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How many watts of solar can a 20amp mppt charge control handle?

Joined
Sep 29, 2019
Messages
34
Location
Martha's Vineyard
Hi everyone,

Over the last little bit, I have collected all (or most), of the parts for a small solar system in my van. I was aiming somewhere between Will's minimalist and classic 400 blueprint. I have an Astro van- so space is limited, and my solar panels will be stored inside the back of the van.

Items I have ready to go are:

2 - 80 watt glass poly solar panels (purchased years ago and they have been sitting in my closet)
2 - 100ah AGM batteries (I figured if one was good, two was better)
Battery monitor
20 amp MPPT charger (purchased based on my solar panels, and not expecting the ability to upgrade so soon)
2000 watt inverter
Fuse block
200amp fuse and holder
Tools and most of the wires (locally sourced), to put it all together.
In addition, a smart battery isolator is being installed in my van- although, right now I drive less than an hour a day.

I don't have:

a bus bar
50 amp breaker, or
pair of branch connectors for the solar panels.

I came into a tiny windfall that means I have a chance to add to my solar, but I am not sure which option (below), would be the wisest choice. My main questions are:

1. I remember reading that mppt charge controllers can handle double the wattage they are rated for. But, is that is true for all mppt charge controllers? If yes, then that means my charge controller's stated rating of 12v/260 watts can be doubled to 12v/520 watts? and,

2. I know this is a loaded question and, is based on many factors but, what would be a reasonable (common sense) amount of solar be to keep 2-100ah batteries charged? i.e.) 50 watts of solar isn't going to reasonably charge 200ah; But would 260-watts? 360-watts? 460-watts be reasonable to charge the batteries?

Answers to the above two questions would help me figure out which option listed below would be the best purchase to make. These are my options:

A. 4-100 poly watt panels (560 watts total)- charge controller rated for 12v/260 (12v/520?);

B. 3-100 poly watt panels (460 watts total) - 20 amp CC rated 12v/260 (12v/520?);

C. 3-100 poly watt panels (460 watts total); a bus bar; a 50amp breaker; pair of branch connectors and attempt to exchange my 20 amp mppt for a 40 amp one;

D. 2-100 poly watt panels (360 watts total) - keep CC rated for 12v/260 (12v/520?);

E. 2-100 poly watt panels (360 watts total); a bus bar; a 50amp breaker; pair of branch connectors and attempt to exchange my 20 amp mppt for a 30 amp one;

F. 1-100 poly watt panels - giving me 260 watts of solar - keep CC rated for 12v/260 (12v/520?);

Thanks,

Clyn

Edited to remove text I forgot to remove.
 
Last edited:
You can plug any in and lose a few amps. My 390w usually does about 19a. Ive seen 20a on low battery. Id say the 360w would be best without wasting anything.
 
Hi Ped,

Thank you for responding, and giving me some figures to see what you're using. So, basically your are say to go with either option C or D. But that I could (safely) get away with option D?

C. 3-100 poly watt panels (460 watts total); a bus bar; a 50amp breaker; pair of branch connectors and attempt to exchange my 20 amp mppt for a 40 amp one;

D. 2-100 poly watt panels (360 watts total) - keep CC rated for 12v/260 (12v/520?);

Thanks,

Clyn
 
Yes. Remember you can have 2 controllers if that makes more $$ sense.
 
I ordered my solar panels today, and expect them to arrive tomorrow. I read the back of my solar panels and made sure the new ones are within 10% of both the VOC and VMP, so they would work well together.

I want to have a solid understanding of what I am doing to prevent any incidences- now or in the future, so I have a couple of more questions....

Since 360 watts of solar is above Will's recommended 100-200 watts for the minimalist blueprint, but below the 400 watts in his classic blueprint- do I need to add a circuit breaker between the solar charge controller and the battery, on the positive wire, and a bus bar? And, should I wire the solar panels based on the Minimalist Blueprint, or in series groups (Classic Blueprint)?

Thanks,

Clyn
 
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