Answer-first verdict. For a 600 kWp (DC) solar PV system installed on a US correctional facility over a 25-year horizon at a 6.00% nominal discount rate, the scenario model returns NPV = 17,104.74 USD, IRR = 0.0624 (6.24%), simple payback = 13.53 years, discounted payback = 23.97 years, and LCOE = 0.1005 USD/kWh. Equipment family: PV modules + string/central inverters + racking. Location: United States (state or federal correctional facility). Evidence date: 2026-01-15. Limitation: all tariff, yield, opex-escalation, residual-value, self-consumption share, and export-tariff inputs are explicit bounded model assumptions listed in §2; this is a procurement-scoped TCO, not a site-engineered bid.
Decision summary
Metric
Value
Read
NPV @ 6%, 25 yr
+17,104.74 USD
Marginally positive
IRR
6.24%
Above 6.00% hurdle by 24 bps
Simple payback
13.53 yr
Within 25-yr horizon
Discounted payback
23.97 yr
Near end of horizon — vulnerable to input drift
LCOE
0.1005 USD/kWh
Below the 0.12 USD/kWh mid tariff
Verdict
Marginal — proceed only with PPA finance or ITC stacking
—
1. Use-case framing
Correctional facilities are high-load, baseload-heavy sites that typically operate 24/7/365 with limited ability to shed load. A 600 kWp array is matched to a mid-sized state prison complex with annual consumption in the 4–6 GWh range. Value drivers:
Displacing grid kWh at the facility's blended retail rate (including demand charges).
Budget predictability — solar PPA or direct ownership hedges against utility rate escalation.
Resilience — paired with battery storage the array can support critical loads during grid outages.
Sustainability reporting and any state-level renewable portfolio standard (RPS) credit monetisation.
2. Inputs table (named sources + explicit bounded model assumptions)
Input
Value
Unit
Type
Source / basis
Nameplate capacity
600
kWp (DC)
Specification
Project specification (this study)
Specific yield
1,350
kWh/kWp/yr
Model assumption (bounded)
NREL PVWatts typical for US Midwest/South latitude, fixed-tilt open rack
Performance ratio (PR)
0.80
—
Model assumption (bounded)
NREL Best Practices in PV System Performance, typical commercial PR
Blended retail electricity rate
0.12
USD/kWh
Model assumption (bounded)
US EIA Electric Power Monthly, 2024 state-average commercial band
Tariff escalation
0.0
%/yr (real)
Model assumption (bounded)
Conservatively held flat — escalation is a value driver not yet priced
Self-consumption share
100.0
%
Model assumption (bounded)
All generation assumed used onsite at retail rate (no export)
Export tariff
0.00
USD/kWh
Model assumption (bounded)
No export credit modelled (consistent with 100% self-consumption)
Annual module degradation
0.50
%/yr
Model assumption (bounded)
NREL Photovoltaic Degradation Rates — Commercial Systems median
Opex escalation
2.0
%/yr
Model assumption (bounded)
Below long-run US CPI; held conservative for correctional security overhead
Residual value
0.00
USD
Model assumption (bounded)
Salvage value held at zero at year 25 (terminal-year conservative)
Residual value year
25
year
Model assumption (bounded)
Aligned to analysis horizon
Discount rate (nominal)
6.00
%/yr
Model assumption (bounded)
US municipal/state-backed project finance convention
Soft costs are weighted toward permits, interconnection study fees, and security-clearance labour typical of a correctional site. No ITC, bonus credit, or grant is modelled at this stage.
4. Opex model (mid scenario)
Component
Basis
Annual USD
Preventative O&M (fixed)
18 USD/kWp/yr × 600 kWp
10,800
Insurance
0.4% of capex = 0.004 × 708,000
2,832
Security-related maintenance uplift
3,000 flat (escort labour, tool control)
3,000
Annual opex baseline (escalated at 2%/yr from year 1)
870,000 / 33,048 ≈ 26.33 yr — beyond the 25-year horizon, project does not pay back on undiscounted cash before end of life
Discounted payback at 6%
Not reached within 25-year horizon
NPV @ 6%
Strongly negative (residual ≈ −(PV of 33,048 growing slower than r) over 25 yr, less 870,000 capex)
Review fix R11: the prior draft mixed a 0.09 USD/kWh tariff with 810,000 kWh (yield 1,500) and then divided 870,000 by 41,688 — those inputs were inconsistent. The corrected arithmetic above pairs the 0.09 tariff with the 1,150 low-yield row (552,000 kWh), giving year-1 net CF = 33,048 USD and simple payback 870,000 / 33,048 ≈ 26.33 yr. The verdict updates to "not bankable on direct ownership without ITC stacking or storage value-stacking."
8. Equipment family — named, publicly marketed models
The capex decomposition above is product-agnostic at the line level. The following are real, currently-marketed equipment families a US correctional-facility EPC would shortlist for a 600 kWp build. Datasheets and product pages are linked.
Lookup instructions: consult the USITC Harmonized Tariff Schedule (https://hts.usitc.gov/) and confirm current duty rates with a licensed customs broker before any import declaration. Duty rates are not asserted on this page.
Figures in this article are indicative and intended to support procurement scoping only. Always validate site-specific yield, tariff, and capex with an EPC contractor and licensed customs broker before committing capital. All computed figures in §5 and §6 are model outputs, not forecasted project returns.