Question 1:

So my Solar system is supposed to be a 3.87 kw system (3,870 watts DC). Yet the AC rating is 3,449 watts. Since it's a grid tie system, shouldn't the listed rating be shown in AC? I don't understand why the installer lists the number as DC, because the inverter shows the power output as an AC number, I would think that is how it should advertised as well.

Answer 1:

The DC rating is the combined output of the Solar Panels under ideal conditions.
The AC rating is the maximum output the Inverter will produce with the Solar panels and MPPT SOLAR CONTROLLER connected to it.
The AC output is always less as the Inverters arnt 100% efficient.

Answer 2:

The power output from a Solar pv System varies over the course of a day, varies depending on what month of the year it is, varies depending on the panel tilt, varies depending on the panel temperature, latitude of the installation etc.
ie there are so many factors which determine how much power that you get out of the Inverter that pretty much any number doesnt mean much.
Any number thats quoted has to be measured under some kind of standard
test environment, hence the DC power rating for the Solar Panels under STC conditions.

Question 2:

But the average consumer doesn't need the "DC" rating.

My inverter doesn't tell me how much "DC" wattage my panels are producing. It only tells me the "AC" wattage and "DC" voltage. So as an average consumer, I look at those numbers and see that my system doesn't get anywhere close to the 3.87 kw "DC" rating. But after digging into the specs, I found my system is rated for 3.44 kw "AC", and now the numbers are very close. And yes I know my numbers will go down depending on the day, and time.

So if power inverters are really only concerned about the "AC" numbers, then it would make sense that the solar industry should be advertising "AC" numbers, instead of "DC" numbers. When someone says they have a 4kw solar system, it would mean they have a 4kw "DC" system. But the way it is now, the general public is unaware the ratings are "DC" and not "AC". I contend the industry is using "DC" numbers because it represents an inflated rating to the average consumer.

Answer 3:

What purpose is served by the customer being told they have a 4KW Power Inverter AC system.
What does the customer do with the number.
A 4 KW DC system tells the customer that the Solar panels on their roof
are rated by the manufacturer at STC conditions as being able to generate 4KW under ideal conditions.
The customer can climb up on their roof and verify that the panels are what they paid for.
Giving them an AC out from the Inverter is meaningless as the output is dependant on so many conditions that you may never see it.
All this will do is cause unneccessary complaint from people who will then beleive that their system isnt working properly.
Solar systems arnt guaranteed to make any particular amounts of power.
A 4KW system , whether its DC to AC power inverter doesnt guarantee that it will ever make 4KW.
All it means is that the panels that are supplied are rated by the manufacturers at 4KW under STC conditions.
That the way the system works.