temperature versus outputpower aurora

[Cor van Houtum]

we where comparing my 4.2 inverter at home with a 3.6 inverter from one of my customers.
I have for testing purpose 18 solar panels mono cristaline 195 watts in two strings of 9
connected to a 4.2 aurora.

my customer has 20 x 180 watts mono cristaline with a 3.6 aurora
in two strings of 10

in flight we are 4 km apart

I am 40 degrees angle and faced south
he is on a flat roof 30 degrees angle and faces also south.

the day production on my customers site is about 23 kwh when good conditions
my day production on the same day is 15 Kwh

so I started to investigate where this difference is coming from, and i think i suspect the inverters location.
his inverter is located insite my inverter is outsite
my inverter reaches 50 degrees and more
so i started cooling with a fan.
the unit went instantly up with hunderds of watts

the manual says that the 4.2 works full power till 45 degrees
the 3.6 does allow temperature of 55 degrees

does anyone have done this test ?
i will try to bring this in chart with use of heating and cooling the aurora
to find out how mutch it goes down to protect it self.

let me know what you think.

cor

[Rob Beckers]

Cor, the temperature numbers Power-One mentions for when derating starts are "guestimates" based on ambient and air movement. They actually base derating on the internal heat-sink temperature; when it hits 70C at their measurement point the firmware starts throttling the inverter. How that correlates to external (air) temperature depends on many factors.

With that in mind, Power-One claims the 3.0kW will do full power up to 50C ambient, the 3.6kW will work at full power up to 60C, the 4.2kW up to 50C, the 5/6kW up to 50C. I would take this with a big grain of salt, since they assume there's air movement to remove heat from the heat-sink. Derating is 10 - 15% per 10C above, depending on model, according to Power-One.

Almost all the inverters we've installed have been outside, very few go indoors. I'm not there to see output on a hot day, but all systems have lived up to their annual predicted energy output. I avoid putting them in the sun, especially noon and afternoon sun, and make sure there's space above the inverter for the hot air to escape. That's as far as it goes.

-RoB-