Renewable Energy Battery Sizing Calculator

Welcome to the Trojan Battery Renewable Energy Sizing Calculator. This calculator is a tool to help you determine the model and quantity of Trojan batteries needed for your renewable energy or backup power system. The calculator recommends batteries based on your inputs and the results are ranked according to cycle life performance.

Step 1

Please Select Your System Design Parameters

System Loads and Battery Capacity Requirements

Values below will change as you enter system parameters and load estimates.
Battery watt-hours per day for AC loads
(including 15% AC inverter loss)
Battery watt-hours per day for DC loads Wh/day
Total battery watt-hours per day
(assuming 97% wiring and distribution efficiency)
Avg daily battery amp-hours needed
(with V battery system )
Amp-hours (@V)
Required system capacity*
(based on desired % DOD) to achieve  days of Autonomy.
Amp-Hours (@V)

DOD describes how much of the total amp-hour capacity is used during a discharge cycle and is expressed as a percentage of its rated capacity (Select 40% as the DOD if you wish to take no more than 40Ah from a battery rated at 100Ah)
Max DOD for off-grid systems is 50%. This value was automatically lowered to 50% when you switched to "Off-Grid".

This is the number of days the battery has to power the designated loads (Select 2 days if you want to power your loads for the desired durations over 2 days)
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Step 2

Please Enter Your Average Daily Load Estimates

AC Load Description DC Load?
(uses AC load unless checked)
Quantity Hours Per Day Watts Total Watt-Hours Per Day* Total Battery Energy Consumed Remove Item
Wh Wh
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Step 3

Recommended Trojan Battery System Design Configurations — Values below will change as you enter parameters and estimates in Step 1 and Step 2

Please enter load requirements above to generate results.
Be sure you have entered all required parameters in steps one and two above.

You are currently missing the following parameter(s):

Step 1:
  • Battery system voltage.
  • Desired depth-of-discharge (DOD).
  • Type of battery.
  • Desired days of autonomy.
Step 2:
  • At least one average daily load estimate.

We are unable to recommend a Trojan solution based on your current system design inputs. Please review the values you entered for system parameters in step 1 and load estimates in step 2 to be sure they are accurate. For support using the online calculator contact Trojan Battery Company at
Note: If you are designing an off grid SMA Sunny Island contact Trojan for additional information on how to calculate your power requirements to obtain accurate results using this calculator.

Please note that the recommended battery configurations can be organized according to any of the design values in the table by clicking on the design variable shown in the column header.
Individual Battery System Design
Battery Trojan Model Number /
Product Line /
Individual Battery Voltage Ah Capacity @ 20 Hour Rate Number of Batteries in Series Number of Strings in Parallel Total Number of Batteries System Voltage Ah Capacity @ 20 Hour Rate Calculated
Cycle Life
Battery Model / /  years %