Diodes - Bypass & Blocking

[Mike90250]

Diodes are a one way valve for electricity. They also cause a bit of loss while in use. The balance is to have enough to prevent panel shutdown, but not so much as to cause reduction in power.

In a PV panel, they allow an electrical route around a group of shaded wafers .
Most PV panels over 50 watts have BYPASS diodes factory installed

In a battery system, they prevent nightime backfeed discharge into the PV panels.
(Note, most controllers built since the 90's, have the BLOCKING diode function built into them, as a FET)

Here's a short article about modernizing panel bypass diodes

http://www.digikey.com/en/articles/techzone/2012/dec/active-bypass-diodes-improve-solar-panel-efficiency-and-performance

So, in closing, 99.6% of the time, the end user never needs to worry about them.

[fivewin]

So if we know that a chargecontroller have a blocking diode we dont need outside in the panel right? Double loss of voltage.

[inetdog]

So if we know that a chargecontroller have a blocking diode we dont need outside in the panel right? Double loss of voltage.

Yep, and one more potential point of failure.
And most panels, except some small "battery maintainer" panels do not contain blocking diodes. And adding them externally to the panels would not be needed.

But bypass diodes need to be tightly integrated with the panels at manufacture since they have to connect to intermediate points in the string of cells that make up the panel. And commercial panels except amorphous thin film panels include bypass diodes.

[fivewin]

Have this panel. Whats wise to charge my hp or powerbank with it. Using dioded or cheap step down module to get constant voltage.