Calculators
Two honest engineering calculators: size an inverter and battery bank against your real load, and estimate rooftop solar savings and payback — before anyone calls you.
Trusted Since 2012
Fifteen years, one standard
Real Engineers On Site
Not salespeople, ever
Load-First Systems
Sized around actual usage
Before you buy anything
These are the eight questions customers ask us most. Open any one — you'll get an engineer's answer, not a pitch.
Tools that actually work
No email. No signup. Live, in-browser estimators built on the same maths we use during site audits.
Guided sizing · 6 quick answers
Tell us what you're powering, how long, and where it sits. We'll show the maths and the reasoning — not a sales price.
Your sizing progress
0/6
Each answer sharpens the sizing — the meter fills as you go.
Estimated Backup
2.1 hrs
at
400W
Recommended Battery
Tall tubular · deep-cycle · 150Ah × 1
12V bank · 4–5 yrs typical life
Recommended Inverter
675 VA · 0.68 kVA
12V pure-sine, sized to 400W @ 0.6 PF
The size you'll probably be quoted
Most vendors would push a 875 VA unit here — one step above the 675 VA your 400 W actually needs. That's roughly ₹1,400 more for the same runtime: backup hours come from the battery bank, not the inverter. A bigger inverter only idles hotter and wastes a little more standby power.
The one time we do recommend stepping up: if you plan to add a motor, pump or AC within the next year — tell us and we'll size for that instead.
Against your 4 h target
You asked for 4 h and this bank delivers ~2.1 h. Add capacity — a second battery, or step up to 200 Ah — before we finalise.Why we recommend this
Installation
Included
Warranty
Included
Battery Passport
Included
Your answers + this recommendation are pre-filled in the WhatsApp message — no re-briefing needed.
How we calculate: Backup = (Ah × V × qty × DOD × inverter efficiency) ÷ Load. Assumes DOD 60% and inverter efficiency 85% for tubular. A healthy 150Ah × 12V tubular at 400W ≈ 2.3 hours — matches the real-world numbers our engineers see on site. Actual runtime varies ±10% with battery age, temperature and cable quality. Indicative estimate. A free site survey confirms the exact system.
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