How to Show ROI in a Solar Proposal

The biggest reason Indian solar salespeople lose deals is not price, it is an ROI section that the customer does not trust. Either the numbers look too good to be real, or the maths is so complex that the customer gives up and asks a "knowledgeable" friend who talks them out of it, or the ROI is buried in page seven of a technical document no one reads.

Showing ROI that customers trust requires three specific numbers, calculated correctly from their actual bill data, presented in plain language. This post teaches you the 3-Number ROI Proof, the framework used by the best-converting EPCs in India.

The 3-Number ROI Proof, The Named Framework

The 3-Number ROI Proof is built on a simple insight from behavioural economics: customers cannot evaluate complex financial tables, but they can evaluate three numbers in context.

The three numbers are:

Number 1: Monthly bill saving in ₹ The immediate, tangible benefit. Calculated from the customer's actual bill and the system's generation estimate.

Number 2: Payback period in months The "when does my investment pay off" answer. Always express in months (16 months, not 1.3 years), because months feel more concrete and shorter.

Number 3: 25-year NPV (Net Present Value) or total saving The long-term wealth creation story. For customers who think about investment terms, NPV is more rigorous. For most residential customers in India, "total saving over 25 years in ₹" is more accessible.

Each number answers a different emotional question:

• Monthly saving: "Will this actually change my life next month?"
• Payback period: "How soon does this stop costing me money?"
• 25-year saving: "Is this actually worth it as a financial decision?"

Step 1, Calculate Monthly Bill Saving

Start with the customer's current monthly bill. Never use an industry average, always use their number.

The monthly saving formula:

Monthly saving = (System generation kWh/month × Self-consumption % × Grid tariff)
                 + (System generation kWh/month × Export % × Net metering rate)

Worked example, 3 kW system, Pune, Maharashtra:

• System generation: 3 kW × 4.2 kWh/kWp/day × 30 days = 378 kWh/month
• Self-consumption at 75%: 378 × 0.75 = 283.5 kWh
• Customer's MSEDCL tariff (residential Slab 3): ₹8.50/kWh
• Self-consumption saving: 283.5 × ₹8.50 = ₹2,410/month
• Export to grid at 25%: 378 × 0.25 = 94.5 kWh
• MSEDCL net metering rate: ₹3.80/kWh
• Export credit: 94.5 × ₹3.80 = ₹359/month
• Total monthly benefit: ₹2,769/month

The customer's current bill is ₹4,200/month. Their new estimated bill: ₹4,200 − ₹2,769 = ₹1,431/month.

Present this as: "Your bill of ₹4,200 reduces to approximately ₹1,431, a saving of ₹2,769 every month."

Step 2, Calculate Payback Period

The payback period is the net system cost divided by the annual benefit.

The payback formula:

Payback period (months) = (System cost − Subsidy) ÷ Annual saving × 12

Worked example, same 3 kW system, Pune:

• System cost (incl. GST): ₹1,20,628
• PM Surya Ghar central subsidy (3 kW): ₹78,000
• Net system cost: ₹42,628
• Annual saving: ₹2,769 × 12 = ₹33,228
• Payback period: ₹42,628 ÷ ₹33,228 = 1.28 years = 15.4 months ≈ 15 months

Always round to the nearest whole month. "15 months" is more credible and more concrete than "1.28 years."

The payback narrative:

"Your ₹42,628 investment (after ₹78,000 PM Surya Ghar subsidy) will pay itself back in approximately 15 months. From month 16 onwards, your solar system earns you free electricity for the remaining 23+ years of its life."

This framing, "from month 16 onwards", is powerful. It shifts the mental model from "cost" to "earning asset."

Step 3, Calculate the 25-Year Projection

The 25-year saving is the cumulative financial benefit over the system's life, accounting for rising electricity tariffs.

Two methods:

Method A, Simple (good for most residential proposals):

Year 1 saving × ((1 + escalation rate)^25 − 1) ÷ escalation rate

At 5% annual escalation and ₹33,228 Year 1 saving: = ₹33,228 × ((1.05^25 − 1) ÷ 0.05) = ₹33,228 × 47.73 = ₹15.86 lakh (undiscounted)

Method B, NPV (for finance-savvy or commercial customers): Apply a discount rate (typically 8–10% for India, matching bank FD rate) to the future cash flows:

NPV = Sum of (Year n saving ÷ (1 + discount rate)^n) for n = 1 to 25

At 8% discount rate and 5% escalation, the NPV of a ₹33,228/year Year 1 saving ≈ ₹6.8 lakh.

For residential customers, use Method A and call it "total saving over 25 years." For commercial customers or those who ask about NPV, use Method B and explain it is the present value of future savings.

State-by-State Tariff Data for ROI Calculations

ROI calculations only work if you use the correct tariff. Here are the 2025–26 residential tariff reference points for major Indian states:

Always verify the current tariff from your state's SERC or DISCOM website before finalising ROI calculations. Tariffs are revised annually and can change your payback calculation by 2–4 months.

External reference for Gujarat tariff: dgvcl.com. For Maharashtra: msedcl.in.

Net Metering Credit: How to Present It

Net metering is often misunderstood by customers. They assume surplus solar power is "free", sold at the full retail rate. In practice, most Indian DISCOMs pay a lower avoided cost rate for exported solar power (₹2.50–₹3.80/kWh depending on the DISCOM) rather than the retail tariff.

How to explain net metering in the proposal:

"When your solar panels generate more power than you are using (typically weekday afternoons), the surplus goes to the grid. Your DISCOM tracks this and credits your electricity bill at ₹3.50/kWh. This credit reduces the portion of your bill that comes from grid power at night or on cloudy days."

Do not describe net metering as "selling electricity", most residential customers are not in the business of selling electricity, and the language creates false expectations about income. Frame it as "credit against your bill."

What to Do When ROI Looks Weak

Some scenarios produce a weak ROI: low electricity tariff, heavily shaded roof, small system size, no subsidy eligibility, or high local panel prices. Here is how to handle each:

Key Stats on ROI Presentation

The ROI Table That Closes Deals

Here is the exact ROI table format the best EPCs use, copy this structure directly:

The three numbers to bold: Monthly saving. Payback period. 25-year total. Everything else is context.

For a deeper dive into payback period methodology, see our guide on calculating payback period in a solar proposal.

How QuickEstimate fits

QuickEstimate's Proposal Generator calculates all three numbers automatically when you enter system size, customer bill amount, location, and self-consumption percentage.

• Monthly saving is calculated from the customer's entered bill amount and the system generation model, no manual formula needed
• Payback period automatically subtracts the correct PM Surya Ghar subsidy slab and divides by annual saving
• 25-year projection uses a configurable escalation rate (default 5%) with compound growth calculation
• Net metering credits are calculated at the DISCOM-specific export rate, not the retail tariff, realistic and defensible
• The WhatsApp Follow-up module sends the PDF with the three key numbers highlighted in the accompanying message
• See also: solar proposal example India for the full proposal layout
• And: how to write a solar proposal for the complete 8-section structure
• Book a demo to see the ROI calculation in action

What to do this week

1. Pull your last five proposals and verify the ROI calculation uses the customer's actual bill amount and the correct state tariff, not a generic estimate. Recalculate any that used assumptions.
2. Change your payback period language from years to months in your proposal template (e.g., "1.3 years" → "16 months") and note whether customers comment on it.
3. Add the three-number ROI table above to your proposal template as the first content table after the financial summary, before the system specifications.

Frequently asked questions

What irradiance figure should I use for generation estimates?

India's average irradiance ranges from 4.5–5.5 kWh/m²/day depending on location. Gujarat has among the highest irradiance in India at 5.5–6.0 kWh/m²/day. A safe planning figure is 1,500–1,600 kWh/kWp/year for Gujarat, 1,400–1,500 for Maharashtra, and 1,300–1,400 for coastal Tamil Nadu. These give conservative generation estimates that are unlikely to under-deliver. Source: MNRE Solar Resource Data.

Should I include system degradation in the ROI calculation?

Yes, for a technically rigorous calculation. Solar panels degrade approximately 0.4–0.5% per year in performance. Over 25 years, a panel with 0.5% annual degradation will produce about 88% of its Year 1 output in Year 25. Many EPCs simplify by using a flat 80% of Year 1 generation throughout to approximate this. For residential proposals, this level of precision is optional but increases credibility with technically curious customers.

How do I calculate ROI when the customer uses solar on loan/EMI?

The correct frame is: "For months 1–60 (EMI period), your solar saving of ₹2,769 partially offsets your EMI of ₹2,100, net extra cost: ₹0 (you are cash-flow neutral). From month 61 onwards, you have no EMI and your saving is ₹2,769/month in pure savings." This reframing makes the EMI case extremely compelling, the customer realises solar costs them almost nothing extra while the loan is running.

What is a credible annual tariff escalation assumption?

5% per year is the most commonly used and is consistent with India's historical average electricity tariff growth over the last decade (CEEW, 2024). For a conservative case, use 3%; for an optimistic case, use 7%. Always state your assumption clearly in the proposal so the customer can adjust their expectations. Never claim a specific future tariff, it is unknowable.

How should I present ROI to a commercial customer vs a residential one?

Commercial customers typically understand IRR (Internal Rate of Return) and LCOE (Levelised Cost of Energy). Present NPV, IRR, and payback period for commercial customers. For residential customers, use monthly saving, payback months, and total saving, these are the most intuitive metrics.

What if the customer's DISCOM does not have a confirmed net metering rate?

Use the last published tariff order rate or the regulatory commission's approved rate. If there is genuinely no published rate, use a conservative ₹2.50/kWh for the export credit and note: "Net metering rate subject to DISCOM tariff order; estimated conservatively at ₹2.50/kWh." Always err on the side of under-promising.

What is the difference between payback period and break-even point?

They are the same concept, calculated the same way: net investment divided by annual benefit. "Break-even" is more common in finance; "payback period" is more common in solar sales. Both give the time in years (or months) until cumulative savings equal the initial investment. After that point, the system is generating pure financial return.