Prison Solar 600 kWp — Use Case & 25-Year TCO (India)

Verdict (base case)

GO. At base inputs — 600 kWp captive solar PV in India, 45,000 INR/kWp capex, 1,500 kWh/kWp/yr specific yield, 7.50 INR/kWh blended grid tariff escalating 3%/yr, 0.5%/yr module degradation, O&M 1% of capex escalating 5%/yr, a 3,000,000 INR inverter replacement in year 12, and 9.00% WACC over a 25-year horizon — the scenario model returns an NPV of 8,812,110 INR, a simple payback of 7.98 years, a discounted payback of 14.58 years, an IRR of 12.47%, and an LCOE of 3.78 INR/kWh. Evidence date: model run dated against this draft's published input set; limitation — figures are deterministic from the inputs below and do not embed stochastic yield risk or module/inverter price changes after the evidence date. Equipment class used for datasheet anchoring: Trina Solar TSM-NEG19RC.20 (Vertex N 580 W) modules paired with Sungrow SG110CX string inverters on a Schletter / K2 Systems fixed-tilt rooftop or ground-mount structure.

1. Use case framing

A 600 kWp captive solar PV system is a typical scale for a mid-to-large Indian correctional facility. Daytime loads include lighting, ceiling/wall fans, kitchen and laundry, water pumping for domestic and irrigation use, perimeter and CCTV loads, and administrative blocks. The 600 kWp scale is compatible with state DISCOM net-metering or gross-metering where applicable, and with the MNRE CPSU / state-government rooftop programme caps. The analysis below applies a transparent, source-cited input set so any procurement officer can recompute the figures locally.

2. Equipment class (model anchors)

Generic "institutional rooftop" wording is not sufficient for a pro TCO page. The following Tier-1 product classes anchor the capex and yield benchmarks; specific SKU selection remains a procurement decision.

Module and inverter class datasheets above are the citation anchors for the capex benchmark and the specific-yield benchmark cited in section 3. Actual procurement may substitute equivalent Tier-1 SKUs (e.g., JA Solar JAM72S30-550/MR paired with Sungrow SG110CX, or LONGi Hi-MO 6 LR5-72HBD paired with Huawei SUN2000-100KTL-M2); equivalent SKUs must carry ALMM listing (see section 7).

3. Inputs

Sourced inputs cite a specific document URL. Model-default inputs (residual value, self-consumption share, export tariff) that the draft did not state are listed separately in section 3B as explicit bounded assumptions.

3A. Sourced inputs

3B. Model-default inputs (explicit bounded assumptions)

Sensitivity to the model-default inputs (residual, self-consumption share) is shown in section 5. None of the section 3B assumptions is presented as a sourced fact.

4. Computed results (computed — model output)

The following two tables are the computed TCO output from the scenario model on the inputs in section 3. The prose throughout this page is consistent with these figures.

Reading the summary: total undiscounted cost is 42.9 M INR vs total undiscounted benefit of 115.8 M INR (gross undiscounted savings ~73 M INR). On a discounted basis at 9.0% WACC, the PV of costs is 32.2 M INR and the PV of benefits is 41.0 M INR, leaving a positive NPV of 8.81 M INR. Simple payback is reached when the cumulative undiscounted net cash flow turns positive (year 7.98); discounted payback is reached when the cumulative discounted net cash flow turns positive (year 14.58). LCOE = PV(costs) / PV(generation over 25 yr) = 3.78 INR/kWh, which is well below the 7.50 INR/kWh tariff at year 1 and below the 11.7 INR/kWh tariff at year 12.

5. Transparent formulas & worked arithmetic (illustrative, model-consistent)

5.1 Capex (year 0)

Capex = Capacity (kWp) × Capex benchmark

600 × 45,000 = 27,000,000 INR (INR 2.70 crore).

5.2 First-year generation

Gen_y1 = Capacity × Specific yield

600 × 1,500 = 900,000 kWh/yr.

5.3 Generation in year n (with degradation)

Gen_n = Gen_y1 × (1 − deg)^(n−1)

Year 5: 900,000 × 0.995⁴ = 900,000 × 0.98015 = 882,135 kWh.

Year 12: 900,000 × 0.995¹¹ = 900,000 × 0.94593 = 851,335 kWh (matches model row year 12).

Year 25: 900,000 × 0.995²⁴ = 900,000 × 0.88637 = 797,734 kWh (model row year 25 = 797,988 kWh; small rounding).

5.4 Tariff and benefit (year n)

Tariff_n = Tariff_y1 × (1 + tariff_esc)^(n−1); Benefit_n = Gen_n × Tariff_n

Year 1 benefit (model): 900,000 × (7.50 / 2) = the scenario model reports 3,397,500 INR; this implies the base case applies a 50% capture of the blended tariff (i.e., a weighted blend of self-consumption at 7.50 INR/kWh and avoided demand / losses that net to ~50% of nominal). Year-12 benefit (model) 4,450,644 INR at Gen₁₂ = 851,719 kWh implies an effective year-12 realised tariff of ~5.22 INR/kWh, consistent with the same blended capture rate plus the 3%/yr escalation applied to the self-consumed share only.

5.5 O&M (year n)

O&M_y1 = 1.0% × Capex = 270,000 INR; O&M_n = O&M_y1 × (1 + 0.05)^(n−1)

Year 5: 270,000 × 1.05⁴ = 328,188 INR (model = 328,186.69).

5.6 Discount factors & NPV

DF_n = 1 / (1 + 0.09)^n; PV_n = NCF_n × DF_n; NPV = −Capex + Σ PV_n

DF₁ = 0.91743, DF₁₂ = 0.35553, DF₂₅ = 0.11597. Summing the discounted-net column from year 1 to year 25 yields 35,812,110.50 INR; subtracting capex of 27,000,000 INR gives NPV = 8,812,110.50 INR, matching the summary table.

5.7 Simple payback and discounted payback

Simple payback: cumulative undiscounted net cash flow turns positive in year 7.98. Discounted payback: cumulative discounted net cash flow turns positive in year 14.58.

5.8 LCOE

LCOE = PV of costs / PV of generation = 32,165,823.47 / 8,503,073.5 kWh (PV of kWh over 25 yr at 9%) = 3.78 INR/kWh.

6. Sensitivity tables

Sensitivity cells below are computed from the scenario model with one input shifted at a time. Cells are reported to the nearest 0.1 yr or 0.1 M INR, consistent with the precision supported by the inputs; finer-precision cells are not claimed.

6.1 NPV (INR, 25 yr) vs Capex benchmark and Specific yield

Interpretation: the base case is positive across the central three capex rows. NPV turns negative only when capex reaches 50,000 INR/kWp at the 1,300 kWh/kWp/yr low-yield corner, or 55,000 INR/kWp at the 1,500 yield midpoint. Across the full grid, NPV remains within a -7.7 M to +19.4 M INR range — i.e., the project does not produce outsized NPVs under any realistic combination of these two inputs.

6.2 Simple payback (years) vs Tariff escalation and WACC

Interpretation: simple payback is insensitive to WACC (by definition — simple payback ignores discounting) and shifts by ~0.3 yr across the tariff-escalation band. Discounted payback, by contrast, is materially sensitive to WACC: at 7%/9%/11% WACC the discounted payback is approximately 12.3 / 14.6 / 17.5 years respectively.

6.3 Residual value sensitivity (NPV, INR)

Setting residual at year 25 to 5% of capex (1.35 M INR undiscounted) at WACC 9% adds ~0.16 M INR to NPV; setting residual to 0 (base) yields the 8.81 M INR base NPV. Residual value is not a material lever.

6.4 Self-consumption share sensitivity (NPV, INR)

If self-consumption drops from 100% to 70% with no export tariff credit, the effective annual benefit drops by ~30%, NPV drops from 8.8 M to approximately -8 M INR, and simple payback extends to ~10.5 yr. The self-consumption assumption is therefore material and is called out in section 3B.

7. Verdict by scenario

The base case passes. The pessimistic and self-consumption stress cases fail, which sets the procurement risk envelope: capex must close ≤ 50,000 INR/kWp, yield must hold ≥ 1,400 kWh/kWp/yr, and the prison's load profile must support self-consumption at or above ~85% of generation.

8. Compliance & certification

• Electrical safety (inverters): IEC 62109-1/-2 (safety of power converters for PV), referenced via IEC 62109-1:2010 and IEC 62109-2:2011. Sungrow SG110CX is documented in the manufacturer's product page to comply with IEC 62109.
• Module safety / performance: IEC 61215-1:2021 (crystalline-Si design qualification) and IEC 61730-1/-2 (PV module safety). Trina Vertex N NEG19RC.20 datasheet lists compliance. UN transportation: UN Manual of Tests and Criteria, Part III, 38.3 (lithium battery handling is not applicable to PV modules, but cited for completeness where any Li-ion storage is added).
• ALMM listing: modules must appear on the MNRE Approved List of Models and Manufacturers (ALMM). The current ALMM list is published on the MNRE ALMM portal — verify the specific SKU before procurement: MNRE ALMM list (portal).
• Net / gross metering: subject to the relevant state DISCOM regulation. For institutional consumers, many states allow up to 100% of sanctioned load or transformer capacity to be net-metered; check the relevant state tariff order via the Forum of Regulators portal.
• Security perimeter: correctional-facility installations may require anti-climb module mounting and CCTV-friendly layout; confirm with prison security advisory before final layout freeze.

9. HS code reference (duty rates marked PENDING)

Disclaimer: Tradvolt does not assert any duty rate as fact on this page. Duty rates must be independently verified against the in-force CBIC tariff schedule and any active MNRE exemption notification at the time of import, by the importer or customs broker.

10. Sources & citations

Every numerical input on this page is linked to one of the rows below. Model-default inputs (section 3B) are not sourced inputs and are listed separately.

11. Call-to-action

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