Instructables

Step 11: Install the Blocking Diode

Each solar panel in a solar power system needs a blocking diode in series with it to prevent the panel from discharging your batteries at night or during cloudy weather. I used a Schottky diode with a 3.3 Amp current rating. Schottky diodes have a much lower forward voltage drop than ordinary rectifier diodes, so less power is wasted. Every Watt counts when you are off-grid. I got a package of 25 31DQ03 Schottky diodes on Ebay for only a few bucks. So I have enough left-overs for lots more solar panels

My original plan was to mount the diode inline with the positive wire outside the panel. After looking at the spec-sheet for the diode though, I decided to mount it inside since the forward voltage drop gets lower as the temperature rises. It will be warmer inside the panel and the diode will work more efficiently. More silicone caulk was used to anchor the diode and wires.
 
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edraq584 years ago
Can I put the diode to the negative side of the panel? If not, what is the effect if diode install to the negative?
thanks for the writeup Do I need a shottky diode per 18 solar cells? or per 36 solar cells? Because the output on 36 for me is 3.5 which is higher than the 31dQ03's maximum of 3.3. Thanks for any pointers. Tony
elpidiode5 years ago
I notice that you are using a different cell now not the same as was started. Anyway, I am getting the guest. I would like you to be specific on where the positive or the negative are. Give us where the main wire (negative or positve) came from . I could see the wiring of your panel connected to all the tabb.
sspence5 years ago
Blocking diodes are not necessary when using a charge controller. The charge controller performs this function. Bypass diodes may be necessary when using high voltage strings in case a panel gets shaded. I run my panels in series for 80 volt strings. I use a Outback MPPT controller to convert it to battery voltage (24v in my case). This way I consistently produce more power than the panel is rated for, even in winter (I'm in NY).
mdavis19 (author)  sspence5 years ago
My charge controller is home-built. It doesn't have any blocking diodes in it. So they are necessary in my application.