Adding panels to an older existing system

[TheLex]

We have an existing 4.2 Kw grid tied system with an approx 10 yr old Sunny Boy inverter. I think the existing panels are Sharps but I'm not 100% sure.

I'm doing a bunch of landscaping in the backyard and will be building a 12x12 pergola. It occurred to me that this would be a good opportunity to add some 2-3 Kw of new solar panels to our system. However I'm reading that it's probably not feasible to do so with an older inverter.

I'd like to know if this is really possible. I'd prefer not having two separate systems if possible.

Can I:
1) Add 300 watt plus panels using microinverters. Is this possible and how would it be added to the existing system?
2) Purchase a new central inverter and then add new panels to the system. However the new panels would not match the old panel outputs exactly. Is this an issue that can be overcome?
3) Some other option.

Here are some photos of the tag from my existing inverter:
Disconnect.jpg
Sunny Boy tag.jpg

[foo1bar]

With 4.2kw DC and 3.8kW inverter, there's probably not a lot of room to expand that with just more DC power.

Adding a new inverter side by side with it is almost certainly possible...
But may or may not be economically wise..

Questions that I think you have to look at:
Will increasing this put me into a different rate bracket than what I'm grandfathered into now?
Can I add more power coming in to the main panel without a main panel upgrade or having to do a line side tap? (or how much will those cost)
Will I use that additional power or am I basically gifting the power company the extra kwh's?

[TheLex]

My true up at the end of the year is usually about $1300-1400. So I would get a return on my money within 2-3 yrs.

What if I were to just upgrade the string inverter with a 7+ Kw version instead? Do I still have to match the output of the new panels with that of the new panels?

Can I use microinverters on the new panels and combine that with the string inverter system?

I need to investigate the panel situation. We have a 400 amp main panel and the solar system current runs to a 200 amp subpanel that's already used up all the breaker positions.

With 4.2kw DC and 3.8kW inverter, there's probably not a lot of room to expand that with just more DC power.

Adding a new inverter side by side with it is almost certainly possible...
But may or may not be economically wise..

Questions that I think you have to look at:
Will increasing this put me into a different rate bracket than what I'm grandfathered into now?
Can I add more power coming in to the main panel without a main panel upgrade or having to do a line side tap? (or how much will those cost)
Will I use that additional power or am I basically gifting the power company the extra kwh's?

[Mike90250]

If you swap inverters, you may have to negotiate a new agreement with the power company and new building permits.

Many newer inverters have several MPPT inputs, the existing array can use one, the new array (would not need to match) can use a different one.

You do need to insure the arrays are within the MPPT ratings of the inverter

[SunEagle]

My true up at the end of the year is usually about $1300-1400. So I would get a return on my money within 2-3 yrs.

What if I were to just upgrade the string inverter with a 7+ Kw version instead? Do I still have to match the output of the new panels with that of the new panels?

Can I use microinverters on the new panels and combine that with the string inverter system?

I need to investigate the panel situation. We have a 400 amp main panel and the solar system current runs to a 200 amp subpanel that's already used up all the breaker positions.

I have never heard of a system that had both micro and string inverters. But then again if you have separate AC connections at the main panel it might be doable. The biggest hurdle is for you to get permission from your POCO and AHJ concerning the additional generating system. One area that may be a show stopper is the size of your Main Panel bus rating. That will limit the total AC connection from solar.

[scrambler]

I don't see any issue mixing a regular string inverter with Micro.
What is important is to make sure you comply with the 120% rule in the Breaker panel where they will be connected.

If both the string inverter and the Micro inverters breaker are going to be in the same panel, the sum of their breakers should meet the 120% rule and they should be at the end of the busbar.

Let us say the 120% rule says you can have 50A of solar in your panel, and your string inverter already has a 30A breaker, you could have a 20A breaker connected to microinverters.

[TheLex]

If the sub panel to which the existing solar is hooked up to is already maxed out, is it permissible to add an independent breaker say on the outside of the house before the new system merges with the old one? Or does the whole sub panel need to be replaced with a larger capacity unit?

I don't see any issue mixing a regular string inverter with Micro.
What is important is to make sure you comply with the 120% rule in the Breaker panel where they will be connected.

If both the string inverter and the Micro inverters breaker are going to be in the same panel, the sum of their breakers should meet the 120% rule and they should be at the end of the busbar.

Let us say the 120% rule says you can have 50A of solar in your panel, and your string inverter already has a 30A breaker, you could have a 20A breaker connected to microinverters.

[Mike90250]

The one advantage of being off grid - I don't have to worry about this.

[scrambler]

Here is some reading for you.
https://www.altestore.com/blog/2018/.../#.XyxNIa-Sl7c
Next would be to make a small schematic of your existing Panels(s) from meter to house panel(s) with their busbar rating and the feeding breaker size.