Your math is off. Each micro inverter is two inverters in one box, 600w max, 500w typically. 2.1A @ 240 VAC per box, 5 boxes per string. 10-12A per string (12 AWG). Loss on the branch circuit is a max of 13w. loss on the line from the breaker panel to the house (8 AWG) is 400w at max power and less than 300w at typical power midday. That's figuring a 250 ft. run.SageBrush wrote: ↑Wed May 11, 2022 8:35 amThe wire resistance losses are proportional to the square of the current. 10 awg copper resistance is about 1.25 ohms per 1000 ft. Your string has about 2x the current as a a DC solution, and then 4x more current after two strings are combined. A rooftop is almost certainly close enough to the inverter to not bother considering but a ground mount may be a different story.
E.,g. if two 20 Amp strings are combined near the panels and then 40 Amps run 250 feet to the inverter, the loss will be
40^2*2*1.25*250/1000 = 1000 watts. 100 watts every 25 feet of home run.
My SMA string inverter cost ~ $1,200 for 8 kW so about 15¢ a watt. AND I get an (admittedly modest, but still very useful) grid-down solution for free.
Each solution has trade-offs. Anybody who says one or the other is always the right answer is missing information or is pushing an agenda.
addendum: 10 awg looks too small for 40 Amps. What is awg of your wires after the strings are combined ?
The inverter string is 12 AWG both on the trunk and from the junction box to the breaker panel. The max distance from an inverter to the panels about 35 ft for the furthest set,20 ft. for the middle set and 5 ft. for the nearest set.. That's a max of 12A on each string at a max distance of 35 FT. From the panel to the house I ran 8 AWG. Most of the time current is about 30A or less. I'm just fine with a slight loss under max power. I had 8 AWG left over from another project so I used that. 6 AWG would have been better but wasn't worth the extra cost. Also I would have had to dig up existing conduit or bury new conduit to accommodate 6 AWG. It wasn't worth the effort. The other set of panels is on a Sunnyboy 8K inverter and is run on 6 AWG over a bit longer distance (50 feet further). The micro inverters and panels actually do better because they are better situated and are set to a higher angle of inclination. If I could do It all over again I'd set all the panels to 45 degrees for better power levels in the winter and more consistent power generation all year long instead of summer peaks and winter troughs.
Keep in mind that I have 18KW of panels. It would be nearly impossible to put that much on a south facing roof of a typical house. Putting them out in a field let me set them for the best operation. The2-3% loss due to distance is made up by the improved siting.