12v/ 24v systems

[sarah2014]

Hi,
I'm new to Solar and am really interested. I have 6 *100 watt solar panels 18v 5.5 amps. And 6 12v* 100amp batteries. My controller is PWM 12/24v 40a controller. I am now looking for inverter and confused to go 12v or 24v. What would give me a sronger system 12v or 24v.
Thanks,
Sarah

[inetdog]

Hi,
I'm new to Solar and am really interested. I have 6 *100 watt solar panels 18v 5.5 amps. And 6 12v* 100amp batteries. My controller is PWM 12/24v 40a controller. I am now looking for inverter and confused to go 12v or 24v. What would give me a sronger system 12v or 24v.
Thanks,
Sarah

For that level of panel and battery, you would be much better off with a 24 volt system. The lower current will make your wiring easier.

Unfortunately, if you want to use all six batteries you will end up putting three strings of two batteries each in parallel. That is a lot better than putting six batteries in parallel, but is still not ideal.

To use your charger to output 24 volts you will need to also wire your batteries in series strings of two each and then put the three strings in parallel to the charge controller (CC) input. That will be fine.
For your amount of panel power, if you had not already purchased the PMW CC I would have recommended an MPPT model. allowing you to wire more panels in series and giving a higher conversion efficiency for power from the panels to the batteries.

For a 600 watt panel system, starting from scratch, an MPPT controller and four 6 volt 200+ AH batteries in series to produce 24 volts would have been a better way to go.

For the inverter, the first thing you need to know is what your power loads will actually be and whether they will tolerate a MSW (modified square wave) output or will need a PSW (pure sine wave) output. Motors and some electronics will usually work better with PSW.

These are just a few highlights. There are some good sticky threads on system sizing that go into much more detail.

[Sunking]

For that level of panel wattage and battery 24 volts is the right choice. It will lower the current and allow smaller wiring.

[porrascarlos80]

sorry friends, I may need more clarification on wiring difference between 12/24v systems.
"The lower current will make your wiring easier. "

would you please share more information about that , maybe a comparison?

I dont really understand the difference , guessing awg # changes between systems?


tks!

[bcroe]

I may need more clarification on wiring difference between 12/24v systems.
"The lower current will make your wiring easier. "

Would you please share more information about that, maybe a comparison? I don't
really understand the difference, guessing awg # changes between systems? tks!

There are 2 basic issues on the conductor sizes. One that always must be observed, is
current capacity. Running 240W at 24V involves 10A (POWER = VOLTAGE X CURRENT),
so you need wire big enough for 10A. Building the system at 12V involves 20A, so the
conductors must be rated twice the current.

HOWEVER, running the 12V system with twice as heavy wire means you will have the
same voltage drop (loss) in the wire as the 24V system (Ohms law). Twice the current
at the same voltage loss means you have doubled your wire power losses. To get back
to the same efficiency (power loss), you need to double the wire size again, to have
half the voltage drop at twice the current. That is, the higher voltage system reduces
the amount of copper needed dividing by the SQUARE of the voltage, for the same losses.

Bruce Roe

[Sunking]

BCROE I fully understand what you are saying, but it could be explained a little easier. For example a 20 amp circuit for safety and to meet code is a #12 AWG copper. But for low voltage under 120 volts is uselsss unless the length is extremely short.

The most important aspect is voltage drop and keeping it to 2 or 3 % or less. So the lower you go in voltage, the larger diameter cable it will take to acheive it which means it gets real expensive real fast.

Real life example a very simple 12 volt 100 watt gizmo circuit that is say 40 feet one way distance. Current is relatively low at 9 amps and to meet NEC compliance you can use the smallest allowed of #14 AWG which is good for 15 amps. However at 12 volts 40 feet with 14 AWG would induce 15% voltage drop resulting in 10 volts at the gizmo which it may not even work or work poorly if a light. To get to 2% would require a # 4 AWG. Now stop and think about that you went from a inexpensive 14 AWG conductor costing some 9-cents per foot, to using #4 AWG costing 85-cents per foot.

24 volt is 200% better but no bargain as it would require 8 AWG copper costing 35-cemts per foot.

So be careful what you folks ask for as you will get it. You might think low voltage is gaining you something, but is far from reality. Low voltage is terrible inefficient and expensive. Only people gaining anything is your copper wire dealer laughing all the way to the bank with your wasted cash.

That same cheap 9-cent per foot 14 AWG operating at 120 volts to full current capacity of 15 amps or 1800 watts aint so bad after all. UK is even better as they use 240 volts which ups power to 3600 watts. You low voltage guys have to suffer with 100 watts limitation. You would have to own a copper mine to get 3600 watts.

[bcroe]

Voltage vs transmission efficiency

BCROE I fully understand what you are saying, but it could be explained a little easier.

Only people gaining anything is your copper wire dealer laughing all the way to the bank with your wasted cash.

Right, left out the part about the copper wire dealer laughing. By contrast, today at 390VDC I sent
16KW 100 yards with 1.4% loss. In 10 hr 44 min made AC 105 KWH, a record here. Bruce

[porrascarlos80]

experts,

now what happen if you put panels in series until you get 120V DC , and you just rectify that voltage into AC, would that be possible?

I think the AC would be modified wave or something like that with interference and voltaje might be unstable, besides that anything else? .

[bcroe]

String

experts, now what happens if you put panels in series until you
get 120V DC, and you just rectify that voltage into AC, would that be possible?

I think the AC would be modified wave or something like that with interference and voltage might
be unstable, besides that anything else?

Putting panels in series to get hundreds of volts is an efficient way to allow moving the power
some distance; here called a "string". The exact voltage will vary considerably depending on
load and temperature; these typically feed a "string inverter" operating at the most efficient
voltage & current. The inverter is used to feed a regulated AC voltage to a grid connect, or
a charge controller could feed it into a battery system. "Rectify" changes AC to rough DC, here
you want to go the other way. Bruce Roe

[Sunking]

experts,

now what happen if you put panels in series until you get 120V DC , and you just rectify that voltage into AC, would that be possible?

I think the AC would be modified wave or something like that with interference and voltaje might be unstable, besides that anything else? .

Yes that can be done and is done. The issue is batteries as not many manufactures offer higher voltage batteries. 48 volts is it with most manufactures.

However there is one manufacture that does and they happen to be the best called Midnite Solar and they make a model # 250KS. It provides for up to 120 VDC battery, and the input voltage of 250 volts + Battery Voltage. So in theory you can input as high as 370 volts with a 120 volt battery.

[porrascarlos80]

amazing information sunking! I see other problem, inverter prices. those ones seems to be costly versions.

thanks for the information

[Sunking]

amazing information sunking! I see other problem, inverter prices. those ones seems to be costly versions.

thanks for the information

Don't let the price of higher voltage inverters throw you off the trail. If you do that you cannot see the forest because trees blind your vision. Bottom line cost is what you look at and efficiency. The higher inverter price is more than offset by savings gained in smaller wiring and less hardware.

[porrascarlos80]

Don't let the price of higher voltage inverters throw you off the trail. If you do that you cannot see the forest because trees blind your vision. Bottom line cost is what you look at and efficiency. The higher inverter price is more than offset by savings gained in smaller wiring and less hardware.

Thank you Master!

[Sunking]

Thank you Master!

Well you are welcome, but my name is Dereck.