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AC Disconnect Sizing and Type for Line Tap (no backfeed)
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Thanks for the tip on the SolarEdge Designer. I was not aware of this tool. I have a SolarEdge installer account so I was able to use that to access the Designer. The Designer would not let me create a string with more DC power than 6,000 watts per SolarEdge's requirements that a string cannot be larger than 6,000 watts. -
Get a free account for SolarEdge's Designer. Then plot out your panels and put in your equipment. It will tell you also, recommended optimizers and figure out string length max for you.Leave a comment:
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I would consult the installation manual. I know for the HD Wave 11.4kW inverter I installed there's a combiner box inside the inverter, the strings are combined before the inverter, there aren't separate channels. If the terminals inside the inverter can take ~30A then there's no difference between combining the strings at the inverter or at the array.
The price difference for the wire to do two strings is about $50. I will follow Solaredge's guidance that strings not exceed 6,000 watts unless I find something official from Solaredge that says otherwise. A decent combiner box will eat up the $50 in savings on wire pretty easily.Leave a comment:
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a given resistance, voltage is only proportional. Bruce RoeLeave a comment:
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For the same wattage, high voltage has lower loss than lower voltage. Most of the loss is in the resistance of the copper wire.
For a 5kw PV array, a HV (500V) DC array feeding a string inverter has lower loss in the cabling than using a long AC (240V) line. You can add heavier copper wires to reduce the loss, but you have doubled your wire expense. Some use even heavier 1 or 2 OO aluminum feeder wire which is less expensive than copper
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I think the conversion losses are not going to change much whether it's before or after the line losses.
At least my assumption is that the conversion losses are basically a percentage of power - so whether you have X * 97% or 97% * X, it winds up being the same result.
I think all the gains you'd have in efficiency would be from less line losses.
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At least my assumption is that the conversion losses are basically a percentage of power - so whether you have X * 97% or 97% * X, it winds up being the same result.
I think all the gains you'd have in efficiency would be from less line losses.
Do you have a performance curve or something that shows less % losses when the DC voltage is lower? Because that would contradict my assumption.Leave a comment:
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Soalredge has a maximum string wattage of 6,000 watts for the 11.4KW model. You have to have two physically separate strings once over 6,000 watts.Leave a comment:
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You can combine the strings at the array and use a pair of #8 home run back to the inverter but a pair of #10 and a pair of #12 would work too.Leave a comment:
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You could probably get away with running a pair #8 from the panels. My voltage drop calculator says that your line losses would be ~2% and if your 11.4kW inverter is maxed line losses are 0. VS if you were to mount the inverter at the panels and run AC you would need #4 to get a 2.3% voltage drop and you would also be required by code to run a separate #6 neutral.Leave a comment:
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Yes, the optimizers still work with new inverter. I replaced one of the two inverters with the 11.4KW one to make sure it worked. It generated power just fine until I disconnected the panels for the move recently.Leave a comment:
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I am relocating an existing solar system and also adding four more panels at the same time. I am changing to a single 11.4KW Solaredge inverter I got cheap since my two Solaredge inverters were maxed out. I want to keep one of the old inverters to add more panels at a later date. Garage is being torn down and replaced with much larger garage so panels have to come off roof and ground mount has to move.
Current config is combo of ground mount and panels on detached garage roof with two Solaredge inverters. AC runs 80 feet to house with about a ten foot run of DC to each string.
New config will be two ground mounts with a single inverter to start. Original plan was to run AC 200 feet to inverter with DC going about ten feet to panels. It sounds like I should mount the inverters close to meter so AC run is a lot shorter and DC run is much longer.
Voltage drop is a function of current squared. At 11.4kW and ~400vdc / 240vac your inverter input is ~30ADC in and ~48AAC out. So line losses on the AC side all things being equal would be ~250% higher.
I would also double check to make sure your optimizers are compatible with your 'new' 11.4kW inverter.Last edited by nwdiver; 10-19-2020, 04:21 PM.Leave a comment:
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