ThePowerPayback
Methodology

How we calculate your numbers

We'd rather show our working than ask you to take our word for it. Here's exactly how every figure on this site is produced, what we assume, and where the underlying data comes from.

Data last reviewed: July 2026

One method, three market models

Every market runs the same engine: bill in, size, cost, incentives, and payback out. What differs is the incentive and export model, which is never shared across borders: India applies PM Surya Ghar subsidy slabs with 1:1 net metering; the US applies each state's rate, sun, and net-metering or net-billing policy with no federal credit after 2025; the UK applies self-consumption at the import rate plus Smart Export Guarantee earnings, with 0% VAT already in the price. The worked example below uses India; each market's own sources are listed on its homepage.

India calculatorUS sourcesUK sources

The calculation, step by step

  1. 1

    Estimate your usage

    Monthly bill ÷ your tariff (₹/unit) = units consumed per month.

  2. 2

    Size the system

    Monthly units ÷ (4 units per kW per day × 30 days), rounded to the nearest 0.5kW, minimum 1kW.

  3. 3

    Cost it

    System size × ₹60,000/kW = gross cost before any subsidy.

  4. 4

    Apply subsidy

    Subtract the PM Surya Ghar central slab, plus any confirmed unconditional state top-up, to get your net cost.

  5. 5

    Find the payback

    Net cost ÷ annual bill savings = years to break even.

  6. 6

    Project 25 years

    Annual savings × 25 × 0.92 (degradation) − net cost = lifetime net savings.

Our assumptions, in the open

Every estimate rests on assumptions. Here are ours, why we chose them, and where they're deliberately conservative so we don't overstate savings.

Cost per kW

₹60,000 (gross, before subsidy)

A mid-range 2026 benchmark for a residential grid-tied system. Real quotes vary ₹45k-₹75k/kW by brand, structure, and location. Adjustable in the calculator.

Generation

~4 units per kW per day

A conservative India-wide average (roughly 1,460 units/kW/year). High-irradiance states like Rajasthan and Gujarat generate more; you can refine this with an installer's site assessment.

Central subsidy

₹30k (1kW) / ₹60k (2kW) / ₹78k (3kW+)

Fixed PM Surya Ghar residential slabs. Capped at ₹78,000, a system larger than 3kW receives the same central subsidy.

State top-up

Added only where confirmed

We apply an unconditional state subsidy only where we've verified one (e.g. Gujarat +₹10k/kW). Conditional incentives (rural, SC/ST, size limits) are shown as notes, not auto-applied.

Bill savings

Assumes ~100% offset

We assume your system offsets your current bill in full, realistic for a correctly sized system with net metering. Net billing states with lower export rates will save somewhat less.

25-year projection

0.92× degradation factor

Panels lose roughly 0.5% output per year. We apply an average retention of ~92% over 25 years and subtract your net cost to show lifetime net savings. Tariff inflation (which would increase savings) is not counted, keeping the estimate conservative.

Where our data comes from

PM Surya Ghar Muft Bijli Yojana

Ministry of New and Renewable Energy (MNRE), Govt. of India

Used for: Central subsidy slabs (₹30k/₹60k/₹78k), application process, disbursal timeline.

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State Electricity Regulatory Commissions (SERCs)

State-level regulators

Used for: Residential tariff orders and net metering / net billing rules per state.

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State DISCOM portals

MSEDCL, PGVCL, BESCOM, TANGEDCO, UPPCL, and others

Used for: Net metering procedures, approval timelines, and any state top-up incentives.

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What this is not

These are planning estimates, not a quote or financial advice. Your real numbers depend on your exact tariff slab, roof orientation and shading, panel and inverter brand, installer pricing, and the current version of the subsidy and net metering rules, all of which change. Always confirm with your DISCOM and an MNRE-empanelled installer before committing money.