Blocking Diodes in Solar Cells

In its most basic form, all that is required for a solar electricity system is a panel to collect the sun's power and a battery to store that energy. When the sun is shining, the panel will produce a voltage higher than that of the battery, causing the battery to get charged. Most panels will include an obstructing diode ( an electrical element that may only allow electricity to pass in one particular direction ) making certain the battery does not discharge thru the panel when the sun isn't shining too.

There are 2 differing types of diodes that may have an important role in the functioning of solar system panels ( really the diodes themselves may be matching as it is the way in which they're used which has 2 chances ). First let us confirm what a diode is and what it precisely does.

What is a Diode

A diode uses a semiconductor material, often silicon, with two terminals attached. Its function in it's a simplest form to allow electricity to pass in one direction though not the other.The diagram to the right shows a simple setup with 2 panels charging a battery ( for simpleness no controller is shown ) with a blocking diode in series with the two panels, which are also wired in series. When the sun shines, as long as the voltage produced by the 2 panels is larger than that of the battery, charging will happen.

However , in the dark, when no voltage is being produced by the panels, the voltage of the battery would result in a current to flow in the other direction thru the panels, discharging the battery, if it was not for the obstructing diode in the circuit. Obstructing diodes will be of benefit in any system using solar panels to charge a battery. Blocking diodes are often included in the construction of solar panels so further obstructing diodes aren't needed.

By-Pass Diodes

Now let us consider what will happen if one of the panels in the above diagram is shaded. Not only will that panel not be making any major power, but it will also have a high resistance, blocking the flow of power produced by the unshaded panel. This is where by-pass diodes come into action as demonstrated in the diagram to the right. Now, if one panel is shaded, the current produced by the unshaded panel can flow through a by-pass diode to bypass the high resistance of the shaded panel.

By-pass diodes may not be of use unless panels are connected in series to produce a higher voltage. They're most certain to be useful where an MPPT Controller or String Inverter involves panels connected in series to supply voltages well above that items minimum input voltage. Some solar cells are made with the cells divided into groups, each group having a built-in by-pass diode. Shading of part of a panel might be due to a tree branch, debris, or snow.


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