How many batteries do I need for a 3kVA inverter
You are here because you want to know how many batteries have sufficient capacity to meet the recommended standard to operate a 3kVA inverter.
When calculating the number of required batteries for 3kva inverter one must know output power (watts), inverter efficiency, input voltage, battery type, and runtime (C-Rate).
Short Answer:- Lead-acid battery: You will need to connect four 24V 200Ah batteries in parallel.
- Lithium Battery: You will need to connect two 24V 200Ah batteries in parallel.
Let me explain the steps taken to reach these values:
How many batteries for a 3kVA inverter
Step #1 Determine how many Amps does a 3kVA inverter draw
The current does a 3kva inverter draw from the battery depends on the output REAL power of the inverter in watts, the system voltage (12V, 24V, or 48V), and the inverter efficiency.
- Look for the rated power output in watts (P).
- The 3kVA inverters are usually 24V units, but there are also 3kVA inverters that accept 12V, or even 48V.
- Look for the energy efficiency of the power inverter.
In order to calculate battery current draw (IBat ), we use the following formula:
IBat (A) = P (W) ÷ [Inverter Efficiency (%) × Battery Voltage (V)]
Suppose we have a solar inverter 3kVA 2.4kW 24V efficiency of ~ 90%.
In that case, our 3kVA inverter will draw from the battery:
IBat (A) = 2400W ÷ [0.90 × 24V] = 111 Amps
Thus, a 3kVA 2.4W inverter will draw a current of 111A from the battery.
Example 2:Suppose we have a solar inverter 3kVA 3kW 24V efficiency of ~ 90%.
In that case, our 3kVA inverter will draw from the battery:
IBat (A) = 3000W ÷ [0.90 × 24V] = 139 Amps
Thus, a 3kVA 3kW inverter will draw a current of 139 A from the battery.
Step #2 Determine C-Rate (or runtime)
The C-rate is a measure of a battery's ability to withstand discharge and charge currents. The discharge C-rate expresses the discharge current that the battery can deliver to the inverter relative to its nominal capacity, or in other words, how fast we can discharge the battery.
For example, if you have a 200Ah battery and you discharge it at a C-rate of 1, then it delivers a current of 200 amps (200Ah × 1). If the C-rate is 0.5, then it delivers a current of 100 amps (200Ah × 0.5), and so on.
There are two types of deep cycle batteries - lead-acid batteries and lithium (LiFePO4) batteries, each one with its own recommended C-rate.
- Lead-acid C-rate: 0.2C
- Lithium C-rate: 1C for one hour runtime or 0.5C for 2 hours runtime
For lead-acid batteries, the nominal capacity is the battery capacity measured when the battery is discharged at its recommended C-rate, for example, 0.05C (20 hour rate), or 0.1C (10 hour rate).
When the batteries are being discharged with strong currents (faster), for example, 1C, this will result in a loss of capacity of up to 55-70% of the battery's nominal capacity. This means that while a lithium battery can last an hour when discharged at 1C, a lead-acid battery will only last between 20-33 minute.
However, we can use a C-rate of 0.2, assuming that the inverter does not usually run at full capacity all the time.
For lithium batteries, you can use a discharge rate of 1 without the battery suffering from capacity loss, or at least not as much lead-acid batteries.
Step #3 Determine the number of required batteries
Number of required batteries = Current Draw (A) ÷ [C-rate × Single Battery Capacity (Ah)]
How many 200Ah batteries for 3kVA inverter
Short Answer:
|
System Voltage
|
Lead-acid |
Lithium
|
||||
|---|---|---|---|---|---|---|
| 12V | 24V | 48V | 12V | 24V | 48V | |
| Number of 200Ah batteries for 3kVA inverter | 7 | 4 | 2 | 2 | 2 | 1 |
We can see that for the 3kVA 3kW 24V inverter you will need 2 24V-200Ah lithium batteries, or 4 12V-200Ah lithium batteries, or any combination as long as the battery bank capacity is not less than 9.6 kWh (2×24V×200Ah).
Let me explain how these values are calculated:
Lead-acid Batteries
Number of required batteries = Current Draw (A) ÷ [0.2C × 200 Ah]
- Lead-acid C-rate of 0.2C
- Single Battery Capacity: 200 Ah
-
For 12V inverter
A 3kVA 3000W 12V inverter will draw a current of 277A from the battery.
Number of required batteries = 277 A ÷ [0.2C × 200 Ah] = 7 Batteries
Thus, 7 pcs 12V-200Ah lead-acid battery is the smallest battery bank recommended for the 3kVA 3kW 12V inverter.
- For 24V inverter
A 3kVA 3000W 24V inverter will draw a current of 139A from the battery.
N batteries = 139 A ÷ [0.2C × 200 Ah] = 3.4 ~ 4 Batteries
Thus, 4 pcs 24V-200Ah or 8 pcs 12V-200Ah lead-acid battery is the smallest battery bank recommended for the 3kVA 3kW 24V inverter.
- For 48V inverter
A 3kVA 3000W 48V inverter will draw a current of 70A from the battery.
N batteries = 70 A ÷ [0.2C × 200 Ah] = 1.7 ~ 2 Batteries
Thus, 2 pcs 48V-200Ah or 4 pcs 24V-200Ah or 8 pcs 12V-200Ah lead-acid battery is the smallest battery bank recommended for the 3kVA 3kW 48V inverter.
Lithium (LiFePO4) Batteries
Number of required batteries = Current Draw (A) ÷ [1C × 200 Ah]
- Lithium (LiFePO4) C-rate of 1C (for 1 hour runtime)
- Single Battery Capacity: 200 Ah
- For 12V inverter
A 3kVA 3000W 12V inverter will draw a current of 277A from the battery.
Number of required batteries = 277 A ÷ [1C × 200 Ah] = 1.7 ~ 2 BatteriesThus, 2 pcs 12V-200Ah lithium battery is the smallest battery bank recommended for the 3kVA 3kW 12V inverter.
- For 24V inverter
A 3kVA 3000W 24V inverter will draw a current of 139A from the battery.
Number of required batteries = 139 A ÷ [1C × 200 Ah] = 0.6 ~ 1 Battery
Thus, a 24V-200Ah or 2 pcs 12V-200Ah lithium battery is the smallest battery bank recommended for the 3kVA 3kW 24V inverter.
- For 48V inverter
A 3kVA 3000W 48V inverter will draw a current of 70A from the
battery.
Number of required batteries = 70 A ÷ [1C × 200 Ah] = 0.3 ~ 1 Battery
Thus, a 48V-200Ah or 2 pcs 24V-200Ah or 4 pcs 12V-200Ah lithium battery is the smallest battery bank recommended for the 3kVA 3kW 48V inverter.
How many 100Ah batteries for 3kVA inverter
By applying the same formula as follows:
Number of required batteries = Current Draw (A) ÷ [C-rate × 100 Ah]
We can calculate the minimum number of 100Ah batteries that meet the recommended C-rate to run a 3kVA inverter.
|
System Voltage
|
Lead-acid |
Lithium
|
||||
|---|---|---|---|---|---|---|
| 12V | 24V | 48V | 12V | 24V | 48V | |
| Number of 100Ah batteries for 3kVA inverter | 14 | 7 | 4 | 3 | 2 | 1 |
How Long Will A 3kVA Inverter Run?
Assuming that the inverter operates at full capacity all the time, the battery capacity can be calculated as follows:
Battery Capacity (Ah) = Current Draw (A) ÷ C-rate
For lead-acid batteries with a C-rate of 0.2, the expected runtime can be around 5 hours before the batteries are completely depleted.
Considering the Depth of Discharge (DOD), which should not exceed 50%
for lead-acid batteries, only half of the capacity should be used.
Therefore, the actual runtime would be around 2.5 hours.
For lithium batteries with a C-rate of 1, the expected runtime is
around 1 hour before the batteries are completely depleted.
You can increase the size of your battery bank to store enough energy.
Conclusion
The calculated values represent the minimum number of batteries that meet the recommended standard for C-rate, allowing a 3kVA inverter to draw current from them without stressing the batteries with a high current draw or charging them with a high current if the inverter is a multi-function (integrate inverter function, solar charge controller and AC charger).
Having a fewer batteries will still work, but remember to maximize the lifespan of your batteries, you need to consider its recommended C-rate (or hour rate).
Mohamed Bellamine
I'm the blogger behind Goo SolarPower. As a solar engineer, and a strong supporter of renewable energy. I've always been interested in Solar devices. I loves to write articles, guides, and tutorials about solar PV technology. Through goosolarpower.com I want to help people build and understand how solar power systems work.