I have to two solar installers. One says I need a $2500 service panel upgrade (See below) and another says my service panel is fine and needs no upgrade. who to believe?
This is the email I got from the installers who says I need an upgrade You need a main panel upgrade because we can only feed a certain amount of solar in a main electrical panel; this rule is referred to as the 120% rule. This rule states that you can only "back-feed" 120% of the main bus bar rating with solar. So now, let me demonstrate this in plain English through some calculations. All calculations will be based off your current situation (a photo of your electrical panel is below):
To the set the stage, you have a 200 Amp-rated main electrical panel with NO main disconnect. In other words, you have 200 Amps being delivered from PG&E to your home and your main electrical panel has no main breaker (I.e. Main disconnect - a breaker to shut off ALL power to your home).
You have the following breakers:
Oven - 40 Amps
Car Charger - 30 Amps
Dryer- 30 Amps
A/C - 40 Amps
Existing Solar - 20 Amps
Sub Panel- 100 Amps
If you add all of these breaker ratings up, you will see that you have 260 Amps worth of main disconnects (every breaker is a main disconnect since you do not have a "main disconnect"). So, finally here is the calculation for solar companies to abide by:
120% of the main panel rating (I.e. Bus bar rating) - main disconnect(s) = the amount of solar you can install in your home.
Given your current situation, here is how many Amps you can install (from a code perspective) in your panel:
200 (bus bar rating) x 1.2 (120% rule) = 240 maximum amount of Amps - 260 (sum of all disconnects) = -20 Amps of solar. So, how can you install a negative number of amps? THAT'S CORRECT, YOU CAN'T!!!
So, now let's do this calculation if you had a panel with a main disconnect:
200 (bus bar rating) x 1.2 (120% rule) = 240 maximum amount of Amps - 200 (sum of all disconnects) = 40 Amps of solar. TADA, everything works.
The only difference in these two scenarios, is that in scenario 2 you have a "main disconnect." So, you don't think that I am full of hot air and pulling this rule out of the sky, I have attached a link that explains this in more detail: https://www.civicsolar.com/resource/120-rule-“what-it-and-why-it-important”-0
This is the email I got from the installers who says I need an upgrade You need a main panel upgrade because we can only feed a certain amount of solar in a main electrical panel; this rule is referred to as the 120% rule. This rule states that you can only "back-feed" 120% of the main bus bar rating with solar. So now, let me demonstrate this in plain English through some calculations. All calculations will be based off your current situation (a photo of your electrical panel is below):
To the set the stage, you have a 200 Amp-rated main electrical panel with NO main disconnect. In other words, you have 200 Amps being delivered from PG&E to your home and your main electrical panel has no main breaker (I.e. Main disconnect - a breaker to shut off ALL power to your home).
You have the following breakers:
Oven - 40 Amps
Car Charger - 30 Amps
Dryer- 30 Amps
A/C - 40 Amps
Existing Solar - 20 Amps
Sub Panel- 100 Amps
If you add all of these breaker ratings up, you will see that you have 260 Amps worth of main disconnects (every breaker is a main disconnect since you do not have a "main disconnect"). So, finally here is the calculation for solar companies to abide by:
120% of the main panel rating (I.e. Bus bar rating) - main disconnect(s) = the amount of solar you can install in your home.
Given your current situation, here is how many Amps you can install (from a code perspective) in your panel:
200 (bus bar rating) x 1.2 (120% rule) = 240 maximum amount of Amps - 260 (sum of all disconnects) = -20 Amps of solar. So, how can you install a negative number of amps? THAT'S CORRECT, YOU CAN'T!!!
So, now let's do this calculation if you had a panel with a main disconnect:
200 (bus bar rating) x 1.2 (120% rule) = 240 maximum amount of Amps - 200 (sum of all disconnects) = 40 Amps of solar. TADA, everything works.
The only difference in these two scenarios, is that in scenario 2 you have a "main disconnect." So, you don't think that I am full of hot air and pulling this rule out of the sky, I have attached a link that explains this in more detail: https://www.civicsolar.com/resource/120-rule-“what-it-and-why-it-important”-0
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