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Ac PV Module Calculations


Q:

Just finished System Components video part 1 and the LG AC Module looks like a great product. I did find out they are going for $618 per module and with (12) modules per string the total cost is $7416.
Question - Does the $7400 sound comparable to (12) 305w modules using micro-inverters? Comparable to (12) 305w modules using a string inverter? I would think design/installation cost would be much lower.
Question - Is my calculation correct? 305W@ 240VAC = 1.27A per module, connect the maximum number of panels (12) in parallel and your are up to 15.25A. If the residence has a 100A main panel, 20A addition from solar is max
Below is some array data
Inverter(s) LM305UE-G1 (Integrated with Module)
Modules 12 X LG305N1C-B3 (305W)
STC Array Power 3,660W
PTC Array Power 3,323W
CEC Power Output 3,256W
Annual Prod. Est. 5,252kwhr
Max AC Output Current 15.24A

A:

Hi Rob,
That sounds expensive! One of the reasons that people get NABCEP Entry Level tested is so that distributors will realize that they are in the industry and give them better pricing:

I just did a quick email search and got this:

"Hi ,

We have about 473 of the LG MonoX ACe 300W module left after the sale and we want to push them out by Monday.
We will give this balance @ $0.995/watt for Mega-Watt Club members or $1.02/watt for other customers who are willing to take the whole balance. Mega-Watt Club members will also get Free Shipping as usual.
If you are interested in a lower quantity, the price would be $1.05/watt for Mega-Watt Club members and $1.07/watt for other customers.

The LG AC module comes with a 305W Microinverter already installed. No trunk cable needed.
See all Accessories you may need here: RENVU AC Modules
Read the datasheet here
Read the Installation Manual here
Read the manufacturer warranty here"

This means the ac module from this salesperson is about $1/watt and $300 for a 300 watt module.

I would also like to clarify what they mean by 300W, since it is not based on the PV. It is a 300W inverter on a 60 cell module, I cannot determine that if the PV was tested at STC by an independent testing lab, that it would be a 300W module. 

300W/1.64 square meters = 183 watts per square meter

183W/square meter is a 18.3% efficient module, which is high end. Is it an exaggeration?

I can tell you one thing, that the 300W inverter is never going to put out 300W.

According to this datasheet:

https://drive.google.com/file/d/0B_7XWOqMQhq9MGVjM2ZVMDhBSk1zekUtOHlkX3lJMEpXVGow/view

The output current of the ac module is 1.27A at 240V

Here is how I would determine how to fit the most on a 20A breaker:

1.27A x 1.25 = 1.5875A

20A/1.5875A = 12.6

12 ac modules per circuit max.

We both came up with the same answer, which is proof that there are many ways to solve a problem!

Good work!!

Sean White


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