Solar Inverter Payback Period, 7 States Compared

ALMM and inverter compliance: MNRE’s current ALMM page publishes solar PV module and cell lists, not an inverter list. Verify the inverter’s exact model documents and applicable scheme or DISCOM requirements separately.

A payback number in a brochure is only as good as its inputs. This guide shows the formula, the inputs and where each one comes from, then works the same 5 kW rooftop through seven states so you can see which input moves the answer. Nothing here is a quotation or a promise of savings: it is arithmetic you can repeat on your own bill.

The formula and its four inputs

• Net system cost = quoted price (including GST) less central assistance less any state top-up that appears in your portal application.
• Annual generation (kWh) = system size (kWp) x specific yield (kWh per kWp per year).
• Annual savings (₹) = generation x [self-consumed share x tariff + exported share x export credit].
• Year-n generation falls by the degradation rate each year: generation in year n = generation in year 1 x (1 - d)^(n-1).

The specific yield already includes typical system losses, so do not multiply by a performance ratio again. If you use plane-of-array peak sun hours instead, annual generation = kWp x sun hours x 365 x PR.

Inputs used on this page, with sources

GST on specified solar devices is 5 percent since 22 September 2025, so a current quote should not carry 12 percent on those items; check the line-by-line treatment in the GST guide. Central assistance is paid on installed capacity, so a quote above or below the benchmark does not change it. The state-wise subsidy guide lists the state schemes we could verify; the Gujarat guide explains why no state top-up is included in the Gujarat example here.

Worked example: 5 kW in seven states

Net cost (same for every state). Benchmark = 2 x ₹50,000 + 3 x ₹45,000 = ₹1,00,000 + ₹1,35,000 = ₹2,35,000. Central assistance = 2 x ₹30,000 + 1 x ₹18,000 = ₹78,000. Net cost = ₹2,35,000 - ₹78,000 = ₹1,57,000. No state top-up is assumed.

Generation = 5 kWp x specific yield. Payback = ₹1,57,000 / (generation x tariff), assuming every unit offsets the stated tariff.

Reading the table. Rajasthan at ₹8: 1,57,000 / (8,730 x 8) = 1,57,000 / 69,840 = 2.2 years. Uttar Pradesh at ₹4: 1,57,000 / (7,305 x 4) = 1,57,000 / 29,220 = 5.4 years. Within one tariff column the spread across states is under a year, while moving from ₹4 to ₹8 in a single state roughly halves payback. That is why the tariff you offset deserves more attention than the state ranking.

These are best-case figures: they assume a quote at the benchmark, every unit credited at the full tariff and no failures. The next section removes those assumptions one at a time.

What stretches the number: Ahmedabad at ₹6

Annual generation is 5 x 1,701 = 8,505 kWh, and annual savings at ₹6 are 8,505 x 6 = ₹51,030.

Size changes the picture: 3 kW and 10 kW

Central assistance is capped at ₹78,000, so it covers a shrinking share of the cost as the system grows. Ahmedabad yield 1,701 kWh per kWp and a ₹6 tariff, benchmark cost and no state top-up:

The assistance is 53.8 percent of the benchmark at 3 kW (78,000 / 1,45,000) and 17.0 percent at 10 kW (78,000 / 4,60,000), which is why bigger roofs show longer payback even with the same tariff. Size the system to your consumption first, because units generated beyond what you can use or export at a good credit earn less.

Which tariff does solar actually offset?

A worksheet for your own roof

1. Write down the quoted price including GST, and the central assistance shown in your portal application. Net cost = price - assistance - any confirmed state top-up.
2. Take the specific yield for your city from the irradiance guide or from your installer’s simulation, and note the source. Annual kWh = kWp x yield.
3. Work out the offset tariff from your bill, as in the slab example, and the export credit from your DISCOM’s current terms.
4. Split generation into self-consumed and exported units. Annual savings = self-consumed x tariff + exported x credit.
5. Payback = net cost / annual savings. Then add any inverter replacement you would pay for, and recompute.
6. If the answer depends heavily on one input, test that input at a worse value before you sign.

Degradation and the 25-year view

Summing generation over 25 years at 0.5 percent a year gives 23.56 times the year-one output (the sum of 0.995^k for k from 0 to 24). For the Ahmedabad example at a flat ₹6, 25-year savings are 51,030 x 23.56 = ₹12.02 lakh against a net cost of ₹1.57 lakh, about 7.7 times. At 7 rupees, payback including degradation is 2.65 years against 2.64 without it, so degradation barely moves the payback year.

Net metering and export credit

If a share s of output is self-consumed at tariff T and the rest is exported at credit E: savings = generation x [s x T + (1 - s) x E]. If E equals T, the split does not matter. If E is lower, a roof that sits empty in the daytime pays back more slowly than one with a daytime load. Rules differ by DISCOM and by year; the net metering guide and your DISCOM’s current order are the references.

How the inverter changes payback

Efficiency. Delivered energy scales with conversion efficiency, so a higher-efficiency inverter delivers more of the same DC. Illustration for a 50 kW plant at the Ahmedabad yield: generation is 50 x 1,701 = 85,050 kWh, taken here as the output with a 95 percent efficient inverter. With a 98 percent inverter the same DC gives 85,050 x 98 / 95 = 87,736 kWh, a gain of about 2,686 kWh (2,685.8 before rounding). At ₹8 per kWh that is about ₹21,486 a year. If the 98 percent model costs ₹1,00,000 more (an assumed price gap), the premium recovers in 1,00,000 / 21,486 = 4.7 years from efficiency alone. Use weighted efficiency or the efficiency curve from each datasheet rather than peak figures, and read the efficiency guide.

Replacement. If an inverter fails inside the payback window and the owner pays, effective payback extends by cost / annual savings. A ₹50,000 replacement (assumed) against ₹51,030 of annual savings adds 0.98 years. Warranty terms, remedy and exclusions therefore belong in the payback model; read the warranty guide and the total cost of ownership guide.

Hybrid and battery. A hybrid inverter and battery add to the price. If they add ₹1,00,000 (assumed) and no extra bill savings, payback extends by 1,00,000 / 51,030 = 2.0 years. A battery earns its place through outage cover or time-of-day tariffs, which are separate values to quantify, not payback. See the on-grid vs hybrid ROI guide.

Common mistakes that inflate the answer

• Using the highest slab. Solar offsets your most expensive units first, but after solar the same house may fall into a lower slab. Recompute the tariff on the units that remain.
• Counting subsidy you may not receive. Use the amount shown in your portal application, not the sales estimate. A state top-up counts only if a current order exists.
• Ignoring the export rule. Confirm what exported units are credited at.
• Forgetting financing. Interest on a solar loan raises the cost of the system; compare the net-of-interest payback. The financing guide covers options.
• Quoting a future tariff. Use the current verified tariff as the base case. Any rise is a bonus, not an input.
• Skipping the quote check. The quotation checklist lists what a quote must itemise.

Where Qbits fits

Qbits makes inverters, not panels or installations, and pricing is quote-based through dealers, so there is no Qbits price in these calculations. What Qbits documents is per model: the on-grid inverter and hybrid inverter pages and the datasheet library give ratings, MPPT arrangement and communication options. Qbits’ datasheets describe an expandable warranty but do not define a universal term or remedy, so request the current written terms for your model before putting a replacement assumption in your model. The string sizing calculator helps check that the array and inverter match before the installer quotes. For commercial roofs, the CAPEX vs OPEX guide applies the same arithmetic with tax, financing and escalation.