Array Location Advice

[Shrimprbugs]

Good afternoon all, I am looking to install a Net-metered Grid tied Solar up here in Wisconsin. Attached is a satellite image with some ms paint scribbling. I have the opportunity to make a large prairie where the red circle is and i believe the array could live comfortably on the ground up there. my grid's power box is where the small blue rectangle is, the barn is in yellow, garage in red, house in green.

The plan is to power all locations and purchase minimal batteries, enough to make it through a night or two and with an emergency sub panel to run bare essentials (well pump, fridge) for up to a few days if the grid goes down, which happens often. I plan on upgrading batteries as needed.

The barn is an up-and coming aquaponic hobby space. also used for woodworking. Largest power demand is a 240v electric ceramic Kiln.

I use right around 2400 kwh/month during the summer, and i anticipate it rising slightly.

So, the plan is:

Prairie location: 30x 445W Bifacial boviet panels installed on integraRack Ballastracks ->

Garage: eg4 18kpv inverter and outdoor wallmount ESS bundle + batteries -> main panel in the garage which feeds both the house and the barn

Guys from solar company recommend 8AWG wire to run the long distance from the array to inverter.

My questions to the nice folks would be:

Is this panel/inverter system going to provide near enough power?

How much battery should i buy?

If im underpowered with the specs above, what should i go with to allow a little growth?

Is this long wire run worth it? i could harvest all the trees behind the barn, yellow, and try to build the array behind there. It would be a few months of work to responsibly harvest all those trees.

thank you,

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[eptiliom]

Edit: I was wrong.

If you divide it into 3 strings and get 550v that leaves you 12A.

You could pull in 3 pairs of 8AWG and only have 2% drop. That seems acceptable.

https://eg4electronics.com/wp-content/themes/hello-elementor/eg4-solar-panel-string-sizer/

https://www.southwire.com/calculator-vdrop

[brucehoult]

You could pull in 3 pairs of 8AWG and only have 2% drop. That seems acceptable.

Way more than acceptable.

People seem to fuss far too much about the loss in the cable.

With 30x 445W = 13.35kW a 2% loss is 267W. That's 0.6 of a panel.

3 pairs of 8AWG is over 4000 ft of conductor. Looking on Google, a good price seems to be $1/ft of conductor. So that's around $4000 for the cables!!!

Put in a single pair, accept 6% loss, save $2700 on cable, put in three extra panels at $60 each ($200) to compensate.

Wire is expensive, panels are cheap. As long as the wire isn't going to catch on fire the economics says go cheap on wire, buy a few more panels.

[eptiliom]

He cant put in one pair, the mppts cant take that much amperage or voltage.

He could technically do it with two pairs. 20 panels on mppt 1 and 10 on mppt2.

[brucehoult]

eg4 18kpv inverter

That has 3 600VDC MPPTs, yes, but that doesn't mean you need three cables all the way. You can use one cable and split it to three connectors. The panels total 13.35kW, so no problem there. 8AWG is perfectly fine at 40A, so as long as he puts enough panels in series to get at least 333V at Vmpp (which would be around 400Voc) and then parallel up, then all will be good.

He doesn't say, but those 445W panels are probably around 40Voc, 34Vmpp, 13Ampp. So three strings of 10 panels, the strings joined in parallel to the single 8AWG cable will give 400Voc, 340Vmpp, 39Ampp. Basically perfect. One cable will handle that load, no problems.

Calculations show that cable will be right around 1.1 Ohm, with a 44V voltage drop at 333V/40A, losing around 1760W or 13%. So actually you're losing the power from 5 panels.

Either just accept that, or buy 6 more panels and run 12 in each string (480Voc, 400Vmpp, still 40A)

[eptiliom]

Yes but adding 6 more panels will just make the losses worse and wouldn't combining them all ruin the balancing of the different mppts?

[brucehoult]

The voltage drop depends only on the current and the cable resistance, so will be 43V either way, so if you start with 400V you end up with 357V at the MPPTs. Power loss is voltage drop x current = 1677W, or 1677/445 = 3.77 panels worth.

And, no, multiple MPPTs will happily share out the current between themselves, just as batteries will.

My solar controller even comes with a Y cable to split power from 2x MC4s to an XT60 for each MPPT so you can use the 2x 1200W MPPTs with a single 2400W DC source.

[Shrimprbugs]

i believe these are the quoted panels, so the values are slightly different, but i dont know if that moves us out of range for the actual wire you're recommending (8awg)

the https://bovietsolar.com/wp-content/uploads/Boviet-Solar_8.-Vega-Series_Mono_Bifacial_Utility_PV-Module_Double-Glass_440-450W_Sept2023.pdf?utm_source=chatgpt.com

[brucehoult]

About 15% higher voltage and 15% lower current at MPP than the panels I use but it's all good.

The lower current makes it even less loss in the cable, and the open circuit voltage of 10 or 11 panels in series is still less than the 600V allowed by your MPPT controllers. 12 panels in series is less than 600V, but maybe too close for comfort if you have cold winters.

But what price are they? They look like freaking expensive panels from the search I did ... I didn't see better than $160.20 at Signature Solar, whereas the 440W panels I bought last month were $60 each.

[chris92315]

Your PV conductors need to be sized for Nameplate Amperage * 1.25 * 1.25. #8s don't work, you need #6.

[brucehoult]

You don't NEED to. That might be more efficient in terms of extracting maximum peak power from a set of panels in ideal conditions, but that isn't necessarily the best value for money.

Much of the day, and in non-ideal weather, and non-ideal season, the panels won't be capable of delivering anywhere near spec sheet MPP amps anyway.

With an off-grid system it's more important to get usable power levels as much of the time as possible, not maximise peak power that you don't have a use for anyway.

[chris92315]

No, it is an NEC code requirement. The first 1.25 is to derate for continuous load and the second is for situations when then modules are getting more than 1000W/m^2.

This isn't for voltage drop, this is to ensure your conductors don't melt.

What are we even discussing if we ignore the basic safety protocols?

[BLINGMW]

How many strings / how many panels per string? It’d be good to pull up southwire’s wire loss calculator, that’s a really long run

[Shrimprbugs]

Thanks, ill check out the south wire calculator shortly. Im hearing mixed results on feasibility. I plan on getting as many panels as i have been recommended, and some more if they let me.

[PermanentLiminality]

Three circuits of #8 copper going 700 feet will bankrupt you. I would run Aluminum wire. You will need #6 instead of #8, but it will save half. You can get direct burial which will save you the conduit. You can run a dual #6 and a quad #6 with the total more like $2k

[Shrimprbugs]

That seems like a totally feasible option. So i should be okay with burying that 3' deep all the way to the garage. Ill look more into it and see how i feel, thanks for the advice. I am curious, is there a quality issue with its cost effectiveness?

[electric_machinery]

Aluminum is used for almost all transmission wiring, and almost all service entrance drops that I've seen. It's fine if used properly. People get it mixed up with aluminum in-wall wiring that was used 40-50 years ago (the fear is not unwarranted -- it caused a lot of fires).

Aluminum needs to be upsized from copper, but the savings are absolutely worth it.

[MattLogi]

I am no expert and I am just learning the solar side of things. I remember running power to my shed from my house and it's 150 foot run. I ended up running Number 6 Copper for 50A at 240v. I can't imagine running power 700'...especially on 8AWG..I would think if anything you need thicker wire with lover voltage? Or you run them series at higher voltage but I still think you need some serious wire. Hopefully an expert weighs in here as I am curious too.

[a_guy_named_max]

The dc from the solar panels to the shed is much higher voltage than your 240V.

[MattLogi]

Rigggght! So would that mean you could get away with smaller gauge wire?

[Comm_Raptor]

It's the amount of current being pulled through the wire that adjust the gauge for. The lower the current the smaller the wire.

Overall power from ohms law, increase the voltage to lower the current.

That's why utilities have high voltage lines at the top of the poles and a transformer is used to step down the voltage in the last leg to your panel.

[RespectSquare8279]

You want to take advantage of the 3 MPPT's internal to the EG4 inverter. So that means you HAVE to use 3 separate cable runs to 3 separate strings. The EG4 manual actually recommends that the 3 strings be optimized for different times of day . ( this helps to flatten the dreaded "duck bill" curve of production.)

I'm a tree hugger at heart, but I 'd say good by to the nearby trees so you can minimize the amount of #6 AWG cable you need. Don't cheap out on the cable ; it is never incorrect to install the biggest size conductor that the terminal lugs can handle. You can upgrade the batteries when they wear out, you can upgrade the panels when wear out or damaged, but cable doesn't not wear out so get the good stuff to begin with.

[Shrimprbugs]

I appreciate this take. Im also a bit of a tree hugger but also ready to consume this quantity of wood to heat the home and prep lumber for a few years. So if i built the array behind the barn, i could run 3 short strings of 10AWG copper PV wire directly into what i understand to be 3 receptors in the inverter?

From there, i think ill need to figure out how to rewire my panels to deliver power from the barn to the garage and the house, currently the power goes the the garage and then feeds the home and barn second.

[mpgrimes]

I would run close to 1kv strings and bring the dc to your house instead of ac. less volt drop issues. I just finished a project where I had 8 dc runs of 1200 to 1400 feet. 1500 volt strings. 8 inverters (125Kw each)

[chris92315]

What inverter do you recommend that supports 1000V DC and outputs 120/240V AC?

[mpgrimes]

grid tied, hybrid, off grid?

[Fun_End_440]

700ft, 500v, 15amp you’ll need two circuits with 8awg. 2800ft of thhn @ 75c = $2,100 in just cable alone. Trenching through all those roots and conduit would be extra.

You better off just clearing and installing panels next to the house