel installation at home to save money. We also recommend leaving this task to the experts because no insurance will cover the damage if the worst comes to the worst.