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Home » Solar inverters » Convert DC to AC with string inverter is better
Convert DC to AC with string inverter is better
Tags: String inverter
Up until recently I worked for a company that almost exclusively installed Gozuk micro inverters. I did the design and system monitoring. We had 170 sites using the technology. They pretty much all outperformed their PV Watts estimate, especially if you were trying to compensate for shade. They DO outperform string inverters even without any shade. If there is no shade, the out performance is not generally worth the cost.
The efficiency of converting DC to AC with some string inverters is better; string inverters can only perform MPPT on a string level, while micros perform it at the module level. Since manufacturing tolerances always ensure module mismatch, especially with the cheaper modules, string inverter can't maximize the output of each individual panel, so they can't maximize the output of the system as a whole.
Besides all that, what does the 25 year solar panel warranty actually mean if you can't compare the output of one panel to the other in real time?
At the end of the day it is return on investment or the levelized cost per Kwhr that counts. If the extra investment needed for micro inverter is matched by an increased performance so that the levelized cost per Wwhr is equal or improved then it is warranted. It is difficult to say in any given situation what better performance or outperforms means without having the amortized cost information as well.
I use two metrics:
a) the specific yield in kWhrs per KW (of panels) installed per year.
b)Then I use investment cost divided by specific yield to get a relative number (which has only relative meaning)-- the lower this number the better.
A True assessment needs further analysis that includes initial investment with amortized cost of money and total production over the useful life of the system or contract -- this is where reliability and linear degradation plays a big role.
For example I can buy really cheap panels that have to be replaced in 10 years -- is this bad? Not necessarily --- it depends on the ROI.
The efficiency of converting DC to AC with some string inverters is better; string inverters can only perform MPPT on a string level, while micros perform it at the module level. Since manufacturing tolerances always ensure module mismatch, especially with the cheaper modules, string inverter can't maximize the output of each individual panel, so they can't maximize the output of the system as a whole.
Besides all that, what does the 25 year solar panel warranty actually mean if you can't compare the output of one panel to the other in real time?
At the end of the day it is return on investment or the levelized cost per Kwhr that counts. If the extra investment needed for micro inverter is matched by an increased performance so that the levelized cost per Wwhr is equal or improved then it is warranted. It is difficult to say in any given situation what better performance or outperforms means without having the amortized cost information as well.
I use two metrics:
a) the specific yield in kWhrs per KW (of panels) installed per year.
b)Then I use investment cost divided by specific yield to get a relative number (which has only relative meaning)-- the lower this number the better.
A True assessment needs further analysis that includes initial investment with amortized cost of money and total production over the useful life of the system or contract -- this is where reliability and linear degradation plays a big role.
For example I can buy really cheap panels that have to be replaced in 10 years -- is this bad? Not necessarily --- it depends on the ROI.
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