How and why do shadows affect solar panels?
Carrying out the installation of a photovoltaic solar system can be somewhat complex since it is important to take into account a series of aspects if we want the installation to provide us with the highest profitability and avoid productivity losses —such as losses due to shadows in solar panels.
How and why do shadows affect solar panels?
In this article we are going to focus precisely on that, on how shadows affect solar panels. Likewise, we explain how you should calculate shadows in solar panels to avoid losses, the distance between solar panels to avoid shadows and possible solutions.
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How do shadows interfere with solar panels?
In order to optimize the operation of solar panels you must avoid shadows at all costs. This is one of the most important aspects that you must take into account when installing them, since they influence the photovoltaic effect —which takes place inside the cells—. Now, what exactly happens with the shadows? The existence of shadows on a photovoltaic panel causes the so-called bypass diodes come into operation in the junction box. This is located on the back of the solar panel, specifically where the interconnection terminals come out. The positive and negative of the panel are marked on it and the bypass protection diodes are located inside it —which avoid the effects that can be produced by the presence of hot spots, as well as by shading—.
Well, both the hot spots, as well as the shadows, make the diodes come into operation and steps are produced in the IV curve, or what is the same, that the energy production decreases —now, it prevents one or several cells from deteriorating. To give you an idea, a solar panel with 20 cells has a total of 3 bypass diodes in the junction box. If at any time, one of these panels receives shade, one of them is activated and the panel ends up producing a third less than it should at that moment. The bypass diode is activated when the sum of the positive voltages of the cells that are not receiving shades—but are associated in series with the shaded cell panel—exceeds the negative voltage of the shaded cell. If this voltage reaches an amount equal to the activation of the bypass diode, then it begins to conduct the energy and offer an alternative path for the current avoiding overheating or hot spots.
And it is that when one or several cells are heated by shadows in solar panels, what happens is that the process is reversed. In other words, it goes from producing electricity to consuming it —due to the polarization of the cells—, which can give rise to the aforementioned overheating which, without diodes, would deteriorate it.
Calculation of shadows in solar panels
There are several ways to calculate shadows on solar panels. For example, using mobile phone applications with which you can check the trajectories of the sun at the solstices and, even, at any date and time of the year —such as Sun Seeker—. This application allows, through the camera, to see the trajectory of the sun at the winter solstice —the most critical throughout the year—. Now, if we want to do an installation and know exactly what the shadow points will be and which ones will not manually, then we can perform a shadow calculation on solar panels to find out the minimum distance (dmin) that the photovoltaic modules must have apart. . In the latter case, what we must do is the following:
- Calculate angle θz. To do this we must apply the angle formula θz = Latitude angle of the place + 23.5º.
- Calculate the angle ɣs to know which is the most critical shadow throughout the year. This formula is ɣs = 90º – θz.
- Calculate the minimum distance formula between the different modules. This is equal to dmin = b [sin (ɣs + β) / sin ɣs].
- β: module inclination angle.
- b: length of the photovoltaic module.
- ɣs: critical angle at the winter solstice.
Losses due to shadows in solar panels
As we explained in the previous points, the shadows on the solar panels can cause losses in energy production —so we will not be optimizing the operation of our solar installation—. To this is added, in addition, the possible consequences of a hot spot —or hot spot— that can cause overheating. Remember that the bypass diodes that each solar panel has serve to bridge the electrical current in order to prevent this from happening, as well as to avoid losses due to shadows in solar panels. Now, depending on the quality of the solar panels, these can be more or less effective.
Solution to shades in solar panels
There are two things that we must take into account to solve shadows in solar panels. First of all is perform a shadow calculation on solar panels —especially when you have a large installation or several panels connected in series and/or in parallel—. The distance between solar panels to avoid shadows indicates the minimum distance at which they must be placed one from the other to avoid shadows being produced between them with their inclination and that of the sun. Above we have explained how the calculation should be carried out and the formulas that we must apply.
The next thing we must do to solve shadows in solar panels is know the inclination that the solar panels should have at different solstices. Of course, it all depends on the region and the country. In the case of Spain, the ideal inclination for solar panels varies between 20º and 40º depending on the latitude. The closer you are to the equator, the smaller the angle of inclination, since the sun’s rays strike more perpendicularly. In the south of the peninsula the inclination is usually around 20º and 25º and in the north around 40º. As we said, the inclination is closely related to the distance between solar panels to avoid shadows.
