Derating Sub Panel For Solar

For example picture a 200a main breaker box feeding a 125a sub panel through a 100a breaker with a 100a main breaker in the 125a sub panel.

Derating sub panel for solar.

Consider that we are using two string inverters. Pvwatts applies derate factors to determine the amount of ac power that will flow into the grid from the solar array accounting for many of the environmental characteristics of the site as well as system design and chosen components. Main panel has 200a bus and breaker. This was the first time i ever replaced a electrical panel directly next to a window.

That sub panel can have a 40a breaker added to it for the 7600w inverter as 100a 40a 140a which is under the 150a. This panel had to be upgraded due to the large 13kw ground mount solar pv system being installed. The pvwatts default overall dc to ac derate factors are based on a system with a string inverter. On this project i was hired as a sub contractor to install the electrical panel for a larger well known solar company.

Pv backfed breaker to be 70a for load side connection to bus. The inverter breaker in the sub panel is the breaker to use in the calculations. The next day a rep from xyz solar came out to his house and after looking at his electric bill told john that he would need an 8 5kw pv system to offset 100 of his past 12 month usage. The result is that you can shave off a few extra amps before you connect the sub panel output to the main panel board.

Design shows main breaker to be derated to 150a in order to stay below 120 of bus rating 150 70 220a 240a. John smith is a homeowner in california looking to reduce his electric bill by going solar and he decided to call an installation company that he found on the internet. Use the derating factor to account for such factors as soiling of the panels wiring losses shading snow cover aging and so on.