johnlocke
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Re: 240 outlet for 2022 leaf EVSE question

SageBrush wrote: Wed May 11, 2022 8:35 am
johnlocke wrote: Tue May 10, 2022 2:51 pm Micro inverters convert to AC at the panel so DC losses are minimal. SMA string inverters are cheaper by a few hundred dollars then the equivalent Micros but not having to work with HVDC and no single point of failure balance that out for DIY'ers.
The 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 ?
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.

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.
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SageBrush
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Re: 240 outlet for 2022 leaf EVSE question

(my bolding)
johnlocke wrote: Wed May 11, 2022 10:42 pm
The inverter string is 12 AWG both on the trunk and from the junction box to the breaker panel.
Aren't you combining strings for the run from box to panel ? I'm surprised the 12 awg can handle the current.

We do seem to agree though that the lion's share of the losses for a microinverter array at a distance from the panel will be the run from combiner box to panel, and that run will be at 240v and somewhere around 20 - 40 Amps, depending on configuration. The current here calculates out to P(ac) / 240

As for your calc of 400 watt losses, doesn't the 250 feet run have 500 feet of wire for the circuit ?
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Bought Jan 2017 from N. Cal
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johnlocke
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Re: 240 outlet for 2022 leaf EVSE question

SageBrush wrote: Thu May 12, 2022 4:20 am (my bolding)
johnlocke wrote: Wed May 11, 2022 10:42 pm
The inverter string is 12 AWG both on the trunk and from the junction box to the breaker panel.
Aren't you combining strings for the run from box to panel ? I'm surprised the 12 awg can handle the current.

We do seem to agree though that the lion's share of the losses for a microinverter array at a distance from the panel will be the run from combiner box to panel, and that run will be at 240v and somewhere around 20 - 40 Amps, depending on configuration. The current here calculates out to P(ac) / 240

As for your calc of 400 watt losses, doesn't the 250 feet run have 500 feet of wire for the circuit ?
The trunk lines do converge at a breaker box on the PV mount. Each trunk line goes into a separate junction box and is connected from there to 12g wire which goes into the breaker box mounted on the PV structure. There is a 40A master breaker and 3 20A breakers, one for each string. From there the power is on 8g wires to a 40A breaker in the house panel. And yes I did calculate the 500 ft. of wire. The trunk lines only carry 12A max each. 12a@240VAC=2880w= the output from 10 panels. Typical output from these panels at noon is more like 240-250 watts. About 10A per string, 3 strings. 500ft. of 8g has a resistance of 0.3141 ohms. At 30a the loss is 282.69w. At 36A, the loss is 407w.

I may have confused you with my other descriptions, hopefully this clears everything up.
2022 SV+ 10/22
2016 SL, New battery at 45K mi. Crashed at 95K mi. 9/22
Jamul, CA
San Diego East County
SageBrush
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Re: 240 outlet for 2022 leaf EVSE question

johnlocke wrote: Thu May 12, 2022 10:26 pm The trunk lines do converge at a breaker box on the PV mount. Each trunk line goes into a separate junction box and is connected from there to 12g wire which goes into the breaker box mounted on the PV structure. There is a 40A master breaker and 3 20A breakers, one for each string. From there the power is on 8g wires to a 40A breaker in the house panel. And yes I did calculate the 500 ft. of wire. The trunk lines only carry 12A max each. 12a@240VAC=2880w= the output from 10 panels. Typical output from these panels at noon is more like 240-250 watts. About 10A per string, 3 strings. 500ft. of 8g has a resistance of 0.3141 ohms. At 30a the loss is 282.69w. At 36A, the loss is 407w.

I may have confused you with my other descriptions, hopefully this clears everything up.
^^ This looks right -- about 2 - 3% losses from the higher current on a long run home. That is ballpark the shading advantage that micros have over serial DC, but it is quite a bit more expensive, locked into a vendor, and has worse reliability. The main upside is panel level monitoring.and simpler troubleshooting. I should add that troubleshooting a serial array is pretty simple. It would take me 3 - 4 DMM checks to find the bad panel.

Regarding cost ...
If the system is enphase, then I think these costs are ballpark:
$125 per microinverter
$3/foot for the run from the combiner box to the panel, based on $1/foot per wire * 3 wires
$20 per trunk cable
Envoy proprietary monitoring hardware and software. -- ?? $300 - $500

A SMA SunnyBoy serial w/ central inverter setup:
15 - 20¢/DC watt, depending on Array size
$1.5/foot home run, based on two strings, 33¢/foot, and 5 wires that are 12 awg

My arithmetic says for a 10 kW array that is 250' from the panel:
SMA: $1,875
Enphase: ~ $4,000
Last edited by SageBrush on Fri May 13, 2022 7:15 am, edited 1 time in total.
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. Cal
Two years in Colorado, now in NM
03/18: 58 Ahr @28k miles. 10/21: 53.4 Ahr @ 40k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018. Sold 11/2021, awaiting Tesla Model Y
wwhitney
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Re: 240 outlet for 2022 leaf EVSE question

SageBrush wrote: Fri May 13, 2022 5:12 am This looks right -- about 2 - 3% losses from the higher current on a long run home.
The AC vs DC choice on a long run from a remote array has various tradeoffs. Microinverters lock you into AC, but sometimes with a string inverter you'd choose to put it at the array anyway. The 2-3% losses you mention could obviously be mitigated with larger (more expensive) conductors, so that's just another tradeoff.

I.e. there's no right answer, just a bunch of tradeoffs. Depending on your goals, either microinverters or string inverters may end up a better choice.

Cheers, Wayne
johnlocke
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Re: 240 outlet for 2022 leaf EVSE question

SageBrush wrote: Fri May 13, 2022 5:12 am
johnlocke wrote: Thu May 12, 2022 10:26 pm The trunk lines do converge at a breaker box on the PV mount. Each trunk line goes into a separate junction box and is connected from there to 12g wire which goes into the breaker box mounted on the PV structure. There is a 40A master breaker and 3 20A breakers, one for each string. From there the power is on 8g wires to a 40A breaker in the house panel. And yes I did calculate the 500 ft. of wire. The trunk lines only carry 12A max each. 12a@240VAC=2880w= the output from 10 panels. Typical output from these panels at noon is more like 240-250 watts. About 10A per string, 3 strings. 500ft. of 8g has a resistance of 0.3141 ohms. At 30a the loss is 282.69w. At 36A, the loss is 407w.

I may have confused you with my other descriptions, hopefully this clears everything up.
^^ This looks right -- about 2 - 3% losses from the higher current on a long run home. That is ballpark the shading advantage that micros have over serial DC, but it is quite a bit more expensive, locked into a vendor, and has worse reliability. The main upside is panel level monitoring.and simpler troubleshooting. I should add that troubleshooting a serial array is pretty simple. It would take me 3 - 4 DMM checks to find the bad panel.

Regarding cost ...
If the system is enphase, then I think these costs are ballpark:
$125 per microinverter
$3/foot for the run from the combiner box to the panel, based on $1/foot per wire * 3 wires
$20 per trunk cable
Envoy proprietary monitoring hardware and software. -- ?? $300 - $500

A SMA SunnyBoy serial w/ central inverter setup:
15 - 20¢/DC watt, depending on Array size
$1.5/foot home run, based on two strings, 33¢/foot, and 5 wires that are 12 awg

My arithmetic says for a 10 kW array that is 250' from the panel:
SMA: $1,875
Enphase: ~ $4,000
SMA no longer makes a 10KW inverter. You'd need two 5KW inverters at $1200 each plus the monitor box @ $900. It's a little cheaper but if you're mounting on a roof you also have to add the rapid shutdown modules for another $1000. If you are ground mounting, you really don't want to run multiple 600VDC lines back to an inverter at the house so you still have the AC transmission losses. You lose MPP tracking per panel and panel level monitoring. I used APS dual micro inverters (15 @ $185 ea) plus $400 for the wireless monitor. Add in the wiring, breaker box, conduit, etc. and you come out at about $4K. For a ground mount the SMA is a little cheaper but on a roof it would cost more and you lose features.

If I were doing an array with high wattage panels (over 350W), I'd use a central inverter just because microinverters won't handle the power. For a small array where a single inverter would work, I'd consider it. For anything else, I'd use microinverters.
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SageBrush
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Re: 240 outlet for 2022 leaf EVSE question

johnlocke wrote: Fri May 13, 2022 12:04 pm If you are ground mounting, you really don't want to run multiple 600VDC lines back to an inverter at the house
Not my setup, but I am curious why you say this.
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. Cal
Two years in Colorado, now in NM
03/18: 58 Ahr @28k miles. 10/21: 53.4 Ahr @ 40k miles
-----
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johnlocke
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Re: 240 outlet for 2022 leaf EVSE question

SageBrush wrote: Fri May 13, 2022 12:31 pm
johnlocke wrote: Fri May 13, 2022 12:04 pm If you are ground mounting, you really don't want to run multiple 600VDC lines back to an inverter at the house
Not my setup, but I am curious why you say this.
Extreme DC in an underground conduit. I worry enough about someone or something cutting or chewing into a 240VAC line. 600V would fry anything on the spot. Also It's a lot harder to find a rated DC breaker especially if you need something over 500V. Can't pick it up from Home Depot. I'd want a breaker or disconnect box at the panels and a breaker somewhere to limit current. 240AC could hurt you, 500-600VDC will kill you.
2022 SV+ 10/22
2016 SL, New battery at 45K mi. Crashed at 95K mi. 9/22
Jamul, CA
San Diego East County
SageBrush
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Re: 240 outlet for 2022 leaf EVSE question

johnlocke wrote: Fri May 13, 2022 12:04 pm
SMA no longer makes a 10KW inverter. You'd need two 5KW inverters at $1200 each plus the monitor box @ $900.
That was news to me about SMA. Related to supply issues, or a sign of the time ?

In any case, there are other manufacturers that sell 10 kW for about $1,500:
https://www.renvu.com/Products/Solar-In ... to16113.09

My SMA comes with its own built in monitoring and comms. I'm not sure about these others, and I'm reasonably sure that they do not have an island AC supply when the grid is down.
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. Cal
Two years in Colorado, now in NM
03/18: 58 Ahr @28k miles. 10/21: 53.4 Ahr @ 40k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018. Sold 11/2021, awaiting Tesla Model Y
goldbrick
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Re: 240 outlet for 2022 leaf EVSE question

Enphase IQ7+ micro-inverters claim to support up to 440W panels with a max output power or 290VA. I don't know exactly how that matches with high output panels though.

The Enphase monitoring hardware and software is not required to use the system AFAIK, but if you pay for the micro-inverters it is nice to see the individual outputs for monitoring and showing off on your phone, etc. :mrgreen:

In my case, it easily shows which panels are producing what and when. I do have partial shading so it was a no-brainer in my case. I'll have to think harder about the cost trade-offs when I do a ground mount system but so far I have been impressed with their design and performance.

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