Noobie looking for advice

[myusername134]

Looking at having roughly a 5 KWh battery bank (lithium) using roughly 70-80% (~3.3 KWh) of this per day. Main usage would be: laptop, chest freezer + fridge. Id like to be able to replenish this usage every day (location Tennessee), so to charge roughly ~3.3 KWh assuming ~4 hours of direct sunlight and ~70% efficiency of the panels im looking at atleast 1200 watt array, or 12 100w panels ( https://www.amazon.com/dp/B09V4ZDJTJ ).

1. I could have a series/parallel setup with two rows of 6 panels (12 panels total). So one row of 6 panels would generate 600w, then both rows connected in parallel would make 1200w. Heres where I get confused, im learning the rated "12v" on the panels is not correct, and its actually generating 24.3v called the "Open-Circuit Voltage", during colder temperate this increases (IDK by how much), im going to assume as much as 30v. So 6 panels would generate 145.8v up to 180v during cold weather at 4.91a. This already exceeds the max voltage for many of the solar charge controllers. With the two rows in series/parallel it would be ~145.8v at 9.82 amps. I couldnt do anymore rows in parallel because the panels fuse rating is "15a" ( is this correct?), however it is in 12AWG wire which is 25a max. Can someone shed some light on how this works?

2. What sort of lithium battery setup should I have and in what voltage? I could get something like this ( www.amazon.com/dp/B0B96WR27C/ ) which is 48v at 100AH. Or should I get smaller batteries to scale more easily? I'll likley desire more then 5 KWh to have battery reserve during bad weather and increase the amount of panels.

Any other advice / suggested products I should get would be apprecaited.

 

[yodamota]

personally I would skip the 100 watt panels. I would look for something like 60 cell panels. I just bought 360w panels.

Here is a handy tool for sizing your system https://www.midnitesolar.com/sizingTool/

There are many charge controllers to look at.

Personally I like the victron for its user friendlyness. The outback power I have is great. the morningstar tristar is clunky to work/program it, however it works flawlessly. I haven't worked with the other charge controllers out there

 

[Rednecktek]

Blurb time!

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the PVwatts.com or JCR Solar Uber-Sun-Hours calculator sites to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that. If you're looking at the All-In-Ones check for correct voltage outputs (120v or 240v Split Phase for North America, 220v Single Phase for European type areas) and make sure it has enough capacity for a little bit of growth and fudge factor.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

Well that's the thing about solar systems, there is no 1-Size-Fits-All answer. Your system will need to be designed to fit YOUR needs. When you design and built the system, it's not going to be the perfect system for me, or Will or 12vInstall or anyone else, but it Will be the right system for You and that's the goal.

As for where to get started, let me throw my standard blurb in here to help point you in the right direction. There's going to be a lot of math and research involved, but that's going to be a LOT cheaper than just buying parts off of someone's list and finding out that it doesn't do what you need.

Don't panic on the Power Audit, you'll actually be doing that a few times. When you do the first pass put in ALL the Things that you might want. AirCon? Sure. Jacuzzi? Why not. MargaritaMaster-9000? Go for it.

The second pass will be the "I Absolutely Need This To Survive" list that isn't going to have much on there.

The third pass will be the "This is what is realistic" audit that you'll use to design the rest of the system.

The Power Audit is going to tell you 3 primary things: 1: How big does your inverter need to be to power your loads? 2: How much battery bank do you need to last $N number of days with krappy weather? and 3: How much solar panel will I need to install to refill those batteries in a 4 hour day (the average usable sun hours rule-of-thumb).

Once you know what you Want and what you Need and what your budget can Afford there will be somewhere in that Venn diagram where those three things meet.

After that, THEN you can start looking at parts.

Yes, it's a long drawn out process, but it's worth it in the end. Not every house has the exact same floorplan, not every vehicle is the same make & model, and not every solar system is designed the same.

 

[Rednecktek]

With an array this large definitely start by looking at Craigslist and FacePage and see if you can find local panels for sale. The most common thing I'm seeing in my area at least are in the 250-275w range for about $100 which beats the pants off of 100w panels for $90 each.

Heres where I get confused, im learning the rated "12v" on the panels is not correct, and its actually generating 24.3v called the "Open-Circuit Voltage", during colder temperate this increases

Yes, that's Marketing Speak for "I create enough voltage to charge a 12v nominal system, but not a 24v or 48v" and likewise the used panels you'll find are often listed as "24v Panels" which again is Marketing-ese for "I generate enough voltage to charge a 12v OR 24v nominal battery, but not 48v." Once you get your MPPT controller involved that means less and less and the numbers you're looking at are the VoC, Vmp and Isc which (as you saw) means:

VoC: The amount of voltage the panel can produce with no load. This is the number used to calculate your controller's input voltage or PVMax rating. If you don't want to do the cold weather calculations you can just go with 80% and be perfectly safe outside of places like Antarctica and Maine and our wives' feet where it just gets too cold. If your SCC says 100v PVMax then try to keep you series string around 80v.

Vmp: This is what the voltage will dip to once the panels are under load. Much like how your room lights dim when you turn on the vacuum cleaner, the voltage from the panels drops once you start pulling amps under load. Useful number for troubleshooting later but not needed so much for initial design.

Isc: The amps the panel can produce under test conditions. The biggest place this comes into play is when figuring out wire and fuse sizes. The more panels in PARALLEL you have, the more amps, in SERIES the amps stay the same but the VOLTS add up. If you have a set of 10 panels each producing 20v and 5a, then in SERIES you'd have 20v * 10 panels = 200VoC @ 5a, but in PARALLEL you'd have 5a * 10 panels = 50a @ 20v which is Honkin Huge Gauge wire.

Overpaneling: This is a term for intentionally installing more panels than a charge controller can use to compensate for krappy weather. If you have a 10a SCC charging 15v to your battery (for nice napkin numbers) then it can use 150w (10a * 15v) but if you throw 200w on there, it'll still only put 150w into the battery, but with the extra overpaneling it will get those 10a in when it's less than perfect sun on a cloudless day in Hawaii. General rule of thumb is 25-50% overpaneling depending on where you live is fine. If you're in Arizona then anything over 20% will probably never get used even when covered in dust and cactus needles, but in Seattle a 100% overpaneling may still not produce enough to charge a battery at all. Location matters.

I couldnt do anymore rows in parallel because the panels fuse rating is "15a" ( is this correct?), however it is in 12AWG wire which is 25a max. Can someone shed some light on how this works?

That's 15a Per String in parallel. When you have 1 or 2 strings usually fuses aren't needed, but over that and you'll need to have a fuse on each string of panels.

The fuse rating is there to protect the wire from damage. Once you start getting into large arrays over 3 strings you start looking at combiner boxes where you can bring multiple strings into a common point using thinner PV wire and then parallel them all together out of one honkin huge wire to the SCC. Each string will be protected by its own fuse so that if something shorts out or a wire gets chewed through or the like the other strings don't go up in smoke. Once everything is together there is a breaker protecting the SCC from over amperage from there. It's all about protecting THE WIRE from things going horribly wrong.

I'll likley desire more then 5 KWh to have battery reserve during bad weather and increase the amount of panels.

Go grab that Power Audit form and start playing with it. That's going to tell you what you're after for panels and battery and the like.