The blocking diode ensures that the current does not flow in a reverse direction. It plays a vital role in protecting against discharge during the night or when your batteries are fully charged. Blocking diode is another name for the rectifier since it allows the current to go in a single direction, but inhibits the flow of opposite current.
To make it simple, a blocking diode can be considered as a one-way valve of your water sprinkler allowing only the water to flow upwards. During old times, blocking diodes were most commonly used as they performed way better than batteries from getting over-charged.
Since most modern designs use MPPT charge controllers that work together with lithium-based battery technologies, one system can withstand some hours or sometimes days without getting under-loaded, hence no concerns of over-charging. Blocking diodes are comparatively cheap and simple to mount. However, they may impair operation with no appreciable improvement.
What is the Purpose of Blocking Diode?
It ensures that once batteries are supplying the load during the evening, the sun’s energy can’t go back to these batteries. Once the sun sets, solar cells stop generating electrical energy. Solar cells differ from the battery or conversion circuit by an electrical charge that tries to send energy to the cells. This can damage or destroy them. In such cases, the energy dispatched to the solar cells gets into the cathode of the blocking diode where it stops and cannot proceed towards the solar cells and hurt them. When the sun comes up again and the photovoltaic cells start generating electrical current, they can once more go through the blocking diode without any restrictions.
Functionally, a blocking diode is almost similar to that of a solar generator. A wind system usually generates AC power using a generator driven by blades or a turbine as opposed to DC power, which is what most solar systems produce. In a similar situation, if the wind stops blowing, its momentum will act in the reverse direction causing the generator to behave as a normal electric motor. Blocking diode prevents the reversal drive of the generator that might destroy the generator and deplete the system batteries.
Blocking Diode Configuration
Its configuration in the solar power system refers to its representation when the panel (at peak voltages) produces electricity and charges the batteries during the day. At night, without generating electricity, the batteries maintain high voltages compared with the panel which has lowered (or zero voltages). The battery may be drained by its reverse current flow to the solar panel during the night.
This results in the installation of a blocking diode which prevents it from occurring. Energy moves from a high-energy state to a low-energy state. It enables passage of the current from a solar panel to the battery and inhibits passage from the battery to the panel. This device is always wired in series behind a solar panel.
Recommended: What is P-N Junction Semiconductor Diode?