Design check

[Sparc343]

So I had developed a much smaller system before realizing there's NO way I could make it work for my electrical "needs"... I am not new to electronics and electricity as a whole, but I am new to "solar"... So, my design drawing does lack things that (at least to me) are obvious. IE: it is NOT a very detailed drawing because it leaves out MANY system design factors such as (but not limited to) wire gauge (AWG), fuses/breakers/etc, junction and combination boxes etc etc etc...

Basically, I just want to confirm that these components, in these quantities, will work together - producing a useful solar system for my other half and I..!

This whole thing feels a lot like when I learned about towing. There's a bunch of numbers that need to line up, but a lot tend not to... So I came up with the following design as pictured (again, sans certain obvious to me aspects). Unless I am doing something wrong, I do believe all the numbers for this design actually "add up"... IE: all of the ratings of the charge controller (PV amps in, PV volts in, charging amps out, etc) I even attempted to assure the various calculations for temperature variations were considered too (IE "VOC @ 30 F° = 241.2" for my setup/design [if my math is correct])..!

I've included two copies, one without any actual "wiring lines" at all, and one WITH "wiring lines" to show/define the series-parallel connections:




Now, I am NOT "set" on those batteries as pictured, they just happen to be the best for my current budget at the moment. Ultimately the only important aspect of the battery/bank is that it's 48v and 600ah... Depending on "how things go", I would not be opposed to starting with 48v 200ah, and building up to 48v 600ah (or beyond)... I am not entirely "set" on the LV6548 either, but it appears to be a unit that would facilitate this design... I AM "set" on the panels because of how cheap they are, and how Mr. Prowse has said they are good panels, so I have actually already picked up 16x of them (would be obviously adding 8x more by this design plan)...

So, in the end, TWO (2) questions:

1) Will this design work, do all the numbers "add up" (have I done all my math correct)?
2) Does anyone have Any input on alternative components (besides these panels) - before I start purchasing the rest of this system?

Thank you in advance to anyone and everyone who is able to chip in their $0.02..!

 

[Don B. Cilly]

The obvious question is, will it work... for what?
What do you plan to power with those batteries?

Alternative components, a good one would be a gasoline/propane generator for rainy days and such.
Assuming this is off-grid, obviously.
-

 

[12VoltInstalls]

just want to confirm that these components, in these quantities, will work together - producing a useful solar system

Are you only looking for backup power in an outage? If for daily use I’d use different batteries- either cheaper marine batts from walmartha or more expensive but lower-priced LiFePo batteries. AGMs don’t last well for constant use imho which makes them expensive over time.

attempted to assure the various calculations for temperature variations were considered too (IE "VOC @ 30 F° = 241.2" for my setup/design [if my math is correct]).

Is 30* the record low for your locale?
You need at least 15% headroom between max solar input voltage and VOC calculated from panel labels at the record low temperature

48v and 600ah

you take AGM battery Ah and divide by two for usable Amp hours from lead acid batteries. You can only discharge the top half of the Ah rating with lead.

do all the numbers "add up"

The battery bank is probably too small comparing to how many panels you have. But you didn’t state what KWh goal you need to achieve or for how long so there’s no way to even wildhat guess

 

[MisterSandals]

Not sure it’s a secret but if your string Voc is 222, panel Voc is 37.0V

30F is -1.1C, a delta of 26.1 dec C.

37V x .0035 x 26.1 = 3.38V x 6 = 20.23, 242Voc array.

 

[Sparc343]

The obvious question is, will it work... for what?
What do you plan to power with those batteries?

Alternative components, a good one would be a gasoline/propane generator for rainy days and such.
Assuming this is off-grid, obviously.
-

Well currently my life is very dynamic... You're definitely correct about 100% off grid - I am living in an RV in AZ on a vacant parcel that I will be building a house on... Although I will eventually likely get a real generator as a "back up", I have been using a 2kw DC-AC inverter on my Prius (work car), turning my prius into a generator. Up until the recent spike in gasoline prices I figured using my prius as a generator with a 2kw inverter would be more fuel economic than a generator that's just always on (regardless of load), since the prius will turn it's internal combustion engine only "as needed"... So far that's been working more than sufficient enough for our "needs" alone. So I figured I'd design a system that COULD accommodate 8x hours per day on our laptops (my other half and myself), up to 8x hours "monitor" (we don't watch TV, just use a TV as a monitor and or for movies)... and 2x hours per day of a coffee maker. I think this system/design would facilitate that no problem...

Even though purely off grid (and always will be from this point forward), I am NOT looking to design a system that would literally facilitate "everything". I see being off-grid and using solar as a "give take" system anyway. I figure if I want to use something I didn't calculate for, then it will cost X minutes/hours of Y use. Example, "ok hun, you want to 'nuke' something for 3 minutes, that is going to 'cost' you/us X minutes/hours of laptop use"... We are completely fine with this because we are NOT dumping $100,000 into a solar system..! Because if we were to use electricity like we did when we were city dwellers, it probably would easily be a 100k system! We have had NO problem being SUPER conservative these last 6 or so months that we've essentially been boondocking on our land while we await the structural engineering for our house that we're going to build..! We are also actually already planning on integrating as much 12v into the house when we build it, just like the RV - we strongly feel there's NO reason to be running 120vac lighting. So even our house will likely have a completely separate 12v system for things such as lighting.

 

[Sparc343]

Are you only looking for backup power in an outage? If for daily use I’d use different batteries- either cheaper marine batts from walmartha or more expensive but lower-priced LiFePo batteries. AGMs don’t last well for constant use imho which makes them expensive over time.

Daily usage... 100% off grid...

Is 30* the record low for your locale?
You need at least 15% headroom between max solar input voltage and VOC calculated from panel labels at the record low temperature

Yes, the avg low is something around 55°. Not 100% sure on the record low but I do believe it's going to be something in the 20° - 30° range. And thinking of it, I should certainly ask ya': Wouldn't this actually be most pertinent for "record low - while the sun is up"? If that's the case, being in AZ, I doubt it will EVER be that low of a temp while the sun is up...! Nonetheless I 'calculated' for 30° - which gave me 241.2 (which is still under the 250v limit of the LV6548.

you take AGM battery Ah and divide by two for usable Amp hours from lead acid batteries. You can only discharge the top half of the Ah rating with lead.

that's why this design is ~600ah bank, if I were going with LiFePO my calculations indicate I'd only need ~400ah - according to the daily watt hour usage we've planned for...

The battery bank is probably too small comparing to how many panels you have. But you didn’t state what KWh goal you need to achieve or for how long so there’s no way to even wildhat guess

Well, I attended the event that San Tan Solar had in Gilbert, AZ this last Saturday and I had a nice long conversation with a tech. there. My original plan was actually only 8x panels but we were talking about how I would (now) seek a "live load" capable device (like the LV6548), so then I would actually need 16x, hence how and why I already own 16x panels. Basically, the way he put it was, 8x of them would be charging the bank during sun hours, and the other 8x would be providing power for "live load"..! So, crunching the numbers though I wanted to know the MAX number of these panels I could use on this LV6548. If everything I've calculated is correct, this number would be 24x. 4x parallel strings of 6x in series... Which means I can buy 8x more panels to "max out"... Which I also figure will not be a bad idea, if and when we decide to expand the battery bank if and when our usage goes up...

Basically, I just really want to know/verify if this setup will work without knowing my daily kwh/usage. Because, I was looking at the LV6548's older sibling (cousin?) the LV6048 - and I see missing specs, or at least it looks this way. I just want to make sure I haven't overlooked anything in terms of, should I be wiring the array this way, will that work with this model?

But I am pretty sure the product sheet and even the manual for the LV6048 are *lacking* the spec for the PV input amperage..! As where I know the LV6548 says, 18A max PV input (each input [2x])... http://www.mppsolar.com/v3/catalogs/LV6548.pdf - http://www.mppsolar.com/v3/catalogs/split phase LV6048.pdf

So my primary concern is making sure there's nothing being missed here - especially since even a products manufacturer isn't always "good" with making sure "everything" is known...! I ran into this problem when learning about towing! You could weigh in at a CAT scale and find out you're actually NOT safe to be towing because ONE of your numbers is "out of line"... In order to be SAFELY towing you NEED to have the correct payload, tongue weight, trailer weight, gross combination weight, etc etc etc... You could very well find yourself weighing in only to find out ALL BUT ONE number is within "spec", and this would technically mean you're NOT safe to continue to tow, until that ONE number is *corrected*... To be specific, my first time towing an RV, ALL my numbers were spot on EXCEPT the tongue weight. Easy solution of course, move more weight to the rear of the trailer... With solar, I need to know if ALL numbers are going to add up or not, BEFORE I start buying (expensive) equipment and batteries etc.., since it will not be something as simple as redistributing (or adding or removing) weight, like it is with towing...! It will be a DO or DO NOT buy this that and the other..!

 

[Sparc343]

Not sure it’s a secret but if your string Voc is 222, panel Voc is 37.0V

30F is -1.1C, a delta of 26.1 dec C.

37V x .0035 x 26.1 = 3.38V x 6 = 20.23, 242Voc array.

I came up with 241.2v (so, pretty darn close) - which either one of these two numbers is below the 250v spec of the LV6548... Right?

 

[Sparc343]

Yes, I am 100% ignorant on (solar) batteries, admitted..! I am 100% open to any (specific) battery recommendations

 

[rmaddy]

Wouldn't this actually be most pertinent for "record low - while the sun is up"?

Plenty of record low temperatures happen in the middle of the day due to a cold front passage, for example.

Most days are coldest just before sunrise. The Voc of a panel can be reached at very first light of the day before anything warms up.

 

[Don B. Cilly]

Well, so you already have a generator - of sorts, for "emergencies".
So yes, I'd say they'll work just fine.
Especially since,

We have had NO problem being SUPER conservative these last 6 or so months

you have what I consider the right attitude to off-grid living. With that mindset, and having learned how to do it, you won't even have to be super careful anymore, but you just won't be drawing power unnecessarily either, will you :·)

One thing... considering you're planning to use the solar in the house, if you can minimally afford it, go Lithium (LFP).
The longevity factor alone would make enough of a case for it, but the "peace of mind" one is... priceless, IMO.
This is what I just did, actually. Lived some six months in an old bus, then bought two 24V LFP batteries, then moved everything to the house.
Best money I ever spent, those batteries.

About the panels, I don't know how you plan to mount them, but I found this idea absolutely brilliant. I wish I'd seen it before.
And about the Voc... if it's minimally dodgy, it's simple and cheap enough to use an additional MPPT controller for some of them.
-

 

[Sparc343]

Well, so you already have a generator - of sorts, for "emergencies".
So yes, I'd say they'll work just fine.
Especially since,

you have what I consider the right attitude to off-grid living. With that mindset, and having learned how to do it, you won't even have to be super careful anymore, but you just won't be drawing power unnecessarily either, will you :·)

One thing... considering you're planning to use the solar in the house, if you can minimally afford it, go Lithium (LFP).
The longevity factor alone would make enough of a case for it, but the "peace of mind" one is... priceless, IMO.
This is what I just did, actually. Lived some six months in an old bus, then bought two 24V LFP batteries, then moved everything to the house.
Best money I ever spent, those batteries.

About the panels, I don't know how you plan to mount them, but I found this idea absolutely brilliant. I wish I'd seen it before.
And about the Voc... if it's minimally dodgy, it's simple and cheap enough to use an additional MPPT controller for some of them.
-

I do think we have the right mindset and even last 6 months of "practice" as well. I am getting "tired" of using my Prius as a generator though, between high gasoline prices and the added wear and tear from the unnecessary and excessive idling (although it does only kick the Internal Combustion Engine (ICE) on about once every half hour for only a few minutes)... There has been nights where we "hook up" the car as a gen. the whole night, "playing away" on the laptops working on "plans" whether it be solar, house and property plans, or even my new-found hobby (drones) and working toward my part 107... And the Prius has an 11 or 12 gallon tank, using it as a generator every night with it's 2kw inverter, that whole tank would last as a generator (only) for 1-2 weeks (of course dependent on usage)...

I have been told a few times now to go LiFePO, I guess they are hugely superior to AGM... I did almost forget that the calculations I performed for AGM, and the 600ah my daily KWh usage would require, a LiFePO bank would/should only really "require" a 400ah bank. But I almost had a heart attack seeing the EG4 being $1500/ea and my heart fell when I thought about the price of buying SIX (6) of them! Though, after I came to a clearer state of mind I did realize I'd have to "redo" the math due to the difference in DoD / allowable SoT... So I guess the price really isn't "that" different between whether I buy 12x AGM or 4x LiFePO... Pretty nominal from what I recall.

Although we have been really good about things, I also envision a time where we are going to need a MASSIVE system. I say that because due to the impending summer (massive) heat, we have one of those "portable" hot tubs. We figure in the winter we'll actually use it as a hot tub (hey, the desert can get cold at night), and in the summer we'll actually use it without the heat as a cooling down tub..!! Well, albeit a "luxury", we will likely one day want to even accommodate powering a hot tub, ALL winter..! We have even been discussing just giving it it's own complete/separate system so that it doesn't "rob" from our house use/needs..! Bearing in mind, even though I'm sure a "real" hot tub draws MUCH more power, even these little portable ones are 120v 1300w..! From what I hear though the problem with them is the initial heating of them, to 104°. Once heated, and especially with the insulated cover(s), they maintain their heat rather well... But I couldn't imagine calculating a bank/array/CC for a 120v 1300w (or was it 1500w) tub heater! My wallet is already cringing at the mere thought of it. But it would be REALLY nice to have a hot tub that is *always* hot (in "winter"), all, off-grid..! I think that would be amazing... Maybe it would be cheaper and more practical to look into actual solar heating (the water directly), IDK...

My only other "unreasonable" use (in the future) would be running a server 24/7... But even that is a MUCH lower consumption than say something like a hot tub..!

As far as panel mounting, I am an anti-establishment kind of person (which I'm thinking goes hand in hand with the whole off grid thing commonly too)... So, I plan on doing anything and everything I possibly can to "skirt" "the man"... So I am figuring, in order to "bypass" things like building permits, inspections, (government bureaucracy) etc - I'd make it a "mobile" system. (I assume) there's no way they can "force" me to get a permit, and inspections, and consider it a property improvement (and maybe even tax it as such) should I make it a "mobile" system. So even though we haven't planned exactly how they'll be mounted. We can pretty safely say it will not be on the roof, and it will not be any sort of "permanent" mount(s)... If I have to - to avoid the bureaucracy - I'll just literally plop em onto the ground! Either way, we didn't want them on the roof to begin with because we'll be using our roof for rain water collecting (when I say off grid, we mean, fully, off grid)! So ultimately, the "mounting" will be whatever we can figure out, that can help us avoid the government overreach

I was even thinking the rest of the system (everything except PV array) we would build into some type of "wagon" or "trailer", as to stick with and really drive home the "it's mobile" aspect, so "the man" can't try to say I need to get permits and inspections and possibly even tax it..! AFAIK they can only force that kind of crap when it's something permanent. The same way, if you put in/install a "real" pool, that's a land improvement that requires permits and inspections and raises your property tax. Yet if you run to China Mart (walmart) and grab one of those chincy above ground/inflatables, well, that's not a land improvement so they cannot force you to get permits, inspections, and raise your taxes because of it..!

 

[Sparc343]

So, if AGM are really that inferior to LiFePO, I'd probably go with this (presuming the rest still "adds up"):

 

[Don B. Cilly]

I wouldn't say they're "really that inferior", no. But LFP... it's got this "no-worries" factor... not easy to explain, but coming from lead-acid...

Still, let's leave the hot tub for a moment... those are a lot of batteries you're planning.
Having learned "off grid mode" ;·) - I've been "off-grid" (mostly on small boats) for half my life - I run a house on 5kWh of batteries and <1kW of panels. I have a fridge, washing machine (I run "cold" cycles - which are not really cold because I preheat the water with black pipe), computers, stereo, the lot. Obviously I don't use electricity for cooking (bleagh ;·) or heating, but my batteries never discharge.

Now, the hot tub. Of course you should use a solar collector for that. You could help it out with a small (preferably propane) heater, but you can really pretty much forget about electricity for that if you want. Simple coiled black pipe is quite surprising actually, even in very little sun.
-

 

[12VoltInstalls]

So you have a two-step plan to some extent.

If it were me I’d start with 6 walmartha batteries NOT agm, and roughly 1200-1500W of your panels. A decent lower-priced inverter like wzrelb or giandel, and an Epever 50A SCC. That gives you the 12V needs, plenty of daytime power, and the 12V lighting etc source.

Then build your ’main’ MPP system as either 24- or 48V. Then you have a bit of redundancy for the unlikely component failure AND have the benefit of time to minimize expenses and scale into the ‘main’ system over time.

That’s what I’d do. And sorta exactly what I did. Buy in to sustain the basics for needs, and then scale into the system to fit your logical/calculated needs. Living in an RV on remote property saves $1000-$2000/month at a minimum- so there’s “free” money every month to do what you need.