max battery for 50w panel

2680

ok, i know your first response will be i am doing this backwards, but i understand that and have a plan in mind.

if i have a 50w mono panel, and am in the cincinnati area, what size battery (12v) would be appropriate for daily usage.

meaning, how much charge would i be able to get from this setup assuming 50% discharge max per day?

thanks!

westbranch

Re: max battery for 50w panel

What are the specs on that 50w panel?

they will give you the answer based on the charge rate you desire. 3%, 5%, 10%? and the number of days autonomy you want

2680

Re: max battery for 50w panel

specs: Maximum Power Voltage: 17.5V; Open Circuit Voltage: 22V; Maximum Power Current: 2.86A

average sun hours here is 3.8 or so. so if i want to use 50% of the battery each night, and charged back full each day, what mah would i need?

westbranch

Re: max battery for 50w panel

Most battery manufacturers advise that you need at least 110% - 120% of the consumed power to recharge a FLA battery.

Using 4 hours sunlight and 2.86A you would generate ~11 Ahr, which at 50% DoD will allow you to recharge a ~15 Ahr battery as there is a ~ 70% efficiency de-rating factor to apply...

NOTE: these are very general, approximate numbers
YMMV

HTH

2680

Re: max battery for 50w panel

perfect! that's exactly the info i was looking for!

THANKS!

inetdog

Re: max battery for 50w panel

The other rule of thumb to be satisfied is that the panel should be capable of delivering current to the battery at the C/10 rate for flooded and higher for sealed.
Applying that rule gives us a maximum battery size of about 25 AH, even if you want to go larger than westbranch's calculation to get more cycles out of the battery.
Using your number of 50% discharge, sets the size based on panel energy, but the real determiner there should be how many watt-hours you want to use, independent of battery size.