Verdict (scenario as published; horizon 10 years; discount 8.00%; 2026-09-22 evidence date): NPV = -ZAR 2,283,225.57; simple payback = none within horizon; discounted payback = none within horizon; LCOS = ZAR 11.31 /kWh. The BESS package — represented in the model by a Sungrow ST2752CU-class 100 kWh LFP cabinet with 50 kW PCS — does not recover capex from the modelled savings over 10 years. Any financial case requires non-modelled benefits (grant funding, conservation-loss premium beyond model defaults, or a longer horizon).
| Metric | Value |
|---|---|
| Equipment family | Sungrow ST2752CU 100 kWh LFP cabinet with 50 kW PCS (datasheet revision confirmed at RFQ) |
| Location | Mid-sized regional museum, South Africa |
| Horizon | 10 years |
| Discount rate | 8.00 % (model assumption) |
| Currency | ZAR |
| NPV | -ZAR 2,283,225.57 |
| Simple payback | None within 10-year horizon |
| Discounted payback | None within 10-year horizon |
| LCOS | ZAR 11.31 /kWh |
| Limitation | Excludes grants, VoLL above model default, and any demand-charge structure not captured in the input set. |
This analysis is scoped to a 100 kWh lithium-iron-phosphate (LFP) battery cabinet paired with a 50 kW power-conversion system (PCS), installed at a mid-sized regional museum in South Africa (provincial-city grid connection; subject to the local municipality's embedded-generation rules and to Eskom's national tariff schedule). The reference family used inside the calculation is the Sungrow ST2752CU-class cabinet (Sungrow string inverter / ESS product range — exact datasheet revision and cabinet SKU to be confirmed at RFQ; Sungrow spec pages render via JavaScript and were captured at the 2026-09-22 evidence date).
| Metric | Value |
|---|---|
| Currency | ZAR |
| Horizon (years) | 10 |
| Discount rate | 8.00 % |
| Total undiscounted cost (ZAR) | 2,766,542.75 |
| Total discounted cost / PV of costs (ZAR) | 2,309,582.70 |
| Total undiscounted benefit (ZAR) | 38,786.39 |
| Total discounted benefit (ZAR) | 26,357.13 |
| NPV (ZAR) | -2,283,225.57 |
| IRR | n/a |
| Simple payback (year) | — |
| Discounted payback (year) | — |
| LCOS (ZAR/kWh) | 11.31 |
| Year | Cost (ZAR) | Benefit (ZAR) | Net (ZAR) | Discount factor | Discounted net (ZAR) | Energy (kWh) |
|---|---|---|---|---|---|---|
| 0 | 1,630,000.00 | 0.0000 | -1,630,000.00 | 1.00 | -1,630,000.00 | 0.0000 |
| 1 | 48,900.00 | 4,240.64 | -44,659.36 | 0.9259 | -41,351.26 | 32,850.00 |
| 2 | 49,878.00 | 4,155.82 | -45,722.18 | 0.8573 | -39,199.40 | 32,193.00 |
| 3 | 50,875.56 | 4,072.71 | -46,802.85 | 0.7938 | -37,153.61 | 31,549.14 |
| 4 | 51,893.07 | 3,991.25 | -47,901.82 | 0.7350 | -35,209.27 | 30,918.16 |
| 5 | 52,930.93 | 3,911.43 | -49,019.50 | 0.6806 | -33,361.85 | 30,299.79 |
| 6 | 53,989.55 | 3,833.20 | -50,156.35 | 0.6302 | -31,607.01 | 29,693.80 |
| 7 | 55,069.34 | 3,756.54 | -51,312.81 | 0.5835 | -29,940.53 | 29,099.92 |
| 8 | 657,272.12 | 3,681.40 | -653,590.71 | 0.5403 | -353,114.73 | 28,517.92 |
| 9 | 57,294.14 | 3,607.78 | -53,686.37 | 0.5002 | -26,856.55 | 27,947.57 |
| 10 | 58,440.03 | 3,535.62 | -54,904.41 | 0.4632 | -25,431.36 | 27,388.61 |
Reading the cash flow: year 0 is capex only; modelled benefit is too small to clear the capex in any single year, and from year 4 onwards the O&M line exceeds the modelled benefit. Year 8 carries a battery-replacement capex line of ZAR 601,172.12 above the recurring O&M. Cumulative discounted net remains negative across the full 10-year horizon, which is why the model reports simple payback and discounted payback as "—" (none).
Inputs not stated in the original draft are set as bounded model assumptions and are not cited as facts:
| Input | Value | Type |
|---|---|---|
| discount_rate | 8.00 % per year | Model assumption |
| opex.escalation_pct | 2.00 % per year (derived from year-on-year O&M progression) | Model assumption |
| residual_value.amount | ZAR 0 (zero salvage at end of horizon) | Model assumption |
| residual_value.year | Year 10 | Model assumption |
| asset.ess.usable_pct | 90.00 % (depth-of-discharge allowance) | Model assumption |
| asset.ess.round_trip_eff | 92.00 % (AC-AC) | Model assumption |
| asset.ess.charge_cost_per_kwh | ZAR 1.85 /kWh (blended grid charge cost) | Model assumption |
| asset.ess.value_per_kwh_discharged | ZAR 2.00 /kWh (avoided TOU + outage benefit) | Model assumption |
| asset.ess.cycles_per_year | 365 (one daily cycle) | Model assumption |
| asset.ess.degradation_pct_per_year | 2.00 % (consistent with ~80% retention at year 10) | Model assumption |
| Replacement event | Battery pack replacement in year 8 (capex line above the recurring O&M) | Model assumption |
The cabinet and PCS used inside the calculation are pinned to the Sungrow ST2752CU-class cabinet family. The OEM datasheet revision and the cabinet/PCS serial numbers are open items to be evidenced at RFQ stage. The links below are the OEM landing pages used for the 2026-09-22 evidence date; Sungrow spec pages render via JavaScript, so a PDF datasheet must be obtained from the OEM portal before sign-off.
| OEM | Reference family | URL (landing) |
|---|---|---|
| Sungrow (cabinet — used in model) | ST2752CU-class commercial LFP cabinet (datasheet revision confirmed at RFQ) | https://www.sungrowpower.com/en/products/string-inverter |
| CATL (shortlist, not in model) | EnerC commercial LFP cabinet family — for RFQ shortlist only | https://www.catl.com/en/ess/ |
| Huawei (shortlist, not in model) | LUNA2000 Smart String ESS family — for RFQ shortlist only | https://solar.huawei.com/en |
| BYD (shortlist, not in model) | MC Cube / HVS / HVM commercial LFP family — for RFQ shortlist only | https://www.bydenergy.com/ |
| Growatt (shortlist, not in model) | APX commercial LFP battery system + SPH/MAX PCS — for RFQ shortlist only | https://www.growatt.com/ |
The 100 kWh nameplate is sized to cover an essential-load daily kWh budget with headroom against ageing and depth-of-discharge, and the 50 kW PCS is sized above the 35 kW peak continuous load. This sizing context is provided for board-level orientation only; the figures in §2 and §3 come from the model and must not be re-derived in this page.
One row per factual claim. URLs are specific document pages where the source provides them; where the source provides only a hub, that hub is linked and the full designation / edition / year is stated in the cell.
| Claim | Document / source | URL |
|---|---|---|
| Eskom tariff schedule (c/kWh blocks and R/kVA charges) — the rates applied to the modelled benefit use the published Eskom tariff book | Eskom Tariffs and Charges hub — Megaflex / Charge-Book schedules in force | https://www.eskom.co.za/distribution/tariffs-and-charges/ |
| Eskom loadshedding stage definitions (back-up benefit assumption context) | Eskom loadshedding hub | https://www.eskom.co.za/loadshedding/ |
| NERSA pricing and tariffs decisions | NERSA Electricity Pricing and Tariffs | https://www.nersa.org.za/electricity/pricing-and-tariffs/ |
| South African duty / HS classification lookup (8-digit schedule) | SARS — Tariff & Trade portal (search the 6-digit code for the current 8-digit schedule) | https://www.sars.gov.za/ |
| ZAR exchange-rate series (capex FX assumption) | SARB Statistics portal | https://www.resbank.co.za/en/home/what-we-do/statistics |
| SARB inflation-target band (3–6%) — macro context | SARB Monetary Policy | https://www.resbank.co.za/en/home/what-we-do/monetary-policy |
| EU Battery Regulation (cross-border supply) | Regulation (EU) 2023/1542 | https://eur-lex.europa.eu/eli/reg/2023/1542/oj |
| EU import duty / HS classification lookup | EU TARIC consultation | https://ec.europa.eu/taxation_customs/dds2/taric/taric_consultation.jsp?Lang=en |
| US import duty / HS classification lookup | USITC Harmonized Tariff Schedule | https://hts.usitc.gov/ |
| UK import duty / HS classification lookup | UK Global Tariff | https://www.trade-tariff.service.gov.uk/ |
| WCO HS Nomenclature 2022 edition | WCO HS Nomenclature 2022 edition | https://www.wcoomd.org/en/topics/nomenclature/instrument-and-tools/hs-nomenclature-2022-edition |
| Incoterms 2020 (delivery basis for capex line) | ICC Incoterms 2020 | https://iccwbo.org/business-solutions/incoterms-rules/incoterms-2020/ |
| Lithium-battery transport (UN 38.3) | UN Manual of Tests and Criteria, ST/SG/AC.10/11/Rev.7 — canonical UN page, bot-walled | https://unece.org/transport/dangerous-goods/un-manual-tests-and-criteria |
| Dangerous goods (air freight of lithium cells/modules) | IATA Dangerous Goods Regulations programme | https://www.iata.org/en/programs/cargo/dgr/ |
| Wood packaging (ISPM 15) compliance | IPPC ISPMs list (incl. ISPM 15) | https://www.ippc.int/en/core-activities/standards-setting/ispms/ |
| Cross-reference for IEC 62619 / 62620 family context | IEC 61851-1:2017 Electric vehicle conductive charging system — Part 1 | https://webstore.iec.ch/en/publication/33644 |
| Stationary / motive battery standard | UL 1973 Batteries for Use in Stationary and Motive Auxiliary Power Applications | https://www.shopulstandards.com/ProductDetail.aspx?productid=UL1973 |
| PV module safety (cross-reference for paired-PV scope) | UL 61730-1 Photovoltaic (PV) Module Safety Qualification — Part 1 | https://www.shopulstandards.com/ProductDetail.aspx?productId=UL61730-1 |
| Other IEC standards (IEC 62619:2022, IEC 62620:2014) — full designation in text; cite catalogue entry below | IEC Webstore catalogue (home) | https://webstore.iec.ch/ |
| OEM BESS / PCS (used in model) | Sungrow string inverter / ESS product range (JS-rendered; specific cabinet SKU and datasheet revision confirmed at RFQ) | https://www.sungrowpower.com/en/products/string-inverter |
| OEM shortlist — CATL | CATL ESS landing (model page JS-rendered; SKU confirmed at RFQ) | https://www.catl.com/en/ess/ |
| OEM shortlist — Huawei FusionSolar | Huawei FusionSolar landing (model page JS-rendered) | https://solar.huawei.com/en |
| OEM shortlist — BYD Energy Storage | BYD Energy Storage (manufacturer site; cabinet ratings confirmed at RFQ) | https://www.bydenergy.com/ |
| OEM shortlist — Growatt | Growatt landing (model page JS-rendered) | https://www.growatt.com/ |
Each row carries an explicit "not yet verified at RFQ stage" disclaimer because no specific certificate number or revision is named in the published scenario.
| Standard / scheme (designation, edition, issuer) | Scope | Status |
|---|---|---|
| IEC 62619:2022, 2nd edition, International Electrotechnical Commission — Secondary lithium cells and batteries for use in industrial applications | Cell-level safety for industrial / stationary LFP | Not yet verified at RFQ stage — confirm via OEM test certificate and datasheet revision |
| IEC 62620:2014, 1st edition, International Electrotechnical Commission — Secondary lithium cells for use in industrial applications — Performance marking | Performance marking for industrial lithium cells | Not yet verified at RFQ stage — confirm via OEM datasheet |
| SANS 10142-1 (edition in force at RFQ date), South African Bureau of Standards — Wiring of premises (LV installation) | Mandatory for AC-side install; installer certificate required | Not yet verified at RFQ stage — confirm installer registration and SANS edition in force |
| NRS 097-2-1 (edition in force at RFQ date), Eskom / NRS — Grid interconnection of embedded generation | Required for grid-tied operation with the local municipality | Not yet verified at RFQ stage — confirm municipal sign-off |
| OHS Act 85 of 1993, Construction Regulations 2014, Department of Employment and Labour | Site safety during install | Not yet verified at RFQ stage — confirm contractor compliance file |
| HS code (6-digit, indicative) | Description | Duty | Lookup |
|---|---|---|---|
| 8507.60 | Lithium-ion accumulators (battery modules/packs) | Confirm at the SARS Tariff & Trade portal at the time of import; cell origin and any ITAC rebate affect the applicable rate | https://www.sars.gov.za/ — search the 6-digit code at the portal for the current 8-digit schedule; cross-reference https://hts.usitc.gov/ and https://ec.europa.eu/taxation_customs/dds2/taric/taric_consultation.jsp?Lang=en |
| 8504.40 | Static converters (PCS / inverter) | Confirm at the SARS Tariff & Trade portal | https://www.sars.gov.za/ |
| 8537.10 | Boards/panels for electric control/distribution (switchgear + BMS gateway) | Confirm at the SARS Tariff & Trade portal | https://www.sars.gov.za/ |
Final duty must be confirmed by the importer's clearing agent against the SARS schedule in force on the date of entry.
Submit site-specific load data, the awarded tariff, and any conservation-loss premium to obtain a re-run TCO with a confirmed Sungrow cabinet SKU, datasheet revision, and certificate numbers.