The single most important number in solar
Everything in solar planning — system size, payback, EMI, subsidy value — depends on how much sun your specific location gets. That number is peak sun hours (PSH), and it varies from 3.5 to 6.0 across India depending on city and month. Sizing a system without accounting for your actual PSH is the fastest way to be disappointed six months after installation.
Why "India gets lots of sun" isn\'t specific enough
India averages ~5 PSH, but that hides a 40% swing across cities. A 5 kW system in Jaipur (5.5 avg PSH) produces 8,000 kWh/year. The same 5 kW in Kolkata (4.6 PSH) produces 6,700 kWh/year. That's a ₹10,000-15,000/year difference in bill savings — enough to change your payback period by 1-2 years.
Shadow is worse than you think
Shading one cell of a 72-cell panel can reduce the panel's output by 30%+ due to string effects and bypass diode behavior. A 10% shaded array can lose 25% of its yield. The fix is expensive (microinverters or optimizers) — the better solution is to avoid shading in the first place. Walk your roof between 10am and 3pm on a sunny day and note every shadow.
Once you know your city's PSH, lock in orientation using our Tilt Angle Calculator and Azimuth Calculator, then convert the final yield into rupees with the Payback Calculator.