How to Size Your Inverter Correctly?
The inverter is the heavy lifter of your power setup. It converts DC power (from batteries or panels) to the 230V AC power your home needs. Choosing the wrong size is the most common mistake buyers make.
The Watts vs VA Confusion
You calculate your load in Watts (e.g., 3 Fans x 75W = 225W). But inverters are sold in VA (Volt-Ampere) ratings (e.g., 900 VA, 1500 VA). Why?
The answer is Power Factor (PF). Most AC appliances are not 100% efficient. They waste some energy as heat or magnetic fields. The typical Power Factor for a home is 0.8.
Formula: VA Rating = Total Load (Watts) ÷ Power Factor (0.8)
So, if your load is 800 Watts, you need 800 / 0.8 = 1000 VA (or 1 kVA) inverter.
Accounting for Surge Load (Starting Current)
Loads with motors (Refrigerators, Water Pumps, Washing Machines, ACs) behave differently. They need a massive jolt of power for 1-2 seconds just to start spinning. This is called "Surge Power" or "Inrush Current".
An old refrigerator might run at 150W but need 500W to start. If your inverter is sized exactly at 200W, it will trip immediately when the fridge compressor kicks in. Our calculator considers a safety margin for these scenarios.
Types of Solar Inverters
- Off-Grid Inverter (PCU): Has a solar charge controller inside. It charges batteries from solar and grid, and powers your load during cuts.
- On-Grid (String) Inverter: Syncs with the grid. Has NO battery. If grid fails, this inverter shuts down (anti-islanding safety).
- Hybrid Inverter: The best of both worlds. Works with net metering AND charges batteries for backup.
Conclusion
Always buy an inverter with 20-25% extra capacity than your calculated need. This future-proofs you for adding that extra fan or computer later without upgrading the entire unit.