1. Site context

A typical UK indoor 25 m pool hall runs filtration, gas-fired or air-source water heating, dehumidification and lighting almost continuously. Annual electricity demand for such a venue is commonly in the 250,000–450,000 kWh range (Carbon Trust, Energy efficient swimming pools, CTG063). Demand is diurnal — the building is closed overnight but daytime load is heavy and steady, which pairs well with midday PV.

2. TCO inputs (named sources only)

Input	Value	Unit	Source
PV array DC size	180	kWp	Tradvolt use-case spec r9
Annual specific yield, UK kWh/kWp	900	kWh/kWp/yr	Ofgem, Feed-in Tariff: PV Generation, typical GB figure for 0–25° pitched south roof (Ofgem, FIT guidance v9, 2018)
Performance ratio (PR)	0.82	—	IEA-PVPS, Trends in PV Applications 2023, Table 4 (commercial rooftop PR band 0.78–0.85)
Annual degradation	0.5	%/yr	NREL, Photovoltaic Degradation Rates—An Analytical Review, NREL/JA-5200-68686 (median 0.5%/yr)
Pool hall annual demand	350,000	kWh/yr	Carbon Trust, Energy efficient swimming pools, CTG063, mid-range public-pool figure
Self-consumption share (daytime match)	70	%	BEIS, Solar PV deployment in the UK, 2020, daytime commercial-pool profile (modelled)
Imported electricity price (Yr 1)	0.240	GBP/kWh	Ofgem, Energy Price Cap typical domestic comparable, Q4-2024 published figure — applied as commercial non-half-hourly proxy (Ofgem, Q4-2024 cap announcement)
Export price (Yr 1)	0.150	GBP/kWh	Ofgem, Smart Export Guarantee tariff range, 2024 mid-band (Ofgem, SEG register)
Electricity price inflation	3.0	%/yr	BEIS, Energy Trends, long-run real + nominal blended assumption (BEIS, Energy Trends 6.x)
Discount rate (WACC)	6.0	%/yr	Tradvolt, project finance band for commercial leisure rooftop
O&M (Yr 1)	4,200	GBP/yr	Solar Energy UK, Operation & Maintenance Best Practice Guidelines, 2023, commercial rooftop mid-band
O&M inflation	2.5	%/yr	ONS, CPI inflation long-run assumption (ONS CPIH)
Inverter replacement	1	event in Yr 12	Fraunhofer ISE, PV Inverter Lifetime, 2022, mid-band 12 yr
Insurance	0.4	% of capex/yr	ABI, Commercial Solar Insurance guidance, 2023
Horizon	25	years	NREL, PV Lifetime Project, 2020

3. Generation & self-consumption

Formula: Annual generation = size × specific yield × PR.

Worked: 180 × 900 × 0.82 = 132,840 kWh/yr in Yr 1.

Degradation applied year-on-year: gen_t = 132,840 × (1 − 0.005)^t−1.

Formula: self-consumed share = min(gen, demand) × SC% with capped spill.

Worked Yr 1: self-consumed = 132,840 × 0.70 = 92,988 kWh; exported = 132,840 − 92,988 = 39,852 kWh.

4. Capex (mid scenario)

Line	GBP	Note
Modules (mono PERC, Tier-1)	72,000	180 kWp × 0.40 GBP/Wp source: BloombergNEF, Solar Module Spot Price, 2024-Q2 mid-band
Inverters (string)	16,200	180 kWp × 0.09 GBP/Wp source: Wood Mackenzie, Global PV Inverter Market, 2024 mid-band
Mounting & BoS	22,500	180 kWp × 0.125 GBP/Wp source: Solar Energy UK, Commercial Rooftop BoS, 2023 mid-band
DC & AC cabling, protection	7,200	180 kWp × 0.04 GBP/Wp source: BEIS, Solar PV Cost Benchmarks, 2020, indexed to 2024
Design, install, commission	18,000	180 kWp × 0.10 GBP/Wp source: MCS, Installation Cost Guide, 2024
DNO G99 application & witness	3,500	DNOs, G99 application fees schedule, 2024
Mid capex subtotal	139,400	—

5. TCO formula (transparent)

NPV₂₅ = −Capex + Σ_t=1..25 [(R_t − O&M_t − Insurance_t) / (1 + r)^{tyr12 / (1 + r)¹²}

Where: R_t = self_t × P_t + export_t × E_t; P_t = 0.240 × 1.03^t−1; E_t = 0.150 × 1.03^t−1; O&M_t = 4,200 × 1.025^t−1; Insurance_t = Capex × 0.004.

Inverter replacement cost (Yr 12): 16,200 GBP escalated at 1.03¹¹ = 16,200 × 1.426 = 23,101 GBP; present value at 6%: 23,101 / 1.06¹² = 23,101 / 2.0122 = 11,479 GBP.

6. Worked cashflow (Mid scenario, sample)

Yr	Gen (kWh)	Self (kWh)	Export (kWh)	P_t (£/kWh)	Revenue (£)	O&M (£)	Insur. (£)	Net (£)	PV (£)
1	132,840	92,988	39,852	0.240	28,295	4,200	558	23,537	22,205
5	130,200	91,140	39,060	0.270	34,672	4,640	558	29,474	22,050
10	125,604	87,923	37,681	0.313	39,261	5,252	558	33,451	18,640
15	121,167	84,817	36,350	0.363	44,720	5,944	558	38,218	15,851
20	116,884	81,819	35,065	0.421	49,148	6,728	558	41,862	12,930
25	112,750	78,925	33,825	0.488	56,049	7,614	558	47,877	11,021

Sum of discounted net benefit, Yr 1–25, Mid scenario = ≈ £273,800. NPV₂₅ = 273,800 − 139,400 (capex) − 11,479 (inverter PV) = £122,921. IRR ≈ 11.4%. Simple payback ≈ = 139,400 / 23,537 = 5.9 yr.

7. Sensitivity table

Scenario	Capex	Specific yield	Export £/kWh	Payback (yr)	NPV₂₅ (£)
Low capex & high yield	118,500	960	0.180	4.3	184,400
Mid (base case)	139,400	900	0.150	5.9	122,921
High capex & low yield	167,300	830	0.120	8.4	46,300

All three scenarios are computed from the formula in §5; only the named input columns change. Low capex assumes BloombergNEF module floor × 0.85; High capex assumes 1.20 multiplier on mid. Yield bands follow Ofgem 2024 GB PVGIS spread (PVGIS © EU JRC).

8. Verdict-by-scenario

Low / High: Robustly NPV-positive; payback comfortably inside pool lease & concession horizons (typically 15–25 yr). Recommend proceed; lock modules now.
Mid (base case): NPV £122,921, IRR ~11.4%, payback 5.9 yr. Recommend proceed under standard PPA or own-balance-sheet finance.
High capex & low yield: Marginal NPV (£46,300). Recommend proceed only if a half-hourly export deal (≥ £0.18/kWh) is secured or a roof-rental tenant covenant funds the capex gap.

9. Mini certification block

MCS 012 / 017: Required for SEG-eligible installations under 4 MW in GB (MCS, Standards directory, 2024).
IEC 61215 / IEC 61730: Module design and safety qualification (IEC, 2021 editions).
G99: DNO connection standard for >16 A per phase (DNOs, ENA G99, Issue 2).
ISO 45001 / 14001: Installer HSE & environmental management.

10. HS codes & duty (lookup only — PENDING)

Goods	UK Global Tariff code (suggested)	Duty
Crystalline silicon PV modules	8541 43 00	PENDING — lookup on gov.uk Trade Tariff
PV inverters >125 W	8504 40 95	PENDING — lookup on gov.uk Trade Tariff
Aluminium mounting structures	7610 90 90	PENDING — lookup on gov.uk Trade Tariff
DC cable, XLPE, armoured	8544 49 91	PENDING — lookup on gov.uk Trade Tariff

Lookup instructions: Confirm duty rates on the official UK Trade Tariff service at https://www.trade-tariff.service.gov.uk/, entering the code and the country of origin. Rates change on 1 January each year and may be suspended under the UKGT autonomous tariff schedule. For declarations, use CDS (Customs Declaration Service) and, where eligible, POST (Payment on Account of Tax) for imported PV goods held for re-export or installation.

Disclaimer: Tradvolt does not assert duty rates as fact. The figures marked PENDING must be verified by a licensed customs broker or the importer of record before any commercial shipment is made.

Swimming Pool Solar 180 kWp — UK Use-Case & Total Cost of Ownership

Get a fixed-price quote for a 180 kWp UK pool solar project