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islander bahama 24
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Myself I would split the panel output between two panels so in the event of a problem or shading I still have at least half of the total output available at any one time at the same time it splits the base loading on the mounting to two separate locations something like this would work great Complete Kit 200 Watt 200W Poly Solar Panel 12V 24V Battery RV Boat Off Grid | eBay however as many have stated I agree a bigger battery would be bettsr
 

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islander bahama 24
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1,842 Posts
OK I have a serious question for you after seeing your real world data with a 420 ah flooded lead acid bank and the 2 100 watt panels running a cool blue holding plate system 24/7and approximately 25 watts led lighting for about 3 hrs a day would it pay to spend the additional moneys on the mppt controller or should I spend it on a third 100 watt panel?
 

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islander bahama 24
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1,842 Posts
What you don't say is how you plan to use this?

*Are you at a dock all week and just want support when out cruising?

*Are you on a mooring and want the fridge to run 24/7?

How you use it is critical because it determines how you design...

I have a customer doing exactly what you want to do but he is a mooring 24/7 guy who wanted to run his Engel... 1 Kyocera 140W panel, with MPPT controller, was not enough when weather went sour... He also has 450Ah's of battery bank as reserve. He often came back to a deficit, not good for the batteries...

I added a second 140W panel and it works perfectly and he has excess to recharge the bank. Remember the 5 hour number is prime conditions and geography determined. It also changes by month and insolation... You can easily have rainy or overcast days/weeks that will result in a 140W panel producing as little as 14 Ah's over an entire day (See Day 1 below). His Engel burns about 30-35 Ah's per day, in Maine. (real world measured/data logged numbers, not marketing)...

I did some data collection / tracking last spring comparing two identical 140W panels, one with MPPT and one with PWM, and allowing the weather to do what it wanted.

The reality was that the PWM controlled 140W panel put out 182 Ah's for an entire 7 day period or an average of 26Ah's per day or 3 hours at full 25C output. The MPPT controller did 220 Ah's or approx 34 Ah's per day or 4 hours at full rated 25C output. Weather is real and needs to be accounted for. These panels can easily do 5+ hours per day but it needs the weather window to do that..

However you would not likely see that type of MPPT gain with a single G-27 battery as it would spend much of its time in absorption when the fridge was not running so MPPT would benefit you little........

The bottom line is when designing a system you design for worst case not the best case, which is what folks tend to do...

Here is the data:


NOTE: The data here can not be easily translated to lead acid because LiFePO4 stays in bulk until about 99.5% SOC with this type of current. MPPT controllers can only "boost" in bulk mode. Unless you had a massive lead acid bank the MPPT gains you see where would be less.
I have a question what do you mean by a massive lead acid bank mine is just over 400 ah and honestly don't expect to use more than 50 or 60 ah per day with 200 watts solar is it worth the expense of a mppt controller the pwm comes with the panels
 

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islander bahama 24
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1,842 Posts
Personally I like the 12 volt 50 amp3 bank marine charger on the boat ( old centaur unit)
I am going out on a limb here but it may be that he actually has a 3 bank 12 volt charger and miss reading as a total of 36 volt charger not three bank 12 volt
 
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