Derating Sub Panel For Solar

The photovoltaic pv derating factor is a scaling factor that homer applies to the pv array power output to account for reduced output in real world operating conditions compared to the conditions under which the pv panel was rated.

Derating sub panel for solar.

The pvwatts default overall dc to ac derate factors are based on a system with a string inverter. 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. This panel had to be upgraded due to the large 13kw ground mount solar pv system being installed. The inverter breaker in the sub panel is the breaker to use in the calculations.

Design shows main breaker to be derated to 150a in order to stay below 120 of bus rating 150 70 220a 240a. This was the first time i ever replaced a electrical panel directly next to a window. A new solar pv system to be installed. On this project i was hired as a sub contractor to install the electrical panel for a larger well known solar company.

Use the derating factor to account for such factors as soiling of the panels wiring losses shading snow cover aging and so on. 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. An sma sunny boy 2500hf and an sma sunny boy 5000. Pv backfed breaker to be 70a for load side connection to bus.

Main panel has 200a bus and breaker. That sub panel can have a 40a breaker added to it for the 7600w inverter as 100a 40a 140a which is under the 150a. The result is that you can shave off a few extra amps before you connect the sub panel output to the main panel board.