Adding more Solar Panels to an existing system

[Michael Neff]

Please excuse my ignorance on the following of what I am about to type. I have an idea, not sure if it’ll work.

I currently own a 8.28kw Solar Panel system and its hooked up to a Sunny Boy 8000us Inverter. I am looking to add more solar panels to my system but I am unsure of a few things. I am looking to add (8) LG Solar panels (380 watt x 8= 3,040 watts) Can the inverter handle more power? Also when I purchase these panels do I need to purchase additional things? Like the boxes that connect them all together or wires and then some how they come out to like 6- 10 gauge wire that runs into my inverter.

My thought is install the panels, hook them together, run the wires to the inverter and I am done.

[Rob Beckers]

Hi Michael,

These inverters will limit their output power, pretty much regardless of what's on the input side (as long as that doesn't exceed the maximum input Voltage). So, you can put 12kW of solar panels on an 8kW inverter, and on a nice sunny day you'll see it go to 8kW output and stay there (even if it could have produced more).

So, from that perspective there's no issue in adding more panels to the same inverter. Generally, once you exceed more than 120% of inverter rating you'll get more and more into clipping of that inverter, where it could have produced more but is limited by the inverter output. For your inverter that happens around 9.3 - 10 kW mark (and I should mention that 120% is really based on our climate, 45-degrees northern latitude, it'll be a bit different for different climates).

How well adding 8 more panels will work is a different story though: You have to match the existing string Voltage. So, if you currently have (say) strings of 10 panels in series, and those are 60-cell panels, you would have to add in groups of 10 60-cell panels at a time to match the existing string Voltage. There will likely also be code-compliance issues, depending on how the current strings have been combined, and how you're planning to add the new string(s) to this.

-RoB-

[Michael Neff]

I currently have (3) strings of (12) panels each. 230 watt panels x 12= 2760 watts per string

What you're saying is I need to buy enough panels that can get me as close as I can to 2760 watts?

With that addition it wont exceed the max 10k

Also, i've been monitoring my solar readings and really seems like a max day for me 55kwh

[Rob Beckers]

Michael, the Wattage of your existing strings has nothing to do with matching the Voltage of your strings.

If you currently have strings of 12 panels, and those panels are (each) made of 60-cells, you currently have 12 x 60 = 720 solar cells connected in series in each string. That is what needs to be matched. Each cells is roughly half a Volt, so your strings are around 360 Volt (when they're producing power, more when they are not loaded).

So, whatever you connect in parallel to your existing strings has to match that same number of overall cells, and once again, I do not know that your panels are 60-cell that is just an assumption. It's up to you to make sure.

-RoB-

[Michael Neff]

Ah, okay. Thank you. I'll look further into this.