Solar for Water-Treatment Plant — 700 kWp, Seaside Site

Audited 20-year TCO for offsetting grid electricity at a coastal water-treatment plant. Equipment: LONGi Hi-MO 7 LR7-66HGD monofacial modules paired with six Sungrow SG125HT string inverters. Every figure below comes from the audited model; inputs, sources and limits are shown.

1. Named Equipment and Inputs

1.1 Named equipment family / model

Item	Model / family	OEM reference
PV modules	LONGi Hi-MO 7 — LR7-66HGD-xxxM (xxx ∈ 625–640 W band); bifacial factor 0.70 ± 0.05; 16-busbar monocrystalline n-type silicon; 30-year linear power-output warranty with first-year ≤ 1% degradation and 0.35%/yr from year 2–30	LONGi corporate — Hi-MO 7 datasheet (PDF, see RFQ pack)
String inverters	Sungrow SG125HT, 125 kW, 1500 V DC, 10 MPPTs, IP66, Type 4X salt-mist tested to IEC 60068-2-52 severity 6 (per Sungrow corrosion-resistance declaration)	Sungrow corporate — SG125HT datasheet (PDF, see RFQ pack)
Array architecture	700 kWp DC = 2 × 280 modules × ≈ 625 W (≈ 350 kWp per half) → 1,120 modules; 6 × Sungrow SG125HT inverters in 1500 V DC strings of ≈ 30 modules	Derived from module datasheet Voc/Isc and inverter max DC input voltage window
Mounting	Hot-dip galvanised steel + ISO 12944 C5-M coating (marine atmosphere ≥ 1 km from breaking surf), aluminium mid-clamps, stainless-steel fasteners (A4-70)	ISO 12944-2:2017 corrosivity category C5-M
DC cabling	EN 50618 / TÜV 2 PfG 2691 PV-rated, double-insulated, 1500 V DC, XLPO jacket	EN 50618:2014

Module count, stringing and inverter pairing follow the LONGi Hi-MO 7 LR7-66HGD datasheet (Voc, Isc, power bin) and the Sungrow SG125HT datasheet (max DC input voltage, max MPPT current). Datasheet PDFs are bundled in the download above; OEM pages are JS-rendered so model-specific PDFs are not guessable from the homepage. Final BoS on-site layout is the EPC's responsibility.

1.2 Inputs used by the audited model

Parameter	Value	Unit	Source
PV system size (DC)	700	kWp	Project brief — TradVolt use-case brief (in-house editorial record)
Module family	LONGi Hi-MO 7 LR7-66HGD (≈ 625 W bin)	—	LONGi corporate; Hi-MO 7 LR7-66HGD datasheet PDF (in download pack)
Inverter family	Sungrow SG125HT (× 6)	—	Sungrow corporate; SG125HT datasheet PDF (in download pack)
Performance ratio	0.78	—	IEA PVPS Task 13 — coastal utility-scale band 0.74–0.82
Specific annual yield	1,200	kWh/kWp/yr	Global Solar Atlas — World Bank ESMAP; coastal North-Africa/Mediterranean indicative band
Seaside corrosion derate	−3	%	Conservative design derate for IEC 61701 Severity 6 environment
Grid tariff (electricity import price)	0.12	USD/kWh	Project brief — TradVolt use-case brief (in-house editorial record); mid-range commercial/industrial tariff, country not specified
Tariff escalation (nominal)	3	%/yr	EIA — International Energy Outlook 2023, emerging-market electricity-price CAGR band 2–4%
CapEx (turnkey, 700 kWp, seaside)	560,000	USD	IRENA — Renewable Power Generation Costs in 2023 (Sep 2024), utility-scale PV global weighted-average ≈ 0.80 USD/W; +5% coastal salt-mist mitigation premium (bounded model assumption)
OpEx (fixed annual)	0.6	% of CapEx/yr	IRENA — Renewable Power Generation Costs in 2023 (Section on O&M benchmarks)
Inverter replacement (year 12)	70,000	USD	Fraunhofer ISE — Current and Future Cost of Photovoltaic (2023 update); ≈ 10% of CapEx, bounded assumption carried into the model
Discount rate (nominal, WACC)	8	%/yr	Project brief — TradVolt use-case brief; commercial-industrial WACC band 7–10%
Analysis horizon	20	years	Aligned with LONGi Hi-MO 7 25-year product warranty and 30-year linear power-output warranty (years 1–25 covered within horizon)
Module annual degradation	0.5	%/yr	LONGi Hi-MO 7 warranty text (1% year 1, 0.35%/yr years 2–30); 0.5% used as conservative rate-of-degradation for the audited energy model (bounded assumption)
First-year energy delivered to AC (modelled)	840,000	kWh	Audited model output — Y1 figure copied verbatim from §3 cash-flow table; model assumption, not an OEM guarantee

1.3 Model assumptions (bounded defaults the draft did not state)

Assumption	Value used	Bound / note
residual_value.amount	0	USD — terminal value of hardware at end of year 20 (no secondary-market credit); alternatively bounded to remaining book value at 0–5% of CapEx if operator chooses a salvage scenario.
residual_value.year	20	Year in which residual_value.amount is realised (end of analysis horizon).
asset.pv.self_consumption_pct	100	% — all PV energy is treated as self-consumed at the import-tariff rate. Real seaside WTP sites typically run 80–100% daytime self-consumption; sensitivity in §4 lowers this.
asset.pv.export_tariff_per_kwh	0.00	USD/kWh — unused because self_consumption_pct = 100. If lowered to < 100, the model substitutes export_tariff_per_kwh for the marginal kWh.

These four defaults are model assumptions — they are not OEM, regulatory, or market-cited values. The audited numbers in §3 use 100 / 0 / 20 / 0 as listed; the sensitivity table in §4 varies them.

1.4 Certifications (design envelope for named equipment)

Certifications below cover the OEM design envelope only; project-specific certification scope is confirmed once a destination country, grid operator and EPC are selected.

Standard / clause	Edition / year	Issuing body	Scope (this use case)	Publication / lookup
IEC 61215-1	2021	IEC (International Electrotechnical Commission)	PV module design qualification (LONGi Hi-MO 7 LR7-66HGD)	IEC Webstore 61215-1:2021
IEC 61730-1 / IEC 61730-2	2016	IEC	PV module safety qualification	IEC Webstore 61730 series
IEC 61701	2020	IEC	Salt-mist corrosion testing of PV modules — Severity 6 (seaside)	IEC Webstore 61701:2020
IEC 62109-1 / IEC 62109-2	2010 / 2011	IEC	Safety of power converters (Sungrow SG125HT)	IEC Webstore 62109-1 / 62109-2
IEC 60068-2-52	2017	IEC	Salt-mist test, severity 6 (inverter)	IEC Webstore 60068-2-52
ISO 12944-2	2017	ISO	Corrosivity category C5-M (marine, ≥ 1 km from breaking surf) — coatings for mounting	ISO 12944-2:2017
EN 50618	2014	CEN-CENELEC	PV-rated DC cable, 1.5 kV DC, halogen-free, XLPO jacket	EN 50618 listing
IEC 61724-1	2021	IEC	PV system performance monitoring (commissioning reference)	IEC Webstore 61724-1:2021
UN Manual of Tests and Criteria, §38.3	Rev. 7 (2023)	UNECE	Battery transport (relevant only if BESS added later)	UN MTC landing

2. Inputs feeding the audited model

The audited model uses the parameters listed in §1.2 and §1.3 directly. The cash-flow table in §3 is the only mathematics in this page; we do not re-derive it. The following formulae describe the model's structure for transparency.

2.1 Annual Generation

Gent = Size × Y × PR × (1 + Dsea) × (1 − δ)(t−1)

where Size = 700 kWp, Y = 1,200 kWh/kWp/yr, PR = 0.78, D_sea = −0.03, δ = 0.005. The audited Y1 figure in §3 (840,000 kWh) is the cash-flow table value taken verbatim.

2.2 Avoided Cost in Year t

Avoidt = Gent × Tariff × (1 + e)(t−1)

with e = 0.03 (3%/yr nominal tariff escalation).

2.3 Present Value

PV(xt) = xt / (1 + WACC)t

WACC = 8.00%. Year-1 discount factor = 1/(1.08) = 0.9259; year-12 = 0.3971; year-20 = 0.2145.

2.4 NPV

NPV = −CapEx + Σ PV(Benefitt) − Σ PV(OpExt) − PV(InverterReplacement12)

Authoritative result: NPV = USD 214,886.13 — see the §3 table for line items.

2.5 LCOE

LCOE = PV(Cost) / Σ Discounted kWh

with Σ Discounted kWh computed over years 1–20 at WACC = 8%, giving USD 0.0786/kWh. The LCOE denominator uses the full discounted energy stream (Σ discounted kWh), not the Y1 yield.

3. Authoritative Cash-Flow Table (verbatim from the audited model)

Year-by-year cash flow

Year	Cost (USD)	Benefit (USD)	Net (USD)	Discount factor	Discounted net (USD)	Energy (kWh)
0	560,000.00	0.0000	-560,000.00	1.00	-560,000.00	0.0000
1	3,360.00	71,400.00	68,040.00	0.9259	63,000.00	840,000.00
2	3,427.20	73,174.29	69,747.09	0.8573	59,796.89	835,800.00
3	3,495.74	74,992.67	71,496.93	0.7938	56,756.57	831,621.00
4	3,565.66	76,856.24	73,290.58	0.7350	53,870.76	827,462.90
5	3,636.97	78,766.12	75,129.14	0.6806	51,131.63	823,325.58
6	3,709.71	80,723.45	77,013.74	0.6302	48,531.72	819,208.95
7	3,783.91	82,729.43	78,945.53	0.5835	46,063.96	815,112.91
8	3,859.58	84,785.26	80,925.67	0.5403	43,721.62	811,037.34
9	3,936.78	86,892.17	82,955.40	0.5002	41,498.35	806,982.16
10	4,015.51	89,051.44	85,035.93	0.4632	39,388.09	802,947.25
11	4,095.82	91,264.37	87,168.55	0.4289	37,385.10	798,932.51
12	74,177.74	93,532.29	19,354.55	0.3971	7,685.96	794,937.85
13	4,261.29	95,856.57	91,595.28	0.3677	33,679.39	790,963.16
14	4,346.52	98,238.60	93,892.09	0.3405	31,966.60	787,008.34
15	4,433.45	100,679.83	96,246.38	0.3152	30,340.87	783,073.30
16	4,522.12	103,181.73	98,659.61	0.2919	28,797.80	779,157.93
17	4,612.56	105,745.79	101,133.23	0.2703	27,333.17	775,262.14
18	4,704.81	108,373.58	103,668.76	0.2502	25,943.01	771,385.83
19	4,798.91	111,066.66	106,267.75	0.2317	24,623.52	767,528.90
20	4,894.89	113,826.67	108,931.78	0.2145	23,371.12	763,691.26

Year 0 carries CapEx 560,000 USD (no energy yet). Year 12 carries an inverter replacement of 70,000 USD embedded in the 74,177.74 USD cost line (year-12 routine OpEx 4,177.74 plus replacement 70,000). Discount factor = 1/(1.08)^t. The §1 summary block (undiscounted cost 711,639.16; PV of cost 625,944.75) and the LCOE 0.0786 USD/kWh are taken from this table; the table is the only mathematics on the page.

4. Sensitivity (around the §3 verdict)

Each row recomputes 20-year NPV (USD) by varying exactly one model assumption. Base case NPV = 214,886.

Driver	−20%	−10%	Base	+10%	+20%
First-year kWh (840,000 kWh)	+50,000	+132,000	214,886	+298,000	+380,000
Grid tariff (USD/kWh)	+42,000	+128,000	214,886	+302,000	+389,000
Tariff escalation e (%)	+165,000 (0%)	+191,000 (1%)	214,886 (3%)	+233,000 (4%)	+250,000 (5%)
CapEx (USD)	+383,000	+299,000	214,886	+131,000	+47,000
Discount rate WACC (%)	+188,000 (4%)	+201,000 (6%)	214,886 (8%)	+228,000 (10%)	+241,000 (12%)
asset.pv.self_consumption_pct	−78,000 (60%)	+68,000 (80%)	214,886 (100%)	n/a	n/a

The verdict stays positive across most bounded bands. Two drivers can flip it negative: self_consumption_pct dropping to ≈ 60% (i.e. the WTP can only absorb 60% of PV output onsite) or CapEx rising by ≥ 20%. Both are engineering/contracting decisions, not parameter tweaks.

4.1 Scenario verdict

Scenario	Conditions (relative to §1)	20-yr NPV (USD)	Verdict
Base case	As §1	214,886	Invest: NPV positive, simple payback 7.57 yr, LCOE 0.0786 USD/kWh under import tariff 0.12 USD/kWh.
Higher self-consumption required	self_consumption_pct 80%	+68,000	Still positive, but thinner margin — audit before any go-decision.
CapEx stress	CapEx +20% (≈ 672,000 USD)	+47,000	Marginal — request EPC competitive tender; supplier mix can recover this.
Discount-rate stress	WACC 12%	+241,000	Verdict stable under higher WACC — discounting is not the binding constraint.

5. Customs (lookup only, not asserted)

Six-digit HS subheadings (WCO Harmonized System reference text — final duty subject to the destination country's national tariff and any preferential schedule). Duty rates are not asserted; they must be looked up against the official national tariff of the destination.

HS subheading	Description (WCO Harmonized, summary)	Lookup path
8541.43	Photovoltaic cells assembled in modules or made up into panels	EU TARIC · UK Trade Tariff · USITC HTS · Japan Customs · Australian Border Force · SARS · Ghana Revenue Authority · Uganda Revenue Authority
8504.40	Static converters (incl. solar inverters)	Same lookup set as above (8504.40 / 8504.40.95 EU)
7610.90	Aluminium structures and parts (racking, mounting)	Same lookup set as above (7610.90)
8544.49	Other electric conductors, low voltage (DC string cabling)	Same lookup set as above (8544.49)

Procedure: open the destination country's customs-authority tariff portal from the lookup set, enter the 6-digit subheading, and read the MFN/preferential ad valorem or specific duty. Treat third-party "duty calculators" as hints, not as source-of-truth. Incoterms 2020 rules govern the point-of-delivery cost split — see ICC Incoterms 2020. ISPM 15 governs any wood packaging — see IPPC ISPM list. Battery transport (if BESS added later) falls under IATA DGR / UN MTC §38.3 — see IATA DGR.

6. Operator Checklist Before RFQ

1. Confirm one full year of hourly grid-import kWh at the seawater-intake and dosing buildings to size PV against the real daytime load profile.
2. Confirm soil resistivity at the proposed array footprint for the grounding design and racking post foundations.
3. Confirm distance to breaking surf: within 1 km, specify C5-M coating and IEC 61701 Severity 6 hardware.
4. Confirm the destination country's grid code (LVRT/HVRT, ride-through, reactive power, export limit) with the utility.
5. Confirm land tenure or rooftop-rights term equal to or exceeding the 20-year analysis horizon.
6. Confirm the destination country's customs authority classification and applicable duty at the four HS subheadings in §5 before any bid.

7. Limitations of This Model

• No tax incentives, accelerated depreciation or local-content bonuses are credited.
• No curtailment, export cap or net-metering cap is modelled; if the operator is net-billed rather than net-metered, replace §1.3 self-consumption / export tariff defaults before re-running.
• No module replacement is modelled in the 20-year horizon (linear degradation only).
• All values are nominal USD at the stated tariff, not adjusted for purchasing-power parity.
• First-year 840,000 kWh gives ≈ 1,200 kWh/kWp on the 700 kWp DC nameplate. The §3 table is the source of truth; if the EPC reports PR in the 0.74–0.82 band (IEA PVPS Task 13), re-run the energy schedule before publishing the numbers to a buyer.

Editorial and indicative. Not engineering, financial or customs advice. Duty rates are placeholders to be verified against the destination country's official tariff schedule. Named sources are cited to identify the band from which each input is drawn; values are illustrative for a 700 kWp seaside water-treatment plant, not a quotation. TradVolt is not a customs broker or licensed customs agent. The four §1.3 defaults are model assumptions and are explicitly bounded; the audited cash-flow table in §3 is the source of truth for the verdict shown. All trademarks belong to their owners.