How To Size Your Inverter and Battery Bank



If you are planning to design for a standalone home solar power system, the most crucial thing you need to take into account is the battery bank and the inverter. We need to make sure all the DC energy that can be stored into our battery bank. By wiring to the inverter where the DC electricity is converted to AC (alternating current) electricity.


Step 1: Determine the peak load or Maximum Watts usages

How to calculate Home appliances’ total wattage usage needed:

Step 1: List out all the home appliances or devices’ load power in watts that consume in daily use
( total hours per day )

Note : Some appliances may take more than its rated power at start-up.

Step 2 : Multiply the wattage of each devise by its run-time to get the energy in watt-hours per day.
Step 3 : Add up all values to get a total watt-hour
Step 4: Multiply by a value of 1.5 in order to get a rough idea of the real value with system loses caused by temperature increases.

Example :

Total watts consumes :
Use 2 units of Fluorescent lights 40w and a TV 21” 60w :
40w x 2 + 60w = 140watts

Daily Power consumption ( watt-hour):
Run Fluorescent lights for 6 hours /day , TV runs for 2 hours/day :

Total watts consumption : 80w x 6hrs + 60w x 2hrs = 600watt-hours
600 x 1.5 = 900 watt-hours


Step 2 : Determine No.of Days of Power Storage

Decide how many days you plan you can store your extra energy power for back up purpose. Generally can be 2-5 days depending your power system design.


Step 3: Determine Battery Bank Capacity

At this step, we can calculate the minimum battery AH capacity. You can take the watt-hours per day and multiply by the number of days you decided and again multiply by 2 (cos estimate a 50% depth of discharge on your batteries). Finally we need to convert the kwh result into Amp-Hours(AH) by dividing with battery voltage.

Example :
from step 1, we have a total of 900watt-hours /0.9kwh per day
from step 2 , we need at least 3 days without recharging on the battery bank

Total capacity of Battery bank needed : 0.9 x 3 x 2 = 5.4kwh

To convert the value into AH, we need to divide by your system voltage ( 12,24 or 48) ;
if you design to use 24v, the minimum AH capacity is : 5400/24= 225 AH.


Step 4: Battery bank Wiring – Final Step

Lastly if you divide by your battery’ rating, you will find the number of batteries that you sure use. This will we a crucial part of the power system. There are 2 methods of wiring in a circuit – parallel and series.
As you can see from the diagrams, we can notice that in a parallel circuit the battery voltage remain the same but the current adds up; but on the other hand, voltage in series circuit will adds up, but current remain the same. You can eventually design and combine your battery wiring in series and parallel circuit that you require.


Battery wiring design plays an important part in your power system. A good wiring configurations can boost up your energy power performances to meet up with your voltage and AH requirements. So do always design and plan ahead before buying the right size inverter and batteries for your home power system.

For more info on battery wiring, you can read more at HERE