Solar ROI Calculation for Residential

Your customer asks: "How long before this pays for itself?" Most EPC sales reps answer with a vague "4–5 years" and move on. The customers who don't convert that day are the ones who weren't convinced by the number. The ones who do convert are the ones who saw the math, broken down, transparent, and specific to their electricity bill.

This guide gives you a working ROI template for residential solar in India, with a complete worked example for a typical 3 kW PM Surya Ghar system. Every number is derived, not estimated.

If you're an EPC owner, this template does something more important than just calculate ROI, it gives you a proposal asset. When your sales rep can show a customer their personalised payback chart in a 10-minute site visit, close rates go up. For the commercial ROI equivalent (with Accelerated Depreciation), see our companion guide on solar ROI calculation for commercial systems.

The 5-Variable Residential ROI Formula, your proprietary calculation engine

The 5-Variable Residential ROI Formula is a named framework that makes residential solar ROI repeatable, auditable, and proposal-ready. Every residential solar ROI calculation reduces to five numbers. Change any one of them and the payback period changes. Know all five and you can answer any customer's question in under 60 seconds.

The formula:

Simple Payback (years) = Net System Cost ÷ Annual Financial Benefit

Where:

Net System Cost = System Cost − PM Surya Ghar Central Subsidy − State Top-up Subsidy

Annual Financial Benefit = Annual Bill Savings + Net Metering Export Income

The 5 variables are:

1. System cost (₹/kWp installed, all-in)
2. PM Surya Ghar central subsidy (₹, determined by system size under MNRE slabs)
3. State top-up subsidy (₹, varies by state, Gujarat, Maharashtra, Delhi, Tamil Nadu have different amounts)
4. DISCOM tariff (₹/unit, the retail electricity rate your customer currently pays)
5. Monthly generation (units/kWh, derived from system size × location's peak solar hours × performance ratio)

1. 1

   Variable 1: System cost, get the all-in ₹/kWp

   Use the total installed cost, panels + inverter + mounting + BOS + installation + GST. For a 3 kW residential system in Gujarat with ALMM modules, a realistic all-in cost in mid-2026 is ₹55,000–₹65,000/kWp, giving a 3 kW total of ₹1.65–₹1.95 lakh. See our 3 kW solar price guide for state-wise benchmarks.

2. 2

   Variable 2: PM Surya Ghar central subsidy, fixed by kW slab

   As per MNRE guidelines: 1 kW = ₹30,000; 2 kW = ₹60,000; 3 kW and above = ₹78,000 (capped). So for a 3 kW system, the subsidy is ₹78,000. For a 5 kW system, it's still ₹78,000, the cap applies at 3 kW. See PM Surya Ghar subsidy slabs for the full table and eligibility conditions.

3. 3

   Variable 3: State top-up, varies by state, add it if available

   Gujarat offers an additional ₹10,000–₹20,000 top-up; Maharashtra has separate state subsidies for below-poverty-line (BPL) households; some states like Delhi offer capital subsidy through DISCOMs. See our PM Surya Ghar cost by system size for state-level net cost after all subsidies.

4. 4

   Variable 4: DISCOM tariff, use the customer's current bill

   Get the customer's last 3 months of electricity bills. Calculate the average cost per unit: total amount ÷ total units consumed. In Gujarat (DGVCL/UGVCL), residential tariff is approximately ₹5.50–₹6.50/unit for consumption above 200 units. In MSEDCL (Maharashtra), it's ₹5.80–₹7.50 depending on the slab.

5. 5

   Variable 5: Monthly generation, calculate from location and system

   Monthly generation (kWh) = System capacity (kW) × Peak Solar Hours (PSH) × 30 × Performance Ratio (PR). In Gujarat: 3 kW × 5.5 PSH × 30 × 0.80 = 396 units/month. In Pune (Maharashtra): 3 kW × 5.0 PSH × 30 × 0.80 = 360 units/month. Use MNRE's solar radiation data for your city from the National Solar Radiation Database.

Worked example, 3 kW system for a typical Indian home

Let's run the full calculation for a representative customer: a family in Surat, Gujarat, with a monthly electricity bill of ₹2,100, consuming approximately 350 units per month. They're considering a 3 kW rooftop solar system under PM Surya Ghar.

Step-by-step calculation:

Variable 1, System cost: 3 kW × ₹61,667/kWp (all-in) = ₹1,85,000

Variable 2, PM Surya Ghar subsidy: 3 kW system → ₹78,000 (MNRE 2024 guidelines, confirmed at PM Surya Ghar National Portal)

Variable 3, State top-up: Gujarat offers ₹0 additional top-up for general category under current 2026 guidelines (was ₹10,000 in earlier years; check current GEDA notification before applying)

Net system cost = ₹1,85,000 − ₹78,000 = ₹1,07,000

Variable 4, DISCOM tariff: DGVCL residential rate for 201–500 units/month = approximately ₹6.00/unit (including fixed charges proportionally applied per unit)

Variable 5, Monthly generation: 3 kW × 5.5 peak solar hours × 30 days × 0.80 PR = 396 units/month

Simple Payback = ₹1,07,000 ÷ ₹26,580 = approximately 4.0 years

The 3.5-year figure quoted at the top of this article applies when state top-up is available (e.g., in states that offer ₹10,000–₹20,000 additional subsidy) or when the tariff is higher (₹7.50/unit in higher MSEDCL slabs, for instance). Both are realistic scenarios for many Indian residential customers.

How to calculate net metering export income

Net metering export income is the credit your customer gets from the DISCOM for surplus solar power exported to the grid. According to the Central Electricity Authority (CEA), most Indian states now have net metering regulations that require DISCOMs to credit surplus generation.

The exported units are credited at the DISCOM's avoided cost of supply (ACoS) or at a fixed rate set by the State Electricity Regulatory Commission (SERC). In Gujarat, the DGVCL net metering credit rate for 2025–26 is approximately ₹2.50–₹3.00 per unit. In MSEDCL (Maharashtra), it's similar. In BESCOM (Bengaluru), the net metering credit rate is approximately ₹3.00–₹3.50/unit.

For customers who generate significantly more than they consume, say a 5 kW system in a home that consumes only 250 units/month, the export income becomes a larger portion of the financial benefit. See our 5 kW solar price guide for the numbers on this scenario.

25-year IRR, how the numbers look over the full system life

Simple payback tells customers when they break even. Internal Rate of Return (IRR) tells them how good an investment this actually is relative to other options, FD rates, equities, or gold.

A solar PV system has a useful life of 25 years with degradation in output. Panel manufacturers guarantee 80–90% output at year 25. For financial modelling purposes, a standard 0.5% per year degradation assumption is widely used by IEEFA (Institute for Energy Economics and Financial Analysis) for Indian residential solar.

IRR over 25 years on the ₹1.07 lakh net investment: approximately 26–30%

This assumes 4% per year tariff escalation (conservative, actual Central Electricity Regulatory Commission (CERC) data shows average retail tariff escalation of 5–6% over the last decade). Even at 4%, the IRR is well above any fixed-income instrument, SBI FD rates in 2026 are approximately 6.5–7%.

When you put this in front of a customer, frame it this way: "You're investing ₹1.07 lakh today, earning a guaranteed 26% return over 25 years, tax-free, because savings on your electricity bill are not income." That's the conversation that closes.

ROI comparison across different tariff scenarios

Not every customer pays ₹6/unit. Your ROI calculation must be tuned to the customer's actual tariff. Here's how payback changes across the tariff range:

Tamil Nadu has subsidised electricity for many consumers, which makes residential solar ROI less compelling. This is why the MNRE data shows lower residential rooftop adoption in states with heavily subsidised grid electricity, the economic argument is weaker. Your sales pitch should adjust accordingly.

What changes the payback calculation most, sensitivity analysis

Five factors can shift your payback period by a year or more in either direction. Understanding them makes you a better consultant for your customer.

Using ROI to close customers faster, the proposal angle

The payback calculation is most powerful when it's personalised. A generic "4–5 year payback" printed on a brochure does nothing. A proposal that says "Mr. Sharma, based on your MSEDCL bill of ₹3,200/month and your rooftop in Pune, your 5 kW system will save you ₹3,500/month from month 1, pay for itself by November 2029, and earn you ₹18,000+ per year thereafter", that closes deals.

For detailed guidance on building this into your sales proposals, see how to show ROI in a solar proposal and solar proposal payback period best practices. For how to calculate the PM Surya Ghar subsidy as part of this, how to calculate PM Surya Ghar subsidy has the step-by-step.

What happens to ROI if tariffs rise, a 5-year projection

Electricity tariffs in India have increased by an average of 5–6% per year over the last decade. Under CERC's regulatory framework, tariff revisions are expected to continue as distribution infrastructure investment grows. This tariff escalation is the solar investor's best friend.

For the Surat example above, if DGVCL tariffs increase from ₹5.50 to ₹6.60 over 5 years (a modest 4% compound annual growth rate), the annual savings in year 5 become ₹27,720 instead of ₹23,100, improving the lifetime ROI substantially. Over 25 years, even a 3% annual tariff escalation adds ₹1.5–₹2 lakh in cumulative additional savings to the model.

This is why EPCs who help customers understand tariff escalation risk, and position solar as a hedge against future electricity price increases, close deals that competitors presenting static payback numbers lose.

How QuickEstimate fits your residential solar ROI workflow

Imran, the solo installer in Aurangabad, can't afford to spend 30 minutes on an Excel model before every site visit. Rohit's field reps in Surat need to give a personalised payback figure on the spot, before a competitor's rep shows up with their own quote.

QuickEstimate's Proposal Generator has the 5-Variable ROI formula built in. Enter the customer's consumption, system size, and DISCOM, the proposal calculates payback, annual savings, and 25-year IRR automatically, then generates a branded PDF in 60 seconds. The customer sees their name, their numbers, and their personalised payback chart, all in a document that looks like it was designed by a professional.

• Proposal Generator, ROI auto-calculated using the 5-Variable formula; PM Surya Ghar subsidy pre-filled; branded PDF in 60 seconds.
• Quotation System, Tariff and generation settings pre-configured per DISCOM; consistent ROI across every rep's proposal.
• Pipeline Management, Track which proposals had ROI < 4 years vs 4–6 years and see how close rates differ, calibrate your targeting accordingly.

Start with QuickEstimate free, no credit card, 10 proposals/month. See what a personalised ROI proposal looks like in your hands before your next site visit.

What to do this week, for your EPC

1. 1

   Build a DISCOM tariff reference sheet for your top 3 markets

   Pull the latest tariff orders from your primary DISCOMs (DGVCL, MSEDCL, BESCOM, or whichever you operate in). Calculate the effective per-unit cost at 200, 350, and 500 units/month for a residential consumer. Laminate it and give it to every sales rep, they'll never fumble the payback question again.

2. 2

   Add the 25-year IRR figure to your standard proposal

   Most EPC proposals show only simple payback. Adding the 25-year IRR (typically 22–30% for Indian residential solar) gives financially literate customers a frame they understand, and it immediately eclipses any alternative investment comparison they're making in their head.

3. 3

   Run the 5-Variable formula for your last 10 customers and compare to what you quoted them

   Go back through your last 10 closed deals. Apply the formula using their actual bill, system size, and subsidy. If your quoted payback was significantly different from the calculated payback, find where the error came from, and fix it for future proposals.

Frequently asked questions

What is the average payback period for residential solar in India?

The average simple payback period for a residential rooftop solar system in India is 3.5–5 years, depending on the DISCOM tariff and PM Surya Ghar subsidy availability. At ₹6/unit tariff with the ₹78,000 PM Surya Ghar subsidy on a 3 kW system (net consumer outlay ₹1.07 lakh), payback is approximately 3.5–4 years. States with lower tariffs like Tamil Nadu and UP see paybacks of 5–6 years, while high-tariff DISCOMs like BESCOM (Bengaluru) and MSEDCL (Pune) deliver 3–3.5-year paybacks.

How does PM Surya Ghar subsidy affect solar ROI?

PM Surya Ghar subsidy dramatically improves residential solar ROI by reducing the consumer's net investment. For a 3 kW system, the ₹78,000 central subsidy reduces a ₹1.85 lakh system to a ₹1.07 lakh net outlay, a 42% reduction in upfront cost. This alone shortens the payback period by approximately 1.5–2 years. For subsidy slabs by system size, see the PM Surya Ghar subsidy slabs guide.

What is a reasonable solar generation estimate for a 3 kW system in India?

A 3 kW rooftop solar system in most Indian states generates 330–420 units per month, depending on location. Gujarat, Rajasthan, and Maharashtra have high solar irradiation (5.0–5.8 peak solar hours/day) and deliver 380–420 units/month. Northern states like UP and Bihar with more cloud cover may generate 330–360 units/month. Use MNRE's solar radiation data for your specific city and apply a 0.75–0.85 performance ratio.

How is net metering income included in solar ROI?

Net metering income is the credit received from the DISCOM for solar power exported to the grid beyond the customer's own consumption. Most DISCOMs credit exported units at ₹2.50–₹3.50/unit. For a 3 kW system generating 396 units/month against 350 units consumption, the 46 surplus units exported earn ~₹115–₹160/month. Over 12 months, this adds ₹1,400–₹1,900 to the annual financial benefit, improving payback by about 2 months.

Is solar ROI calculation different for a flat vs a bungalow?

The ROI formula is the same, but the roof orientation and shading profile change Variable 5 (monthly generation). Flat roofs with optimal east-west mounting structures can achieve up to 25% more generation than a shaded pitched roof facing the wrong direction. Always conduct a site survey before quoting, and use a solar irradiance tool to calculate the actual generation for the specific roof conditions.

How does a concessional solar loan affect payback?

A PM Surya Ghar concessional loan at 7% interest (available through nationalised banks) changes the economics for customers who don't have the full ₹1.07 lakh upfront. The EMI on ₹1.07 lakh at 7% over 5 years is approximately ₹2,120/month. Since the system saves ₹2,215/month from day one, the EMI is almost exactly covered by the savings, meaning the customer goes solar at near-zero net cash flow from month 1. See our detailed guide on solar EMI options for Indian customers for the full comparison.

What is the IRR on a residential solar investment in India?

The Internal Rate of Return (IRR) on a residential solar investment in India, calculated over 25 years, is typically 22–30% depending on tariff level and subsidy. For the Surat 3 kW example (₹1.07 lakh net investment, ₹26,580 year-1 savings, 4% annual tariff escalation), the IRR is approximately 26%. This significantly exceeds bank fixed deposit rates (6.5–7% in 2026) and comparable inflation-linked instruments.

How does panel degradation affect the 25-year ROI model?

Solar panels degrade at approximately 0.5% per year, with most manufacturers guaranteeing at least 80% output at year 25. In the 25-year ROI model, this reduces Year 25 generation by about 11% compared to Year 1. Despite this, the cumulative generation over 25 years is substantial, the ₹1.07 lakh investment in the worked example generates approximately ₹8 lakh in cumulative electricity savings, a 7.5× return over the system life.