Why shading drastically affects the whole output of a solar power system
Author: Darvin Tocmo Date Posted:27 July 2018
Shade is a wonderful thing, especially in the summer; however, it is bad for solar power and solar lighting applications as shading drastically affects the whole output of a solar power system. In fact, a shadow cast on even just part of one solar panel in your solar array can potentially compromise the output of the whole system. I this article we will be tackling on why shading affects solar power and what are some strategies that we can do for dealing with potential shading of solar arrays.
Why does shading have such a dramatic impact on energy production?
In sunlight, each solar cell in an array acts as a little electron pump, pushing electrons from one side of the cell to the other, and giving a voltage boost to the system as they do so. A single cell isn't very powerful though, so in order to get a useful voltage, you need to put quite a number of cells in series. The output of one cell becomes the input to the next cell.
When a cell is shaded, the number of electrons it can pump from one side to the other drops. That, in itself, wouldn't be too bad you might think - you would just lose out by the power output of one cell. But unfortunately, because it is not pumping so many electrons up to its neighbor now, it limits the number of electrons that the neighbor can pump too. Same for the next cell in the line - and the next, and so on.
You can think of a string of panels as something like a piece of pipe, and the solar power is like water flowing through that pipe. In conventional solar panel strings, the shade is something that blocks that flow. If, for example, shade from a tree or a chimney is cast on even one of the panels in the string, the output of the entire string will be reduced to virtually zero for as long as the shadow sits there. If there is a separate, unshaded string, however, this string will continue to produce power as per usual.
In extreme cases, a shadow does not necessarily need to fall on an entire panel – depending on the technology used in the solar panel in question, shading of even just one cell could flatten the output of the panel and in turn the entire string. Many modern panels, however, come equipped with devices called bypass diodes which minimize the effects of partial shading by essentially enabling electricity to ‘flow around’ the shaded cell or cells.
How to deal with shaded solar panels
Although the performance and therefore the return on investment (ROI) from a solar power system can be severely affected by shading – especially shading that occurs regularly due to an object that casts a shadow at the same time every day as the sun passes through the sky – there are a number of ways to avoid or mitigate these effects.
- Use a string inverter that has MPP Tracking capability
Maximum Power Point Tracking (MPP Tracking or MPPT) is a technology that now comes standard in most quality inverters. An inverter equipped with an MPP Tracker (or several of them) is able to squeeze the most usable energy possible out of a string of solar panels (even when shaded) by adjusting the voltage to always suit the inverter’s preferred input range. In a nutshell, an MPP Tracker helps to minimize output losses associated with partial shading and other panel output mismatches. Inverters without MPPT capability simply lose the output from the weaker string once it passes below the required output threshold.
You can also break the array into chunks, and put an inverter on each or use an inverter with dual MPPT. You can even go to the length of putting an inverter on every single panel - Enecsys micro inverters and Tigo voltage optimizers, for example, work on this principle. This will increase the price of your system, but it will be more effective.
- Use Seraphim Blade Series
The Seraphim Blade Series boasts two identical parts, each comprising cells that are half the size of ordinary solar cells. Instead of 6 internal strings of cells, the series has 2 X 6 shorter ones – resulting in dramatically improved performance.
Six strings are connected in a series per block, and the two blocks connected in parallel. A split junction box is positioned in the middle of the module to the output current.
When a module is shaded, only one side shaded arrays current will be affected, while the other array will be functionally producing power. Under the circumstances, when a module is shaded, the affected working areas of the blade will be 50% less.
With the technology used in Blade Series, the internal power loss will be lowered and the hotspot effect will be reduced.
The graph below shows the effect of shading on Conventional vs Blade modules.