Two Separate systems on the same house?

hackenbush · March 2023

Hard to find an answer to this-

I have an existing 2 string system running through a solaredge se5000 inverter - a total of 5.775kw.

I want to add more capacity but Sunrun won't touch their existing system, and nobody else seems to want to either. But I'd like to add a couple panels. Makes sense to me to use Enphase microinverters so I can add more later if needed. The Enphase IQ8 inverters would be fed to a junction box between the se5000 ac output and the solar meter, or to another breaker in the panel.

Can anybody think of a reason this wouldn't work? For example, cause problems with the grid sensing rapid shutdown of the se5000 or IQ8 inverters.

BB. · March 2023

It looks like, power wise, you can add panels up to 7,750 Watts to your array... If you meet the other array requirements (Voc, Imp/Isc, etc.) it should not be difficult.
https://www.amazon.com/SolarEdge-SE5000H-US-5000-Watt-Grid-Tied-Inverter/dp/B07C5WBZFN

The typical "over paneling" of a GT inverter allows for an array efficiency of ~77%, or for a 5,000 Watt inverter:

5,000 Watt inverter rating * 1/0.77 typical array+inverter deratings = 6,494 Watt "optimal array"

Basically, an approximately 6,494 Watt (standard marketing numbers) will rarely clip the output to 5,000 Watts on very cool/clear days around solar noon. (note that solar numbers are "fuzzy"... If you are 10% over or under on Wattage numbers--You probably will not be able to measure the differences).

You will need to look at your existing array (panel specifications, your local minimum temperature, Series * Parallel strings of panels, etc.) if you want to add to the existing array... It could be as easy as adding panel(s) in series to the existing array... Or it could require the array to be reconfigured (i.e., 5s*2p to 4s*3p or something like this--Just made up numbers).

Otherwise, you could add micro inverters to your home--Ideally, you would need to add another 240 VAC double pole breaker, and wire that to the new micro-inverter(s)... Certainly not very difficult, but could be costly just to add (for example) racking for new panels, a couple of panels and inverters, plus Enphase monitoring hub, possible building permits, minimum service/installation chargers, etc. May not be "worth" adding just a couple panels.

-Bill

hackenbush · April 2023

Thats good information! Thank you Bill. I'm probably not going to go the route of messing with the existing Sunrun/Solaredge system since they aren't willing to add more capacity and I don't want to break my warranty.

I might be trying to find a problem where there isn't one but it seems to me that adding another system might create the potential to form a loop where enphase microinverters and Solaredge Power Optimizers feed each other and don't do a rapid shut down if the grid goes down. I don't understand how they work well enough to rule it out.

BB. · April 2023

No problem... The Inverters "follow" the AC voltage and frequency supplied by the utility. If utility power "goes down" or out of spec (high/low frequency, high/low voltage), the inverters (all GT inverters) will shutdown and wait until good voltage and frequency returns (should be a 5 minute delay after "good AC power").

GT Inverters (like these) do not have the capability to supply 120/240 VAC @ 60 Hz by themselves... They always "follow" the utility AC power.

Where you could get into a bit of an issue---If you have a backup AC genset and connect the GT Inverters to the AC genset output powering your home... Depending on type of generator, the GT inverters can cause issues when connected to a running AC genset (from GT Inverters not generating power--which is fine; to GT inverters "syncing" with genset and feeding power back to home (again, depending on lots of variables--An operating GT inverter feeding power back to the genset could damage/ruin the genset).

-Bill

hackenbush · April 2023

Exactly what I wanted to know. Thank you Bill for taking the time.

BB. · April 2023

You are very welcome.

Take care,
-Bill

Two Separate systems on the same house?

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