Connecting Solar PV Panels

[tcrenshaw]

I have been looking into solar panels for future energy at

a remote home in the Colorado Rockies. I've started purchasing my panels, mostly

Arco panels and I understand much about how I need to use a charger controller

and inverter with my battery bank. The simple concept is easy to understand.

When it comes to start wiring things up I have questions. If someone could

either give me an answer to my question or point me to a good book, website..etc

that would help, then I would be grateful. I presently have two Arco M51's that

have a positive and negative connection. I have measured the output of each

panel. One is 19vdc at 40 watts. The second is at 18.5vdc at 42 watts. I have a

charger controller with 10 amp input so it'll easily handle the to panels. If I

connect the panels together in parallel I should get my 12vdc at around 82

watts. My question is, do I need to install a diode on the negative side of the

panels to isolate them from each other so that the stronger panel does not feed

back current into the weaker panel? Thanks for any help you can provide.

[ghurd]

I would say no.

As the current flows at say 13v to the controller, the 2 will balance out to the same 13v. One will just put out a little more amps.  Same when one is a little shaded.

As the current goes down the voltage goes up.  They will find a balance where each gives what it can.

Don't use any diodes at all.  The charge controller takes care of all that.

G-

[Tom in NH]

For the purpose that you state, I believe the answer to your question is no. There just isn't enough difference between your panels to make it worthwhile.Your stated voltages are open circuit voltages (i.e. nothing is connected). When you connect the panels to your battery system through the charge controller the voltage will be forced down to the battery voltage. If you were to isolate your panels from each other with diodes, you would actually reduce your total output because of the inherent voltage drop across the diode itself.

In another situation where one panel would be shaded while the other is in sunlight, the shaded panel will kill the output from the illuminated panel unless they are isolated from each other with blocking diodes... at the expense of reduced output due to voltage drop across the diodes. Everything's a tradeoff.

--Tom

[tcrenshaw]

Cool! Thanks for the quick response from both of you. So for an array that may see shade on one ore more pannels while others are in direct sunlight the diode method may be needed. Since these are solar pannels and under most circumstances will be in direct equal sunlight at all times then I guess I won't need the diodes. I was pretty sure they would act just as several batteries in parallel might, the power output of all batteries is only equal to the weakest, but I wasn't sure. Now I am. Thanks!

Todd

[ve6aym]

If I remeber right, most panels today include blocking diodes. I have five 15 watt panels that have been running for five years with no problems..Look up spec sheets of your panels or contact the manufacturer to confirm that blocking diodes are included in the panels..

cheers!

[ve6aym]

If I remeber right, most panels today include blocking diodes. I have five 15 watt panels that have been running for five years with no problems..Look up spec sheets of your panels or contact the manufacturer to confirm that blocking diodes are included in the panels..

cheers!

[tcrenshaw]

Actually I have two ARCO panels and I may be purchasing two more but I also ordered PV cells and will be building my own. From what I have learned the blocking diodes will block power feeding back into a panel, but also that this will not damage the panel, it only brings the overall output down. So yes they are good and no they are not required. I'll just have to look at my final configuration and decide if I need them or not. Thanks for the response.

Todd