08-09-2021, 05:36 PM
You just answered the $64,000 question!
How much solar do I need? Enough to replace the power that you use. This goes even for lithium that does not have to be charged back to 100% all of the time. Do not cover your needs and eventually you will simply run out of power without a alternate source of charging.
First you figure it out on a daily basis and then consider how many days that you may be without sunshine within the limitations of your roof. Then you consider the resistance of your battery bank. A small array on a big bank drawn down will get hung up around 13.1 volts because it can't overcome the resistance of the batteries being charged. I can't speak for lithium but it is true for marine, AGM and especially 6 volt banks which have the most resistance of all.
A member on another forum was the first I heard mention the 1 watt per Ah of battery rule of thumb. It's become a given except the rest of the formula is that is what you need to equalize a battery at 77 degrees. The formula should be 2 watts per Ah or 1 watt per usable Ah at the least.
How much solar do I need? Enough to replace the power that you use. This goes even for lithium that does not have to be charged back to 100% all of the time. Do not cover your needs and eventually you will simply run out of power without a alternate source of charging.
First you figure it out on a daily basis and then consider how many days that you may be without sunshine within the limitations of your roof. Then you consider the resistance of your battery bank. A small array on a big bank drawn down will get hung up around 13.1 volts because it can't overcome the resistance of the batteries being charged. I can't speak for lithium but it is true for marine, AGM and especially 6 volt banks which have the most resistance of all.
A member on another forum was the first I heard mention the 1 watt per Ah of battery rule of thumb. It's become a given except the rest of the formula is that is what you need to equalize a battery at 77 degrees. The formula should be 2 watts per Ah or 1 watt per usable Ah at the least.
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