Solar for off grid cabin - how to size properly?

[Forester]

Hey guys!

My head is about to blow up from all the math, amps, watts, volts... Please help me to understand how to size a system which would be used in an off grid cabin, living there full time. I'm still in the phase where I'm trying to figure out the costs of moving into the sticks and going off grid full time so I just need to do a rough estimation of costs. Obviously, I need to get the numbers right in order to have that estimate and I hope someone can help me out.There's a ton of explanations and videos online and it's often somewhat contradictory and confusing. So far I think I have been able to get a few things correctly, so let's start with that.

Every of those "how to" articles and videos agree on one thing and that's you need to know your daily consumption. So in my case, a rough estimate would be:

1.Fridge 640w/day (A++ rating, almost the best there is. Might be different than in the States but that's how energy efficiency is marked in Europe)
2.Freezer 575w/day, also A++
3.Water pump 370w/day
4.Mini washing machine 210W/cycle ( this is a bit confusing as it wouldn't be used on daily basis, more like once or twice a week. As it's just 210W I thought I could just cout it as it would be used every day and have those 210w extra for some odd, short usage of stuff like blender or something similar)
5.Laptop 280w/day
6. LED light bulbs 240w/day

Water heater and oven would be running on LPG. So this comes to 2315w, guess it can be rounded up to 2.4Kw

Now the rest is unclear. Some move on by calculating what battery size is needed for that much of Kw, which makes sense to me. They say discharge shouldn't be more than 50% for flooded batteries(can't afford Li) and few days of autonomy should be accounted for. As I'm on a budget, I added 1.5 days for that.

Hence it's 2400w x 1.5(to account for that 50%) x 1.5(days of autonomy) = 5400w
Then what comes next is, according to those instructions, to get total amps of the batteries needed, so 5400w/12v=450A
And then to figure out how many panels you need, 5400w/5 hours on average of peek sunlight = 1080w, guess we can round that up to 1.2Kw
Logically, this seems to be correct so far.
But is it??

It gets confusing when it comes to the controller. I read that MPPT are better so I'd go with that one but I'm not sure how to calculate it. One article said you just need to divide wattage of panels with volts(battery volts??) So it would be 1200/12= 100A, but that seems too much. If 1200/24= 50A, it sound like it could be correct as I've seen those controllers in 50&60A size, but not in 100A.
But this is confusing, are volts here those coming of the panels or it's related to the batteries?

The last one, inverter, seems to be quite straightforward if I got it right. They say just take your total consumption(2.4Kw) and, kind of , assume everything will be on at the same time. So with 2.4Kw the inverter would be about 3Kw?? And it should have charging capability, to hook it up with a generator.

Please guys, correct what's wrong and if someone has nothing better to do I'd really appreciate if you could do the whole calculation and wright it down so that I can learn how it's done correctly.

 

[DThames]

You need to convert your watts per day to watt hours per day. This to get watt hours per day. That will allow you to know your demand per day. If you had nothing charging your batteries, how long do you need your batteries to run with that demand/load? One day, three days? Solar charging is next to zero for heavy overcast. So if you think you might not get good sun for a few days, you need a much larger battery bank or you need a gas generator. Once you determine your battery size, you can then look at your charging options, how much solar, what type charger, how a generator might be part of your plan, etc.

 

[Forester]

You need to convert your watts per day to watt hours per day.

Maybe it's not clear but I did that. For example, my laptop uses about 70w/hour and I'd be charging it for about 4 hours so it's 280Wh/day, isn't it?

This to get watt hours per day. That will allow you to know your demand per day. If you had nothing charging your batteries, how long do you need your batteries to run with that demand/load? One day, three days? Solar charging is next to zero for heavy overcast. So if you think you might not get good sun for a few days, you need a much larger battery bank or you need a gas generator. Once you determine your battery size, you can then look at your charging options, how much solar, what type charger, how a generator might be part of your plan, etc.

Apparently, you didn't read my post carefully enough as I've addressed most of the things you've mentioned...

 

[DThames]

Maybe it's not clear but I did that. For example, my laptop uses about 70w/hour and I'd be charging it for about 4 hours so it's 280Wh/day, isn't it?



Apparently, you didn't read my post carefully enough as I've addressed most of the things you've mentioned...

Sorry, I was going really fast before having to start my workday. Yes, I missed some things. Your original text says, " Laptop 280w/day " not 280wh/day, so I locked on that.

MPPT charging, to reduce your wire size, it is common to connect panels in series. Say you have four 300w (24v type)panels. If you connect two in series, and two series strings in parallel, you might have 80volts open circuit and 10 amps x 2...20 amps going into your MPPT charger. But charging a 24v battery with something less than 30v, the charger might be sending 30+ amps to the batteries. MPPT amp rating is on the battery side.

 

[toms]

Use LiFePO4 cells
Work out your maximum overnight useage.
Make your battery bank useable storage 125% of this value
Find out a PV profile for your area (to work out how much power will be available from PV)
Size your PV to fully charge batteries around 75% of the year.
Run a generator when required to top up batteries after sundown.

Yes you can oversize your batteries or PV to get some extra time without generator running - but i’ve setup dozens of systems, and have never seen one that uses over 10kwh/day that has not needed a generator - so if you have a generator your system will be way more efficient (cost effective) if you use it.

 

[efficientPV]

Big batteries can make up for a lot of bad decisions, but it is costly. Besides running for a couple days without much sun, you will need to recharge that battery. Invariably everyone goes cheap on solar panels and they are probably the cheapest part of the system. Use power when it is available and not from the battery. My array will support primary functions even in the rain. Buying more panels is money much better spent than on batteries. The camp systems I see here are just horrendous, but that is all most are capable of doing. Guaranteed you will kill your first set of batteries because you underpaneled.

 

[DThames]

Here is a more specific example. I have some old 295w panels. Call them 300w. Here are the specs.
Open circuit volts, 45v
Max power voltage 36v
Max power amps, 8a

Suppose you have six of these panels. Max watts would be about 1800w. You get a 80amp MPPT controller that will charge a 24v battery. 80amps x 25v is about 2000 max watts output from the charger. Say this MPPT controller can handle up to 150volts open circuit input. So if you series three panels, times two, and connect the two series strings parallel on the charger input, you will see about 135 open circuit volts and up to about 8x2 amps (16a) max on your wires going into the charger. But if your battery is low and the sun is bright on the panels, you will see about 70amps going to the battery.

So 1800 watts times the number of hours per day in perfect sun will give you a watt hour per day guess, not considering any loses.

 

[Forester]

Thanks everyone for chipping in!

MPPT amp rating is on the battery side.

So ho do you size MPPT correctly?

Max watts would be about 1800w. You get a 80amp MPPT controller that will charge a 24v battery.

Judging by the above quote, it seems like you added up your panel power and then divided it by battery volts?? 1800/24=75V, rounded up to 80v.

Say this MPPT controller can handle up to 150volts open circuit input.... you will see about 135 open circuit volts

135v is what would be coming from the panels, right? So that means you need to calculate both incoming voltage and that of your batteries, the amount they can safely handle? And then you have the numbers needed to know which MPPT you need?

Use LiFePO4 cells

That's out of my(financial)league. I know that, in the long run, it is actually cheaper to run on Li but here in Europe you can get a whole PV off grid system for the total price of Li batteries such system would need. Maybe the price will drop down in one life cycle of flooded batteries. Then I'd consider if money would allow.

..uses over 10kwh/day..

Nah, for me it would be around 2,4Kwh/day , rounded up to 3Kwh/day it's still waaay less than 10. But it makes sense to have a generator, just in case. I'm in south-eastern Europe and usually there's plenty of Sun. But December and January might be a bit critical and you never know when PV might break down. I'd definitely get a generator.

Buying more panels is money much better spent than on batteries.

Meaning you can charge your batteries faster which would be helpful on rainy, cloudy and winter days? Is that the idea?

 

[Steve_S]

I live Offgrid, am remote & rural in North Eastern Ontario Canada near Algonquin Park.

My solar panels are Fixed Ground Mounted @ 45 degrees which for my locale is the median average for the 4 seasons.
8 Canadian Solar CS-260P panels are configured in, 4 Series - 2 Parallel. On peak days I see 2000W and close to 200V DC.
Currently, my panels produce around 5.5kWh per day on a nice day.
Solar Controller is a Midnite Classic 200 MPPT which is capable of 78A charging CLASSIC-200 LINK
Inverter is a Samlex EVO-4024 (4000W from 24VDC) capable of delivering up to 12,000W surge. SAMLEX 4024 LINK

When I designed my system, I built it based on a Minimum of 3.5kWh per day x 3 days autonomy or 10.5kwh minimum storage. With my new LFP System with 728AH useable (using 80% of 910AH) gives me 17.4kWh. Because I am "Power Frugal" this leaves me lots of room to play with for if/when I need to.

Batteries:
I started with Lead Acid using serious "Heavy Lead" from Rolls Surette. 8x Rolls S-550 batteries for 856Ahr @ 20hr. Cost was $3500.00 CAD when I bought them, cost currently is similar. OF that 856AH, only 428AH was useable because you cannot discharge FLA past 50%, otherwise batteries are being damaged. I am now completing my transition to LFP (LiFePo4) which will provide me with 910AH "gross" meaning 100% or 728AH @ 80% DOD.
I am using 2X 24V/280AH packs providing 560AH: LINK XUBA's 280AH CELLS
my cost was $ 2,433.32 USD DPP shipping & duties paid to my door. (S&H was 1,100.00 of that cost)
I have 2X 24/175AH packs providing 350AH:
These came from the ShunBin disaster (link in my signature). A BAD Prebuilt pack bought from Amazon - $3,000 USD and expensive lesson learned.

When Comparing the cost of FLA, 428AH useable for $3500 CAD versus 560AH LFP @ $ 2,433.32 USD (3,228.04 CAD) the dollars & cents make the difference, even with having to buy a BMS for each pack @ $200 (my choice there are cheaper & more expensive too). LFP is maintenance-free, will last 10+ years if not abused and a LOT smaller than lead too.

And one may wonder what I can run... quick run down.
120V SoftStart GrundFos SQ5 Deep well pump (260 feet deep)
1200W Inverter Microwave, Oster Coffee maker with thermal carafe (1000W), Danby EnergyStar rated fridge (240kWh per yr), several LED Lights between 4-11W ea, as needed, Computer, 47"LED Screen, Satelite Modem-Router-Etherswitch.
* Heating is Radiant Heat using an LPG (Propane) On-Demand heater. (dedicated system with glycol)
* Hot Water from another LPG On-Demand water heater.
* "Unique " brand Offgrid LPG cookstove
-- Can run my 3HP Compressor, 120V MIG Welder (I can BUT use them with Genny Power, I prefer to be polite to my power system)

To properly assess your power use, you should invest into a "Kill-A'Watt" type meter and see what the actual appliance / device uses in the real world (stickers are often not that accurate).

 

[ianganderton]

And then to figure out how many panels you need, 5400w/5 hours on average of peek sunlight = 1080w, guess we can round that up to 1.2Kw
Logically, this seems to be correct so far.
But is it??

You seem to be getting pointeres in the right direction. The only problem I can see is your maths based on 5 hours a day. This is fine for grid tied but not off grid. 5 hours is the world wide average, you need to plan for the average of the days you will be using the system when its below average.

Where about are you and what times of the year are you planning to use the system? All Year? 3/4 of the year and mothball it for winter

 

[Forester]

Where about are you and what times of the year are you planning to use the system? All Year? 3/4 of the year and mothball it for winter

I'm in Croatia.
This is the exact location, but I don't know what to make of the data cos there's no mentioning of average peak sunlight per month. Probably it can be calculated based on those charts but I have no idea how.

Global solar atlas-Žumberak,Croatia

I'd be living there throughout the year, topping the batteries up with a generator when necessary.

 

[ianganderton]

So I've found this site to be useful - http://www.solarelectricityhandbook.com/solar-irradiance.html

Here is irradiance data for Zagreb. The problem with this site is it only lists the cities but there oly has to be something close enough.



You can see that using the number 5 just isn't giving you good information on which to base decisions. This data is for flat

For panels optimally tilted for winter (a good starting point for off-grid use) you get this data



So that 3 months of the year where data shows an average closer to 2 solar hours average a day.

Sorry to be a buzz kill but better to have good information to make decisions in my opinion.

Fortunately, solar panels provide the best value components of any system.

When planning on using a generator it's worth planning on using it for the bulk phase of charging (typically in the morning when the batteries are lower from the night) and letting solar top-up through the slow absorption phases.

 

[ianganderton]

Judging by the above quote, it seems like you added up your panel power and then divided it by battery volts?? 1800/24=75V, rounded up to 80v.

1800W divided by 24 Volts = 75 AMPS

so 24 volts at 75amps towards the battery

When sizing the MPPT you need to pay attention to the Volts going in and the Amps coming out.

You can adjust the volts going in by varying the way the array is structured. So if you put all the panels in series all the voltages will add up. This makes for small losses from the wires but may create too high a voltage for the solar charge controller. By splitting the panels into 2 arrays in parallel you will halve the voltage and this might fit better with the controllers you are looking at

Remember while the relationship between volts and amps means they might change Watts are Watts. Any 1800W array should produce 1800W into the SCC and it will be outputting close to 1800W on the other side just at an optimised voltage for charging your battery

Hope this makes sense

 

[DThames]

Some of the things you said/asked from my previous post have been answered by other members. But I will add a bit, hoping it might help. As ianganderton stated, Pay attention to the input and output. This true throughout your system. For example.
1. Understand your inverter output rating compared to your expected load/demand at any one instant in time.
2. Understand the discharge current you will need from your battery when the inverter is at max load. Will your batteries and wires/connections handle this current?
3. What is the max current that the batteries can handle when being charged?
4. What is the current that your charger can output and will that current for the space of time that you have sunshine charge your batteries enough for your overall plan to work.
5. What is the max input voltage of your charger and the max power that it can handle? If more than that power is available on the panels, will this specific charger be able to manage the extra power or is it your job not to over power/panel the charger?
6. Is the panel output voltage in the range of the charger input voltage?
7. Is the total panel output able to meet your expected charging (and daytime load) demand.
8. Is your panel wiring and wiring/connectors to your charger able to handle the circuit voltage and the amps going to the charger?

If you can read and understand the questions above, then you search out how to get answers for each as you move through your design.

Chargers in general (I am trying to make this simple and not technically exact) have the basic job to regulate/control the current (amps) going into the battery under a set of conditions that will result in the goal of putting power into the battery, avoiding damage to the battery. A very simple charger will take 18 volts and control the amp flow to a 12 volt battery until the battery is properly charged. When I say "control" in the previous sentence, I mean like a throttle or a valve, to choke the flow of electric current to be friendly to the battery. A more advanced charger (MPPTs are included as advanced) can create an electrical power source that is exactly what the battery needs for best charging or create a load on the power source (solar panels, etc) that is exactly what the power source needs to create best power output. Some chargers can take AC and charge batteries. Some chargers can take a low DC voltage and charge a battery of higher DC voltage. Some chargers can take a high DC voltage and charge a battery of lower DC voltage.

Because of wiring concerns (higher volts and lower amps for the same power) we tend to think of solar wiring being higher voltage, or much higher voltage and once we get that power delivered to the charger, depend on the charger to down converter to a lower DC voltage and manage the current flowing to the battery. If you look carefully at the MPPT max input voltage you will commonly find some about 100v and some about 150v. These seem to be fairly common steps/levels. As you pick out panels and chargers, think about how many series panels you can connect and stay safely under that max input voltage. The amp output of the charger needs to be in alignment with your charging plan. Someone already said, "less batteries and faster charging" should be considered. So your battery size and how fast you charge them will play directly into the max amps your charger can output. Then your solar input power (regardless of solar volts) needs to be more than your charger output power in order to deliver those amps that you want to put into the battery.

 

[efficientPV]

I'm over paneled and my panels face east and south west. That gives more consistant output throuought the day instead of slamming the batteries at noon. You can get away with a smaller charge controller. East is great for quick recovery in the morning and you should have some panels face that way. I'm for using raw power when you can get it without going thru a charge controller. All my hot water comes from excess PV that others just waste. Got a dishwasher with heated dry and large capacity clothes washer. I just added another 40 gallon hot water tank in the garage where the washer is because ai was still wasting PV power. The solar community is really missing it by not making hot water. I manage to run everything with just a car battery.

 

[Forester]

@efficientPV, @DThames, @ianganderton, thanks guys!
I'm, kind of, getting somewhere with it. This is like day 5 of me trying to figure out how to get the numbers right?

I've found this in some other thread so I got everything right except the size of MPPT charger.

The process is:

1. determine the number of what-hours the equipment consumes in a day (say 800 wh/d).
2. Divide that number by .8 for losses (800 / .8 = 1000 wh/d)
3. Divide that value by .5 to get the base battery size if lead acid or .9 if LiFePO4 batteries (100 / .5 = 2000 wh/d). Divide by system voltage to get battery amp-hours (e.g., a 12V system would be 2000 / 12 = 166 Ah battery).
4. Multiply the watts in step 3 by the number of days of backup (e.g., 3 days is 3x2000=6000 wh, or 500 Ah).
5. Get the value from an insolation map for your location that represents hours-of-sun-at-100%-output (say 4).
6. Divide step 3 by the value from step 5 and again by .8 for losses (2000 / 4 / .8 = 625 watts) to get the minimum number of watts the panels must supply to meet your needs (minimum as clouds/shade will reduce output). If you expect 50% clouds, double the panel wattage. Keep in mind that in winter the cold weather will negatively impact the battery and solar output, see the battery FAQ for more information. If you get a larger inverter than you'll think you need (or use microinverters) you'll be able to add more panels later if needed.

Then I've found Victron's calculator, figured out which panels I could use, found the datasheet and used it to fill in the numbers. But It looks like I'm doing something wrong as I'm getting some quite high numbers.
Could someone please take a look?







I'm not sure about panels being connected in parallel or series(I know it affects amps and volts, depending how it's connected)so I played with different combinations(and with the voltage too) but the calculator always ends up recommending either 250/100 or 150/100, depending on the numbers under "Series" and "Parallel". There are 7 panels, 320w each.
Does the calculation seem correct? Is there any way, like connecting panels in a particular way, to lower amps?

This is how the numbers look like for 250&150/100
141.6V is quite close to 150V so I guess 250V would be better.

Max. input voltage:	150 V
Max. PV voltage @ min. temperature:	141.6 V
Min. input voltage @ MPP:	25 V
Min. PV voltage @ max. temperature:	77.2 V
Max. output current:	100 A
Max. current @ MPP min. temp.:	100 A
* Power limiting @ low temp.
Max. current @ MPP max. temp.:	100 A
** Power limiting @ high temp.

Max. input voltage:	250 V
Max. PV voltage @ min. temperature:	141.6 V
Min. input voltage @ MPP:	25 V
Min. PV voltage @ max. temperature:	77.2 V
Max. output current:	100 A
Max. current @ MPP min. temp.:	100 A
* Power limiting @ low temp.
Max. current @ MPP max. temp.:	100 A
** Power limiting @ high temp.

 

[ianganderton]

I’ve just been messing with this planning a set up

you can juggle input voltage to optimise that by varying the configuration of the array.If you have more than 2 strings you may need to put breakers in there to prevent possible fire if one string failed (not sure on this but remember reading something about it so worth checking)

Generally speaking you want the input voltage to be high enough to give good headroom above the charge voltage, high enough to make wiring work efficiently without thick expensive cable to prevent losses but low enough to have wiggle room at the controller maximum and be safe to handle (not kill you) as a non professional

you can’t vary the output voltage or amps. That’s what the MPPT is doing to optimise the charge to the battery. It’s always going to be your watts divided by the charge voltage. If you have a lot of panels/pv wattage it will be high

 

[svetz]

Hi Forester! Welcome to the forums!

I'm a bit late to the party (as usual ;-) and it looks like you've got stuff pretty much figured out.

...I'm not sure about panels being connected in parallel or series(I know it affects amps and volts, depending how it's connected)...

It sounds like you've got this down, but if you need it the FAQ has: What does it mean to have solar panels in parallel and series?

...I played with different combinations(and with the voltage too) but the calculator always ends up recommending either 250/100 or 150/100, depending on the numbers under "Series" and "Parallel". There are 7 panels, 320w each.
Does the calculation seem correct? Is there any way, like connecting panels in a particular way, to lower amps?

Watts = Volts x Amps, so to reduce amps increase Volts.

I'm never sure what "magic" calculators are doing, but it's easy to work out, here's how from the FAQ: Figuring out how many panels in series and parallel based on your MPPT.

 

[Forester]

you can juggle input voltage to optimise that by varying the configuration of the array.

That's something I need to understand better. I'll have a look into it.

you can’t vary the output voltage or amps. That’s what the MPPT is doing to optimise the charge to the battery. It’s always going to be your watts divided by the charge voltage. If you have a lot of panels/pv wattage it will be high

So does that mean that some people need to have multiple MPPTs? Like if they have large systems?

That's also confusing cos most of the videos I saw show folks having one MPPT but they can run a decent number of things in their off grid home. But my consumption would be, I'd say modest, at 1.5Kw in a day and following @svetz 's instructions from another thread I ended up with about 2.2Kw of panels necessary for that kind of consumption. I'm still thinking I did the calculation wrong. Dunno...

Hi Forester! Welcome to the forums! I'm a bit late to the party (as usual ;-)

Thanks and not really! I used your instructions from another thread to calculate stuff, except MPPT size which wasn't mentioned. So you've already helped.

It sounds like you've got this down

The gist of it, yeah. But series of parallel still sound a bit confusing, especially with all those wires going all over the place?
Anyway, I'll check out that article. Cheers!

 

[ianganderton]

So does that mean that some people need to have multiple MPPTs? Like if they have large systems?

That's also confusing cos most of the videos I saw show folks having one MPPT but they can run a decent number of things in their off grid home. But my consumption would be, I'd say modest, at 1.5Kw in a day and following @svetz 's instructions from another thread I ended up with about 2.2Kw of panels necessary for that kind of consumption. I'm still thinking I did the calculation wrong. Dunno...

Apparently sailing yachts often have multiple solar charge controllers, it helps them deal with the inevitable shade problems they experience unavoidably.

I havent looked at your calculations directly I'm afraid

Ok I have now, so 1200W of solar panels, thats probably going to be 4 x 300W panels. 300W panels are the default residential panel so tend to be very available and therefore probably the most cost effective.

Looks like you are mainly running off an inverter so 24V is probably going to be your best option

I know a lot of people stateside use San Tan Solar for panels so a quick look at their site and the first 300W panel is this one https://store.santansolar.com/product/santan-300w/ - NB I know you are Croatia, I just wanted to grab some specs from somewhere as an example

Its a 60 cell panel, the higher the number of cells the higher the voltage

• Rated Power: 300w
• Open Circuit Voltage (VOC): 39.85V
• Max Power Voltage (VMP): 32.8V
• Short Circuit Current (ISC): 9.71A
• Max Power Current: 9.16A
• Maximum System Voltage: 1000V IEC
• Fuse Rating: 15A
• Weight: 41 lbs
• Dimensions: 65″ x 39″ x 1.5″

In series the max voltage from the panels will be 4 x VOC = 4 x 39.85V = 159.4V. Thats over 120V so quite high, I personally would rather play with less

So we could have 2 strings of 2 panels in parallel. When in parallel you dont add up the Voltage, the amps add up so you end up with 2 x 39.85 = 79.7V, thats a lot nicer and still gives your MPPT heaps of room to downsize to 24V. You dont want to be close to the 24V because in low light conditions the voltage drops and it makes it too hard for the charge controller

This article covers this much better than I am https://www.explorist.life/how-series-vs-parallel-wired-solar-panels-affects-amps-and-volts/

so you've got 1200W (actually potentially a bit more in cold weather) going into your charge controller at about 80V & 15A and coming out you'll have 1200W / 24V = 50A (maybe slightly more if its cold, solar panels are rated at 25deg I think)

so now you've got the pieces to the puzzle. Worth noting that many SSC like being over panelled slightly. Check the manuals for info on that, often its up to 20% so 1400W

Victron SmartSolar MPPT 100/50 - https://www.victronenergy.com/solar-charge-controllers/smartsolar-100-30-100-50
Manual - https://www.victronenergy.com/uploa...r-MPPT-100-30---100-50-EN-NL-FR-DE-ES-SE-.pdf

1.1 PV voltage up to 100V The charge controller is able to charge a lower nominal-voltage battery from a higher nominal voltage PV array.The controller will automatically adjust to a 12 or 24V nominal battery voltage

1.8 Automatic battery voltage recognition The controller will automatically adjust itself to a 12V or a 24V systemone time only.If a different system voltage is required at a later stage, it must be changed manually, for example with the Bluetooth app.

● The controller will operate only if the PV voltage exceeds battery voltage (Vbat).
● PV voltage must exceed Vbat + 5V for the controller to start. Thereafter minimum PV voltage is Vbat + 1V.
● Maximum open circuit PV voltage: 100V.

Nominal PV power, 24V 1a,b) MPPT 100/50 1400W
1a) If more PV power is connected, the controller will limit input power.
1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V.

Maybe for an easy life one of these https://www.victronenergy.com/inverter-charger-mppt/easysolar

I havent looked at the manual for that

So I think you are looking for 4 x 350W 60 cell panels in 2 strings going through a Victron SmartSolar MPPT 100/50 to a 24V battery

That was an interesting exercise, hope it helps

Ian