Connecting Solar Panels in Series
Welcome to this information page Mppt Solar. After you have learned in the previous article how to connect solar panels in parallel, this page will teach you how to connect them in series to obtain an output voltage increases available, while maintaining the rated current. We also explain the difference between a series connection of two or more photovoltaic panels equal and a series connection of two or more photovoltaic panels with different technical characteristics. Finally we will provide valuable and practical tips for getting a really efficient system and avoid the dreaded hotspot effect that can occur in the presence of clouds in the sky or partial shade along the bodies of our solar cell strings.
What is a solar panel and a solar cell?
Well, to better understand the connection in series, we start with a little theory about the solar panel! A photovoltaic panel is an optoelectronic device made by more photovoltaic cells normally connected in series. In Italy the most panel is marketed by 230Wp 32V and is composed of 60 polycrystalline silicon solar cells connected in series. A photovoltaic cell, or solar cell is an element that has the ability to transform solar energy into electricity by capturing the sun's rays. This phenomenon is known with the name of the photovoltaic effect. The solar cells that are more commercially are made of semicrystalline material (silicon) and have a black or blue.
Series connection of two or more identical solar panels
If we have two or more solar panels of the same current and power, and we want to increase the voltage, the connection that suits our case, the series connection.
When connecting several panels in series increases the voltage. In a photovoltaic system, greater is the system voltage and lower are the energy losses along the cables. To find out the maximum system voltage we can get, you need to check the Maximum System Voltage, normally reported on the label of the panels. After these clarifications, let's see how is the series connection. It 's very simple. As is clearly visible in the figure on the left, simply connect the positive terminal of one panel to the negative terminal of the other one and we will find a doubling of output voltage. Considering the example of the figure, two panels 12V 5A connected in series, produce an output voltage of 24V and a current of 5A. The current remains unchanged. In parallel to each panel we have added a diode, called a bypass diode (not to be confused with the blocking diode), which has a particular function, which we will explain later.
What does it happen in case of shading?
To obtain an optimal performance of the whole photovoltaic system is good that the panels do not shadow each other, which have the same angle and that they are positioned away from possible causes of shading as for example may be trees, poles or protuberances. Of course, in case of shading due to weather conditions is not physically possible to do much. Knowing the behavior of the entire string in case of shading is essential to avoid drastic yield losses of production of electrical energy. As we explained previously, a photovoltaic panel is composed of multiple solar cells connected in series. If a part of the panel is obscured, in that part is formed a high resistance that hinders the flow of the current. In the worst case instead of shaded solar cells produce energy, absorb, making the loads. The current which passes through them, by Joule effect, causes an increase in temperature and this rise in temperature can even cause the fire of the cells or the dissolution of welds (hotspot effect).
It is unclear how the presence of a small shadow can result in a major loss of energy of the entire system. To avoid or better to reduce this problem, some manufacturers of photovoltaic panels have divided the panel in various sections comprising a certain number of cells, and in each section has been inserted a bypass diode. This diode has the function to exclude the section of the panel which is located in the shade, so that this section does not adversely affect the entire panel. E 'therefore very important to choose, during the design of the photovoltaic panels that have the bypass diodes. More bypass diodes have and is divided into several sections panel. But if the shadow covers an entire panel and the other not? Here is that we must be inserted in parallel to each panel bypass diode. In this way if a panel is shaded, will be excluded through the bypass diode and will not adversely affect the production of the other panels connected in series. In a photovoltaic system connected to the network (grid-connected), the role of search for the maximum power point tracking (MPPT) is performed by the inverter grid-connected, while in a stand-alone photovoltaic (stand alone) the role is played from the mppt solar charge controller.
Which bypass diode should I choose?
The choice of the bypass diode must be based on two factors: the first factor is the proper protection of the string in case of shading and the second factor is the lower power dissipation in the diode itself. It 'is therefore important to select particular diodes, called Schottky diodes, they can safely withstand the current of the panels and which have a very low threshold voltage. The lower the threshold voltage and the lower the power dissipation on the photovoltaic diode.
Serial connection of two or more different photovoltaic panels
If we have two or more photovoltaic panels with equal voltage but with different current it is NOT possible to connect in series but it is possible to connect them in parallel. The parallel connection allows to increase the current, maintaining the same voltage. For more information, visit the page how to connect solar panels in parallel.
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