Just signed a 4.6kW systems...

[solar_newbie]

5 kW SolarEdge is rated to produce 21 A (@240 Vac) continuous. 21 A requires at least 1.25 * 21 = 26.25 A of overcurrent protection... a 30 A breaker is typical.

In a conventional installation, the max supply to the MSP is 120% of the busbar rating.
20% of a 100 A panel (w/ 100 A main breaker) = 20 A max PV supply breaker.
20% of a 125 A panel (w/125 A main breaker) = 25 A max PV supply breaker

A 5 kW can go into a 125 A panel with a 100 A main breaker, or a 200 A panel.

Thanks ... foo1bar corrected me that I am safe to put 40amp supply from solar (plan for up to 8kw in future) and 40amp charge for electric car on the 100a panel
My decision to go with the second panel of 125amp for solar and electrical is right then.

I just do the math - solar (40) + ac (40) + ev car (40) = 120a. So I need 100a or 125a panel to be sure.

[sensij]

Thanks ... foo1bar corrected me that I am safe to put 40amp supply from solar (plan for up to 8kw in future) and 40amp charge for electric car on the 100a panel
My decision to go with the second panel of 125amp for solar and electrical is right then.

I just do the math - solar (40) + ac (40) + ev car (40) = 120a. So I need 100a or 125a panel to be sure.

Solar is a supply, the A/C and EV are loads. Those three won't add together.

With a subpanel, you have more flexibility because you can drop the feed breaker as low as you'd like. With the main service panel, my utility (and presumably, most others) mandates that the minimum service allowed is 100 A, so you can't swap out the 100 A feed breaker on the MSP with something lower (like 80 A) in an attempt to shift more of the busbar capability to the PV source.

[solar_newbie]

Solar is a supply, the A/C and EV are loads. Those three won't add together.

With a subpanel, you have more flexibility because you can drop the feed breaker as low as you'd like. With the main service panel, my utility (and presumably, most others) mandates that the minimum service allowed is 100 A, so you can't swap out the 100 A feed breaker on the MSP with something lower (like 80 A) in an attempt to shift more of the busbar capability to the PV source.

Oh now I understand . You mean total supply 100a from the grid, so the max supply from solar should not more than 20a to reach 120% You guys are right ... I could put a new 100a breaker, a new 125a panel . With 120% rule, I could put solar supply up to 50a ... New things learn today.

[foo1bar]

Thanks ... foo1bar corrected me that I am safe to put 40amp supply from solar (plan for up to 8kw in future) and 40amp charge for electric car on the 100a panel

I don't see anything from me about that in this thread...

First of all - 40A would actually be 7.6kW inverter (7600 / 240 = 31.6A; 31.6A * 1.25 = 39A ==> 40A breaker)

Can you do a 40A (or even 50A) on a 125A panel - yes.
BUT as sensij points out, the way you calculate that is that the breaker feeding the panel's bus has to be 100A.
And you have to feed the solar in from the opposite end of the panel.
And then you can use the 120% rule. Which means you can have up to 1.2 * 125A feeding the bus.
1.2 * 125A > 100A +50A (where 100A is the "normal" breaker feeding the panel and 50A is the breaker for PV feeding the panel)

I just do the math - solar (40) + ac (40) + ev car (40) = 120a. So I need 100a or 125a panel to be sure.

Usually people do it with the above calculation.
But if the sum of all the breakers is less than the busbar rating, that's acceptable too.
A good idea in that case (and possibly required by the AHJ) is to make sure that you can't add more breakers in. (ie. no empty spots where someone can add a breaker 3 years later)

[solar_newbie]

I don't see anything from me about that in this thread...

First of all - 40A would actually be 7.6kW inverter (7600 / 240 = 31.6A; 31.6A * 1.25 = 39A ==> 40A breaker)

Can you do a 40A (or even 50A) on a 125A panel - yes.
BUT as sensij points out, the way you calculate that is that the breaker feeding the panel's bus has to be 100A.
And you have to feed the solar in from the opposite end of the panel.
And then you can use the 120% rule. Which means you can have up to 1.2 * 125A feeding the bus.
1.2 * 125A > 100A +50A (where 100A is the "normal" breaker feeding the panel and 50A is the breaker for PV feeding the panel)


Usually people do it with the above calculation.
But if the sum of all the breakers is less than the busbar rating, that's acceptable too.
A good idea in that case (and possibly required by the AHJ) is to make sure that you can't add more breakers in. (ie. no empty spots where someone can add a breaker 3 years later)

I got that now foo1bar. Thank you for correcting me....

[sjsun]

I got that now foo1bar. Thank you for correcting me....

For ~5kw system, a 125Amp panel might be sufficient but later, if you want to add more panels or switch to higher efficiency panels (add more supply amps) then you will have to upgrade to a 200Amp. At that later date, FTC might not apply to your panel upgrade. But you can do the service/panel upgrade now as part of the Solar install and it will qualify for FTC. Or, at least, that's the theory Also, I have been told that PG&E currently does not charge anything for a 100Amp to 200Amp service upgrade for overhead supply. Might change later if they see lots of people getting service upgrades.

[solar_newbie]

For ~5kw system, a 125Amp panel might be sufficient but later, if you want to add more panels or switch to higher efficiency panels (add more supply amps) then you will have to upgrade to a 200Amp. At that later date, FTC might not apply to your panel upgrade. But you can do the service/panel upgrade now as part of the Solar install and it will qualify for FTC. Or, at least, that's the theory Also, I have been told that PG&E currently does not charge anything for a 100Amp to 200Amp service upgrade for overhead supply. Might change later if they see lots of people getting service upgrades.

I have 125amp for solar mostly, so I can safely go to 10kw as needed.
-- Breaker : 80A
-- Panel : 125A
-- Solar can go up to 125*120% - 80A = 70A .
70A can support up to 13KW system.
70A * 240V = 16.8KW .. Take down 125% to avoid peak power --> 13KW system

[sensij]

For ~5kw system, a 125Amp panel might be sufficient but later, if you want to add more panels or switch to higher efficiency panels (add more supply amps) then you will have to upgrade to a 200Amp.

Only the inverter dictates the overcurrent protection required, not the number of panels. 7.6 kW inverter can be installed on a 40 A breaker, and will typically accept 9.5 kW of panels, maybe more in some installations.

You don't need to go up to 200 A until you have an array over 10 kW, or in solar_newbie's case, dropping down to an 80 A main breaker on the subpanel accomplished the same thing on the 125 A panel. That extra 20 A allows an 11.4 kW inverter, and over 14 kW of array. More than that and you are more or less in commercial range, and probably looking at higher voltage or three phase.

[sjsun]

I have 125amp for solar mostly, so I can safely go to 10kw as needed.
-- Breaker : 80A
-- Panel : 125A
-- Solar can go up to 125*120% - 80A = 70A .
70A can support up to 13KW system.
70A * 240V = 16.8KW .. Take down 125% to avoid peak power --> 13KW system

Caveat: I am not an electrician, city inspector or a lawyer!

Best I know, you cannot have the inverter output to be more than 20% of your bus rating as per NEC code (and I believe PGE broadly follows the same code although they have their own code book). So if your bus is rated for 125A then your Solar system will be limited to 25A (6kW).

Edit: Actually, If you have a 125Amp bus, your solar sub-panel is limited to 20%, that is, 25A. Now, your 25A breaker has to be 1.25 times the inverter output - that limits inverter output to 20A or 4.8kW system.

On the load side, want to add an EV fast charger? That's a 30A load that needs a 40A breaker. Got two EVs? And, you see how they quickly add up leaving your 100Amp service and 125Amp panel feeling pretty inadequate?

[sensij]

Best I know, you cannot have the inverter output to be more than 20% of your bus rating as per NEC code (and I believe PGE broadly follows the same code although they have their own code book). So if your bus is rated for 125A then your Solar system will be limited to 25A (6kW).

A 125 A main panel with a 125 A main breaker will accept a maximum of 25 A breaker protecting PV... that gets you up to a 3.8 kW inverter in the SolarEdge series, or the 4 kW in the SMA SB-TL series.

If you drop the main breaker down from 125 A to 100 A, that gets you another 25 A to work with, or 50 A total, doubling the inverter size relative to what could be accommodated with the 25 A breaker.

On the load side, want to add an EV fast charger? That's a 30A load that needs a 40A breaker. Got two EVs? And, you see how they quickly add up leaving your 100Amp service and 125Amp panel feeling pretty inadequate?

There are reasons to upgrade a 125 A panel to a 200 A panel. PV installation, with no other expected changes to the load profile, does not usually require it. Most installers will be happy to sell the upgrade though.

[solar_newbie]

Caveat: I am not an electrician, city inspector or a lawyer!

Best I know, you cannot have the inverter output to be more than 20% of your bus rating as per NEC code (and I believe PGE broadly follows the same code although they have their own code book). So if your bus is rated for 125A then your Solar system will be limited to 25A (6kW).

Edit: Actually, If you have a 125Amp bus, your solar sub-panel is limited to 20%, that is, 25A. Now, your 25A breaker has to be 1.25 times the inverter output - that limits inverter output to 20A or 4.8kW system.

On the load side, want to add an EV fast charger? That's a 30A load that needs a 40A breaker. Got two EVs? And, you see how they quickly add up leaving your 100Amp service and 125Amp panel feeling pretty inadequate?

Actually I got 2 subpanels:
1 with : 100A breaker and 100A panel
1 with : 80A breaker and 125A panel

If you combine both, I have 180A breaker and 225A panel.

That is enough for 4 40A breaker loads and 90A solar supplier. Much better than just 200A breaker and 200A panel.

Talk about cost:
Upgrade from 100A breaker/100A panels to 200A breaker/panel cost 2000 - 3000.
Add a new 80A/125A sub-panel cost 200-400 and get more flexible and more load.

[sjsun]

Actually I got 2 subpanels:
1 with : 100A breaker and 100A panel
1 with : 80A breaker and 125A panel

If you combine both, I have 180A breaker and 225A panel.

That is enough for 4 40A breaker loads and 90A solar supplier. Much better than just 200A breaker and 200A panel.

Talk about cost:
Upgrade from 100A breaker/100A panels to 200A breaker/panel cost 2000 - 3000.
Add a new 80A/125A sub-panel cost 200-400 and get more flexible and more load.

Curious, if adding a sub-panel is cheaper and provides more flexibility then why does anyone upgrade main panel and service at all?

[newe70]

[QUOTE=sensij;174196]A 125 A main panel with a 125 A main breaker will accept a maximum of 25 A breaker protecting PV... that gets you up to a 3.8 kW inverter in the SolarEdge series, or the 4 kW in the SMA SB-TL series.

If you drop the main breaker down from 125 A to 100 A, that gets you another 25 A to work with, or 50 A total, doubling the inverter size relative to what could be accommodated with the 25 A breaker.





Calling out sensij for help...I am in this exact scenario. The onsite plan called out the 125A main service panel to downsized to 100A. Can you please explain more? I am confuse.

[sjsun]

There are reasons to upgrade a 125 A panel to a 200 A panel. PV installation, with no other expected changes to the load profile, does not usually require it. Most installers will be happy to sell the upgrade though.

And, that's what I was trying to highlight - design for expected load profile changes while you are adding capacity/source. Assuming a standard home with a 100/125A service/main-panel, upgrading to a 200A panel/service might give you sufficient room to expand in the future. I think there's hardly a thread about Solar that doesn't also talk about EV usage and EV consumption is only going to grow - bigger and more power hungry batteries. Gave me some food for thought in terms of having spare capacity in the entire system.

[solar_newbie]

Curious, if adding a sub-panel is cheaper and provides more flexibility then why does anyone upgrade main panel and service at all?

Material cost for 2 options are almost the same. The different is the labor cost. If you are installers, which option should you offer?
For me, any installers offer me the upgrade option for 2-3K. I never response to them.
Any installers look at my 100% full load sub-panel and cry about they need to re-arrange it to get space for solar, I ask them if they do it for free. Otherwise, don't talk more as there is no cost to re-arrange the sub-panel circuits.