Photovoltaic panels can be used to generate electrical energy in both domestic and commercial applications.
Photovoltaic modules are made up of a set of photovoltaic cells interconnected with each other. The photovoltaic panel is in charge of directly transforming the energy from solar radiation into electricity, in the form of direct current.
The rest of the elements of the photovoltaic system will be in charge of managing and transforming this voltage into alternating current, if necessary. This function is performed by:
- Charge regulators.
- Power inverters.
Where should I locate and orient the panels?
The most appropriate orientation and inclination in each location depends on the latitude and the time of year. The most advisable is a study of solar radiation received for each location.
In the northern hemisphere, for example, the plates must be oriented in a southerly direction and with a certain inclination.
On the other hand, the inclination of the modules will vary depending on the planned energy needs and the period of use, in order to make a seasonal (winter, summer) or annual balance.
How is electricity generated by photovoltaic panels?
The solar cell is only capable of generating a voltage of a few tenths of a volt (+/- 0.5 V) and a maximum power of 1 or 2 Watts. Therefore, it is necessary to connect several cells in series (which behave like small current generators) to achieve voltages of 624 V, accepted in many applications.
Photovoltaic panels produce electricity in the form of direct current and usually have between 20 and 40 solar cells. In any case, it is usual for the modules to be made up of 36 cells to reach the volts necessary to charge the batteries (12V).
Connection of several solar panels
Photovoltaic solar panels can be joined together in two ways:
- Parallel connection . This type of connection is made by joining the positive poles on the one hand and the negative poles on the other. The parallel connection between the solar panels provides a voltage equal to that of the module (12-18 V)
- Serial connection . The way to connect two or more photovoltaic panels in series is to connect the positive pole of the first one with the negative pole of the second one and so on. The series connection gives a voltage equal to the sum of that of each module (for example 12 V, 24 V, 36 V, etc.), depending on the number of interconnected boards.
What are the different technologies of photovoltaic modules?
Of the many materials that can be used to build photovoltaic modules, silicon is the most widely used. Silicon is obtained in wafers which are then joined to form a photovoltaic module.
The most common types of photovoltaic cell construction are:
- Monocrystalline silicon: cells have an efficiency of 18-21%. They tend to be expensive and are also present, they are cut with cylindrical ingots, it is difficult to cover extended surfaces with them without wasting material or space.
- Polycrystalline silicon: cheaper cells, but less efficient (15-17%), whose advantage lies in the ease with which it is possible to cut them into suitable shapes to join in modules.
- Amorphous silicon deposited by vapor phase: photovoltaic cells have a low efficiency (8%), but are much cheaper to produce. Amorphous silicon (Si-a) has an important band of crystalline silicon (Si-c). This means that it is more efficient in absorbing the visible part of the spectrum of solar radiation, but less effective in collecting the infrared part. Since nanocrystalline silicon (with nanometer order crystalline domains) has approximately the same Si-c band gap, the two materials can be combined to create a layered photovoltaic cell, in which the upper Si-a layer absorbs visible light and leaves the infrared portion of the spectrum to the lower nanocrystalline silicon cell.
- CIS: The cells are based on layers of calcogenuro (for example, Cu (InxGa1-x) (SexS1-x) 2). They have an efficiency of up to 15%, but their cost is still too high.
- Photoelectrochemical cells: These photovoltaic cells, first built in 1991, were originally designed to mimic the photosynthesis process. This type of cell in a photovoltaic module allows for more flexible use of materials, and production technology appears to be very convenient. However, the dyes used in these cells suffer from degradation problems when exposed to heat or ultraviolet light. Despite this problem, this is an emerging technology with a commercial impact expected within a decade.
- Hybrid Photovoltaic Cell - Combines the advantages of organic semiconductors and various types of inorganic semiconductors.
- Concentrated photovoltaic cell: the use of this cell in a photovoltaic module combines the aforementioned technologies with solar concentration lenses that significantly increase efficiency. They represent the promising new generation of panels still in development.
- Monocrystalline silicon, in which each cell is made of a wafer whose crystalline structure is homogeneous (monocrystalline), appropriately doped to form a pn junction;
- Photovoltaic module with polycrystalline silicon, in which the aforementioned wafer is not structurally homogeneous, but is organized in locally ordered grains.
What materials are used for the structures of solar panels?
When using a support structure for the solar modules, it is advisable to use materials that have good mechanical properties, as well as great durability, taking into account the long useful life of the installations. Normally, the support elements are:
- Anodized aluminum (light weight and high resistance)
- Galvanized iron (suitable for heavy loads
- Stainless steel (for highly corrosive environments, it is the highest quality and highest price)
There is also the possibility of making the structures of the photovoltaic modules with wood, duly treated.
Wooden structures must have minimal maintenance operations, and must present acceptable conditions for this use. Fixing parts, such as screws, should always be made of stainless steel.
How can the performance of photovoltaic modules be improved?
In certain cases, in order to increase the yields of the collection system, you can choose the following techniques:
- Solar trackers. Provide movement to the support structure with solar tracking systems.
- Light diffraction. Diffraction is a characteristic phenomenon of waves that is based on the deviation of the waves when encountering an obstacle or crossing a slit.
The solar trackers work by means of a motor normally associated with a computer that, depending on the date and time of day, adjusts the orientation of the panels, either with respect to one or the two axes of the plane that contains the panel. These systems are naturally more complex and involve greater expense and higher maintenance.
The phenomenon of light diffraction makes it possible to obtain photovoltaic panels with a transparency index higher than the apparent one, since the shadow cast by each cell inside the building is less than the surface it occupies.
This implies that the solar panel is perceived significantly more opaque from the outside than from the inside.
It is also possible to obtain greater transparency if, within the same plate, the distance between the cells is increased.
How is a photovoltaic module composed?
The photovoltaic plate is designed to withstand the conditions that occur outdoors and to be part of the "skin" of the building. Its useful life is considered 25 years.
The cells are encapsulated in a resin, and placed between two sheets to form the photovoltaic modules. The outer sheet is glass and the back can be opaque plastic or glass, if you want to make a semi-transparent module.
Crystalline silicon and gallium arsenide are the typical material choices for solar cells. Gallium arsenide crystals are created especially for photovoltaic uses, but silicon crystals are also produced for consumption by the microelectronics industry.
Polycrystalline silicon has a lower conversion rate, but at a reduced cost.
When exposed to direct 1 AU light, a 6-centimeter-diameter silicon cell can produce a current of 0.5 amps at 0.5 volts. Gallium arsenide is more efficient.
The glass is cut into small discs. It is polished to eliminate the danger of cutting. Dopants are inserted into the discs. Metal drivers are deposited on each surface: a small connector on the sun-facing surface and a connector on the other side. Solar modules are built with these cells cut into appropriate shapes, protected from radiation and damaged by applying a layer of glass and cemented onto a substrate (either a rigid or flexible panel).
The c electrical onnections performed in series-parallel to determine the total output voltage.
The protective layer must not be a thermal conductor. Since heating the cell reduces operating efficiency, it is desirable to reduce this heat.
Currently, the costs associated with solar modules are cheap in applications where power from electric stations is available.
The cost of fossil fuels is increasing, and the production experience is reducing the costs of solar cells, this may not be seen in the very near future, but in the long run the trend is an increase in the use of this type of energy renewable.
Photovoltaic plates as a constructive element
The photovoltaic panels used in systems connected to the network are not different from those used by autonomous systems. Those that are integrated into buildings are normally standard modules.
A common problem is the fact that they can configure independent structures, superimposed on the building, added without meeting aesthetic criteria. At best, they are integrated into the facades or the roof. For this reason, some companies have developed photovoltaic elements integrated into buildings that can replace some traditional elements of architecture.
The photovoltaic panels can therefore be treated as a constructive element and combined with other materials in prefabricated modules with a large surface area (currently up to 14 m² are manufactured).
They are appropriate for the formation of facades, the best orientation of which is the south, although the influence of a deviation of between 30º and 45º to the east or west is not important in the annual computation of energy capture.