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Adding additional solar panels

Merrill

Merrill
Jan 23, 2013
3,699
1,259
Sonoma, California
I have 21 10 year old 210 solar panels on a 4000w inverter and I added 6 more 327 panels in 2016 on a 3000w inverter. I want to add another 6 panels and wonder if I can use micro inverters for the 6 new panels instead of buying and replacing one of the existing inverters.
 

miimura

Well-Known Member
Aug 21, 2013
6,074
5,657
Los Altos, CA
As long as you have room in your load calcs to put an additional 20A double pole breaker in your panel, I don't see why you can't add those micros.

Edit: by load calcs I mean 20A more back-feed. I don't think you can use a smaller breaker than that, but I may be wrong.
 

miimura

Well-Known Member
Aug 21, 2013
6,074
5,657
Los Altos, CA
I wonder if it would make more sense to replace the 10 year old Sunpower 4000w inverter with a larger one.
I would think replacing the 210W panels with 300+W panels and a new inverter would be easy if you could re-use the same racking.

I am seriously considering replacing my 9 year old and degraded 240W polysilicon panels with new ones, re-using the old Enphase Micro-inverters. The primary consideration is keeping the same panel frame size and 60 cell panel type so they drop in with no other changes.
 

Merrill

Merrill
Jan 23, 2013
3,699
1,259
Sonoma, California
I was thinking about that possibility but the panels are working well and should last another 10 years, I do have a spot for about 6 more of the latest panels.
 

nwdiver

Well-Known Member
Feb 17, 2013
7,578
9,669
United States
I wonder if it would make more sense to replace the 10 year old Sunpower 4000w inverter with a larger one.

Good chance. For the cost of 6 micro inverters and the trunk cable and all the other ancillary stuff you'd need you're almost at the cost of a 7.6kW SMA inverter that can handle ~11kW of solar. How does your solar play with your Powerwalls off-grid? New Rule 21 inverters are able to adjust their output so they're not just on or off.
 

nwdiver

Well-Known Member
Feb 17, 2013
7,578
9,669
United States
if you have only 6 327w panels on a 3kw inverter could you just stick another 6 on there and have ~1.3 dc:ac ratio?

That's a good idea. Would be SUPER-easy if you can get the voltages to roughly match. You'd lose a little on the mis-match but it would probably be worth it. Just run a second string in parallel.
 

Merrill

Merrill
Jan 23, 2013
3,699
1,259
Sonoma, California
if you have only 6 327w panels on a 3kw inverter could you just stick another 6 on there and have ~1.3 dc:ac ratio?
Maybe I’m wrong on this but 6 327w panels is almost 2000w which would leave me only 1000w on that inverter and 6 more of those panels would be another 2000w. I’m I thinking correctly.
 

nwdiver

Well-Known Member
Feb 17, 2013
7,578
9,669
United States
Maybe I’m wrong on this but 6 327w panels is almost 2000w which would leave me only 1000w on that inverter and 6 more of those panels would be another 2000w. I’m I thinking correctly.

That would be fine. I have 10.7kW on a 8kW SMA inverter. Do you have SMA? For some reason that's my recollection. Might have a 'SunPower' brand label on it.
 

Merrill

Merrill
Jan 23, 2013
3,699
1,259
Sonoma, California
I did some research on inverters and it looks like you can use a 1.42% of your inverter rating to determine the total solar panel watts. So my 3000w SMA inverter should handle up to 4250 watts.
 
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