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Hi Genesis, How are your 4 6v batteries arranged to give you 1200ah? As it is a 12v system, if you have 2 parallel pairs of 2 x 6v in series, then you would actually have a 600ah battery bank. You don't say whether the batteries are LiFePO4, AGM or something else, this will greatly affect the usable AH from the battery bank and how important it will be to keep the batteries topped up to 100% SOC. You also need to make an estimation of your daily energy usage. Given all that, the rule of thumb that I was given is number of amp hours you want to put into your batteries x 4 = solar wattage. So if you need to put in 100ah per day to your batteries you should aim for 400w of solar. This is a very rough guide and will depend heavily on how sunny it is where you will be sailing. If the panels are on your bimini you need to think about affect of shading from your boom. I would make sure panels are arranged so separate panels are on either side of the boom and use two separate MPPT charge controllers, one for port and the other for starboard.

Thank you, for your answer (gone-sailing) I just started to understand a little bit more about how the batteries are connected and what type of Ah i have to store. So I went back to the boat and took measurements of the Bimini, I'd noticed that the boom does not reach or cover the Bimini area so I think I can put at least 3 or 4 solar panels up there with no shade. Now, if I have 600Ah of battery bank, ohh and by the way, the batteries are AMG Lifeline GLP-6CT. How many watts I need on the panels to charge the batteries, and now here comes a few more questions, Do you recommend to have 2 separate MPPT solar controllers or just one, and also what type of solar panels (rigid or Flexible) I'll be in Puerto Vallarta, Mexico and I think it is sunny most of the time. I really appreciate you for taking the time to hear me out and clarified all my questions, I'm new to this so any suggestions are very much welcome. thank you

Hi Genesis, The big question is how much power do you expect to use in a day. Only you will know that :-) If you regularly consume 100ah in a day then realistically you would only need enough solar to put that 100ah back into the batteries. Based on the rule of thumb I gave earlier then 400w of solar would be the target to go for. Worst case scenario would be you reduce the batteries to a their minimum (probably around 40-50% of available Ah for AGMs) in which case you would need to generate about 360Ah, so 1.4kw of solar. In reality your main constraining factor is the surface area of your Bimini on which to fit panels. Take a look at Victron and Renogy panels as examples and work out what combination (like a jigsaw) fills the space the best. To give you a very rough idea, 160w rigid panels are roughly 1.5m x .6m but every make and model varies somewhat. Flexible panels are considerably more expensive but lighter. Rigid panels are heavier but tend to come in larger sizes and produce more watts. Which you go for will depend on how big and strong your Bimini is. Many people who want big rigid panels fit a stainless steel solar arch to the back of the boat to carry the weight of 2 or more rigid solar panels.

Pardon my ignorance, but if I have 600Ah of storage power why not to try to keep the batteries top off all the time if they are not in use, solar power is free (right?) or is it bad for the batteries to keep them top off, I just don't know enough about this subject, I was just thinking like a gas tank in a car, why not keep it fill up if you are getting the fuel for free, that's my take, but you can explain to me and to all of us that have this same question, I repeat myself I'm very ignorant with this subject. Thanks again for taking the time to explain and share your knowledge. You're AWSOME!!!!!!

Genesis, with AGMs you should definitely aim to maintain a 100% state of charge to prolong their life. The limitation you have is physical space on a boat. If you wanted to regularly generate 600ah you would need roughly 2400w of solar panels (based on the rule of thumb). That’s the equivalent of 15 rigid 160w panels. I don’t know how big or strong your Bimini is but I would be surprised if it could take 15 panels. Obviously there are different size panels and flexible panels are lighter but I doubt you have enough space to generate that amount of power. So you have to work out based on what space you have what is the maximum Ah you can expect to generate. If that doesn’t cover your daily energy consumption (fridge + freezer + lights + audio + navigation instruments + inverter etc) then you might want to think about how else you might generate enough power to cover your needs.