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Old 02-04-2015, 06:37 PM   #1
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12 volt vs 24 volt panels

I am looking to install solar on my motorhome.

Seeing as there is always a chance of shade, would there be any advantage of using 2 200 watt 24 volt panels over 4 100 watt 12 volt panels if they are all wired parallel?

I will be using an mppt charge controller.
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Old 02-04-2015, 07:02 PM   #2
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Hi Rod,

If you can separate the 4 PV modules to different areas of the RV roof where they may be free from the shadow, you may gain more from smaller modules. If they will be close to each other, I recommend using higher voltage and Wattage PV modules as your cost will be lower and your wire to the controller can be much smaller.

There are many different voltage PV solar modules, as high as 90 volts. One of our top sellers is 54.7 volts. Be sure to choose the right controller for the voltage you want to use.
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Old 02-04-2015, 07:29 PM   #3
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Attached here is a write up on my solar system, with comments as to why I selected 12v 100w panels and a PWM controller. YMMV.
Attached Files
File Type: pdf VSheetz - Solar Setup for my RV v1.1.pdf (473.7 KB, 154 views)
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Old 02-05-2015, 08:01 PM   #4
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Higher voltage can use smaller wires. So it has a slight advantage.
Our previous system where 2 100W panels with PWM controller and worked extremely well for 2 group 27 batteries.
We since changed units and have now 600W with a MPPT controller and larger inverter.
What we found is the flexible solar panels are far better tovworkvwith and very efficient...

Reiner
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Old 02-06-2015, 09:43 AM   #5
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Quote:
Originally Posted by reinerka View Post
Higher voltage can use smaller wires. So it has a slight advantage....

Reiner
Hi,

Slight advantage?

Using high voltage can save a lot of money and time. For example, two 60 cell PV modules, 500 Watts total, two MC4 branch adapters with a 30 foot cable run from roof to the controller will have about 1.1% voltage drop using #8 AWG, well below our design maximum of 2%.

Compare that to five 100 Watt, 12 volt nominal modules:
  1. It will require #2 AWG wire for the same run.
  2. You need 5 sets of mounting brackets compared to two.
  3. You need 5 wire runs to the modules.
  4. It takes much more time to install 5 than the two.
  5. You will need a combiner box on the roof capable of connecting #2, not easy to find.
  6. The wire is too big for most controllers so you need to install terminal blocks at the controller or splice the wire to adapt to the terminals.
  7. Then there is the size of holes you must make and bending difficulty with large wire.
Now add to that the much lower cost of 60 cell modules over 12 volt and you can see the significant cost and time advantage of using high voltage modules.

Larry
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Old 02-06-2015, 10:51 AM   #6
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Quote:
Originally Posted by BatteryPro View Post
Hi Rod,

If you can separate the 4 PV modules to different areas of the RV roof where they may be free from the shadow, you may gain more from smaller modules. If they will be close to each other, I recommend using higher voltage and Wattage PV modules as your cost will be lower and your wire to the controller can be much smaller.

There are many different voltage PV solar modules, as high as 90 volts. One of our top sellers is 54.7 volts. Be sure to choose the right controller for the voltage you want to use.
X's 2. If starting from scratch, more upsides to going with higher voltage. You'll also find many that recommend leaving headroom in your selected components, especially MPPT's, to allow for future expansion of panels.

Best of luck to you!!!
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Old 02-06-2015, 03:26 PM   #7
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You guys are lucky. Solar components are a lot cheaper in the US than they are here in Canada .

Are flexible solar panels worth using or are they still too inefficient compared to the rigid panels.
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Old 02-06-2015, 03:32 PM   #8
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I know I am derailing my own thread, but is the Tracer 4215bn mppt controller any good or should I get a Midnite solar kid?
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Old 02-06-2015, 04:06 PM   #9
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which panel has better specs for my purpose :

panel 1

Module Type: SPM200M-72
Maximum Power at STC(Pmax): 195Wp
Maximum Power Voltage(Vmp): 36.72V
Maximum Power Current(Imp): 5.45A
Open-circuit Voltage (Voc): 44V
Short-circuit Current (Isc): 5.50A
Cell Efficiency(%): 17.12


panel 2 :

Pmax : 150w
Voc : 22.32v
Vmp : 19.08v
Isc : 8.49a
Imp : 7.87a
cell efficiency 17.5%
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Old 02-06-2015, 05:15 PM   #10
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Quote:
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I know I am derailing my own thread, but is the Tracer 4215bn mppt controller any good or should I get a Midnite solar kid?
No way to compare a TOP quality, US made, highly engineered Midnite charge controlle with the bottom of the barrel MPPT China made controller. Its apples and, eh....lemons.

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Old 02-06-2015, 05:19 PM   #11
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Quote:
Originally Posted by RodK View Post
which panel has better specs for my purpose :

panel 1

Module Type: SPM200M-72
Maximum Power at STC(Pmax): 195Wp
Maximum Power Voltage(Vmp): 36.72V
Maximum Power Current(Imp): 5.45A
Open-circuit Voltage (Voc): 44V
Short-circuit Current (Isc): 5.50A
Cell Efficiency(%): 17.12


panel 2 :

Pmax : 150w
Voc : 22.32v
Vmp : 19.08v
Isc : 8.49a
Imp : 7.87a
cell efficiency 17.5%
There's really nothing to compare here. If using MPPT, both PV modules will work. What you should be looking at is the cell type, sorting tolerance and temperature coefficient at Vmp. If there is a significant difference in cost per Watt, just go for the lowest as a very small system like this will not reveal much difference.

Larry
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Old 02-06-2015, 05:33 PM   #12
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...Are flexible solar panels worth using or are they still too inefficient compared to the rigid panels.
Your asking a nonsensical question. Don't feel bad, most people that I talk to have the same misunderstanding. Efficiency has to do with how many square feet it take to convert the x amount of energy. It has nothing to do with how well a PV solar module performs. Example: Uni-Solar, one of the least efficient solar modules ever made is, to this day, the highest performance module. So sad they went broke.

Efficiency is how many Watts of power can you convert per square foot of cells. SunPower cells are the most efficient production cells commonly available. Many flexible modules are made from SunPower cells. The potential downside for flexible is the encasement of the cells may not last nearly as long as the low iron tempered glass used in framed modules.

Larry
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Old 02-06-2015, 05:34 PM   #13
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Quote:
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No way to compare a TOP quality, US made, highly engineered Midnite charge controlle with the bottom of the barrel MPPT China made controller. Its apples and, eh....lemons.

Larry
The tracer gets alot of good reviews on amazon and epsolar appears to be a well respected company unlike a lot of other chinese manufacturers . There is over $100 price difference between the 2 controllers .
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Old 02-06-2015, 05:44 PM   #14
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There's really nothing to compare here. If using MPPT, both PV modules will work. What you should be looking at is the cell type, sorting tolerance and temperature coefficient at Vmp. If there is a significant difference in cost per Watt, just go for the lowest as a very small system like this will not reveal much difference.

Larry
Using the kid sizing tool, it shows 7 more amps @14.4 v with the 200w higher voltage panels.
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