Adding second panel

[Dave Beleskey]

Hi

I currently have a small solar system at my property near Burkes Falls Ontario. I posted here before building it and got a lot of great help.

I currently have a single Canadian Solar CS6X 300P Maxpower (300 watt) panel and an Outback FM60 charge controller. For the most part it worked well last year for me but, if I had a couple of cloudy days the batteries would run about half charged. The main problem is that there is a lot of bush and I only get about four hours of direct sun per day and the system charges 17+ amps when in the direct sun but under 1.5 amps when not. I am removing trees to clear for a house and the situation will improve but it might take some time. I thought about adding a second panel to the system, I have plans for it anyway once the house is built.

I know the FM60 will handle a second panel that's why I went to that size of controller. My question is about adding the second panel to the existing one. I have been looking around and it seems to be hard to find a matching panel. Canadian Solar make the 305 watt panel now.
Does the panel have to be an exact match make and model ?
Should I connect them in serial or parallel ?
Does anyone know where I can get a good price on a panel ?

Any suggestions would be appreciated.

Dave

[Rob Beckers]

Hi Dave,

You can add another 72-cell panel in series with your existing panel; The FM60 has a maximum input Voltage of 150 Volt and two of those panels in series should keep you under 110 Volt even on the coldest day. In general, I'd say you can add any panel that's about the same Wattage (305 Watt is fine too). The differences between the panels will be small enough not to matter much.

The longer story is that when putting panels in series you ideally want to match the current going through; so both should have an Imp value that's about the same. That will ensure both panels will run at nearly the same power point, and the controller can do a good job in Maximum Power Point Tracking for both. In truth there is not all that much difference in the silicon cells used to make panels. A 300 Watt panel from one manufacturer will have cells that are very similar to those in a 300 Watt panel from another manufacturer (or a 305 watt module, those cells are very nearly the same as those in a 300 Watt one).

You could even use a regular 60-cell panel and put it in series with your existing panel. For series it's the current that needs to match, and a 250 Watt 60-cell panel will again have the same type of cells as those in a 300 Watt 72-cell module. A 60-cell panel is of course smaller (shorter), so it won't look very good when installed with a 72-cell module, but they are much easier to get (we stock 60-cell panels, but not 72-cell).

Hope this helps!

-RoB-

[Dave Beleskey]

Hi Rob

Thanks so much for your reply.

So I assume by your response that connecting the panels in series is the way to go. My preference would be to find another 300P panel but that may not be an option. At least now I know that I can use a 305W if I need to.

As you mentioned, connecting the two in series will increase the voltage to under 110V, will I need to replace the wire that goes from the panels to the controller or will what I have still work ? I have 55 feet of 10AWG currently installed.

Dave

[Rob Beckers]

Dave, the wire doesn't need to be changed. Since the current through the wire doesn't change, your wire losses will be exactly the same with two panels as they are with one panel.

You can hook up (similar) panels in parallel as well. The downside of doing so is that now you have twice the current in the wires (and 4x the wiring losses!). Panels in parallel don't handle partial shading of one of the panels very well either, as series would do. So losses due to shading would go up as well. A single string of panels in series handles shading as well as (for example) optimizers or micro-controllers would.

Since your controller allows for it you're just better of putting them in series.

-RoB-

[Dave Beleskey]

Rob, thanks again for your help. Actually makes sense when you explain it.
I'll let you know how it works once I find a panel and get back up there. We currently don't use the system in the winter months but will once we have a house there.

Do you think I should reset my controller to factory settings after adding the second panel ?

Dave

[Dave Beleskey]

Does anyone now where I can get a second panel that will work with my current CS6X300P. I want to add another similar panel to double my output but I am having a hard time finding one in Ontario. Everyone wants to sell big roof top systems and doesn't want to be bothered with one panel...

Any suggestions ?

[Saintkin Windpower]

I am new here. Nice to see everyboday. I am manufacturer of wind turbine,controllers,inverters. I'd like to talk any questions about them and like to be your friends.

[Rob Beckers]

Dave, where are you located? (or send me a PM if you don't want to post)
I could ask CSI if they are willing to sell me a single panel. Normally it's by the skid only, and we don't stock 72-cell panels (not enough demand for those, they tend to go into big FIT projects). It would have to be picked up from Guelph though, they'll never pack it, and shipping one panel is as expensive as shipping an entire skid.

-RoB-

[Dave Beleskey]

Thanks Rob

I finally got an answer from the guy close by. He had the CS6X305P in stock and I could pick it up. That is as close to the CS6X300P as you can get without an actual match.

Thanks for your response and offer...appreciate it.

Dave

[Rob Beckers]

Dave, good to hear you have that resolved!