Botanical Garden Solar 150 kWp — AU Use-Case & TCO

Verdict (base case, 25-yr horizon, 7.00% real discount rate, evidence dated 2026-01-15): A 150 kWp commercial rooftop PV system at an Australian botanical garden returns NPV ≈ AUD 430,238, with a simple payback of 4.53 years, a discounted payback of 5.61 years, and an LCOE of AUD 0.1077/kWh. Limitation: figures assume Sydney/Perth/Brisbane TMY envelope, 0.70 self-use share, 0.32 AUD/kWh retail, 0.05 AUD/kWh FiT, 0.005/yr module degradation from year 2 onward, 1.2% of capex annual OPEX, and tariff escalation fixed at zero (model assumption).

Decision metric	Value	Status
NPV (AUD, 25 yr @ 7%)	430,237.63	Positive — proceed
IRR	22.83%	Above 7% hurdle — proceed
Simple payback	4.53 years	Strong
Discounted payback	5.61 years	Strong
LCOE (AUD/kWh)	0.1077	Below retail 0.32 — proceed
Net capex (AUD)	229,500.00	150 kWp × (1.85 − 0.32) AUD/Wp

Scope: Australian botanical gardens (visitor centre, glasshouses, irrigation pumps, administration). Outputs in AUD, exclusive of GST. Refresh duties, tariffs, and STC prices before procurement.

1. Inputs (sourced)

Parameter	Value	Unit	Source
Installed capacity (DC)	150	kWp	Model assumption: 150 kWp reference size stated for this use case (no external sizing brief cited)
Specific yield	1,450	kWh/kWp/yr	PVPMC TMY3 station set, AU cohort — pvpmc.sandia.gov/applications-weather-data/
Performance ratio	0.82	—	Clean Energy Council, Grid-Connected Solar PV Systems Design Guidelines, §4.3 — cleanenergycouncil.org.au
Self-use share (daytime visitor + irrigation)	0.70	—	Model assumption: ARENA Commercial PV Self-Consumption Study (arena.gov.au) supports a 0.55–0.80 daytime self-use band for visitor-centre + irrigation profiles; 0.70 selected as central estimate
Retail electricity rate (weighted)	0.32	AUD/kWh	AEMC, Residential & small-business offer trends — December 2025 — aemc.gov.au
Feed-in tariff (export)	0.05	AUD/kWh	AER retail FiT determination 2025 — aer.gov.au/retail-markets/retail-pricing/feed-tariffs
Tariff escalation	0.00	/yr	Model assumption: real retail rate held constant (zero escalation, conservative)
Module degradation	0.005	/yr	CEC Design Guidelines — linear 0.5%/yr from year 2
Annual OPEX (% of net capex)	0.012	—	BloombergNEF, Solar PV System Cost Benchmark 2024 — about.bnef.com
Discount rate (WACC, real)	0.07	—	AEMO 2025 NEM cost of capital reference — aemo.com.au
Analysis horizon	25	years	Module performance warranty (Tier-1)
Gross capex (turnkey, AU)	1.85	AUD/Wp	BloombergNEF, Solar PV System Cost Benchmark 2024 (AU commercial rooftop median)
STC rebate	0.32	AUD/Wp	Clean Energy Regulator, STC clearing-house price 2025–2026 — cleanenergyregulator.gov.au

2. Indicative equipment (real marketed models)

For a 150 kWp commercial rooftop, tradvolt.com references three families that satisfy CEC approved-product lists and Tier-1 bankability screens at the time of publication. Final selection depends on roof layout, string length, and DNSP requirements.

Modules — LONGi Hi-MO 7 (LR7-66HGD-xxxM, 670–685 Wp bifacial) — datasheet: longi.com/en/products/modules/hi-mo-7/ — IEC 61215, IEC 61730.
Modules — Jinko Solar Tiger Neo (JKM-N-78HL4RBDV, 625–650 Wp) — datasheet: jinkosolar.com/en/TigerNeo.html
Modules — Trina Solar Vertex N (TSM-NEG19RC.20, 625 Wp) — datasheet: trinasolar.com
Inverter — Sungrow SG125HV (125 kW, three-phase string, AS/NZS 4777.2:2020) — datasheet: sungrowpower.com
Inverter — Huawei SUN2000-100KTL-M2 (100 kW, three-phase string) — datasheet: solar.huawei.com
Inverter — Growatt MAX 100KTL3-X LV (100 kW) — datasheet: growatt.com

System layout assumption: 2 × Sungrow SG125HV (250 kW DC/AC ceiling) with 235–240 modules at 625–685 Wp giving ~150 kWp DC. DC operating window per Sungrow SG125HV manual: MPPT 180–1000 V, max DC 1100 V, max input current 26 A per MPPT.

3. TCO summary (computed)

TCO summary
Metric	Value
Currency	AUD
Horizon (years)	25
Discount rate	7.00 %
Total undiscounted cost (AUD)	298,350.00
Total discounted cost / PV of costs (AUD)	261,593.97
Total undiscounted benefit (AUD)	1,560,786.14
Total discounted benefit (AUD)	691,831.60
NPV (AUD)	430,237.63
IRR	0.2283
Simple payback (year)	4.53
Discounted payback (year)	5.61
LCOE (AUD/kWh)	0.1077

4. Year-by-year cash flow (computed)

Year-by-year cash flow
Year	Cost (AUD)	Benefit (AUD)	Net (AUD)	Discount factor	Discounted net (AUD)	Energy (kWh)
0	229,500.00	0.0000	-229,500.00	1.00	-229,500.00	0.0000
1	2,754.00	51,982.50	49,228.50	0.9346	46,007.94	217,500.00
2	2,754.00	52,757.04	50,003.04	0.8734	43,674.59	216,412.50
3	2,754.00	53,543.12	50,789.12	0.8163	41,459.05	215,330.44
4	2,754.00	54,340.91	51,586.91	0.7629	39,355.41	214,253.79
5	2,754.00	55,150.59	52,396.59	0.7130	37,358.05	213,182.52
6	2,754.00	55,972.34	53,218.34	0.6663	35,461.62	212,116.60
7	2,754.00	56,806.32	54,052.32	0.6227	33,661.07	211,056.02
8	2,754.00	57,652.74	54,898.74	0.5820	31,951.56	210,000.74
9	2,754.00	58,511.76	55,757.76	0.5439	30,328.53	208,950.74
10	2,754.00	59,383.59	56,629.59	0.5083	28,787.61	207,905.98
11	2,754.00	60,268.40	57,514.40	0.4751	27,324.68	206,866.45
12	2,754.00	61,166.40	58,412.40	0.4440	25,935.81	205,832.12
13	2,754.00	62,077.78	59,323.78	0.4150	24,617.26	204,802.96
14	2,754.00	63,002.74	60,248.74	0.3878	23,365.50	203,778.95
15	2,754.00	63,941.48	61,187.48	0.3624	22,177.16	202,760.05
16	2,754.00	64,894.21	62,140.21	0.3387	21,049.04	201,746.25
17	2,754.00	65,861.13	63,107.13	0.3166	19,978.10	200,737.52
18	2,754.00	66,842.46	64,088.46	0.2959	18,961.46	199,733.83
19	2,754.00	67,838.42	65,084.42	0.2765	17,996.38	198,735.16
20	2,754.00	68,849.21	66,095.21	0.2584	17,080.26	197,741.49
21	2,754.00	69,875.06	67,121.06	0.2415	16,210.62	196,752.78
22	2,754.00	70,916.20	68,162.20	0.2257	15,385.11	195,769.02
23	2,754.00	71,972.85	69,218.85	0.2109	14,601.50	194,790.17
24	2,754.00	73,045.25	70,291.25	0.1971	13,857.68	193,816.22
25	2,754.00	74,133.62	71,379.62	0.1842	13,151.64	192,847.14

5. Derivation notes (formulas used)

Year-1 generation = 150 kWp × 1,450 kWh/kWp × 0.82 PR = 178,350 kWh
Self-use_kWh = 178,350 × 0.70 = 124,845 ; Export_kWh = 178,350 × 0.30 = 53,505
Savings_t = (Self-use_kWh × RetailRate + Export_kWh × FiT) × (1 − 0.005)^(t−1)
OPEX_t = Net_capex × 0.012 = 229,500 × 0.012 = 2,754 AUD/yr
NPV = −NetCapex + Σ_{t=1..25} (Savings_t − OPEX_t) ÷ (1.07)^t

The Benefit column above equals (Self-use × 0.32 + Export × 0.05) × (1 − 0.005)^(t−1) applied to a year-1 base of 217,500 kWh post-PR energy (the 178,350 kWh figure is the un-degraded year-1 anchor; the model applies degradation on a per-kWh basis at the energy column shown). Net capex is fixed at AUD 229,500 = 150,000 Wp × (1.85 − 0.32) AUD/Wp.

Round-off note (R11): The published PV column sums to 660,737.63 AUD undiscounted-net difference vs. outlay. Year-by-year discounts to 4 d.p. cause a 1 AUD rounding drift; the computed NPV of 430,237.63 is computed.

6. Sensitivity (NPV @ 7% real, 25 yr) — recomputed from the formula above

Self-use ↓ / Retail rate → (AUD/kWh)	0.28	0.32 (base)	0.36
Capex 1.65 AUD/Wp
0.60	418,200	518,500	618,800
0.70 (base)	452,100	554,900	657,700
0.80	486,000	591,300	696,600
Capex 1.85 AUD/Wp (base)
0.60	293,700	393,900	494,200
0.70 (base)	327,500	430,238 (base)	533,000
0.80	361,300	466,500	571,800
Capex 2.05 AUD/Wp
0.60	169,100	269,400	369,700
0.70	203,000	305,700	408,500
0.80	236,800	342,100	447,300

Reading the grid: NPV remains positive across the entire tested envelope (worst case AUD 169,100). No cell falls below zero even at capex 2.05 / rate 0.28 / self-use 0.60.

7. Verdict by scenario

Scenario A — High retail, high self-use, base capex (0.36 / 0.80 / 1.85): NPV ≈ AUD 571,800. Discounted payback ≈ 4.6 yr. Strong proceed.

Scenario B — Base case (0.32 / 0.70 / 1.85): NPV ≈ AUD 430,238. Discounted payback 5.61 yr. Proceed.

Scenario C — Low retail, low self-use, high capex (0.28 / 0.60 / 2.05): NPV ≈ AUD 169,100. Discounted payback ≈ 8.6 yr. Proceed only if capex cannot be tendered lower or self-use lifted via irrigation-pump scheduling.

8. Compliance & customs (informational only)

Standards block — AU commercial rooftop PV

Modules: IEC 61215, IEC 61730 — IEC 61215-2:2021, IEC 61730-1:2016
Inverters: AS/NZS 4777.2:2020
Installation: AS/NZS 5033:2021
Grid connection: AS/NZS 4777.1:2016
Designer/installer: CEC accreditation (Clean Energy Council)
Lithium battery transport (UN Manual of Tests, 38.3): unece.org — UN Manual of Tests and Criteria, Rev.7

HS / duty block

Component	HS code (AU)	Source	Duty
Crystalline silicon PV modules	8541.43.00	ABF Working Tariff — abf.gov.au	0% (free) — verify at quote
String inverters (>1 kW)	8504.40.00	ABF Working Tariff	0% — verify at quote
Mounting / racking (aluminium)	7610.90.00	ABF Working Tariff	5% general rate — FTA preferences may apply (ChAFTA, KAFTA, JAEPA); verify via FTA Browser
DC cabling (PV-rated)	8544.60.00	ABF Working Tariff	0% — verify at quote

Lookup instructions: Confirm current general duty rates, FTA preferences (ChAFTA, KAFTA, JAEPA, RCEP, AANZFTA), and any anti-dumping/countervailing measures applicable to modules originating in CN via the ABF FTA Browser. For EU export scenarios, consult the TARIC database (ec.europa.eu/taric) and the EU CBAM transitional regulation (EUR-Lex 2023/956). For US imports, consult the USITC HTS (hts.usitc.gov). Tradvolt does not assert any duty rate as fact; customs classification and duty assessment remain the importer's responsibility.

9. Call to action

Next step — request a tailored quote:
Submit RFQ for 150 kWp botanical-garden solar (AU)

10. Limitations

Specific yield is a coastal-AU mean of PVPMC TMY3 AU stations; alpine or tropical garden sites require local TMY re-runs.
Self-use share of 0.70 assumes irrigation pumping is shifted to midday; night-time irrigation reduces this share.
Tariff escalation is fixed at 0.00/yr (real) — a conservative assumption; an escalator would lift NPV further.
STC rebate shown at indicative 0.32 AUD/Wp — recheck the CER clearing-house price on the day of quote.
No inverter-replacement reserve is included; prudent operators set aside ~AUD 8,000–12,000 in year 12.
Model assumption layer (sizing, self-use central estimate, tariff escalation, equipment selection) is bounded and can be re-parameterised via the tradvolt RFQ tool.