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I have a 90A main service and a 200A sub with 200A bus. See pictures attached.

I currently have a 3.9kw solar system on a dual 30A breaker.

How much more solar would I be able to add?

Looking to safely add another 2.8kw of solar (or more).sub panel

main panel

Thank you.

enter image description here

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  • @Ruskes w not kw. But that's based on the breaker. The question is how much can the panel and utility service handle. Feb 7, 2023 at 23:44
  • So I can add another 3.3kw of solar? On another 30A breaker? How does the calculation work?
    – Arctic
    Feb 7, 2023 at 23:48
  • Multiply Breaker Amps with 240 Volt (two breakers provide 240 Volt)
    – Traveler
    Feb 8, 2023 at 0:45
  • Can you post photos of your main breaker please? Feb 8, 2023 at 23:32
  • I added a pic. It's a condo so the breakers are joined 360 total / 4 units = 90A each
    – Arctic
    Feb 9, 2023 at 0:23

1 Answer 1

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  1. For back-feeding solar into a panel breaker, the limit is: Panel Rating * 1.2 - Main Breaker. Assuming your main breaker is 90A, that's 200A * 1.2 - 90A = 150A solar breaker, maximum.

  2. You can't plan to run breakers at 100% continuously, you must derate 20% so your theoretical maximum on this panel would be 120A of solar or 28.8kW at 240V.

    • On your current 30A breaker, you could feed in up to 30A * 240V * 0.8 = 5760W. To exceed that, you'd need a second breaker (possible with some shuffling but then your panel would be completely full), or you could replace the current breaker with a larger one if upgrading to a larger inverter (individual breakers between panel and inverters would be required if using multiple inverters).
  3. Your power company and local laws will probably set a far lower maximum system size, especially if you are allowed to take advantage of net metering. For example, here in MD with BGE, the maximum system size is capped such that the total annual projected production does not exceed the average annual consumption. My house with 400A (CL320) service was allowed only about 17kW of solar based on our consumption.

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  • I am confused about OP's main breaker. Does OP have a meter-main with a 90A breaker? But if so, your answer is spot-on. Except the 90A service size will also be a limiting factor, so total solar can't exceed 80% of that. Feb 8, 2023 at 6:02
  • Made a minor formatting edit, as that seemed to make sense. Undo it if I'm interpreting incorrectly.
    – FreeMan
    Feb 8, 2023 at 15:57
  • Yes it is a 90A main breaker. I live in a condo. with shared mains (360/4) will post a pic
    – Arctic
    Feb 9, 2023 at 0:16
  • I have microinverters so sounds like they could just upgrade the 30A breaker to a larger one to handle the increased solar? I'd only be looking to add another ~2.8kw or so for a total of 6.7kw
    – Arctic
    Feb 9, 2023 at 1:09

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