PHOTOVOLTAIC SOLAR PANELS SPECIFICATIONS

Generally speaking, there are three  types of solar panels  based on how their cells are: monocrystalline, polycrystalline and amorphous.

In all the manufacturing processes, one of the first steps is the obtaining of  metallurgical silicon , with purities close to 98%, from pieces of quartz stones from the different deposits. In these processes sands are not usually used.

They are subjected to carbon reduction processes and then to purification of the material by chemical distillations until they reach purities suitable for the manufacture of photovoltaic elements.

Monocrystalline solar cells

The panels manufactured with monocrystalline cells are those that have a  higher performance  and are more stable over time. Logically, they are also usually the most expensive.

Its cells are manufactured by a complex crystallization process   controlled at high temperatures, close to 1500 ° C, from a single germ that achieves a cylindrical ingot forming a unique crystalline structure. This crystalline bar is cut into thin sheets or  wafers  with thicknesses of around 0.3 mm.

Polycrystalline solar cells

Polycrystalline cells are manufactured from metallurgical silicon by  less extensive solidification processes  . The growth of the silicon crystals is not controlled so that different crystalline structures are formed  . This allows the manufacture of ingots of rectangular shape that facilitates the later conformation of the photovoltaic cells.

Panels with polycrystalline cells have slightly lower yields at lower costs.

Amorphous cells

The third method of manufacturing consists in depositing in a controlled manner thin layers of photovoltaic material on different materials that act as  support . Silicon, cadmium telluride, copper, gallium or selenium are fixed to plastics, glass or tissues allowing the manufacture of flexible cells   or integrated into different building materials.

The thickness of the cells is reduced up to fifty times, which also allows considerable savings in raw materials.

This allows a reduction of the panels that integrate this type of cells and diverse applications: photovoltaic modules integrated in tiles or glass, flexible panels, transparent or of different colors, etc.

With the improvement of the different manufacturing systems, the differences in the performance of the different types of cells have been reduced. The economies of scale have allowed a  cheapening  of the products and the technological advances allow to increase the efficiency of all the systems.

Photovoltaic panels are characterized, from an electrical point of view, by a series of  parameters  or curves. The most representative and that should facilitate the manufacturers to assess their suitability are:

• Maximum power : It is the most important feature of the panel. It results from multiplying the maximum or peak voltage by the maximum intensity of current or peak.

• Open circuit voltage : The maximum voltage that the panel provides if there is no current flow through its circuits.

• Short circuit current : It will be the maximum current that the panel provides if there is no resistance.

• Total efficiency : It will be the result of dividing the electrical power produced by the panel and the power of the radiation incident on it.

Technical characteristics of a solar panel

There are basically 5 concepts that are those that can escape us, such as:

Open circuit voltage or VOC  (Open circuit Voltage): means the voltage in volts that the panel delivers when it is disconnected, that is, if we put a voltmeter in the terminals of a panel that is in the sun and disconnected from the installation, that it will be the voltage that we can measure. This data is very important because it must be taken into account for load regulators, network inverters, etc.

Short circuit current or ISC  (Short Circuit Current): means the current in Amperes that the panel can produce when shorted. It means that if we join the positive cable of the panel with the negative cable it is short-circuited, and by means of a measuring clamp we can check the maximum intensity that the panel is capable of producing.

Voltage at maximum power or VMP  (Maximum Power Voltage): is the figure that determines what type of panel is, 12V, 24V or whatever. To be a 12V panel the figure must be between 15 and 19V , while  to be 24V this figure must be between 36 and 39V . This is so because in isolation, the voltage offered by the panel must always be higher than the battery’s charging voltage. In the case at hand, it is a 12V panel.

Intensity at maximum power or IMP  (Maximum Power Current): It indicates the maximum intensity in amps that the panel produces when it is connected to the installation. It is the figure to take into account to not be limited by the charge controller. If as the example panel of the image produces 11.13A, we can not use a 10A regulator, since it will be short for the power that the panel can deliver.

Maximum power or PMAX : is the power figure that determines the model of the panel, we can also calculate it if we multiply the VMP x IMP. This figure is given in Watios and in the example we see, they are 200W.

All these measurement figures, as expected, are made in a controlled environment in temperature and radiation. In a laboratory with 1000W / m2 of radiation and with a cell temperature of 25º as it also says in the attached sticker. This happens because at room temperature, the performance of the panel gets worse if it gets hotter. An increase of 20ºC reduces the yield between 8 and 10%

Other data of interest also appear, such as the maximum voltage of the system, which determines that the panel is designed to be installed together with others but that as a whole they do not exceed a certain voltage, in the case at hand, of 1000Volts. We can also see the manufacturer’s weight, dimensions and technical certifications, as well as other commercial and contact information.