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I'm in the process of designing a solar system to power an Engel refrigerator/freezer and keep a Group 27 battery (also used to power occasionally used inverter) charged.

I've decided on a 140W panel and am thinking of mounting it - independent of my bimini - on a vertical, twin pole platform that is about 1' aft of the stern pulpit.

The size of the panel is about 51 x 27. I was planning on mounting the framework to a piece of 1/4 or 1/2" starboard with on inverted deck flange at each end and then mounting the Z-brackets that come with the panel to the starboard.

The mount would be 7/8" stainless with the two vertical poles tied together with a horizontal brace.

Questions:

  1. Is the starboard desirable for having a rigid mount or should I just attach the solar panel to horizontal runs of tubing?
  2. Is it desirable to have whatever mount I use adjustable or is completely flat acceptable?

Murph

S/V Amalia
1965 Cal 30
Muskegon, MI
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.
 
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