The Solar Panel, composed of photovoltaic modules or solar plates (popular name), is one of the key equipment of a solar photovoltaic system and is responsible for converting sunlight into electrical energy, with a standard useful life of 25 years and resistant to the most adverse climatic conditions.
When we mention solar photovoltaic systems, the image that comes to mind for most people is that of the solar panel installed on the roofs of homes and businesses, which captures sunlight and transforms it into electrical energy.
However, do you know what these plates are made of, how are they manufactured and what is the exact process that results in the generation of electrical energy using solar energy?
Even though it is the most important component in a photovoltaic solar system (also known as solar photovoltaic generators), the so-called solar panel is by far the most apparent.
All this exposure happens because, especially when installed in a house in the city, the space available on the land is usually reduced, implying the use of the solar panel on the roofs.
The big secret is the positioning of the solar panels so that they receive a greater direct solar radiation, without the interference of shadows, thus taking advantage of this source of renewable energy so abundant that it is the sun.
The direct incidence of solar radiation is very important for photovoltaic cells to have the best efficiency in converting solar radiation into electrical energy, because the more direct light the photovoltaic panel receives, the more electrical energy will be generated.
This is because the functioning of the photovoltaic cells that make up the photovoltaic modules (as solar panels are correctly known) is extremely dependent on the entry of light particles (the photons) inside.
Understanding how the Solar Panel works
What makes a photovoltaic cell generate electricity is the photovoltaic effect, which is nothing more than the appearance of a potential difference (that is, a voltage, popularly known as voltage) inside, caused by the action of photons (particles of light) that interact with the electrons of the atoms of the material used for the production of the photovoltaic cell.
It is common to represent the photovoltaic effect through an image that symbolizes a photovoltaic cell, as shown below:
The sunlight particles, the photons, when in contact with the photovoltaic cell, cause the electrons of the silicon atoms to energize and detach themselves, being transported from the negative side to the positive side, thus creating a continuous electric current.
The disadvantage of photovoltaic modules
A disadvantage is that, of all the solar radiation that reaches the photovoltaic modules, only a percentage of it arrives in adequate conditions for the photovoltaic effect to occur in its cells.
Of this usable part, only a small amount can be used by the modules for the generation of solar electric energy, due to the losses due to its electrical and physical factors.
By definition, a photovoltaic module (the correct name for what is popularly called a solar plate) is a set of associated photovoltaic cells (usually in series) and encapsulated with materials that provide mechanical strength, allowing light to enter, aiding in cooling and allowing the association of several modules and their fixation in an appropriate structure.
A typical photovoltaic module (solar plate) made with crystallized silicon photovoltaic cells (c-Si) has the physical structure shown in the image below:
Physical structure of a typical photovoltaic module made with crystallized silicon cells
What we see in the image above is a “sandwich” of the photovoltaic cells between a glass slide, on the top of the module.
A thermoplastic elastomer blade (whose acronym in English is TPE, of thermoplastic elastomer), on the bottom.
Between glass, photovoltaic cells and TPE, ethylene vinyl acetate sheets are used (also called ethyl vinyl acetate; in English: ethylene vinyl acetate; better known by the acronym EVA).
The whole set is pressed and heated in a laminator, which permanently unifies the blades, and the set, when perfectly laminated, is extremely difficult to separate.
At the end of the process, the frame, made of aluminum, and the electrical connection box are assembled, which allows the interconnection between the photovoltaic modules.
Resistance of the Solar Panel to Hail
The hail resistance is tested using a device that fires 25 mm² ice spheres (with a mass of 7.53 grams) at a speed of 82 km / h.
The test is done with 11 impacts, that is, 11 spheres are fired in different places of the photovoltaic module (plate or solar panel), which must come out intact, without breaking the front cover glass.
In real life the ice crystals that form hail are much less dense than an ice sphere, and fall at much lower speeds.
In practice, photovoltaic modules are extremely resistant to hail.
Solar Plate Holder
The fixing structures are as important as the panel of a photovoltaic system, because its poor performance can completely invalidate the investment in technology.
A fixing structure is vitally important for a photovoltaic system as it is what, as the name makes clear, fixes the modules on the roof or on the ground.
Wind loads are a very important factor to be considered when installing the photovoltaic panel, as they project on the plates (flat structures and without flow), and consequently on the structure, an excessive weight depending on its strength.
As the structure plays a key role in wind resistance, it has to be measured and measured in wind tunnels to be strong enough to withstand storms, either on the roof or on the ground.
To ensure that the system works correctly during its long service life of more than 25 years, it is recommended that you purchase a good quality structure with a manufacturing guarantee.
Another important role of the support is to provide the ideal inclination of the modules so that they are able to capture the largest amount of sunlight possible, increasing their efficiency and generation.
The correct orientation allows to capture the maximum energy at the solar noon and close hours, as well as improves the annual capture of the panel as a whole, compensating for the less irradiance during the winter periods.
The ideal inclination of the photovoltaic panels varies according to the Latitude of the locality, and as to the type of photovoltaic system.
For systems connected to the grid, lower slopes provide greater uptake in periods close to the summer solstice, generating more energy and more energy credits.
Photovoltaic panel – 10 things to know when choosing yours
There are several pieces of information that must be considered when choosing a photovoltaic panel. We have chosen 10 items that we consider most important for you to know and buy the right photovoltaic panel:
1- Photovoltaic panel warranty
It is not possible to determine the quality of the photovoltaic panel (solar panel) just by looking at a budget, it is necessary to look at its technical data sheet.
Solar Panel Power
There are different powers of solar panels for various applications. Generally, solar panel wattages range from 305 w, 310 w, 320 w, 330 w, 335 w, 340 w, 345 w, 350 w, 355 w to 405 w.
The vast majority of photovoltaic panels have a power guarantee of 80% of their original power for up to 25 years. The main criterion is to verify if the guarantee is supported by a Brazilian entity that will comply with the consumer protection laws, in case there is any failure in the performance of your photovoltaic panel.
Ask your installer how to deal with a defective photovoltaic panel, ask yourself if that company will be there for the next 10, 20 years to assist you if that happens.
Maximum panel power (Pmax – STC)
The maximum power of a solar panel, indicated in Pmax – STC, is characterized by the reference number when we talk about “size” of the solar panel. This means that a 250 W solar panel has a maximum power of 250 W, therefore, its classification is based on the energy production measured in laboratory conditions, “Standard Testing Conditions” (STC – Standard Testing Conditions) that do not represent the real conditions in our country.
The power tolerance is measured by the interval that the manufacturer of the photovoltaic solar panel refers to the module that can deviate from its maximum power (Pmax – STC). That is, if you have + 10% / – 10% power tolerance in a 250 W photovoltaic panel, in fact, this panel has between 225 W and 275 W.
Thus, it is very common to have a negative energy tolerance of 0%, which means that the panel will always have the maximum rated power (Pmax – STC) greater than or equal to that specified in the data sheet. Therefore, it is recommended that the consumer look for panels with a negative energy tolerance of 0%.
Maximum power in NOCT
In the case of the maximum power in NOCT, the number is measured by the maximum power of the photovoltaic plate when tested under more severe conditions in relation to the maximum rated power (Pmax – STC). Therefore, the power is dimensioned with less sun and higher panel temperatures, typically between 70 and 75% of the power reported in Pmax, being very useful to evaluate the amount of energy lost due to rising temperatures and in a lower condition. Sun light.
Still, it is worth noting that not all panels have this number, so if this data is not reported on your material, it is a sign that it does not belong to one of the best manufacturers.
2- Efficiency of the photovoltaic panel
When we talk about the efficiency of the photovoltaic solar panel (photovoltaic plate), we are talking about the percentage (%) of energy from the sun that reaches the surface of the solar plate and is transformed into electrical energy for our consumption. That is, how many Watts / hour per m2 the solar panel generates energy.
The higher the efficiency of the photovoltaic panel, the more Watts per square meter your photovoltaic system will generate and the smaller the photovoltaic solar panel for the same energy production.
3- Manufacturer of the photovoltaic panel
There are hundreds of manufacturers of photovoltaic solar panels in the world and most of the photovoltaic panels (photovoltaic plates) are still imported. Do a quick Google search for the manufacturer of the photovoltaic panel. How is his website? Is there a warranty section on their website? Do they have an office in Brazil? Are there any complaints about this manufacturer?
4- Type of photovoltaic panel
Is it a mono-crystalline, multi-crystalline, thin film or other technology photovoltaic Solar Panel? The types of photovoltaic solar panels (photovoltaic plates) and their pros and cons are discussed in the section of the link above. Make sure that you are happy with the technology you are choosing.
5- Power tolerance of the photovoltaic panel
This is the variation between the power indicated on the technical sheet and the actual energy generated. For example, a 330W photovoltaic solar panel with a tolerance of + 5 / – 5% can produce anything from 313.5W to 346.5W.
Be aware of this number, as it will directly affect the amount of energy you are going to generate.
Some manufacturers of photovoltaic panel (photovoltaic plate) have a guarantee of “positive tolerance”, this means that the energy production is guaranteed to be at least what is specified in the solar panel. For example: a photovoltaic solar panel with a specified power of 330W and a tolerance of + 5% / -0% will produce a minimum of 330W and a maximum of 346.5W.
6- Quality of the aluminum “frame” of the photovoltaic panel
The aluminum frame, which goes around the photovoltaic solar panel is a good indicator of the overall quality of the photovoltaic panel manufacture.
Look at the corners. Are they perfectly united? Has the frame been glued (not advisable), screwed or welded in the corners?
If looks are important to you – then look for a photovoltaic panel that has been anodized in black – they are beautiful! (but can be more expensive)
7- The bottom layer of the photovoltaic panel (backsheet)
All photovoltaic solar panels (photovoltaic plates) have a plastic bottom sheet glued to the back of the photovoltaic panel to protect the photovoltaic cells. If the sheet has air bubbles or signs that it is coming off, this is a sign of a low quality photovoltaic panel.
8- Photovoltaic panel bypass diodes
If your photovoltaic panel is mono or multi crystalline then Bypass diodes are mandatory. They are diodes that cost a few cents each and are placed in each “series of photovoltaic cells” on the back of the photovoltaic solar panel. If you do not have bypass diodes, a small shadow on a small part of your photovoltaic solar panel can affect the energy production of the entire panel.
9- Cost of the photovoltaic panel
The obvious calculation to make is to calculate how many “Watts” for “R $” you are buying. Remember, most of the time you get what you pay for, so be careful when choosing a solar system just for the price. However, there are promotions and some suppliers actually have more competitive prices for photovoltaic panels than others. Just be sure to compare correctly taking into account warranty, service, product, quality, etc. Note: the cost of solar energy systems can be substantially affected by the difficulty of installation. (the more difficult it is to install, the more expensive it will be).
10- Temperature coefficient of the photovoltaic panel
The temperature coefficient is a number that describes how the photovoltaic solar panel handles hot temperatures – where hot is defined as a temperature greater than 25 degrees Celsius.
The units of this coefficient are expressed in “%” by degrees “C”
The lower this number, the better!
The more sun you have on your roof the more energy you can generate. Not if this number is too high … The higher this number, the less energy it will produce on very hot days, when the sun is in full swing!
A high temperature coefficient is a sign of a poor quality panel. A reasonable number is between 0.4 and 0.5%. Above 0.6% is a warning sign. Between 0.45 and 0.3%, it is a sign of an excellent photovoltaic solar panel.