48 volt system is it feasible in the uk with a 2kw array

[mr-k]

hi all, currently weve got 3 solar arrays, ( due to the orientation of my panels) we have 2 arrays both with 2*400w panels, these are facing s/e and 1 array which is 2*250 panels.

Each array is connected to victron mppts and i have a victron 24/3000va inverter and 4 lithium LiFePO 4 batteries wired in 2s2p.

I use this mainly to power my offgrid office and lounge entertainment system including tv. there have only been a few days when i have had to rely on mains power since i set this up last september, anyhow i am thinking of changing to a 48v system, currently when i get full sun the mppt stops charging, when we get full sun i regularly use my setup to boil kettle / use air fryers / toasters etc. I have used the air fryer for 1.5hrs and still the batteries were fine to run the lounge and charge the delta 2 + extra battery and keep the pc and mac going till 6pm

my question is - is a 48v system harder to charge in low light conditions such as we regularly get in the uk, in summer i am sure i will be able to charge the 48v battery(s) as my panels get sun from 10 - 2 ish and the 500 w array gets sun from 12 - 4, will i need more panels to keep the battery topped up ? anyone else in the uk using a 48v off grid system with around 2.1 kw of solar

 

[sunshine_eggo]

hi all, currently weve got 3 solar arrays, ( due to the orientation of my panels) we have 2 arrays both with 2*400w panels, these are facing s/e and 1 array which is 2*250 panels.

Each array is connected to victron mppts and i have a victron 24/3000va inverter and 4 lithium LiFePO 4 batteries wired in 2s2p.

I use this mainly to power my offgrid office and lounge entertainment system including tv. there have only been a few days when i have had to rely on mains power since i set this up last september, anyhow i am thinking of changing to a 48v system, currently when i get full sun the mppt stops charging, when we get full sun i regularly use my setup to boil kettle / use air fryers / toasters etc. I have used the air fryer for 1.5hrs and still the batteries were fine to run the lounge and charge the delta 2 + extra battery and keep the pc and mac going till 6pm

my question is - is a 48v system harder to charge in low light conditions such as we regularly get in the uk, in summer i am sure i will be able to charge the 48v battery(s) as my panels get sun from 10 - 2 ish and the 500 w array gets sun from 12 - 4, will i need more panels to keep the battery topped up ? anyone else in the uk using a 48v off grid system with around 2.1 kw of solar

You will need a higher array voltage to charge a 48V battery.

"low light conditions" are the big concern and the driving factor. Sure, higher array voltage helps, but the difference is pretty small because there's just not much insolation. I mean... 10 W feels like a lot vs. 0W.

Given the typical voltages for the panels you have, 2S may be insufficient. If the panels are 72 cells with Voc in the 45-50V range, you're good. Going to higher voltage also means the charge controller Voc limit may be a driving factor.

Which MPPTs and panel data?

Now... why 48V? Are you looking to draw more power/energy? If so, the voltage change has very little to do with it. Your consumption will.

Conceptually, it helps to understand:

The amount of PV determines how much energy you can use per day
The amount of battery determines how much energy you can go between charges.

 

[mr-k]

You will need a higher array voltage to charge a 48V battery.

"low light conditions" are the big concern and the driving factor. Sure, higher array voltage helps, but the difference is pretty small because there's just not much insolation. I mean... 10 W feels like a lot vs. 0W.

Given the typical voltages for the panels you have, 2S may be insufficient. If the panels are 72 cells with Voc in the 45-50V range, you're good. Going to higher voltage also means the charge controller Voc limit may be a driving factor.

Which MPPTs and panel data?

Now... why 48V? Are you looking to draw more power/energy? If so, the voltage change has very little to do with it. Your consumption will.

Conceptually, it helps to understand:

The amount of PV determines how much energy you can use per day
The amount of battery determines how much energy you can go between charges.

my setup

hi, currently using three victron mppt all are 100/50, i will need to replace these as they arent the 48v models, going to go for 2 (one on each of the 800w arrays) looking at victron mppt 150/35, the panels will be 2 in each array and will be wired in series. this is the panel specs

panels are
Perlight Delta 400W Total Black Monocrystalline
Electrical Specifications
Peak power: 400W
Vmpp: 41V
Voc: 49.5V
Impp: 9.76A
Isc: 10.12A


I am going to sell the other 2*250 panels as they are crap and get 2 more perlights but 295w models. these will also have a victron 150/35

Reason for the change is - i dont see how i can expand my battery bank, unless i go down to 12volt, battery manufacturer only recommends max of 2s2p. i want to move to a rack mount type of battery bank as its expandable. its not summer here yet but on a half decent day my mppt are stopping charging the batteries by 13.00 uk time, so i plug the delta into the inverter to draw some power off the batteries. at the moment here in not so sunny derbyshire, i am charging the delta 2 and its additional battery at 700w from the inverter, total input from my solar right now is 797w, thats just the 4 400 watt panels. 2 of which are in the shade. Id rather go for a 24v rack type battery but cant find one here, hoping to sell my current kit except the panels,

My usage - i work in IT, my usage during a work day is 125watts per hour between 7.30 and 5 pm, then turn off the pc and mac or leave it on if my partner needs to use it, at night time we use about the same, so we have a decent size tv it uses about 100w an hour from 6pm to midnight, if we have a good day weather wise and the forcast is good for the next day, during the evening we will use the solar to power air fryers etc.
During the working day i use kettle in my office about 6 times a day and its about 1600w max and a toaster once a day.

When its sunny i have too much solar for my batteries when not sunny its enough to power pc and tv, when it middle of winter and the weather is dire i just use it for the pc.

Can you see another option, other than going to 48v, i do have 2 spare lifepo4 batteries 12.8v 100a, I thought about getting another 2 batteries putting them in parallel together with a smaller inverter for the tv / lounge, and when the main battery bank is full, push the solar generation to these 4, from at least 2 of the panels does that sound feasible, i setup the system last autumn, i balaced the batteries before connecting them together, when we next have a bad weather day I am going to check the voltages to see how they are doing, one of my concerns is the bms, 4 batteries each with their own bms.

 

[sunshine_eggo]

First, battery manufacturers often make recommendations purely for their own benefit or for unstated reasons that are ultimately for CYA purposes rather than a meaningful restriction. There are reasons that > 2P can be a problem, but they are very easily addressed. Putting more in parallel and even of different brands can be done safely if approached sensibly.

Second, if you are 2S with those panels on a 100v controller, you're lucky they haven't popped the controller. For the 400W to run in 2S, you need a 150V controller. You don't dare taunt the Voc limit.

From my perspective simply adding additional 12V in 2S in parallel with your existing bank gets you there the quickest and for the least amount of $ (what we use here in the Colonies).

I think you have an incorrect preconceived notion that only server rack batteries are expandable. That's just not true. Paralleling multiple strings of batteries can be easily done with some extra cable and care. 1600W max means you can likely make minimal effort and come out on top.

 

[mr-k]

Hi sorry, the two arrays of 400 are in paralell, explorist has a mppt calculator on their site i used that to calculate the size of mppt, i appreciate what you say about the battery manufacturer but at the end of the day, safety has to come first, the batteries are in my house, if there was a fore in one of them, idealy i would put the batteries on the wall outside but then i guess i would have to heat them in winter. My inverter has 2 positive and 2 negative inputs on the dc side, i am going to investigate wether its feasible to have 2 seperate banks of four feeding the inverter, currently my connections go through a lynx distributor, so i guess get another lynx distributor. Another option is to have a totally seperate system for home entertainment, home office and fridge based on a smaller inverter say a 12/1200,
the reason i like the 48v rack mount batteries is because they are buildt and designed to be a unit, as opposed to me connecting 4 batteries together, yes i have put fuses in place and the correct wire size. perhaps i am being overly cautious

 

[sunshine_eggo]

Hi sorry, the two arrays of 400 are in paralell, explorist has a mppt calculator on their site i used that to calculate the size of mppt

Good!

i appreciate what you say about the battery manufacturer but at the end of the day, safety has to come first, the batteries are in my house, if there was a fore in one of them, idealy i would put the batteries on the wall outside but then i guess i would have to heat them in winter.

You're operating under an assumption that rack batteries are in some way safer. They're not. A properly configured LFP bank is as safe as the next. The only way one battery is safer than another is if there is some sort of built-in fire suppression, and that's pretty rare.

My inverter has 2 positive and 2 negative inputs on the dc side, i am going to investigate wether its feasible to have 2 seperate banks of four feeding the inverter, currently my connections go through a lynx distributor, so i guess get another lynx distributor. Another option is to have a totally seperate system for home entertainment, home office and fridge based on a smaller inverter say a 12/1200,

Victron provides two inputs because some installation require two cables to prevent excessive voltage drop with long wire runs. Note that while it may seem like a separate battery, by joining them at those two terminals, you have actually turned them into one bank. That said, a carefully planned setup utilizing both of those connections could optimize 2X 2S2P batteries and ensure they are all well balanced. 2S2P banks are pretty easy to ensure they share current equally. 2S4P gets a little more complicated, but 2X 2S2P in parallel are actually optimized.

the reason i like the 48v rack mount batteries is because they are buildt and designed to be a unit,

You may need to read the fine print. Many also recommend that you buy their server rack enclosure and connect to bus bars rather than parallel to the terminals - something you could accomplish with paralleled 2S 12V.

as opposed to me connecting 4 batteries together, yes i have put fuses in place and the correct wire size. perhaps i am being overly cautious

You are.

I would encourage you to set all assumptions aside and look at what it would take you to get where you need to go sticking with your 24V setup or switching to 48V.

 

[mr-k]

Hi, so we went with 2 * us3000c and a victron multiplus 48/5000, its not wired into the house consumer unit but we had an electrician wire a small consumer unit to the inverter then wire 2 sockets in the kitchen to the new consumer unit, using the kitchen appliances during the day and early evening we get the batteries down to about 70%, but after 2 hours of pv input during the day were backup to 90%, the panels will be in the sun for about another 3 hrs, i appreciate we wont get this amount of pv in winter. still got alot of reading to do on the pylontech and the multiplus.