Inverter battery capacity calculation is vital for designing a solar power system. To calculate the correct size for your inverters, you will need to know how long it takes an inverter to recharge from its discharge state or vice versa.
It’s also crucial to understand the difference between kW and kWh, as this will change your calculations. This article provides some helpful tips on calculating battery capacity for your inverters.
How to Calculate Battery Capacity for Inverter
Inverter Battery Capacity Formula
Inverter Battery Capacity Calculator calculates the battery capacity required for your inverters. Enter all known values below and press calculate to get the results.
- Battery Capacity (Ah) = Battery Voltage (V) x Total System Power in Watts / Maximum Discharge Current of the Inverter or Maximum Charge Current of the Inverter
- Battery Voltage (V) = System Power in Watts / Discharge or Charge Current of the Inverter (Amps)
- Maximum Discharge Current of the Inverter (A) = Watts / Voltage
- Maximum Charge Current of the Inverter (A) = Battery Capacity Required for a Solar Inverter with DC Coupled Battery Charger is the total battery capacity required by the solar inverter.
- Solar Inverter with DC Coupled Battery Charger (Watts) = System Power in Watts / Maximum Discharge Current of the Inverter.
Related Read: Charging 12v battery with inverter
Ways to Calculate the Battery Capacity Required for Inverters
There are different methods to calculate the battery capacity needed by an inverter.
1. Calculate the Load in Watts
To calculate the load in watts, you will need to know the wattage of the devices you want to power. You can find this information on the device’s label or the manufacturer’s website.
Once you have this information, add up the wattages of all the devices you want to power. This will give you the total load in watts.
For example, if you have a refrigerator that consumes 200 watts, a TV that consumes 300 watts, and a light bulb that consumes 60 watts, the total load would be 560 watts.
Once you have the total load, use this formula: Battery Capacity (Ah) = System Power in Watts / Maximum Discharge Current of the Inverter.
The battery capacity required in this case is 560 watts / 30 amps = 18.33 amp-hours.
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2. Calculate Battery Capacity in Amps
To calculate battery capacity in amps, you will need to know the battery’s amp hour rating.
The amp hour rating of a deep cycle lead-acid battery is determined by multiplying its nominal voltage (for example, 12 volts) by its amp hour rating (for example, 100).
Battery Capacity in Amps = Battery Voltage x Amp Hour Rating
For this example, you would have to multiply 12 volts x 100 amp hours = 1200 amps.
3. Calculate Battery Capacity in Hours
To calculate battery capacity in hours, you will need to know the battery’s watt-hour rating. The watt-hour rating is determined by multiplying the battery’s voltage (in volts) by the amp-hour rating of the battery (in amps).
4. kWh vs. kW
It’s essential to understand the difference between kWh and kW when calculating battery capacity. A kilowatt-hour equals 1000 watts of energy being used for one hour.
Alternatively, a kilowatt-hour can be considered the amount of energy used to light a 100-watt bulb for ten hours. A kilowatt is equal to 1000 watts.
kWh = Watts (100-watt bulb for ten hours)
kW = Watts (1000 watts of energy used for one hour)
If you are unsure which to use, it is best to use kWh when calculating battery capacity.
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Battery Capacity for Inverters
Now that you understand the different ways to calculate battery capacity, it’s time to put this information into practice.
For example, you want to power a refrigerator that consumes 200 watts and has an amp hour rating of 100. You will need to do the following:
- Calculate the load in watts: 200 watts
- Convert amps to watt-hours by multiplying amps by hours: 100 amps * 100 hours = 10000 watts-hours
- Convert watt-hours to kWh by dividing the total watt-hours by 1000: 10000 watts-hours / 1000 =
- The battery capacity required for this inverter is: 11 kWh
When sizing a battery bank, it’s important to remember that you will need to round up the battery capacity required by the inverter. In this example, the battery bank would need to be 12 kWh.
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Frequently Asked Questions about Inverter Battery Capacity
What Size Inverter Do I Need for a 100ah Battery?
The size inverter you need for a 100ah battery would be a 0.8 kVA inverter. This inverter can deliver 650 w(appx.) for continuously two hours.
What Is the Difference Between kW and kWh?
A kilowatt-hour equals 1000 watts of energy being used for one hour, or equivalently it’s the amount of energy used to light a 100-watt bulb for ten hours. A kilowatt is equal to 1000 watts.
kWh = Watts (100-watt bulb for ten hours)
kW = Watts (1000 watt of energy used for one hour)
If you are unsure which to use, it’s best to use kWh when calculating battery capacity.
How Much Battery Capacity Should I Have in My Off-grid System?
The amount of battery capacity you need in your off-grid system will vary depending on the size of your inverter, the number of appliances you are using, and how often those appliances are being used.
A good rule of thumb is to have at least 20% more battery capacity than the inverter requires.
What battery capacity is required for a refrigerator that consumes 200 watts and has an amp hour rating of 100?
The battery capacity required in this case is 560 watts / 30 amps = 18.33 amp-hours. To calculate battery capacity in hours, you will need to know the battery’s watt-hour rating. The watt-hour rating is determined by multiplying the battery’s voltage (in volts) by the amp-hour rating of the battery (in amps).
The battery capacity for this inverter would be: 18.33 ah * 12 volts = 220.96 watt hours / 1000 = .22 kWh
There are different ways how to calculate battery capacity for inverter. Whichever way you choose, make sure you have a battery bank equal to or larger than the calculated capacity.
Rounding up is always a good idea to be safe. You can confidently choose the right battery bank for your inverter with this information. Check out our website for more informative articles.
