LIT_068: Majdi Nasab et al. (2021) — Hybrid Wind & Tidal Turbine Microgrid for a Remote Off-Grid NZ Community (Stewart…

LIT_068: Majdi Nasab et al. (2021) — Hybrid Wind & Tidal Turbine Microgrid for a Remote Off-Grid NZ Community (Stewart…

Source

https://doi.org/10.3390/en14123636 — original source (opens in a new tab; the file is not redistributed)

Majdi Nasab et al. (2021) — Hybrid Wind & Tidal Turbine Microgrid for a Remote Off-Grid NZ Community

HOMER Pro techno-economic case study of a wind + tidal + biodiesel-backup microgrid for Stewart Island/Rakiura — gives an NZ off-grid diesel-cost baseline (SIESA 62–67 c/kWh; 23 c/kWh diesel operating cost) and component CAPEX + system LCOE (20.8–27.9 c/kWh) for five hybrid scenarios

Peer-reviewed (Energies, MDPI) feasibility study for a ~408-customer NZ island community currently on five diesel generators. Optimises five wind/tidal/diesel configurations in HOMER Pro; the 2W+4T design (2 wind + 4 tidal + 1 diesel) supplies 75.3% of demand from renewables and cuts diesel fuel ~60%, at a levelized cost of 21 c/kWh vs the present 23 c/kWh five-diesel operating cost. Primary read, figures verbatim → data_quality: verified. ⚠ Component costs are HOMER generic/adapted values in ”$” (currency not stated — likely USD, not NZD) and EXCLUDE offshore construction/marine cabling/shore converter (the authors flag this), so the CAPEX/LCOE are component-only and optimistic vs true installed cost.

Summary

This paper evaluates the feasibility of a hybrid wind-and-tidal microgrid, with a biodiesel generator for back-up and lead-acid battery storage, to supply a remote off-grid coastal community in New Zealand. The case study is Stewart Island/Rakiura, where 408 customers are served by five diesel generators run by the Stewart Island Electrical Supply Authority (SIESA) at a retail charge well above the grid-connected mainland. Resource data (tidal current, wind) are taken for the “Foveaux site” in Foveaux Strait; generation, cost, renewable-fraction and emissions outcomes are simulated in HOMER Pro across five configurations (1W+1T, 1W+2T, 2W+2T, 2W+4T, 1W+10T) using WRPLOT-derived wind/tidal frequency distributions. The 2W+4T design is identified as the optimal hybrid for maximising renewable generation and minimising emissions, while 2W+2T gives the lowest net present cost and lowest levelized cost of energy. This is the first study to investigate tidal energy for Stewart Island, and it resolves the RT_023 backlog target (NZ-specific CAPEX and system design data for a remote off-grid community). It sits at the high (marine-tech + diesel-heavy) end of the NZ off-grid LCOE envelope alongside the Rakiura (LIT_033, CR_051), Totarabank (LIT_032) and Great Barrier (LIT_031) community-microgrid cases already in the corpus.

Key claims

- claim: "Stewart Island/Rakiura is supplied to just 408 customers from a small diesel power station in the main settlement Oban by the Stewart Island Electrical Supply Authority (SIESA). The retail charge is 62 c/kWh, of which 23 c/kWh is the direct cost of operating five diesel generators. Replacing diesel by a renewable source is a top priority for residents."
  source_location: "Section 2.1 Site Selection, p.3"
- claim: "The present retail charge is stated as 67 c/kWh in the conclusions (⚠ differs from the 62 c/kWh given in Section 2.1 — both figures appear in the paper). The paper's optimal design's levelized cost of equipment and resources over project life (21 c/kWh) is lower than the present operation cost of the five diesel generators (23 c/kWh, written '5D = 0.23 c/kWh')."
  source_location: "Section 4 Conclusions, p.20 (67 c/kWh, 21 vs 23 c/kWh); Section 3.4, p.19 (5D = 0.23)"
- claim: "For Stewart Island, fuel cost makes up 40% of operations & maintenance expenditure and drives the price charged to customers. Fuel cost is on a 5% annual increase; additionally, fuel consumption is anticipated to increase 1% annually."
  source_location: "Section 2.1, p.4 (Figure 2 Operational Expenditure)"
- claim: "Demand: peak values are in January (209 kW) and at 6–7 pm (239 kW); lowest values are in August (162 kW) and at 3–4 pm (121 kW). Peak hourly load is 209 kW. Daily demand for the year averages 3452.9 kWh/d with a load factor of 0.69; total demand is 1,260,332 kWh/year. Stewart Island's mean power demand is 143.9 kW."
  source_location: "Section 2.2, p.4 (peaks); Section 3, p.11 (3452.9 kWh/d, 0.69, 1,260,332 kWh/yr); Section 3.3, p.17 (143.9 kW mean)"
- claim: "Environmental parameters of the Foveaux site (Table 1): Latitude −46.6325° S, Longitude 168.2025° E, annual average water speed 0.52 m/s, water depth 30 m, annual average wind speed 8.31 m/s. The Foveaux site is on the opposite side of Foveaux Strait, 40 km away from Stewart Island's community at Oban. Wind speed exceeds cut-in for 90.5% of the year; tidal water speed exceeds cut-in for 68.4% of the year."
  source_location: "Table 1 + Section 2.3, p.6; Section 4, p.20 (40 km); Section 2.4.1, p.7 (90.5%); Section 2.4.2, p.9 (68.4%)"
- claim: "Wind turbine = XANT M-21 (100 kW, XANT, Brussels). Capital, replacement, maintenance and life are taken as $50,000, $50,000, $2,500/year and 20 years respectively. Specs (Table 2): rated capacity 100 kW, cut-in 3 m/s, cut-out 20 m/s, rated wind speed 11 m/s, hub height 31.8 m, swept area 346.36 m², rotor diameter 21 m."
  source_location: "Section 2.4.1 + Table 2, p.7"
- claim: "Tidal turbine = Schottel (54 kW, Schottel, Spray, Germany) bidirectional. Capital, replacement, maintenance and life are taken as $54,000, $54,000, $2,700/year and 10 years respectively. Specs (Table 3): rated capacity 54 kW, cut-in tidal speed 0.7 m/s, cut-out 4.6 m/s, rated power at 2.6 m/s, swept area 7.06 m², rotor diameter 3 m."
  source_location: "Section 2.4.2, p.9 + Table 3, p.10"
- claim: "Back-up generator = 320 kW CAT-400 kVA-50 Hz-PP (Caterpillar), covering base load at less than 25% of nominal capacity consuming just 6.37 L/h fuel; lifetime 90,000 h. Capital cost = 500 × 320 = $160,000; replacement cost = 400 × 320 = $128,000; O&M cost = 0.015 × 320 = $4.80/h."
  source_location: "Section 2.4.3 Biodiesel Generator, p.10"
- claim: "Biodiesel was selected over diesel because: diesel with 88% carbon content produces more carbon emissions than biodiesel with 77%; the lower heating value (LHV) of biodiesel is 43.20 MJ/kg vs 38.5 MJ/kg for diesel; and the price of biodiesel ($/L 0.53) is cheaper than diesel ($/L 1.00)."
  source_location: "Section 2.4, p.6"
- claim: "Battery = generic 12 V lead-acid, 1 kWh. Capital, replacement, maintenance and life are $154, $154, $15.40/year and 10 years respectively. Properties (Table 4): nominal voltage 12 V, round-trip efficiency 80%, lifetime throughput 800 kWh, max charging current 16.67 A, max discharge current 24.33 A. Converter: capital/replacement/maintenance/life/efficiency = $154/$154/$15.40 per year/15 years/90%. Controller (load-following, LF): $200/$200/$5.00 per year/25 years."
  source_location: "Sections 2.4.4–2.4.6 + Table 4, pp.10–11"
- claim: "Financial analysis by scenario (Tables 8 & 14) — Capital (k$) / Fuel cost (M$) / Operating cost (k$) / Total NPC (M$) / Levelized cost ($/kWh): 1W+1T = 350 / 3.3 / 323 / 4.53 / 0.278; 1W+2T = 402 / 3.2 / 321 / 4.55 / 0.279; 2W+2T = 484 / 2.0 / 225 / 3.39 / 0.208; 2W+4T = 593 / 1.8 / 222 / 3.47 / 0.213; 1W+10T = 799 / 2.2 / 284 / 4.48 / 0.274. 2W+2T has the lowest NPC and lowest COE; construction/installation costs are NOT included."
  source_location: "Table 8, p.15 (four scenarios); Table 14, p.18 (incl. 1W+10T)"
- claim: "Renewable fraction by scenario. HOMER optimizer 'Ren Frac (%)' (Tables 9 & 10): 1W+1T 30.2, 1W+2T 32.5, 2W+2T 57.1, 2W+4T 61.1, 1W+10T 52.7. Renewable Fraction as % of production (Table 12): 33.1 / 35.8 / 61.7 / 66.0 / 57.0. Wind+tidal generated power as % of demand (Table 12): 34.6 / 37.7 / 69.1 / 75.3 / 62.5."
  source_location: "Tables 9–10, pp.16–17; Table 12, p.18"
- claim: "Optimal design: 2W+4T (two wind + four tidal turbines, plus one diesel generator) is optimal for power generation — it produces the highest renewable energy fraction and can supply 75.3% of Stewart Island's total power demand from renewables, reducing diesel fuel consumption by 60%. ⚠ SCOPING FIX (verified against the PDF): the 90.5 kW figure the paper attaches to this design is the MEAN OUTPUT OF THE WIND-TURBINE COMPONENT (Table 11 row 'Mean Output of Wind Turbine', matching Table 5 'Mean output of W'), NOT the system mean output. The paper's own prose is internally inconsistent/loose here — it writes '2W+4T's mean output is the highest at 90.5 kW, it can meet the peak load (209 kW)', but a 90.5 kW wind-component mean cannot meet a 209 kW peak. Per Table 11 the SYSTEM total mean output for 2W+4T is 217.4 kW (wind 90.5 + tidal 17.9 + generator 109), and Stewart Island's system MEAN demand is 143.9 kW — so it is the 217.4 kW total (not the 90.5 kW wind mean) that exceeds the 209 kW peak. Do NOT cite 90.5 kW as the system output. Power production 2W+4T (Table 5): wind 792,785 kWh/yr, tidal 156,495 kWh/yr, generator 490,358 kWh/yr, total 1,439,638 kWh/yr."
  source_location: "Sections 3.3 & 4, pp.18–20; Table 11, p.18 (mean-output rows: wind 90.5 / tidal 17.9 / generator 109 / TOTAL 217.4; mean demand 143.9); Table 5, p.14 (production + 'Mean output of W' 90.5)"
- claim: "Emissions and fuel consumption by scenario (Table 13) — Carbon Dioxide (kg/year): 1W+1T 677,709; 1W+2T 657,185; 2W+2T 415,995; 2W+4T 378,894; 1W+10T 462,949. Total Fuel Consumed (L): 256,757 / 248,981 / 157,604 / 143,548 / 175,393. Nitrogen Oxides (kg/yr): 3,713 / 3,600 / 2,279 / 2,076 / 2,536. Sulfur Dioxide (kg/yr): 1,684 / 1,633 / 1,034 / 942 / 1,151. 2W+4T is the most environmentally friendly scenario (CO₂ −44%, fuel −44% vs 1W+1T)."
  source_location: "Table 13, p.18"
- claim: "The maximum outputs of a single selected wind and tidal turbine at the Foveaux site are 100 kW and 39.3 kW respectively. A problem with HOMER Pro's financial analysis is that it evaluates only equipment, operating and resource costs when calculating NPC and COE; a realistic comparison should include construction and installation costs, particularly offshore platforms, marine cables, and a DC–AC shore converter station."
  source_location: "Section 3, p.12 (100 kW / 39.3 kW); Section 3.4, p.19 + Conclusions, p.20 (HOMER cost caveat)"

NI relevance

This is the document behind RT_023 and it feeds two pages: D01 (renewable energy & storage / off-grid economics) and I09 (environmental sustainability). Its value to Neobiome Intelligence is four-fold.

• NZ off-grid diesel-cost baseline (D01/D21). SIESA’s real numbers — 408 customers, five diesel generators, 62 c/kWh retail with 23 c/kWh the direct diesel operating cost (67 c/kWh present retail per the conclusion) — are a hard NZ anchor for the diesel-displacement case in a remote off-grid community. The 23 c/kWh diesel operating cost is the number the paper beats with its 21 c/kWh optimal-hybrid levelized cost, and it corroborates the Rakiura diesel-up-to-52-c/kWh figure in CR_051 and the Chatham Islands diesel economics in URL_012.
• NZ-specific component CAPEX (D01 cost cells) — with a strong currency caveat. The study prices a full off-grid stack: wind 50,000 for 100 kW (= 500/kW), tidal 54,000 for 54 kW (≈ 1,000/kW), diesel genset 500/kW (160,000 for 320 kW), 1 kWh lead-acid battery 154/kWh, converter 154, LF controller 200. These are useful order-of-magnitude anchors, **but** (a) they are HOMER generic/adapted values, (b) the paper writes "” without stating currency — the biodiesel/diesel 0.53/1.00 per litre are drawn from a non-NZ reference, so the component costs are most likely USD, not NZD and must be treated as such before entering any NZD cost cell, and (c) the authors explicitly note the NPC/COE exclude offshore construction, marine cabling and the DC–AC shore converter station — so this is component-only cost, not installed-project cost (relevant to the ±20% installed-CapEx cost-output goal).
• System-level LCOE in the NZ off-grid envelope (D01). Hybrid LCOE spans 20.8–27.9 c/kWh (lowest 2W+2T 20.8; optimal-renewable 2W+4T 21.3). This is the high end of the NZ community-microgrid envelope — well above the grid-tied Totarabank (0.094–0.109/kWh, [[lit_032_mohseni-2020-totarabank|LIT_032]]) and Great Barrier (0.09–0.10/kWh, LIT_031) cases, and comparable to the Rakiura PV+wind+battery+H₂ optimum (~24 c/kWh, LIT_033) — reflecting expensive marine/offshore technology plus a diesel-heavy dispatch. Use it as the marine/island upper bound, not a design point for inland communities.
• Community-scale demand yardstick (D01). A ~408-customer NZ island community draws 209 kW peak / 143.9 kW mean / 1,260,332 kWh/yr, load factor 0.69 — a clean real-world demand profile for calibrating community-scale sizing.
• Environmental / emissions displacement (I09). The renewable fraction rises to 75.3% of demand (2W+4T) and CO₂ falls from 677,709 to 378,894 kg/yr (−44%) with a ~60% cut in diesel fuel — a quantified diesel-to-renewable emissions benefit that parallels the Chatham Islands 1,300 t CO₂/yr saving in CR_012. It reinforces the I09 evidence that a renewable transition delivers measurable emissions reduction at community scale.

Scope caveat: tidal/marine generation is only relevant to coastal/island NZ communities (the Schottel turbine is an offshore bidirectional unit); most of NI’s national/inland scope will not have a tidal resource, so tidal enters the technology menu as a niche coastal option rather than a core generation lever.

Research targets

Documents to retrieve

• RT_364 — Nasab, N.M.; Kilby, J.; Bakhtiaryfard, L. (2020) “The Potential for Integration of Wind and Tidal Power in New Zealand”, Sustainability 12(5):1807 (this paper’s grid-connected predecessor, ref [2]); likely carries national/regional NZ wind+tidal resource and potential data. → D01

Research gaps

• RT_365 (low priority — marine/coastal only) — a national NZ tidal-current / marine-energy resource layer: Huckerby, Johnson & Nobbs (2008) “New Zealand’s wave and tidal energy resources and their timetable for development” (ICOE 2008, ref [16]) + the MetOcean Solutions NZ-wide POM tidal model (0.06° ≈ 5.6 × 6.6 km, ref [17]). Would let NI assess tidal feasibility nationally if marine generation enters scope; deprioritised because tidal applies only to coastal/island communities. → D01

Resolved

• RT_023 (RESOLVED → this page): Majdi Nasab et al. (2021) hybrid wind and tidal turbines for a remote NZ community — NZ-specific CAPEX and system design data now held and read verbatim.

Notes

Primary peer-reviewed article (Energies 14(12):3636, doi:10.3390/en14123636), read verbatim via pdftotext — data_quality: verified. HOMER Pro techno-economic feasibility study; the LCOE/NPC/CAPEX figures are simulation outputs (component-only, EXCLUDING offshore construction / marine cabling / DC–AC shore converter, which the authors flag), not a built-system outturn — same status as the sibling NZ community-MG studies (LIT_031 / LIT_032 / LIT_033). All monetary values are in unspecified ”$” — most likely 2020-era USD, not NZD (the biodiesel/diesel unit prices are non-NZ references); convert before use in any NZD cost cell. context: ni — the calibration value is the cost + demand data.

⚠ Mis-scoped 90.5 kW (corrected against the PDF): the paper presents 90.5 kW for the 2W+4T design as though it were the system mean output that “can meet the peak load (209 kW)”. Verified against the raw PDF, 90.5 kW is the mean output of the WIND-TURBINE COMPONENT (Table 11 / Table 5), not system output; the paper’s own prose is internally inconsistent (a 90.5 kW mean cannot meet a 209 kW peak). The system total mean output for 2W+4T is 217.4 kW (Table 11) and system mean demand is 143.9 kW. The “Optimal design” key claim above records that corrected reading; 90.5 kW is not the system output.

⚠ Consumer-count cross-reference: this paper states Stewart Island is supplied to 408 customers (Section 2.1), whereas LIT_033 records ~405 permanent electricity consumers (as of Aug 2021) for the same island. Both figures are verbatim-faithful to their respective sources — the small difference reflects a customers-vs-permanent-consumers definition / reporting-date gap; the 408 figure is retained here as written (not changed).

Connections

Links to

Sources (6): CR_012 · CR_051 · LIT_031 · LIT_032 · LIT_033 · URL_012

Referenced by

Sources (7): LIT_069 · LIT_072 · LIT_078 · OT_115 · OT_119 · OT_121 · OT_122

SSI indicators (1): I09: Environmental Sustainability

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