07/01/2026
How to Calculate Peak Load to Know the Right Inverter Size
One common mistake in solar is this:
Let me just buy a big inverter so it can carry everything.
That approach wastes money and can damage batteries.
The right way is to calculate your peak load.
The Simple Technical Truth
Peak load is the maximum power your appliances can demand at the same time.
Inverter size is based on:
• Total running watts
• Starting (surge) watts
• Nature of the loads (motor or electronics)
If the inverter cannot handle the peak load,
it will trip or fail.
Step 1: List All Appliances You Want to Power
Write down:
• Appliance name
• Power rating (watts)
• Quantity
Example:
• TV – 150W × 1
• Fan – 120W × 2
• Fridge – 600W × 1
• Lights – 200W
Step 2: Add All Running Watts
Total running load:
150 + (120 × 2) + 600 + 200
= 1,190W
This is your continuous load.
Step 3: Identify Appliances with Starting Surge
Some appliances need extra power to start:
• Fridge
• Freezer
• Pump
• Air conditioner
A fridge rated at 600W may need:
• 1,200–1,800W for a few seconds at startup
That surge must be included.
Step 4: Calculate Peak Load
Peak load =
• Total running watts
+
• Highest starting surge
In this example:
1,190W + 1,200W surge
≈ 2,390W peak load
Step 5: Add Safety Margin
Always add 20–30% headroom:
2,390W × 1.3 ≈ 3,100W
So you need an inverter of at least:
• 3kW (or about 4kVA, depending on power factor)
Now Let Me Explain It the Way I Explained to Mama Debo
Mama Debo asked:
Engineer, why my inverter dey off when fridge start?
I asked her:
“Mama, if everybody stand up same time inside small bus, wetin go happen?”
She laughed and said:
The bus go shake!
I told her:
That shaking moment is peak load.
The inverter must survive that moment -
not just normal running.
She smiled and said:
So inverter size na for worst moment?
Exactly, Mama 😄
What You Should NOT Do
❌ Don’t size inverter by guess
❌ Don’t ignore starting surge
❌ Don’t size inverter only by kVA without checking watts
❌ Don’t forget future small expansions
What You SHOULD Do
✅ Calculate peak load properly
✅ Separate motor loads from electronics
✅ Check inverter surge rating
✅ Match inverter to battery capacity
As I always say:
An inverter is sized for the moment of stress, not comfort.
Final Lesson
If you size your inverter by peak load,
you get:
• Stable power
• Longer battery life
• No unnecessary shutdown
Wrong sizing always shows up -
sooner or later.
Let me ask
Have you ever experienced inverter tripping when a fridge or pump starts?
What appliance caused it?
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