Why load calculation is the right starting point for solar
Most solar buyers start with the question “how much does a 3 kW system cost?” — but that's the wrong first question. The right first question is: what are you actually trying to power? A 3 kW system covers a typical family with 2-3 fans, 6-8 lights, a fridge, TV, washing machine, and occasional AC use. But the same 3 kW will fall short if you run two ACs for 8 hours a day or a solar atta chakki during business hours.
The appliance load calculator flips the problem. Instead of guessing a system size, you tell us what you run and for how long — and we derive the exact kW you need, the inverter VA to handle surges, the battery Ah to carry you through outages, and the roof area required. The end result is a system that exactly matches your household, with no overspending and no under-sizing.
How the calculator works
The math is straightforward but easy to get wrong without a tool:
- Daily kWh = Σ (wattage × quantity × usage hours) ÷ 1000. We sum this across every appliance you add.
- Solar kW = Daily kWh ÷ (4.5 peak sun hours × 0.8 system efficiency) × 1.1 safety factor. Peak sun hours reflect UP's annual average; we derate 20% for wiring, inverter, and temperature losses; and we pad 10% for seasonal variation.
- Panel count = Solar kW ÷ 540 W (our recommended Mono PERC standard). A 3 kW system = 6 panels; a 5 kW system = 10 panels.
- Inverter VA = Peak load (with 70% diversity) × 1.5 surge factor ÷ 0.8 power factor. Surge covers the inrush current when motors (AC, fridge, pump) start up.
- Battery Ah = (Peak load × backup hours) ÷ (48 V × depth of discharge). Lithium DoD is 0.9, lead-acid DoD is 0.5 — that's why the same backup needs roughly 1.8× the Ah on lead-acid.
Typical sizing for Indian homes (2026)
| Home Profile | Monthly kWh | Solar Size | Inverter | Net Cost |
|---|---|---|---|---|
| 1 BHK, no AC | 150-200 kWh | 1.5-2 kW | 2.5 kVA | ₹60-80K |
| 2 BHK, 1 AC (seasonal) | 250-350 kWh | 2.5-3 kW | 3.5 kVA | ₹90-120K |
| 3 BHK, 2 ACs (daily) | 500-700 kWh | 5-6 kW | 5 kVA | ₹2-2.5L |
| 4 BHK + home office | 800-1000 kWh | 7-8 kW | 7.5 kVA | ₹3.5-4L |
| Farmhouse + pump + chakki | 1200+ kWh | 10 kW+ | 10 kVA | ₹4.5-5L |
Net cost = system cost after PM Surya Ghar 2026 subsidy. UP state subsidy of ₹15,000/kW (max ₹30,000) applies on top for residential installations.
Common mistakes to avoid
- Ignoring seasonal AC load. If you use AC for only 4 months a year, size the system for your annual average, not peak summer. Net metering covers the seasonal gap.
- Skipping the fridge. Fridges run 24/7 — a 250W fridge = ~6 kWh/day = 180 kWh/month, which is 30-40% of a small home's total. Always include it.
- Under-sizing the inverter. An inverter that matches only running wattage will shut down when the AC compressor or water pump kicks in. The 1.5x surge margin is non-negotiable.
- Over-sizing the battery. Every extra Ah costs ₹450-600 (lithium). Most homes don't need full-day backup — 4-6 hours covers 90% of real-world outages in UP.
- Forgetting roof area. 1 kW needs ~70 sq ft of shadow-free south-facing roof. If your roof is 200 sq ft, you can't install more than 2.8 kW no matter what your load is — plan for ground-mount or carport solar instead.
What to do with your results
Once you have the recommended system size, take three next steps:
- Check 2026 solar panel prices in UP for the kW you need, so you know a fair market rate before getting quotes.
- Run the subsidy calculator to confirm your eligibility and exact central + state subsidy amount.
- Use the EMI calculator to compare bank loan, NBFC, and zero-cost EMI options if you're financing.