LIT_033: Off-Grid Multi-Carrier Microgrid Design Optimisation: Rakiura–Stewart Island

LIT_033: Off-Grid Multi-Carrier Microgrid Design Optimisation: Rakiura–Stewart Island

Source

https://doi.org/10.3390/en14206522 — original source (opens in a new tab; the file is not redistributed)

Summary

Peer-reviewed techno-economic optimisation study (Energies 14(20):6522) presenting a first-of-its-kind off-grid multi-energy-carrier microgrid (MECM) design for Rakiura/Stewart Island, Aotearoa New Zealand. The system serves the island’s electricity (including electrified space heating), hot water, and hydrogen transport-fuel demands entirely from on-site renewables — solar PV and wind generation backed by a three-timescale storage stack (super-capacitors for transient, LiFePO4 batteries for daily/weekly, and a hydrogen electrolyser–reservoir–fuel-cell chain for seasonal mismatch). A moth-flame optimisation algorithm (MFOA) minimises lifetime net present cost subject to a 0% loss-of-power-supply-probability reliability constraint across all three carriers. The numerical case study uses real NIWA climate data and NZ household demand profiles, and concludes the design is a low-risk, high-yield community investment that cuts the diesel-dependent island’s electricity costs by ~54%.

Key claims

• Rakiura/Stewart Island (46.9973°S, 167.8372°E), ~30 km south of the South Island, has ~405 permanent electricity consumers served by a central diesel station in a 4(+1) configuration with 1646 kW total nameplate capacity (as of Aug 2021). LIT_033
• The island’s electricity costs ~0.52 NZD/kWh on average — nearly three times mainland NZ grid electricity; the diesel station runs at an average ~4.28 kWh/litre, diesel costs ~1.75 NZD/kWh (as printed at p.15, line 915 — the per-kWh unit is a probable source typo for ~1.75 NZD/litre, since it is quoted as a fuel price), and each litre burned produces 2.7 kg CO2 (Section 3.8.1, p.15). LIT_033
• The proposed off-grid MECM serves electricity (incl. electrified space heating), hot water, and hydrogen transport fuel via solar PV, wind turbines, a hydrogen chain (electrolyser + reservoir + fuel cell), a hybrid super-capacitor/battery bank, a hot water tank, a heat exchanger, an inline electric heater, and a hydrogen refuelling station (Abstract; Figure 3, p.9). LIT_033
• The MFOA-optimised least-cost design specifies 796 PV panels (280 W each), 31 wind turbines (100 kW each), 329 SC modules, 18 battery packs (1 kWh each), a 964 kW electrolyser, a 619 kg hydrogen reservoir, a 261 kW fuel cell, a 283,301 L hot water tank, a 97 kW inline heater, a 17.2 kg-H2/h hydrogen station, and a 741 kW inverter (Table 4, p.18). LIT_033
• The minimised total net present cost (NPC) of the MECM is NZD 7,940,348 over a 20-year life-cycle at a 6% real discount rate; all costs are reported in 2019 NZD (2019 average rate NZD 1 = USD 0.69) (Section 4, p.18; Section 2.1 / Eq. 1, p.7; Section 3.7, p.13). LIT_033
• The blended levelised cost of energy is 0.27 NZD/kWh, with carrier-specific LCOEs of 0.24 NZD/kWh for electricity, 0.0091 NZD/L for hot water, and 6.97 NZD/kg-H2 for hydrogen (Section 4.4, p.23). LIT_033
• The MECM electricity LCOE of 0.24 NZD/kWh against the current island cost of ~0.52 NZD/kWh underpins the headline ~54% electricity-cost saving achievable if the system is financed as a community renewable energy project (Abstract; Section 4.4–5, p.23 and p.25). LIT_033
• The system’s green hydrogen at 6.97 NZD/kg-H2 sits well below recent NZ green-hydrogen production LCOEs of 14 NZD/kg-H2 (small-scale) and 8.91 NZD/kg-H2 (large-scale) (Section 4.4, p.23). LIT_033
• Cost-benefit appraisal returns a discounted payback period of 8.79 years, a profitability index of 2.45%, and an internal rate of return of 13.68%, characterised as a low-risk, high-yield, subsidy-free investment (Table 8, p.24). LIT_033
• Cost breakdown of the NPC: non-dispatchable generation (WT + PV) is NZD 4,127,158 (~52% of total; of which 74% WT, 26% PV); the hydrogen storage chain (fuel cell + electrolyser + tank) is NZD 2,811,765 (~35%); all remaining components total NZD 1,001,425 (~13%) (Section 4.2, p.21; Figure 11). LIT_033
• Annual energy balance: wind supplies ~79% and solar PV ~21% of total generation; on the demand side electric load is ~48%, hydrogen load ~21%, and heat load ~19% of consumption, with system-wide losses of ~12% (Section 4.3, p.23; Figure 12). LIT_033
• The fuel cell is replaced twice over the 20-year project (in years 8.11 and 16.22), because its 10,000-operating-hour rated lifetime equates to ~8.11 years at ~1233 operating hours per year under the dispatch strategy (Section 4.2, p.21; Table 2, p.14). LIT_033
• Component techno-economics (Table 2, 2019 NZD): PV panels 437 NZD/unit (280 W, 20-yr life); wind turbines 120 k NZD/unit (100 kW, 20-yr); battery packs 910 NZD/kWh (90% efficiency, 12-yr); electrolyser 1 k NZD/kW (60% efficiency); fuel cell 1.1 k NZD/kW (50% electrical efficiency, 10,000-hour life); hydrogen reservoir 470 NZD/kg (98% round-trip) (Table 2, p.14). LIT_033
• Load modelling draws on NIWA CLiFlo 2011–2020 climate data and the NZ GREEN Grid Household Electricity Demand Study (which includes space heating); hot water is modelled at 44 L/person/day; the hydrogen demand profile covers one 100-seat HFC ferry, 5 heavy-freight trucks, 5 heavy-duty tractors, and 30 light-duty HFC vehicles (Section 3.8.2, p.15–16; Figures 7–9). LIT_033

Neobiome Intelligence relevance

This is the most complete published off-grid renewable techno-economic design for a NZ island community and a high-value anchor for D01 (Renewable Energy & Storage). Unlike the LCOE benchmarks already in the wiki, it supplies a fully sized, multi-carrier system (electricity + heat + hydrogen mobility) with component-level capacities, capital/replacement/O&M costs in NZD, and a complete NPC and LCOE result — exactly the structure a Neobiome energy-sizing skill produces. The 0.24 NZD/kWh electricity LCOE and 0.27 NZD/kWh blended LCOE are NZ-specific reference points for validating any off-grid community design, complementing the Totarabank (CR_007) and all-NZ (LIT_002) cases by the same author group.

For I01 (Financial & Economic Self-Sufficiency), the cost-benefit metrics (DPP 8.79 yr, PI 2.45%, IRR 13.68%) give a concrete worked example of community-energy investment returns, and the ~54% cost saving versus diesel quantifies the financial case for displacing fossil generation in a remote community.

For I06 (Resistance to External Shocks), the design demonstrates full off-grid islanded operation at 0% loss-of-power-supply-probability across three energy carriers — the strongest form of energy resilience — using a three-timescale storage stack (super-capacitors, batteries, hydrogen) to ride out transient-to-seasonal mismatch.

For I07 (Fulfilment of Basic Needs), the system meets electricity, space heating, hot water, and transport-fuel needs of a ~405-person community simultaneously from on-site renewables, a direct multi-need self-sufficiency demonstration.

The methodology (MFOA meta-heuristic, NPC + LPSP objective, NZD component cost table) is directly reusable as a design pattern for the NI energy skill, and the component cost figures in Table 2 are candidate calibration inputs.

Research targets

Documents to retrieve

• Mason & McNeill (2016) — “Edging towards sustainability: a 100% renewable electricity system for Stewart Island” (EEA Conference, Wellington, ref [65]); the resource-assessment study behind the choice of PV + wind for this site. → D01 (region-specific: this is the Stewart Island pilot resource study, no national equivalent)
• NZ GREEN Grid Household Electricity Demand Study 2014–2018 (Anderson et al., 2018, UK Data Service, ref [67]); the national half-hourly household demand dataset (incl. space heating) used to build the load profile — a national all-NZ demand benchmark worth retrieving directly rather than via secondary citation. → D01, I07
• Concept Consulting (2019) — “Hydrogen in New Zealand, Report 1” (ref [77]); national green-hydrogen production cost study reporting the 8.91–14 NZD/kg-H2 NZ benchmark figures. → D01, I01 ⚠ PARTIALLY RESOLVED (RT_166) → OT_122: Report 1 (Summary) now held and read verbatim — the **8.91/kg (large-scale)** figure is verified there in NZD, but the **"14 NZD/kg (small-scale)"** figure is **NOT in this Summary** (Table 1's highest current value is off-grid bulk storage 12.56/kg); the 14 likely lives in the unretrieved Report 2 (Analysis), so RT_166 is kept OPEN on that leg. Do not treat “14 NZD/kg” as verified against a primary. → 2026-07-19: Concept Consulting’s Reports 2 (Analysis) + 3 (Background) now retrieved and ingested as OT_151. The full cost model contains no 14/kg green-H₂ production figure (highest current = off-grid bulk storage 12.56/kg) — LIT_033’s “14 (small-scale) NZD/kg” attribution to Concept 2019 is not substantiated by the primary. The $8.91 (large-scale) figure is verified; treat the “14” as an attribution error.

Research gaps

• A national (all-NZ) green-hydrogen levelised cost benchmark, updated post-2019, to recalibrate the 6.97 / 8.91 / 14 NZD/kg-H2 figures used here against current electrolyser and electricity prices.
• A national reference set of off-grid / island community load profiles (electricity, heat, transport) so NI can parametrise designs for remote NZ communities beyond the GREEN Grid mainland-household basis.
• Updated NZD component cost benchmarks (PV, wind, battery, electrolyser, fuel cell) to refresh the 2019-NZD Table 2 values, since renewable and storage capital costs have fallen materially since 2019.

Connections

Links to

Sources (4): CR_007 · LIT_002 · OT_122 · OT_151

Referenced by

Sources (12): LIT_032 · LIT_048 · LIT_067 · LIT_068 · LIT_069 · LIT_072 · LIT_078 · OT_104 · OT_115 · OT_121 · OT_122 · OT_151

Technologies (3): Diesel Genset (community-scale backup) · Hydrogen Storage (community-scale, seasonal) · community-scale)

SSI indicators (3): I01: Financial & Economic Self-Sufficiency · I06: Resistance to External Shocks · I07: Fulfilment of Basic Needs

EDT domains (1): D01: Renewable Energy & Storage Systems