How we calculate your solar estimate

You tell us your typical monthly electricity bill. We subtract your DISCOM's fixed monthly charge, then work backwards through that DISCOM's published telescopic tariff slabs to find the number of units (kWh) that bill represents.

monthly kWh = invert(bill − fixed charge) over the DISCOM slab table · annual kWh = monthly kWh × 12

We model five DISCOMs — BESCOM (Karnataka), MSEDCL (Maharashtra), TANGEDCO (Tamil Nadu), KSEB (Kerala) and APSPDCL (Andhra Pradesh). Each tariff card on the site shows its last-verified date and a link to the official tariff order. Tariff structures change; treat the slab data as current to its verified date, not a billing source of truth.

We size the system to cover your yearly consumption, using the solar yield for your state — the units a 1 kW system produces per year after real-world performance losses.

system kW = annual kWh ÷ state solar yield (kWh per kW per year)

State yields: Karnataka 1,500 · Maharashtra 1,550 · Tamil Nadu 1,550 · Kerala 1,400 · Andhra Pradesh 1,500 kWh/kW/year. Where you allow a satellite roof scan, we use the measured sunlight for your specific roof instead of the state average. Systems are capped at 10 kW (the residential ceiling) and may be constrained further by your usable roof area.

panel count = round up( system kW × 1000 ÷ 545 W per panel )

We model installed cost at a benchmark of ₹55,000 per kW— a mid-market, fully-installed figure for a grid-tied residential system. Actual quotes vary with panel brand, inverter, structure height, and city; the installer comparison shows each partner's real price-per-kW band.

total cost = system kW × ₹55,000

We apply the central PM Surya Ghar: Muft Bijli Yojana subsidy, which is tiered by system size:

• ₹30,000 for the first kW
• ₹30,000 for the second kW
• ₹18,000 for the third kW
• Capped at ₹78,000 — systems above 3 kW receive no additional central subsidy

net cost = total cost − subsidy (never below ₹0)

The subsidy is disbursed by the government after installation and inspection, not deducted upfront. Some states add their own subsidy on top — we do not yet model state-level top-ups.

First-year savings are the value of the units your system produces, priced at your average tariff (your bill after fixed charges, divided by your annual units).

year-1 savings = annual production kWh × average tariff · payback years = net cost ÷ year-1 savings

Rooftop panels are warrantied for roughly 25 years, so we project savings across that horizon with two real-world adjustments:

• Panel degradation — 0.5% per year. Output drops slightly each year as panels age.
• Tariff inflation — 5% per year. Grid electricity gets more expensive, so each saved unit is worth more over time.

The lifetime figure is cumulative bill savings minus your net cost. It is a projection on stated assumptions — not a guarantee.