Calculating possible load for existing system

[h_1985]

Hello,

I'm testing a simple off grid system already all its components exists, i connected them and now i'n trying to find suitable load to run for 12 hours/day

i used this equation to calculate proper load for this system as coming:

Battery (AH)=(Total watt-hour per day used by loads)/(battery efficiency ×depth of discharge ×battery voltage)

I have 2 batteris in series each 12V 200 Ah

i have c-ratings for battery C100= 200 Ah C20 = 180 Ah C5 = 135 Ah

i will take the C20

i assumed battery efficiency 75 % (not found in data sheet)

and Max. Depth of discharge 50 % (not found in data sheet)

180= (Total watt-hour per day used by loads)/(0.75 × 0.5 ×24)

∴ Total watt-hour per day used by loads = 1620 wh

divide by 12 hours

∴ load power = 1620 / 12 = 135 watt



this method is right or i can use another method??

any help

[SunEagle]

That 1620 wh daily load could be made up of a number of single loads running for different lengths of time. Deciding it will only be one load of 135 watts for 12 hours could be misleading.

Your battery system is based on dividing that daily wh load by the battery voltage x a factor depending on the type of battery or length of time you want to have in reserve. Most batteries provide a cycle count based on the % of discharge.

That % could be between 20 and 25% for an FLA type battery but could be more for a Li type.

So for your battery system of 2 x 12v 180Ah rated wired in series, the total watt hour ~ 24volt x 180Ah = 4320 watt hour.

If you only use 1/5 of that or a 20% DOD then you get ~ 864 watt hours which is about 1/2 of that 1620 watt hour calculation. Draining a battery by 50% daily will shorten it's life.

So IMO you need to increase your battery system to be twice as big as you already have.