Solar IRR Calculation Methodology India: 2026 Buyer Guide

TL;DR — Solar IRR Calculation Methodology

• The bottom line: the most important Solar IRR (Internal Rate of Return) calculation principle for Indian industrial buyers is to model 25-year cash flows including: capex, annual O&M, performance degradation, tariff escalation, banking dynamics, accelerated depreciation tax savings, and salvage value.
• The answer to "what's a good IRR?" for Indian C&I solar is 24-29% (post-tax, with AD benefit) for typical projects, 25-32% for tier-1 segments (hospitals, hotels, malls, food processing, dairy), and 18-22% for agrivoltaics and BIPV which trade IRR for other strategic value.
• The key calculation steps: (1) build year-by-year energy generation forecast with degradation, (2) calculate avoided grid cost with tariff escalation, (3) subtract O&M cost, (4) add tax savings from 40% Year-1 AD, (5) compute NPV at WACC, (6) solve for IRR (rate at which NPV = 0).
• In short, the most cost-efficient sensitivity analysis examines: (a) tariff escalation rate (6% vs 4% vs 2%), (b) PR shortfall scenarios (75% vs 78%), (c) discount rate (8% vs 10%), (d) capex variance (±10%).
• Sun Wave Technologies, a leading solar EPC company in India, builds detailed IRR models for client projects with sensitivity analysis and 25-year cash flow projections.

What Is Solar IRR?

Internal Rate of Return (IRR) is the discount rate at which the Net Present Value (NPV) of a project's cash flows equals zero. For a solar project:

• Initial outflow: capex (Year 0)
• Annual inflows: avoided grid cost + AD tax savings + banking credits − O&M − insurance
• Salvage value: residual asset value at end of analysis horizon (Year 25)

IRR > WACC (Weighted Average Cost of Capital) means the project creates value. For Indian C&I corporates with WACC of 10-13%, IRR of 24-29% is exceptional value creation.

Step-by-Step IRR Calculation

Step 1: Build Year-by-Year Energy Generation Forecast

For a 1 MW (DC) plant:

• Year 1 generation = 1,500 MWh (typical India yield)
• Annual degradation = 0.40% (TOPCon) — see our Mono PERC vs TOPCon vs HJT comparison
• Year 2 generation = 1,500 × (1 - 0.015) = 1,478 MWh
• Year 3 generation = 1,478 × (1 - 0.004) = 1,472 MWh
• ... continue through Year 25

Year 25 retention: ~87.5% of nameplate = 1,313 MWh

Step 2: Calculate Avoided Grid Cost

For grid HT-I tariff of ₹8.00/kWh in Year 1, with 5% annual escalation:

• Year 1 avoided cost = 1,500 × 8.00 = ₹1.20 Cr
• Year 2 avoided cost = 1,478 × 8.40 = ₹1.24 Cr
• Year 3 avoided cost = 1,472 × 8.82 = ₹1.30 Cr
• ... compounds significantly over 25 years

Step 3: Subtract O&M Cost

O&M cost typically 1.0-1.5% of capex annually, escalating 4-5% annually:

• Year 1 O&M = ₹3.5 Cr × 1.5% = ₹5.25 lakh
• Year 2 O&M = ₹5.25 × 1.04 = ₹5.46 lakh
• ... etc.

Step 4: Add Accelerated Depreciation Tax Savings

Year 1: 40% × ₹3.5 Cr = ₹1.40 Cr depreciation. At 25.17% effective tax rate = ₹35.2 lakh tax savings. Years 2-10: 20% × WDV per year. ~₹15-20 lakh annual tax savings each year.

See our solar accelerated depreciation guide.

Step 5: Compute NPV and IRR

For a 1 MW project at ₹3.50 Cr capex, with above generation/cost/tax projections:

NPV at 10%: ~+₹430 lakh (positive) IRR: ~26.5% (rate at which NPV = 0)

This is a strong IRR for a typical C&I corporate.

Key Variables and Their Sensitivity

Tariff Escalation Rate

Indian C&I tariff escalation history: 5-7% pa over FY 2020-26. Modeling 5% as base case is reasonable.

Performance Ratio (PR)

Insist on PR guarantee with monetary LDs. See our how-to-choose-solar-EPC guide.

Discount Rate (WACC)

Even at high WACC of 14%, the project remains positive — solar's economic resilience.

Capex Variance

The capex range reflects EPC quality + state-specific factors. See our solar EPC cost per MW guide.

Levered vs Unlevered IRR

Unlevered IRR

Project cash flows (no debt). For a self-funded project, this equals IRR.

Levered IRR

Equity holder's return after debt servicing. With 80% LTV bank loan at 9.25% pa:

• Equity contribution: 20% of capex = ₹70 lakh
• Annual debt servicing: ~₹65 lakh (Year 1, declining as principal repays)
• Equity IRR: ~35-50% (project IRR amplified by leverage)

For Indian C&I corporates with bank credit access, levered IRR of 35-50% is the "true" return on equity. See our solar finance options India guide.

Frequently Asked Questions

What's a good IRR for Indian industrial solar in 2026?

A good unlevered IRR for typical Indian C&I solar in 2026 is 24-29% (post-tax, with 40% AD benefit). Tier-1 segments (hospitals, hotels, malls, food processing, dairy, electronics PLI) achieve 25-32%. Agrivoltaics and BIPV deliver 18-22% — lower because they trade pure economics for strategic value (land-use, brand, ESG).

How is solar IRR different from rooftop ROI?

Solar IRR accounts for full 25-year cash flows discounted to NPV at WACC. Simple ROI (Return on Investment) is just total return ÷ capex over a period. IRR is more rigorous because it accounts for time value of money. For most Indian solar projects, IRR is 24-29% (post-tax) while simple 25-year ROI is 800-1,200% — both metrics measure the same value but IRR is the comparable industry standard.

What's the difference between levered and unlevered IRR?

Unlevered IRR is the project's intrinsic return on capex (no debt). Levered IRR is the equity holder's return after debt servicing. With 80% LTV bank loan at 9.25% pa, levered IRR is typically 35-50% on Indian C&I solar — the project IRR (24-29%) amplified by financial leverage. Levered IRR is the right metric for equity decisions; unlevered for capital allocation.

How sensitive is IRR to PR shortfalls?

Each 1 percentage point of PR shortfall costs approximately 0.7-1.0 percentage points of IRR. For a 1 MW project at 78% guaranteed PR with 26.5% IRR, dropping to 75% actual PR reduces IRR to ~24.5%. Insist on PR guarantee with monetary LDs at 1.5-2.0% per percentage point shortfall. See our how-to-read-solar-EPC-quote guide.

How does accelerated depreciation affect IRR?

The 40% Year-1 accelerated depreciation under Section 32(1)(iia) captures ~₹35-40 lakh per MW of tax savings in Year 1 for a tax-paying corporate at 25.17% effective tax rate. This adds approximately 1.5-2.0 percentage points to baseline IRR. Subsequent year depreciation (20% WDV) continues for years 2-10 with declining magnitude. See our solar accelerated depreciation guide.

Should I use 8% or 10% WACC for IRR analysis?

Use your corporate's own WACC. Most Indian C&I corporates have WACC of 10-13% (factoring in equity cost of 14-18% and debt cost of 8.5-10.5%). For sensitivity, model 8% (low) / 10% (base) / 12% (high) to understand IRR robustness across WACC scenarios.

How does tariff escalation affect IRR?

Tariff escalation is the strongest IRR driver after PR. Indian C&I tariffs have escalated 5-7% pa over FY 2020-26. Each 1 percentage point of escalation adds ~1.5 percentage points to IRR over 25 years. Conservative modeling at 4% escalation produces 24-25% IRR; base case at 5% produces 26-27%; upside at 6% produces 27-28%.

Should I include salvage value in IRR analysis?

Yes, but at conservative ~5-10% of capex. Solar plants at end of 25-year life retain measurable salvage value (modules at 80%+ rated power, structures, switchgear, monitoring equipment). For ₹3.5 Cr capex, salvage of ₹20-35 lakh in Year 25 adds ~0.3-0.5 percentage points to IRR — modest but positive.

Sources

• Section 32(1)(iia) Income Tax Act, 1961 — Accelerated Depreciation
• IRR / NPV calculation per CFA Institute standards
• India installs record 45 GW solar capacity in FY2026 — pv magazine India