Inverter Sizing Suite
Avoid system crashes by calculating your peak simultaneous load. Ensure your inverter handles startup surges effectively.
Peak Load Analysis
Startup surge can be 3x-5x continuous rating.
Professional designers always size inverters at 120-125% of the total continuous load to prevent over-heating and efficiency loss.
The Sizing Formula
An inverter must handle both continuous load and sudden startup surges simultaneously.
Minimum Inverter Size
VA = max(Cont × 1.25, Surge Load) The 1.25 safety factor prevents overheating and ensures the inverter runs efficiently below its rated ceiling.
Motor Surge Rule of Thumb
Surge ≈ Continuous Rating × 3–5× Compressors, fridges, and pumps draw 3–5 times their running watts at startup. Always check the motor nameplate.
How to Size a Solar Inverter
An inverter converts DC power from your solar panels or battery bank into AC power that your appliances use. Choosing the right size is critical — an undersized inverter will trip under heavy loads, while an oversized one wastes money and runs inefficiently at partial load. The two key numbers you need are total continuous wattage and largest motor surge wattage.
Continuous vs. Surge Power
Continuous power is what your devices draw during normal operation. Surge (or peak) power is the brief spike that motors, compressors, and pumps demand at startup — often 3–5 times their running draw. Your inverter must handle the surge without shutting down, even if it only lasts a fraction of a second.
Step-by-Step Inverter Sizing
- List All Loads: Write down every appliance you'll run simultaneously. Include lights, fans, TVs, and any motors (fridge, pump, AC).
- Sum the Continuous Watts: Add up the running wattage of every device that could be on at the same time.
- Identify the Largest Motor: Find the appliance with the highest startup surge. This is usually a refrigerator compressor or water pump.
- Apply the 125% Rule: Multiply your continuous total by 1.25. This is the minimum continuous rating your inverter must meet.
- Take the Higher Value: Compare the 125% continuous result to your surge load. Your inverter rating must exceed whichever is larger.
- Select a Standard Size: Inverters come in standard sizes (1000VA, 1500VA, 2000VA, 3000VA, etc.). Always round up to the next standard size.
Off-Grid vs. Grid-Tie Inverters
- Off-Grid (Standalone): Converts battery DC to AC with no grid connection. Must be sized for your full peak load since there's no grid backup.
- Grid-Tie: Syncs with the utility grid and can export surplus power. Does not work during outages unless a battery backup is added.
- Hybrid: Combines both — charges batteries from solar, uses grid as backup, and can export excess. Most flexible but highest cost.