Solar Inverter Size Calculator 2026

How to size a solar inverter

Step-by-step guide to picking VA/kVA with correct surge and topology for your load.

Sum your running wattage

Add up the wattage of every appliance. AC = 1500W, fridge = 250W, fan = 75W, light = 10W, etc.

Estimate motor load percent

What fraction of your load is motor-driven (AC, fridge, pump, washing machine)? 30% is typical residential.

Set diversity factor

Realistically, 60-80% of connected load runs simultaneously. Single family home = 70%.

Add headroom

20% extra for future appliance additions. More if you plan to add AC units.

Pick topology

Pure sine wave for motor-heavy loads. Grid-tied for on-grid subsidy. Modified sine only for light loads.

Review surge warning

If the calculator flags high surge, look for inverters rated for 3× surge (30 seconds).

Why inverter sizing matters more than panel sizing

You can under-size the solar array by 10% and the only penalty is slightly longer charging time. You under-size the inverter by 10% and it shuts down every time the AC compressor kicks in. Inverter sizing is the single most common field mistake in residential solar, and it's the easiest to avoid if you account for surge and motor loads from day one.

The formula our calculator uses

Required VA = (Running load × Diversity factor × (1 + Headroom)) ÷ Power factor. Then we compute surge requirement = Running load × (1 + motor% × 2). Finally we snap the result to the next standard inverter size. Any inverter you shortlist should handle both the required VA and the peak surge for at least 3-5 seconds.

Topology decision tree

Pure sine wave: Always the safe default. Required for any motor load, microwave, or sensitive electronics. 2026 price premium is minor.
Modified sine wave: Only for resistive loads (bulbs, chargers). Cheap but destroys motors and creates audible buzz in transformers.
Grid-tied (on-grid): Required for PM Surya Ghar net metering. No battery, exports excess to grid.
Hybrid: Best of both — grid-tied + battery backup. 20-30% more expensive but future-proof.

Get the sizing chain right by starting with the Appliance Load Calculator to lock in your running and surge load, then use the Battery Size Calculator to match Ah capacity for hybrid or off-grid setups.

Frequently Asked Questions

How do I pick the right inverter size?

Take your total running load in watts, multiply by your diversity factor (60-80%), divide by power factor (0.8 for mixed loads), add 20% headroom, then round up to the nearest standard inverter size (1.5, 2, 2.5, 3, 5 kVA etc.). Our calculator does this automatically and flags surge issues.

What is the difference between VA and Watts?

VA (volt-amperes) is apparent power; Watts is real power. For resistive loads (bulbs, heaters) VA = Watts. For motor loads (AC, fridge, pump) VA > Watts because of reactive power. Inverters are rated in VA, so always divide your Watts by the power factor (0.75-0.95) to find the right VA size.

Pure sine wave vs modified sine wave — which should I buy?

Pure sine wave. Modified sine is 30-40% cheaper but damages motor-heavy loads (fridges burn out, ACs run hot, pumps stall). In 2026 the price gap is small and the risk is real — always go pure sine unless your only load is lights and phone chargers.

What is surge power and why does it matter?

Motor-driven appliances (AC compressors, fridges, water pumps) draw 2-3× their running wattage for a fraction of a second when starting. A 1.5 kW AC can momentarily need 4.5 kW. If your inverter can't handle that surge, it shuts down and trips. Our calculator sizes for a 1.5× surge multiplier so you get inverters rated for real-world motor startup.

What is a diversity factor?

Diversity factor is the realistic fraction of your connected load that runs simultaneously. Rarely does a home run every appliance at once. Residential diversity is typically 60-80% — meaning if your connected load is 5 kW, actual peak is 3-4 kW. Using 100% diversity over-sizes the inverter by 20-40%.

Should I oversize my inverter?

Yes, by 20-30% for future growth. If your current peak is 3 kW, size for 3.6-3.9 kW → pick a 4 kVA inverter. Oversizing beyond 50% wastes money and reduces efficiency at low loads.

Grid-tied vs off-grid inverter — what's the difference?

Grid-tied (on-grid) inverters export excess power to the grid via net metering — no batteries. Off-grid inverters charge batteries and run appliances when the grid is down. Hybrid inverters do both. For PM Surya Ghar residential subsidy, you need a grid-tied or hybrid inverter with MPPT and anti-islanding protection.

How much does a solar inverter cost in 2026?

₹6,000-10,000 per kVA for pure-sine off-grid, ₹8,000-14,000 per kVA for grid-tied (more expensive due to certification and MPPT). A 5 kVA pure-sine off-grid inverter costs ~₹40,000-55,000. Hybrid inverters cost 20-30% more than grid-tied.

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