Solar System Sanity check

[vortextangent]

I'm looking to pull the trigger on an Amazon piecemeal Renogy system for my shed.

2 - 320W 24v Renogy panels $645 for both https://www.amazon.com/gp/product/B08D644VFN
1 - Renogy Rover 40A Charge controller $140 https://www.amazon.com/gp/product/B01MSYGZGI
1 - Sprance Solar combiner with lightning arrester $100 https://www.amazon.com/gp/product/B09NNCNZVG
2 - Renogy 12v 100AH AGM batteries $210 each ($420 total) https://www.amazon.com/gp/product/B075RFXHYK
1 - Giandel 1200W Inverter 24V ($210) https://www.amazon.com/gp/product/B07PQTMD6P

$~1500 total

It'll keep my tool batteries topped up and power a small home office (possibly a small window ac). Shed office area will be insulated.

It's a very large shed with a loft for wood storage maybe 24x24 and office area is maybe 8 x 24?

Is there any important component I should consider adding?
I'd like to have a 24v battery bank but 24v lithium is a bit too expensive for me and 12v seem to not want to be wired in series? later i'll probably build a battery bank but want to check viability of solar on the shed and gain some practical working solar knowledge before attempting that.

Edit:

Forgot to mention wires

I have a lot of spare MC from when I wired my house a few years ago that i'll probably use (unless solid wire is a big no-no?) but will need to get some MC4 connectors for the panel extension wires.

 

[Hedges]

$1/W for PV panels?
Check Craigslist and eBay for local sellers. There could be some in the $0.20 to $0.50 range.
For small quantities, new extras left over from jobs are available.
It would be good to put up excess PV, so long as max charge current limit of battery is observed.
You can over-panel about 50% while keeping same peak current by having multiple orientations. So maybe 4 panels, 2 facing SE and 2 SW.

AGM will last a couple to several hundred cycles. If shallow cycle, much long. So if only a small light at night, maybe can last 10 years.
During the day idea would be to power most loads direct from PV, with battery just providing a surge to start A/C or run a microwave.

A/C motor will draw about 5x nameplate rating for a fraction of a second when starting. Inverter surge rating has to cover that.

Combiner and lightning arrester seems overkill for a 2-panel (or 2 string) system on the roof. Unless you get lots of nearby lightning.

 

[12VoltInstalls]

AGM will last a couple to several hundred cycles.

Since “good” AGMs are over two to five times the price of flooded lead batteries I wouldn’t buy those. Plus you probably need more batteries anyway as your selection is only 100Ah usable between the two.

I'd like to have a 24v battery bank

600W of panels (which aren’t enough I don’t think) is going to charge 4 batteries, and wildhat guessing you’d need at least 800- 1200Ah of storage to handle the AC

I’m coming at this backwards I know- and some may point that out- but the AC wattage per hour needs to be less than the recharging needs of the batteries while on solar to be daily usable.

Figure out the watts per hour and how many hours you need, then you can compute battery and solar needs

 

[vortextangent]

Check Craigslist and eBay for local sellers. There could be some in the $0.20 to $0.50 range.
For small quantities, new extras left over from jobs are available.

I can't seem to find anything nearby on craigslist or ebay. I'm in Decatur, GA. What I am finding is high voltage panels; I'd really like to stick to 12v/24v panels if possible.

It would be good to put up excess PV, so long as max charge current limit of battery is observed.

You can over-panel about 50% while keeping same peak current by having multiple orientations. So maybe 4 panels, 2 facing SE and 2 SW.

shed has north/south facing roof, not ideal for multiple orientation solar. If this goes well I may add some to main house which has east/west so I could do that there. Best would probably be a pergola in front yard with panels on top (no HOA).

AGM will last a couple to several hundred cycles. If shallow cycle, much long. So if only a small light at night, maybe can last 10 years.
During the day idea would be to power most loads direct from PV, with battery just providing a surge to start A/C or run a microwave.

No microwave but maybe a small 400-600w window ac unit to take the edge off if it gets too hot / small 750W heater if it gets too cold. this would be a 9-5 office type dealy with just a laptop, monitor, phone charger and float chargers for power tool batteries during my renovation construction. I do have a table saw but that'll be plugged in with extention cord from main building, or maybe gas generator?

Combiner and lightning arrester seems overkill for a 2-panel (or 2 string) system on the roof. Unless you get lots of nearby lightning.

I was thinking of adding more panels later if this goes well (after renovation is over) and thought this would be an easy way to add panels in the future.

Since “good” AGMs are over two to five times the price of flooded lead batteries I wouldn’t buy those. Plus you probably need more batteries anyway as your selection is only 100Ah usable between the two.

I was trying to get a 24v battery solution for more power with smaller wires (same with panels).

600W of panels (which aren’t enough I don’t think) is going to charge 4 batteries, and wildhat guessing you’d need at least 800- 1200Ah of storage to handle the AC

I was looking to replicate something like this:

the office area is the same or smaller size and i'd be trying to keep within the same temp range.

Figure out the watts per hour and how many hours you need, then you can compute battery and solar needs

Max Watts continuous looks to be something like 569Watts 600 - 800 watts with external monitor and depending on AC I find.

 

[12VoltInstalls]

I'd really like to stick to 12v/24v panels if possible.

Why?

shed has north/south facing roof,

ground mount the panels

trying to get a 24v battery solution for more power with smaller wires (same with panels).

it’s the same power just different volts and smaller cable- it’s the battery cable arrangement that makes 24V

Max Watts continuous looks to be something like 569Watts 600 - 800 watts

So that is like 6.4kWh/day so wildhat guessing 1200-1500W of panels, minimum

 

[Hedges]

I can't seem to find anything nearby on craigslist or ebay. I'm in Decatur, GA. What I am finding is high voltage panels; I'd really like to stick to 12v/24v panels if possible.

Why?

Nothing wrong with "36V" or higher panels. All that matters is Voc of the panel (or series string of multiple panels) is below max input voltage of SCC, even when adjusted for record coldest temperature. Voc will go up maybe 16% when cold. More or less; you can get specs and sharpen your pencil if 16% would be too much.

A/C surge current: Inverter page says "1200W Rated, 2400W peak"
2400W could be enough to start the A/C, but only if inverter can deliver that for a couple seconds. Sometimes, quoted peak output is only for 30ms, not enough to start a motor.

Is 600w enough

I plan on putting 600w of solar panels on the roof of a small camper. The Panels will be able to tilt so I can get as much power as I can. My main use is to run a 5000 BTU AC tha draws 450w in the summer and a 500w space heater in the winter & a few little items like phones, tablets and led...

diysolarforum.com

Since “good” AGMs are over two to five times the price of flooded lead batteries I wouldn’t buy those. Plus you probably need more batteries anyway as your selection is only 100Ah usable between the two.

I was trying to get a 24v battery solution for more power with smaller wires (same with panels).

FLA is a cheaper way to get big storage.

A pair of 100A AGM from SunXtender would cost about $700. More expensive than Renogy and proportionately longer cycle life. Your choice.
Small bank like that can work if it is just a buffer. Cycled 50% or 70% DoD, 1200 Wh or 1680 Wh of storage. By only drawing maybe 200 Wh over night for an LED lamp, and only running A/C when PV delivers enough to power it, small battery should last a long time.

I have 400 Ah 48V AGM for whole-house backup. I just avoid running much when the sun is down.

 

[MichaelK]

Having gone the Renogy route myself, I would dissuade you from buying either Renogy panels, or Renogy controllers. Shop on Craigslist and buy those high voltage panels. I wouldn't pay more than 33cents/watt. Get a high voltage Epever controller like the Tracer 5415AN or 5420AN. Look at Costco's 210Ah golf cart batteries for 99$ each. Four hundred dollars would get you twice as many amphours as the AGMs you are looking at.

All the money you save could be applied to a higher quality inverter then the Giandel.

 

[joeExotic]

Get the Zooms or Chins battery on Amazon they are LiFePO4 batteries. You'll save $$$

I have the Renogy Rover Li 40A Charge controller and it doesn't read LFP battery voltage correctly.

Get a 1,500 pure sine wave inverter

 

[12VoltInstalls]

really like to stick to 12v/24v panels if possible.

I meant to expand on my “why?” question.

With an MPPT charge controller the panel voltage doesn’t matter as long as you don’t exceed the max volts of the charge controller.
I have a 12V battery bank (a “12V system”) and my panels in full sun are 88VDC to as high as 94VDC. The charge controller outputs 14.6V in boost and 13.8V in float- perfect voltages for flooded lead acid batteries. I’ve seen as high as 42 amps or so charging.

If you were a 24V battery system the charge controller would put out appropriate voltages for that as well.

You don’t have to suppress panel voltage or limit what you buy to battery voltage.

 

[Rednecktek]

Combiner and lightning arrester seems overkill for a 2-panel (or 2 string) system on the roof. Unless you get lots of nearby lightning.

With only 2 panels you don't need the combiner box. Those only start being a thing when you've got 3 or more strings of panels.

What I am finding is high voltage panels; I'd really like to stick to 12v/24v panels if possible.

Your MPPT controller will take care of that. Just don't over-volt your controller and you'll be fine. I should post my little lecture about "12v Panels" and marketing.

FLA is a cheaper way to get big storage.

This is very true. I use a lot of the WalMart 120Ah 29DC batteries for my projects, they're almost exactly $100 out the door and good for 60Ah at 50% DoD. If you can afford decent AGM's though, look at the Ampertime/Chins/Zooms. They're only a few dollars more but you get twice the usable Ah out of them. There are only a few brands that don't like being hooked up in series and that'll be in the descriptions usually. Strangely it tends to be cheaper to get 2x 12v than a single 24v often. No idea why.

1 - Giandel 1200W Inverter 24V ($210) https://www.amazon.com/gp/product/B07PQTMD6P

Get the Pure Sine version. Your electronics, compressors, and fridge will thank you. It's cheaper than buying new appliances.

You don’t have to suppress panel voltage or limit what you buy to battery voltage.

However with a 12v @ 40a he can only utilize 480w of panel which gimps him right out the gate with those 320w panels. At least doing 24v will let him get 960w potentially.

 

[12VoltInstalls]

with a 12v @ 40a he can only utilize 480w of panel which gimps him right out the gate with those 320w panels. At least doing 24v will let him get 960w potentially.

Yes, true. In ideal sun and at peak time of production. Angling panels differently and the “partial” production on either side of noon truncates the unharvested portion of the curve.
More volts/watts early and late with over paneling may be a preferable upside.
They’ll have to figure that out.

 

[Rednecktek]

Sadly he's stuck with a North/South roof so if he mounts up there the wide range thing isn't going to help him out.

Now, back to the OP, if you ground mount you'll have more flexibility for angling your panels to pick up power over a longer period of time. Especially if you add panel strings later and really put that MPPT voltage to work.

 

[Bluedog225]

Lots of good advice here. I love this place.

And welcome!

And I think solid wire is def not preferred. May even be a problem. More research needed on this.

 

[Rednecktek]

And I think solid wire is def not preferred. May even be a problem. More research needed on this.

Anyone who tries to tell you "Electrons travel on the surface" or "Stranded wire carries more amps" is full of shite!

 

[12VoltInstalls]

Stranded wire carries more amps

I was told that for years and I believed it ?‍

 

[Bluedog225]

Victron feels strongly about the issue. I wonder why?

 

[12VoltInstalls]

Victron feels strongly about the issue. I wonder why

Because solid wire can break by work hardening from movement and or vibration
Plus certain screw terminal connections and crimping are not secure fastenings on solid wire because it can’t conform and has potentially poor contact area.

 

[Hedges]

Victron feels strongly about the issue. I wonder why?

Maybe for the reason they gave?

"In case of thicker strands the contact area will be too small and the resulting high contact resistance will cause severe overheating, eventually resulting in fire"

Also, stranded cables are limber, won't put as much mechanical stress on terminals, either when installed or when they heat up and try to move.


The thing about surface area, Litz wire, and so on is only for AC. "Skin depth".
At 60 Hz, skin depth is 8.5 mm, meaning about 2/3 of the current flows in the outer 8.5 mm annular ring of the wire. If your wire is no more than 17mm diameter you aren't likely to notice.

If you carefully measured voltage drop vs. current you could detect it. The current distribution vs. depth follows an exponential decay based on 1/e (which is close to 1/3)

Skin effect matters for RF, shape and thickness of conductors, even plating on the surface because sometimes one skin depth is only microns.
But for a PCB "microstrip" (rectangular cross section conductor over a ground plane) plating on the outside doesn't matter much. It is the surface of the copper trace in contact with FR4, facing the ground plane, which carries current.

DC? No effect at all.

 

[Hedges]

shed has north/south facing roof, not ideal for multiple orientation solar.

Sadly he's stuck with a North/South roof so if he mounts up there the wide range thing isn't going to help him out.

Now, back to the OP, if you ground mount you'll have more flexibility for angling your panels to pick up power over a longer period of time.

With only two or four panels on South-facing shed roof, just tilt half of them East at a 45 degree angle, half of them West. Meeting together to form a triangle. If the panels are about 60" long, 40" wide, 40" hypotenuse of an isosceles right triangle, standing 28" above roof.

That reduces area presented to sun to 0.7x as much.
Steeper 60 degree angle, meeting at 60 degrees for equilateral triangle, would present 0.5x as much area, but further reduces total production due to angle of sun that drops below horizon.

 

[vortextangent]

This is my first solar project. It's not a full time living situation, just a day office for remote work. It will be in use mostly mon-fri 9-5 (ish).
I misstated the size of the shed, it's a 12ft x18ft and currently has a 30amp subpanel installed. we had to cut wire to inspect septic tank though so it's not on right now.

EDIT: I'll end up adding the hvac to the 30A service at some point in the near future but until that happens i'd like the option of using it with solar if possible.

The area is a little shady in the morning and evenings which is another reason why I was trying to go with these (or similar) half cut perc panels.

I was thinking to keep panel voltages low-ish for shock safety more than anything; so series 12v panels to 24v or just use 24v panels, not necessarily to match battery voltage. Probably a newbie move but that's why I'm here

I was on the fence trying to do 12v bank so 12v accessories would work easier but in the end figured I could just get a transformer or something since I have no actual plans to use 12v stuff, they are just cheap and easy if I wanted to get, i dunno, a phone charger or something.

The batteries will be "indoors", so I was thinking something sealed would be good. the shed has double swinging 4ft doors that have some gaps around the edges so it's "vented" but ?‍. The office is an insulated room inside the shed with two small wood windows.

This is everything that will be in the shed for the next year during construction.

Device	Watts (Max)
Laptop	85
Phone (3A USB charger; may just plug into laptop all the time)	15
Screwdriver charger (Makita 18V)	54
Window AC	400-600?
LED lights	15
Monitor	30

so max watts if i had everything on at full capacity 600-800 watts (assuming I can trust ratings on power bricks, etc). I should probably account for inefficiencies too but, meh.

After renovation on main house is done I'll know if I want to put in a larger DIY system (probably ground mounted in front yard as a pergola or something) or maybe a Tesla system since they price match local installers.

With only 2 panels you don't need the combiner box. Those only start being a thing when you've got 3 or more strings of panels.

I will be skipping the combiner for now. I was thinking it would make it super easy to add panels later but i'll just buy it later with new panels if that happens.

Get the Pure Sine version. Your electronics, compressors, and fridge will thank you. It's cheaper than buying new appliances.

This says it's pure sine. I think I'll size it up to 2000W though just in case I need to power a fridge for a few hours or something?

Having gone the Renogy route myself, I would dissuade you from buying either Renogy panels, or Renogy controllers. Shop on Craigslist and buy those high voltage panels. I wouldn't pay more than 33cents/watt. Get a high voltage Epever controller like the Tracer 5415AN or 5420AN. Look at Costco's 210Ah golf cart batteries for 99$ each. Four hundred dollars would get you twice as many amphours as the AGMs you are looking at.

All the money you save could be applied to a higher quality inverter then the Giandel.

I liked the Renogy controller for the solar system monitoring but am open to other systems. I almost went with PowMr 60 amp but was unsure about monitoring production, etc with it. I'm willing to pay a little more now for packages and features that are a bit harder to DIY for this smaller system because I am also doing a complete gut renovation on my house at the same time.

Stranded wire is just more durable/flexible AFAIK? But I have a ton of armored cable wires left over from my old house renovation so was thinking to just use what I have until I do a larger system (probably gridtie) on the house.