Solar Panel Blocking Diode

As long as the sun shines, voltage is produced by the Solar Panel panels connected to your battery in your Solar Power System but come night time in the dark, when no voltage is being produced by the panels, the voltage of the battery would cause a current to flow in the opposite direction through the panels, discharging the battery, if it was not for the blocking diode in the circuit. What is a Solar Panel Blocking Diode?

Because current naturally moves from high to low, a Solar Panel Blocking Diode uses a semiconductor material, that prevents batteries from releasing voltage in reverse through the solar panels during the evening when no energy from the sun is being produced and moving through to the battery.

In the world of Solar Power, all the components involved in the system need to function for the system to do what it’s supposed to do, which is to make Solar energy and move it in one direction to charge your batteries, where it can be stored then used when it’s needed.

What is a Blocking Diode


A Diode uses a semiconductor material, usually silicon, with two terminals attached. Its function in its simplest form is to allow electricity to pass in one direction but not the other. In plumbing, a Diode works like a check valve keeping water moving one way so it won’t back -up.

Blocking diodes are used to keep batteries from releasing power in reverse through the solar panel boards during the evening when no energy from the sun is moving through to the battery.

Current streams from high to low voltage, so on a bright day, the voltage of a panelboard will be higher than the voltage of a profound cycle battery and this energy will normally spill out of the PV panel to the battery.

By function, all diodes block electrical current; however, blocking diodes are used specifically to prevent a reverse flow of electrical power in order to protect batteries, charging systems, or power generation systems. Blocking diodes are used heavily in green-energy systems such as solar or wind-powered electrical generators. Most Diodes are involved in Solar Systems and wired in Solar Panels these days but not all. All Solar Systems now use a Charge Controller as a block between the Solar Panels and the Battery


Bypass Diode

A Blocking and By-pass Diodes are basically the same things it’s just how they’re wired and what their function is that makes them different. By-Pass Diodes are used to reduce the power loss that happens when shading occurs in the Solar System this is because current flows from high to low voltage. By-pass diodes will not be of use unless Solar Panels are connected in series to produce a higher voltage.

When a solar panel has cells that are partially shaded it creates high resistance and the current will be forced through those lower voltage shaded cells. This will cause the cell on the panel to heat up and creates power loss. Those shaded cells become consumers of solar panel energy instead of being providers of energy.

However, at night, if the panel board is associated specifically with a battery, the voltage of the panel board will be lower than the voltage of the battery, so there is a probability of some retrogressive stream, which means it draws power out of the battery. It will not be as much as the stream in the day, however. This figure shows the By-Pass Diode in a PV panel, which shows the wiring position for preventing the backward flow of voltage.


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How to Test a Diode in a Circuit

Testing a Diode is a very easy procedure to perform. You will be needing a Digital Volt-Multimeter and the procedure, here in this video I picked out a good explanation of how to test it. One thing to remember is that when you measure the voltage across a Diode there is a voltage drop called Vf since there is a voltage drop from the beginning to the end across the Diode there is some heat being generated inside the Diode. Vf x the current gives the current in watts. This formula might come in handy working with Solar power.

Solar panels need a diode to prevent current flow back into the battery when there is little or no light. For solar panels, use a 3 amp or an 8 amp diode that can be used for this purpose. You might also want to install a bypass diode to prevent a shaded panel from drawing down other panels that happen typically when using an array of Panels in a bigger system. These same diodes can be used. Place diodes in an ABS project box at the back of the panel.

If you are using a solid-state charge controller, such as the C150-SMA charge controller, you may not need a blocking diode. Charger Controllers are inexpensive and can be added after each Solar Panel if you desire. There are vast amounts of Charge Controllers that run from 20 bucks to 500 dollars so that you direct the flow of electric current through your system. It’s a very important piece of equipment but you don’t need to go broke buying one. This one on Amazon will do Solar Charge Controller 20A Solar Panel Battery Controller 12V/24V PWM Auto Parameter Adjustable LCD Display Solar Panel Battery Regulator with Dual USB Load Timer Setting ON/Off Hours

If it is a full sun outside, and you are still getting fewer volts out of a Solar Panel than you normally do and you suspect that the Diode in the junction box is blown then test the Diodes, using this easy procedure. Using a dependable Digital Multimeter like this Fluke 117 Electricians True RMS Multimeter at Amazon is a fine piece of equipment.
  • Bring the Solar Panel inside and out of the Sunlight and artificial light inside
  • Open the Junction Box if it is available on the back of the Panel
  • Turn your Multimeter to the Diode setting(the sitting with the arrow and line through it) this shows the anode and the cathode
  • Connect the positive to the anode side of the diode and the negative side of the cathode side of the diode.
  • You should get a reading somewhere between 0.2 and 0.6 resistance between each side that will show you its blocking and working
  • Change the meter’s probes around to the opposite side-negative to the anode side and positive to the cathode side and you should get an.OL reading which means out of level or no reading.
  • If the Diode is bad swap



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JimGalloway Author/Editor



Bocking and By-Pass Diodes in Solar Panels




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