Switching from 12V to 24V.?

[deserthorizons]

It appears I have reached the roadblock of 12V power and have finally succumbed to the lure of 24V.
This is my current 12V setup:
6- 100W panels series string facing west
6- 100W panels series string facing east
all parallel connected with one set
of wires thru a 'baby breaker' box
into Midnite Classic 150 MPPT CC,  then
thru a 'baby breaker' box to 16- 6 Volt
Trojan T-105's connected in series to
equal 8 - 12 Volt connected in parallel
connected to an Aims 2000/4000 watt
12 Volt inverter..
: so :
12 - 100 W
Classic 150
8 - 12V - 225 Amp hour batteries
12V Inverter
+ (PLUS) +
4 - 100 watt panels paralleled into
one set of wires to PWM Charge Controller
(to same 8 - 12 Volt batteries.)

Is it really as simple as getting a 24V Inverter and disconnecting a few battery cables.?
What am I missing.?

[Robin]

Not quite so simple, but not terrible either.
You have 12V solar panels. You will need to put some of them in series. You have 18 12V panels. That divides up nicely into three strings of 6 in series. If I remember correctly, your panels should have a VOC of about 22 volts max. That means you can put 6 in series. Get an MNPV3 combiner and three appropriate breakers. They are usually 15 amps, but for a 12V panel, it may be less. Look on the back of your panels and see what they recommend for a series fuse or breaker. That will be the breaker to get. We have them all. MNEPV10 or MNEPV15. Something around those values.
Throw away the PWM controller. You do not need or want to use it.
Configure the batteries for 24V. 4 sttrings of 2 in series.

That is pretty much all you need other than a 24V inverter. Make sure your battery cables and overcurrent devices are correct. You may need a MNDC125 or 175? It all depends on which inverter you get. I frankly would be going all the way to 48V if you can swing that.
You get twice the power out of the Classic at 48 vs. 24.

[ClassicCrazy]

And also you can get a Samlex DC to DC converter to make your 12v loads ( smaller loads - not inverter)
With all the batteries you have seems like 48v might be the way to go for better battery health .

Larry

[deserthorizons]

You get twice the power out of the Classic at 48 vs. 24.

This is the part that always confuses me..
Where exactly do you get "twice the power" from.?

I checked and what I thought I would be able to do,, double my panels,, is not the case..
I do not want more breaker boxes and more wire,, so trying to do it without even more expenses..
So now I am back to thinking it is just more money being thrown at this and I still
get the exact same amount of power out of it,, whether it is 12V or 24V or 48V..
Now I have 8 - 12V batteries giving 1800 amp hours..
If I go to 24V I will then have 4 -24V batteries giving 900 amp hours..
so then it goes that 2 - 48V batteries give 450 amp hours.. yet it all adds up to the same amp hours total..
( 12 x 1800 = 24 x 900 = 48 x 450 )
There has to be something to this that I have not grasped yet..

[ClassicCrazy]

You get twice the power out of the Classic at 48 vs. 24.

This is the part that always confuses me..
Where exactly do you get "twice the power" from.?

I checked and what I thought I would be able to do,, double my panels,, is not the case..
I do not want more breaker boxes and more wire,, so trying to do it without even more expenses..
So now I am back to thinking it is just more money being thrown at this and I still
get the exact same amount of power out of it,, whether it is 12V or 24V or 48V..
Now I have 8 - 12V batteries giving 1800 amp hours..
If I go to 24V I will then have 4 -24V batteries giving 900 amp hours..
so then it goes that 2 - 48V batteries give 450 amp hours.. yet it all adds up to the same amp hours total..
( 12 x 1800 = 24 x 900 = 48 x 450 )
There has to be something to this that I have not grasped yet..

You get double the capacity that the Classic can put out.
For example lets say  you have 10 amp at 12v  that would equal 10 x 12 = 120  watts
if you had  10 amps at 24v that would equal  10 x 24 = 240 watts

The Classic is rated at it's output amps .  If you are running the capacity output amps at 12v that is half of the output capacity than if your batteries were at 24v .
It won't change the capacity of the batteries you already have now - that will stay the same.
What you get is that depending on your PV and their ratings you can add more PV  and get more power out of the Classic at 24v or 48v than you can at 12v.
This of course depends on what kind of PV you have and how you configure them - which you would still need to do using the Midnite Classic string calculator . You can change the battery voltages on the calculator  and see the power output differences for adding panels.

For my system my Classic at 24v is maxed out at 2700 watts . If I changed my batteries to 48v setup then I could add more PV and use the same Classic to handle more power.

In regards to your existing battery wiring - you can probably keep it . As the system voltage goes up  you need smaller wire so if you already have larger sized wire you are okay.
Your breakers are based on the wire capacity so it won't make a difference if you go up in voltage as long as the amps don't exceed the rating of your wire. Usually amps goes down not up as you increase voltage. Same for PV wiring. But  you need to consider the PV input voltage limit of  the Classic and the string calculator will tell you that. 

The advantage of higher battery voltage is smaller gauge wire needed to inverter and any other wiring on battery side.
Same for if you increased the PV input voltage - smaller wire guage needed for longer wire runs because of less voltage drop.
But one of the design considerations is to keep the PV input voltage closer to the battery voltage since that way the Classic doesn't have to do so much conversion which means it runs more efficiently and doesn't get as hot.

Hope that makes sense .
Larry

[deserthorizons]

Thank you for the explanation but the comment I was referring to was getting "twice the power.".
That is a huge misconception with going to 24V vs 48V vs 12V
It runs through wire better, yes, but since I have my system setup for 12V using appropriate wiring
I would not see a gain from that by switching to 24V..

if  V x A = W  then in any scenario I get the same amount out of the batteries..
12V x 1800A = 21,600W
      &
24V x 900A = 21,600W
       &
  48V x 450A = 21,600 watts,
then I am not getting the
advantage of spending more money on an existing
system to swap to 24V when I will still get the same juice out of the batteries..
It is actually easier and cheaper for me to add more solar now as 12V than if I switch to 24V..
or again, what is it I am missing.?  there has to be something..
do I need slappin upside the head.?

[deserthorizons]

This of course depends on what kind of PV you have and how you configure them - which you would still need to do using the Midnite Classic string calculator .
You can change the battery voltages on the calculator  and see the power output differences for adding panels.

The only way I can add more panels is through more strings.. I was hoping I could keep it at 2 strings of 8 panels..
I checked after posting that is not how it works.. So I would need more wiring,, more breaker boxes,, to run 4 strings..
Unless there is some way to break my 16 panels into 4 strings that enter the house on (2) 10ga solar wires..
Remember2 strings would face east and 2 would face west so I never get a full blast out of all the panels at any one time..
When the sun is directly overhead it at best is shining 40 degrees on one set of 8 panels or the other..

[ClassicCrazy]

Thank you for the explanation but the comment I was referring to was getting "twice the power.".
That is a huge misconception with going to 24V vs 48V vs 12V
It runs through wire better, yes, but since I have my system setup for 12V using appropriate wiring
I would not see a gain from that by switching to 24V..

if  V x A = W  then in any scenario I get the same amount out of the batteries..
12V x 1800A = 21,600W
      &
24V x 900A = 21,600W
       &
  48V x 450A = 21,600 watts,
then I am not getting the
advantage of spending more money on an existing
system to swap to 24V when I will still get the same juice out of the batteries..
It is actually easier and cheaper for me to add more solar now as 12V than if I switch to 24V..
or again, what is it I am missing.?  there has to be something..
do I need slappin upside the head.?

The only advantage to changing is if you have the Classic maxed out on PV and want to add more.  If your Classic isn't maxed out then you are right -  you can just add more to existing setup.
But you need to use the string calculator to make sure you don't exceed PV voltage limits for input to the Classic.

Larry

[ClassicCrazy]

This of course depends on what kind of PV you have and how you configure them - which you would still need to do using the Midnite Classic string calculator .
You can change the battery voltages on the calculator  and see the power output differences for adding panels.

The only way I can add more panels is through more strings.. I was hoping I could keep it at 2 strings of 8 panels..
I checked after posting that is not how it works.. So I would need more wiring,, more breaker boxes,, to run 4 strings..
Unless there is some way to break my 16 panels into 4 strings that enter the house on (2) 10ga solar wires..
Remember2 strings would face east and 2 would face west so I never get a full blast out of all the panels at any one time..
When the sun is directly overhead it at best is shining 40 degrees on one set of 8 panels or the other..

I haven't drawn out and analyzed your present system and thought about it in depth.
I am just giving some general solar design criteria .
The Midnite String calculator is the best place to start to evaluate different potential upgrades for your system.

Larry

[deserthorizons]

The only advantage to changing is if you have the Classic maxed out on PV and want to add more.  If your Classic isn't maxed out then you are right -  you can just add more to existing setup.
But you need to use the string calculator to make sure you don't exceed PV voltage limits for input to the Classic.

Larry

ayyyyyyyyyy, there's the rub.. I am maxed out on 12V incoming.. I have 4 more panels I wanted to add to the 12 in use by switching to a 24V setup.. but in any case, to do that requires more breaker boxes , disconnect switches and more solar wire.. I was hoping a 24V inverter was going to be it.. then i could set aside the 12V for secondary backup redundancy..
but no,, it means 4 sets of wires coming into home instead of just 2.. etc..
so starting to be - not worth it.. cheaper to put a couple of cheap PWM's onto the 4 current additional panels for no additional cost..
and then i can add more panels at 20 bucks for additional charge controller per <40 amps..
My ultimate goal is to get an additional 500 watts via 2 panels for a grand total of 2100 watts in 18 panels with 4 charge controllers..
I have everything except the (2) -250W panels which I can get for 50 bucks each..

which is the way i was going to go do it until i started rethinking 24V..
I will stick with my 12V as it runs everything I need out here in the Arizona desert off grid..
it runs my refrig 24/7 and my 6K Btu A/C in summer,, all the lights, computers, tv's etc..
but when you are on a very strict budget, you do what you gotta do..

[deserthorizons]

I guess the question comes down to the fact that I have (2)- 10ga solar wires coming into the MC150
running from (12)- 100W panels in 2 strings,, so there is one "Y" connector between 2 sets..

Is it possible to run 4 sets of (4)- 100W panels through 1 more set of "Y"s.?
so it still enters home on the same 1 pair of 10ga cables..?

[Highflyer]

DH,
You can still have two wires (one from the east and one from the west) IF you have a small combiner (breaker) box out at the panels.  The two strings would each have a breaker out at the panels then combine to the east and west wire back into the house.  Yes there is a little more cost, but your efficiency will also rise.  I found that when I went from 24 volts to 48 volts I went from 4.9 kWh for the same set of panels to 7.2 kWh of usable energy captured by my system.  It is also simpler to maintain and my charge controller does not get as hot (think longer lived). 

Does that help?

[Vic]

desert ..,   most of the issues have been covered previously,   but  ...

12 V solar systems are not as efficient as 24 V,   or 48V ones.   A 2000 W load on your Inverter,   will require about 200-ish Amps of current.  This is huge!   This large current result in a large voltage drop in battery/cables,  AND,  even inside the inverter.   If you really need a 2000 W inverter to handle your loads,   24 V is really the minimum system voltage,   but that is still four parallel battery strings (too many).  At 48V,  of course,   there are "only" two parallel battery strings,   which is much better (or, less-bad)  from the string balance standpoint,   and a very manageable battery current.  The voltage drops with high currents of 12 V systems with large loads,   represent a larger percentage of the system voltage,   so a large hit to efficiency and reduction in system performance.

AND,   EIGHT parallel strings of batteries  is almost impossible to get in charge/discharge balance,   let alone,  trying to keep them balanced.   This usually results in some strings not getting properly charged (particularly in off-grid systems).   And early death of batteries in those strings.

The above is usually a hidden cost,  that will not appear for some months of use.

Inexpensive inverters often have a relatively high idle power consumption (tare),   with no load,   and are less efficient,  under load, than the higher-tier models.

The Y connectors for adding PVs often increase the FIRE risk,  compared to having each PV string on its own Combiner circuit breaker.

Many trade-offs.  Not to rag,  too much,   on your system.   Good Luck, Vic

[deserthorizons]

Does that help?

Yes, Thank You..
It helps explain to me not to do it..

[deserthorizons]

Many trade-offs.  Not to rag,  too much,   on your system.   Good Luck, Vic

No please,, rag on it if it "deserves" it.. not just because you ran out of beer for your crunchberries,, if you know what I mean..
for 1, the biggest load I put on the system is the toaster.. so 1200 watts
other than that it is the A/C in the summer.. built in soft start and runs at max 575 watts.. It ran fine last  year but I think I want a little more cushion in my charge ability..
It is not top of the line but it is an AIMS 2K/4K -12V inverter that has run flawlessly for 3 years now..
It was my thinking of getting a backup inverter for redundancy and backup that started me down the road of 24V..
at this point in time it will be a journey left untraveled..