Should I upgrade to a 48 volt system? advantages?

[Jamie.sanders]

I am currently putting together my system and learning as I go, I'm curious of the advantages of a 48V system over a 24V.
I read somewhere you can use smaller wire, but which wire is this referencing? I did not see that info needed on a wire sizing calculator
for my wire from panels to Charge controller? can you run smaller wire there with 48V, that would save $$$

I currently have 12, 440 watt panels (5,280 watts total)
I have 2 Midnight 150 charge controllers
I currently have 24 lithium cells, to make 3, 24V batteries, each consisting of 8 cells.

I am considering buying another 8 cells, to make a total of 2, 48V batteries. and I need to decide this before I order my inverter.

suggestions? input, is it worth it?

 

[Don B. Cilly]

5kW at 25V is roughly 200A. At 50, 100.
In theory. In practice... those panels will likely charge from zero to... say 4kW at maximum solar exposure.
So say 160 and 80 (max). But, going to the charge controller, you'll have a lot more volts, so a lot less amps per watt.
How many depends mostly on how your panels are wired.

IMHO, - depending on the size (Ah) of the batteries, obviously - not a critical enough power source to warrant 48V.
Now, if you plan to draw a lot of amps for extended periods of time, that's another matter.
I quite like 24 (I don't really draw much power). It's quite useable as DC itself for lots of things.
.

 

[chrisski]

48 volt versus 24 volt is really based off the inverter size you need. My very conservative rule is:

12 volt system: 1000 watt limit
24 volt system: 2000 watt limit
48 volt system: 4000 watt limit

WIth those numbers its oK to go higher, just not a lot. So for my 12 volt system and 2000 watt inverter, its OK for me to use 2000 watts to warm a meal up in the microwave a couple minutes at a time, a few times a day, but not run AC at 2000 watts All day long.
============
For wiring from SCC to Panels, all depends on how you wire them. You did not give specs of panels, but my guess is with a 150 volt limit, you can only wire two panels in series before going to parallel. My guess is without reading panel specs your 2 X 150 volt SCCs will be onfigures 2S3P, coming in around 120 volts for the coldest day of the year, and a max production of 30 amps, but again depends on panels specs.
=============
I am doing a 12 volt upgrade to 24 volts. I would have preferred a 48 volt upgrade, but I would have to re-purchase three SCCs which would do 12/24 volt but not 24. Also, a lot of the Fuses and other busbars were not rated above 48 volts.

So in my case, any money saved by wiring would be more than spent on buying new components.

I also found there were far fewer choices at 48 volts for components. Not impossible, just made choosing stuff quite a bit harder.
============
Very simplified explanation on wiring. I like a 100 amp limit on wires. Not everyone does that limit, but the wiring stuff would apply. This limits me to the following:

12 volts: 1200 watts (1 AWG Wire)
24 volts: 2400 watts (1 AWG Wire)
48 volts: 4800 watts (1 AWG Wire)

To do 4800 watts, on all systems the wire size would need to be:

12 volts: 400 amps (750 MCM)
24 volts: 200 amps (4/0 Wire)
48 volts: 100 amps (1 AWG Wire)

Prices are:

 

[Jamie.sanders]

48 volt versus 24 volt is really based off the inverter size you need. My very conservative rule is:

12 volt system: 1000 watt limit
24 volt system: 2000 watt limit
48 volt system: 4000 watt limit

WIth those numbers its oK to go higher, just not a lot. So for my 12 volt system and 2000 watt inverter, its OK for me to use 2000 watts to warm a meal up in the microwave a couple minutes at a time, a few times a day, but not run AC at 2000 watts All day long.
============
For wiring from SCC to Panels, all depends on how you wire them. You did not give specs of panels, but my guess is with a 150 volt limit, you can only wire two panels in series before going to parallel. My guess is without reading panel specs your 2 X 150 volt SCCs will be onfigures 2S3P, coming in around 120 volts for the coldest day of the year, and a max production of 30 amps, but again depends on panels specs.
=============
I am doing a 12 volt upgrade to 24 volts. I would have preferred a 48 volt upgrade, but I would have to re-purchase three SCCs which would do 12/24 volt but not 24. Also, a lot of the Fuses and other busbars were not rated above 48 volts.

So in my case, any money saved by wiring would be more than spent on buying new components.

I also found there were far fewer choices at 48 volts for components. Not impossible, just made choosing stuff quite a bit harder.
============
Very simplified explanation on wiring. I like a 100 amp limit on wires. Not everyone does that limit, but the wiring stuff would apply. This limits me to the following:

12 volts: 1200 watts (1 AWG Wire)
24 volts: 2400 watts (1 AWG Wire)
48 volts: 4800 watts (1 AWG Wire)

To do 4800 watts, on all systems the wire size would need to be:

12 volts: 400 amps (750 MCM)
24 volts: 200 amps (4/0 Wire)
48 volts: 100 amps (1 AWG Wire)

Prices are:
View attachment 75336

Correct, I will be wired 2S3P, (6 panels) and another 2S3P (six panels), each one using 1 midnight 150 charge controller.
my panel specs are listed in yellow in the attached pic.

 

[MichaelK]

It's not so much how thick the wire needs to be as it is how many amps is your controller designed to handle. As posters mention about the amps are half at 48V as compared to 24V. So, if your controller can handle a maximum of 100A, that would only be 2400W at 24V but you could have 4800W at 48V.

For the Midnight 150, that is not completely correct though. At 24V the controller has a 94A limit, while at 48V it's only 83A. So, it's 2256W vs. 3984W. Still, you get much more wattage at 48V as compared to 24V.

 

[MrM1]

If I could do it again I'd do 48v over 24v more options in my opinion, bigger arrays.

That said I am about to double my array size on my 24v 2526w array and classic 150. Yes it will be way over paneled, but midnite says it's no problem as long as I don't exceed VOC. It will just clip the excese.

On days like today, when my max power generation was no more than 1.5 kw at any given moment and I managed 9.7kWh for the day, I think with an array over 5000w on a single classic probably would have seen about a 50% or more increase.

 

[Jamie.sanders]

Well my inverter will only be 3,000 watts, so am I in beteeen 24v and 48v?

 

[chrisski]

Well my inverter will only be 3,000 watts, so am I in beteeen 24v and 48v?

If you want to fully use the inverter, then I think 48 volts is better.

I have am adding a 3000 watt inverter on my 24 volt upgrade, but will be well below that. I expect I may pull 2000 watts for up to 15 minutes. THe 3000 watt inverter is to help cover surge, and if the inverter gets hot, cuts back on power production Maybe 25% at certain temps, and then 50% at higher temps.

 

[Don B. Cilly]

Well, it depends on how much you actually plan to draw, of those 3000.
I have a 3K inverter. 24V. I draw some 50 to 120W (depending on whether the fridge is running - with the PC monitor off, some 15-20) most of the time, but occasionally use power tools, vacuum cleaner, etc. For brief periods.

 

[rmaddy]

For a 3000W inverter, both 24V and 48V work fine. 150A vs 75A.

Let your solar decide between the two. 48V allows smaller charge controllers due to the lower amps or it allows more solar.

 

[robby]

Besides the wire size issue and dealing with higher currents, if all things are equal your still going to get more efficiency from the same design type Inverter at 48V vs 24V due to less heat being generated by the switching Transistors. This is not a problem if the power usage is low but at higher power it becomes a factor to consider.

 

[Deleted member 1888]

48 volt versus 24 volt is really based off the inverter size you need. My very conservative rule is:

12 volt system: 1000 watt limit
24 volt system: 2000 watt limit
48 volt system: 4000 watt limit

I have to degree with you on the limits as I have a 24v system with 6000w(75% efficient so more like 4500w) of panel on 3 MPPT. They are all hooked to a 1000a bus bar with 50kw of batteries . I made a 24v over a 48v due the the safety factor of 24v wont kill me but 48v will, and I have been shocked several times. Now yes 48v would have been a cheaper option and if I needed more than 6000w(4500w) I would have to go 48 as I have maxed out my 24v system. At 48v with the same Charge controllers wire and bus bars I could push 10000w on my system

What it all come done to is how much power you need, how safe you feel messing with 48v, and how much you want to spend. For me the safety of 24v was worth the added cost over a 48v system. With the knowledge I have now if I was to do it over I would go 48v and be running 10k worth of panels for the same price.

 

[ArranP]

SOROTEC REVO VM II ( 24V ) inverter can parallel upto 9 i.e. 9x 2.5KW = 22.5KW total.

 

[chrisski]

I have to degree with you on the limits as I have a 24v system with 6000w(75% efficient so more like 4500w) of panel on 3 MPPT. They are all hooked to a 1000a bus bar with 50kw of batteries

What size is your inverter? I should have wrote:

12 volt system: 1000 watt inverter limit
24 volt system: 2000 watt inverter limit
48 volt system: 4000 watt inverter limit

Can you confirm you have a 50 kwh battery bank?

 

[MrM1]

12 volt system: 1000 watt inverter limit
24 volt system: 2000 watt inverter limit
48 volt system: 4000 watt inverter limit

Old truth you don't see talked about much these days, but still a really good rule of thumb.

 

[Deleted member 1888]

What size is your inverter? I should have wrote:

12 volt system: 1000 watt inverter limit
24 volt system: 2000 watt inverter limit
48 volt system: 4000 watt inverter limit

Can you confirm you have a 50 kwh battery bank?

I use a 24v 6000w Aims split phase inverter

 

[Don B. Cilly]

Yeah well. I have a 3kW inverter. On 24V. It doesn't mean I draw 3kW from it. Like, ever. Or even 2.
Most I've drawn from it for more than a minute or so, was 800W. It didn't like it :·/
I believe it's a good idea to have a bigger inverter than you actually need, it doesn't really use much at all when idle.
Conversely, I think it's not a very good idea to use anywhere near 80% of its rated power for anything more than a minute or two.
.

 

[chrisski]

I use a 24v 6000w Aims split phase inverter

What are your loads and times along with inverter to battery wiring?

 

[Deleted member 1888]

What are your loads and times along with inverter to battery wiring?

I run my RV, fridge,freezer,well pump. The main wires between the bus bars is 4/0 and to each battery is 2/0 I feeding the bus bar.

 

[Jamie.sanders]

Well, it depends on how much you actually plan to draw, of those 3000.
I have a 3K inverter. 24V. I draw some 50 to 120W (depending on whether the fridge is running - with the PC monitor off, some 15-20) most of the time, but occasionally use power tools, vacuum cleaner, etc. For brief periods.

My max power usage out of the 3,000 watt inverter will be about 2,400 watts if I run everything at the same time with the big pull being the 1,500 watt air fryer