Doc #64 — Hydrogen for Mobile Use

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RECOMMENDED ACTIONS

Phase 1 — First year (low priority)

Hydrogen for mobile use is not a Phase 1 priority. The hydrogen production infrastructure does not exist; the vehicles do not exist; and petroleum rationing, electrification, and wood gasification address the immediate transport fuel gap. Phase 1 actions are limited to knowledge capture and modest preparatory steps.

1. Include electrolyser equipment in the national asset census (Doc #8) — university chemistry departments, industrial gas suppliers (BOC NZ), laboratory equipment. Identify any existing alkaline or PEM electrolysis systems.
2. Inventory pressure vessel fabrication capability — which NZ workshops can fabricate and test pressure vessels, and to what ratings? This information supports both hydrogen and other industrial gas applications (Doc #132).
3. Preserve technical literature on hydrogen combustion, electrolysis, and storage as part of the digital-to-print priority schedule (Doc #132).

Phase 2 — Years 1–3 (preparatory)

4. Develop low-pressure hydrogen production as a stationary energy application first (Doc #63). Mobile applications follow from stationary production experience.
5. Begin engine conversion trials — convert one or two spark-ignition farm engines (stationary first, then tractor or utility vehicle) to run on low-pressure hydrogen. Document the process, measure performance, identify problems.
6. Design and test low-pressure storage vessels rated to 10–20 bar using NZ-available mild steel and stainless steel. Develop testing and inspection protocols.

Phase 3 — Years 3–7 (initial deployment)

7. Deploy hydrogen farm vehicles at sites co-located with electrolyser installations near the grid. Target: 5–10 converted tractors or utility vehicles as proof-of-concept fleet.
8. Develop standardised conversion kits and refuelling procedures for common NZ farm vehicle engines.
9. Assess metal hydride alloy sourcing through Tasman trade channels (Doc #142) if trade has developed.
10. Train operators and maintenance technicians through the trade training programme (Doc #157).

Phase 4 — Years 7–15 (expansion if feasible)

11. Scale deployment to farms and industrial sites with grid-connected electrolysers.
12. If metal hydride storage becomes available through trade, develop higher-range vehicles for rural road transport.
13. Assess whether compressed hydrogen at moderate pressures (50–100 bar) is achievable with NZ-fabricated vessels and whether the range improvement justifies the engineering effort.

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ECONOMIC JUSTIFICATION

The niche hydrogen fills

The transport fuel transition creates a hierarchy of solutions, each covering different applications:

Application	Primary fuel solution	Why hydrogen might matter
Urban passenger transport	Electricity (EVs, bicycles, rail)	Does not
Light freight, short range	Electricity, wood gas	Does not
Heavy freight, intercity	Rail electrification, wood gas trucks, biodiesel	Does not (insufficient range)
Farm tractors and machinery	Wood gas, biodiesel, electricity where near grid	Hydrogen fills gaps where wood gas is impractical and electrification is too remote
Site vehicles (ports, quarries, forestry)	Electricity where grid-adjacent	Hydrogen for sites near grid but needing mobile power without battery weight
Coastal shipping	Sail, biodiesel	Possible long-term but not near-term

Hydrogen’s mobile niche is narrow: heavy farm and site vehicles that operate within a short radius of a fixed refuelling point connected to the electrical grid. This is a real niche — NZ has an estimated 70,000–100,000 tractors and a significant number of other off-road vehicles — but it overlaps substantially with wood gas and biodiesel.⁴

Person-years and cost

Electrolyser construction: A basic alkaline electrolyser producing enough hydrogen to fuel one farm tractor (estimated 5–10 kg H₂/day for moderate use) requires approximately 200–400 person-hours of skilled fabrication, assuming designs are developed and materials are available.⁵ This is comparable to building a wood gasifier (40–80 hours, Doc #56) but the electrolyser also requires ongoing electricity consumption and produces a fuel that is harder to store.

Engine conversion: Converting a spark-ignition engine to hydrogen takes an estimated 40–100 person-hours per vehicle, depending on the engine and the quality of injection system achieved.⁶ This is comparable to wood gas vehicle conversion.

Comparison with alternatives:

• A wood gasifier is cheaper to build, uses no electricity, and fuel (wood) is abundant. It is the superior choice for most farm vehicle applications.
• Biodiesel is a direct drop-in fuel requiring no engine modification. Where tallow and alcohol are available (Doc #57), it is simpler than hydrogen.
• Battery-electric conversion (Doc #54) provides better energy efficiency (battery round-trip ~85–90% vs. electrolysis-to-combustion ~20–25%) but is limited by battery availability and weight.

Hydrogen’s economic case is weak compared to alternatives for most applications. It is justified only where: (a) wood gas is impractical (very short-duration tasks where 15–30 minute gasifier startup is unacceptable, or chassis too small for gasifier mounting); (b) biodiesel feedstock is unavailable locally; and (c) battery electrification is not feasible (too far from charging, too heavy-duty for available battery packs). This intersection of constraints is real but small.

Breakeven assessment

A hydrogen programme serving 50 farm vehicles would require approximately 5–10 person-years of development and infrastructure construction (electrolyser fabrication, storage vessels, engine conversions, training).⁷ The alternative — continued use of rationed petroleum or wood gas for those same vehicles — costs petroleum stocks that are finite or wood gas infrastructure that could be built instead for less effort.

The breakeven case for hydrogen depends on whether the niche it fills is genuinely unserved by other fuels. If wood gas and biodiesel cover 95% of farm vehicle fuel needs, a 5–10 person-year hydrogen programme to cover the remaining 5% has a poor return. If the gap is larger — perhaps 15–20% of farm vehicle-hours where hydrogen is genuinely the best option — the investment becomes more reasonable.

Honest assessment: Hydrogen for mobile use is a Phase 3–4 programme that should proceed only after wood gasification (Doc #56), vehicle electrification (Doc #54), and biodiesel (Doc #57) are well-established. It is a gap-filler, not a primary solution.

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1. HYDROGEN PRODUCTION FOR MOBILE USE

1.1 Electrolysis basics

Hydrogen is produced by passing electrical current through water, splitting it into hydrogen and oxygen:

2H₂O → 2H₂ + O₂

The energy required is approximately 50–55 kWh per kilogram of hydrogen produced by alkaline electrolysis at practical efficiencies (60–70% of the thermodynamic minimum).⁸ One kilogram of hydrogen contains approximately 120 MJ of chemical energy (lower heating value), but an internal combustion engine converts only 25–35% of that to mechanical work — meaning the effective energy delivered is approximately 30–42 MJ per kg, at a cost of 50–55 kWh (180–198 MJ) of electricity.⁹

The efficiency problem is severe. For every unit of useful mechanical work from a hydrogen ICE vehicle, approximately 4–6 units of electrical energy are consumed. By comparison, a battery-electric vehicle converts the same electricity to mechanical work at roughly 75–85% overall efficiency — approximately 3–4 times better.¹⁰ Hydrogen in an internal combustion engine is one of the least efficient ways to use NZ’s renewable electricity for transport.

This inefficiency is acceptable only where batteries cannot do the job — and only because NZ has surplus renewable generation capacity (approximately 42,000–44,000 GWh/year, far exceeding domestic demand even under recovery conditions) that would otherwise be curtailed.¹¹

1.2 Electrolyser types NZ can build

Alkaline electrolysis is the relevant technology. It uses a potassium hydroxide (KOH) solution as the electrolyte, nickel or nickel-plated steel electrodes, and a porous diaphragm separator. The operating temperature is 60–90°C, and the operating pressure is typically 1–30 bar depending on design.¹²

NZ can fabricate alkaline electrolysers:

• Electrodes: Nickel sheet or nickel-plated mild steel. NZ has some nickel stocks (industrial supply) and nickel plating capability in engineering workshops. Nickel is also present in stainless steel alloys. Long-term nickel supply depends on recycling and possibly Tasman trade (Australia has significant nickel production).
• Electrolyte: Potassium hydroxide, producible from potash (wood ash leaching) or from potassium chloride by electrolysis. NZ has potassium-bearing minerals and abundant wood ash. Concentration control is important — typical operating concentration is 25–30% KOH by weight.
• Diaphragm: Asbestos was the traditional separator material (and NZ has asbestos-bearing rock in the South Island), but health risks are severe. Modern alternatives include zirconia-coated fabric (requiring zirconium oxide powder and a suitable base fabric — zirconia is obtainable from zircon sand, which NZ has in limited quantities in West Coast black sand deposits), porous nickel (sintered from nickel powder, feasible if nickel stock is available), or polymer membranes (dependent on imported polymer stock). NZ’s ability to produce suitable separators is uncertain and requires experimentation.
• Cell frames and containment: Mild steel or stainless steel, within NZ fabrication capability.
• Electrical supply: DC power at low voltage (1.6–2.0 V per cell), high current. Rectifiers can be fabricated from NZ-available components (transformer + diode bridge), or cells can be powered directly from DC sources (solar panels, appropriately configured generators).

PEM (Proton Exchange Membrane) electrolysis requires platinum-group-metal catalysts and perfluorosulfonic acid membranes (Nafion or equivalent) that NZ cannot produce. PEM electrolysis is not a viable NZ pathway.¹³

1.3 Production rates and scale

A modular alkaline electrolyser with a 50 kW electrical input produces approximately 1 kg of hydrogen per hour (at ~70% efficiency).¹⁴ Operating 10 hours per day, this produces 10 kg of hydrogen — enough to fuel one to two farm tractors at moderate use levels (a tractor performing 4–6 hours of work per day might consume 3–8 kg of H₂, depending on load).¹⁵

Scaling to serve 50 vehicles would require approximately 500 kW of dedicated electrolysis capacity, consuming ~5 MWh per day. This is well within the output of a single small hydro or wind installation, or a grid connection to one of NZ’s substations.

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2. THE STORAGE PROBLEM

Storage is the central challenge of hydrogen for mobile use. Hydrogen has excellent energy per unit mass (120 MJ/kg, roughly three times petrol by weight) but terrible energy per unit volume — at atmospheric pressure, one kilogram of hydrogen occupies approximately 11 cubic metres.¹⁶ Making hydrogen compact enough for a vehicle requires either compressing it, liquefying it, or absorbing it into a solid material.

2.1 Low-pressure gaseous storage (achievable)

Storage at 10–20 bar (150–300 psi) is within NZ’s fabrication capability. Mild steel vessels rated to these pressures are standard industrial equipment — compressed air receivers, LPG vessels, and similar items are fabricated and tested in NZ workshops routinely.

The range problem: At 20 bar, hydrogen density is approximately 1.6 kg/m³. Storing 5 kg of hydrogen (enough for 50–80 km of tractor operation, estimated) requires a vessel volume of approximately 3.1 cubic metres — roughly the size of a large chest freezer.¹⁷ This is impractical for a road vehicle but tolerable for a farm tractor or site vehicle that does not travel far and can mount a large, heavy tank on a frame or trailer.

Weight: A mild steel vessel rated to 20 bar at this volume weighs approximately 300–500 kg, depending on wall thickness and safety factor. Again, unacceptable for a road car; tolerable for a tractor.

Range at low pressure: With 5 kg of usable hydrogen, a converted tractor engine operating at 25–30% thermal efficiency produces approximately 150–180 MJ of mechanical work — equivalent to roughly 4–5 litres of diesel in useful work output. This represents a few hours of moderate tractor operation.¹⁸ Refuelling would need to happen at least daily, possibly twice daily for intensive use. The tractor must operate within return distance of the refuelling point.

2.2 Moderate-pressure storage (uncertain)

Storage at 50–200 bar would significantly improve range — at 200 bar, the 5 kg storage vessel shrinks to approximately 250–350 litres depending on compressibility corrections (still large, but more manageable).¹⁹ However, this introduces two challenges NZ must solve:

Hydrogen embrittlement: Hydrogen diffuses into steel grain boundaries, causing progressive embrittlement and eventual catastrophic failure. At pressures above approximately 50 bar, standard mild steel and many common alloys become susceptible.²⁰ Resistant alloys include certain austenitic stainless steels (316L), aluminium alloys (6061-T6), and chromium-molybdenum steels (4130, 4140 with specific heat treatments). NZ Steel’s Glenbrook works (Doc #89) produces carbon steel, not alloy steels suitable for hydrogen service. Stainless steel stocks in NZ are finite and imported.

Compression: Compressing hydrogen to 200 bar requires multi-stage compressors with inter-stage cooling. Reciprocating compressors suitable for hydrogen service require special seals and materials to prevent leaks (hydrogen’s small molecular size makes it leak through seals that contain other gases). NZ could fabricate such compressors given sufficient engineering effort, but the materials constraints for hydrogen-compatible seals and valves are significant.

Assessment: Moderate-pressure hydrogen storage (50–200 bar) is not feasible in Phase 3 with NZ-only resources. It might become feasible in Phase 4–5 with imported alloy steels or aluminium alloys from Australia, plus development of local testing and certification capability. This remains uncertain.

2.3 High-pressure storage (not feasible)

Modern hydrogen fuel cell vehicles store hydrogen at 350–700 bar in Type III (aluminium liner + carbon fibre overwrap) or Type IV (polymer liner + carbon fibre overwrap) composite pressure vessels.²¹ NZ cannot produce carbon fibre — it requires polyacrylonitrile (PAN) precursor and specialised high-temperature carbonisation furnaces that represent a significant industrial chemistry capability NZ does not have.²² Without carbon fibre, high-pressure hydrogen storage for vehicles is not achievable.

All-metal vessels at 350–700 bar are theoretically possible but would be extremely heavy (thousands of kilograms for a vehicle-sized vessel), defeating the purpose.

2.4 Liquid hydrogen (not feasible)

Liquefying hydrogen requires cooling to -253°C, consuming approximately 30–40% of the hydrogen’s energy content and requiring a cryogenic plant with multi-stage refrigeration.²³ NZ has no cryogenic hydrogen capability and building one is a major industrial project with no precedent in NZ. Boil-off losses (1–3% per day in even well-insulated vessels) make liquid hydrogen impractical for vehicles that are not used daily.²⁴ This pathway is not considered further.

2.5 Metal hydride storage (possible with imported materials)

Certain metal alloys absorb hydrogen at low pressure (1–10 bar) and release it when heated (typically to 50–300°C, depending on the alloy). This avoids the high-pressure problem entirely. The hydrogen is stored within the crystal lattice of the alloy, achieving volumetric density comparable to or exceeding liquid hydrogen in some alloys.²⁵

Candidate alloys and NZ availability:

Alloy	Operating temp (°C)	H₂ capacity (wt%)	NZ availability
LaNi₅ (lanthanum nickel)	20–50	~1.4%	Lanthanum: not available. Nickel: limited stocks, possible Australian import
FeTi (iron titanium)	20–50	~1.8%	Iron: NZ Steel. Titanium: not produced in NZ; Australia has significant Ti resources
MgH₂ (magnesium hydride)	250–350	~7.6%	Magnesium: not produced in NZ; limited natural deposits; possible Australian import
Mg₂Ni	200–300	~3.6%	Both materials not produced in NZ
NaAlH₄ (sodium alanate)	100–180	~5.5%	Sodium: from salt electrolysis (feasible). Aluminium: Tiwai Point if operational

The weight problem: Metal hydride systems are heavy. A FeTi system storing 5 kg of hydrogen weighs approximately 280 kg of alloy alone, plus the containment vessel, heat exchanger, and control systems — total system weight of 350–500 kg.²⁶ This is comparable to the low-pressure gaseous storage option in weight, but in a much more compact volume and without the high-pressure safety concerns.

Assessment: Metal hydride storage is the most promising medium-term pathway for extending hydrogen vehicle range beyond the low-pressure gaseous limit. However, it depends entirely on importing alloy materials — primarily titanium and nickel from Australia, or magnesium and rare earths from further afield. If Tasman trade develops (Doc #151) and these materials become available, metal hydride storage could enable hydrogen vehicles with usable ranges of 80–150 km — still short by pre-war standards, but adequate for rural district transport.²⁷

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3. ENGINE CONVERSION

3.1 Hydrogen in spark-ignition engines

Hydrogen burns in air and can fuel any spark-ignition (petrol) internal combustion engine with modifications. The key properties that differ from petrol:²⁸

• Wide flammability range: Hydrogen burns at fuel-air ratios from 4% to 75% by volume (petrol: 1.4–7.6%). This means hydrogen engines can run very lean, improving efficiency but requiring careful mixture control.
• High flame speed: Hydrogen burns approximately 6–8 times faster than petrol. This allows higher engine speeds but also creates a risk of pre-ignition and backfire if mixture and timing are not properly controlled.
• Low ignition energy: Hydrogen ignites at approximately 0.02 mJ (petrol: ~0.24 mJ). Hot spots, carbon deposits, or residual exhaust gases can cause uncontrolled ignition.
• No carbon: Hydrogen combustion produces only water vapour and (due to nitrogen in air) small amounts of NOₓ. No carbon monoxide, no particulates, no CO₂.

3.2 Required modifications

Converting a petrol engine to hydrogen requires:

Fuel delivery system: The carburetor or fuel injection system must be replaced or modified. For low-pressure hydrogen, a simple venturi mixer or port injection using modified gas injectors is adequate. Fuel pressure regulators appropriate for hydrogen (which leaks through seals more readily than hydrocarbon gases) must be fabricated or adapted from natural gas / LPG components — NZ has an LPG vehicle conversion industry that provides a base of relevant experience and components.²⁹

Ignition timing: Must be retarded (delayed) relative to petrol calibration to prevent backfire, which occurs when the hydrogen-air mixture ignites during the intake stroke while the intake valve is still open. Cold-type spark plugs (which dissipate heat faster) reduce hot-spot pre-ignition.

Intake manifold: Should be modified to prevent backfire damage. A backfire arrestor (flame trap) on the intake is essential. Some builders use a water injection system to cool the intake charge and reduce pre-ignition risk.

Compression ratio: Hydrogen’s high octane rating (approximately 130 RON equivalent) allows higher compression ratios than petrol, improving thermal efficiency.³⁰ However, modifying compression ratio requires machining the cylinder head or fitting different pistons — significant workshop effort. Initial conversions should run at the existing compression ratio with timing adjustments; compression ratio optimisation is a later refinement.

Crankcase ventilation: Hydrogen can leak past piston rings into the crankcase. Positive crankcase ventilation must be maintained to prevent hydrogen accumulation in the crankcase (explosion risk).

3.3 Performance expectations

A petrol engine converted to hydrogen with no compression ratio change will produce approximately 70–85% of its original power output.³¹ This power reduction is partly offset by the wide lean-burn capability — operating at lean mixtures improves thermal efficiency, potentially reaching 30–38% (vs. 25–30% for petrol at stoichiometric mixture).

Practical implication: A 75 kW petrol tractor engine converted to hydrogen produces approximately 50–65 kW. For farm tractor work — ploughing, hauling, PTO-driven equipment — this is usually adequate, though the heaviest tasks (deep ploughing in heavy soil) may be marginal.

3.4 Diesel engine considerations

NZ’s farm vehicle fleet is predominantly diesel. Diesel engines are compression-ignition and cannot run on hydrogen alone — hydrogen’s autoignition temperature (~585°C) is higher than diesel fuel (~210°C), so it does not reliably ignite under compression.³²

Options:

• Dual-fuel: Inject a small amount of diesel as a pilot ignition source while supplying hydrogen as the primary fuel. This is analogous to the dual-fuel approach used with wood gas (Doc #56). Diesel substitution rates of 60–80% with hydrogen are reported in research literature.³³ This preserves the diesel engine and uses hydrogen for most of the energy, but still requires some diesel supply.
• Spark ignition conversion: Add a spark ignition system to a diesel engine. This is a significant modification — diesel combustion chambers are designed for compression ignition and may not perform well with spark ignition. Feasible but complex, and the engine may need derating.

Dual-fuel is the more practical approach for NZ’s diesel tractor fleet. It requires less modification than full spark ignition conversion and allows flexibility between hydrogen and diesel depending on availability. However, dual-fuel operation typically reduces peak torque by 5–15% compared to straight diesel, and the diesel pilot injection (20–40% of total energy at low loads) means diesel consumption is reduced but not eliminated.³⁴

3.5 What NZ needs for engine conversion

Requirement	NZ capability	Gap
Fuel regulators	LPG conversion industry provides base	Hydrogen-specific seals and materials needed
Gas injectors	Adaptable from CNG/LPG systems	Testing and calibration for hydrogen properties
Backfire arrestors	Fabricable from steel mesh/perforated plate	Design development needed
Ignition system modifications	Automotive electrical skills available	Hydrogen-specific timing calibration
Fuel lines and fittings	Stainless steel tubing available (finite stock)	Hydrogen-rated fittings require specific materials
Testing and tuning equipment	Engine dynamometers exist in NZ workshops	Gas analysis for mixture optimisation may be limited

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4. SAFETY

4.1 Hydrogen hazards

Hydrogen is not more dangerous than petrol or wood gas, but it is dangerous in different ways that require different safety practices:

Explosion risk: Hydrogen-air mixtures are flammable over a wide range (4–75%) and detonate more readily than hydrocarbon-air mixtures. Hydrogen leaks in enclosed spaces create explosion risk. Unlike petrol vapour, which is heavier than air and pools at ground level, hydrogen is buoyant and rises — outdoor leaks disperse rapidly (a safety advantage), but indoor leaks accumulate at ceiling level (a hazard, as detection is harder).³⁵

Invisibility: Hydrogen flames are nearly invisible in daylight. A hydrogen fire may not be visually apparent until something else ignites.³⁶

Leak propensity: Hydrogen’s small molecular size (diatomic, 2.016 g/mol) means it leaks through seals, threads, and even some metals at rates much higher than larger molecules. All connections must be tested for leaks regularly. Soap-bubble testing is effective for accessible joints; electronic hydrogen sensors are preferable where available (finite stock).

Embrittlement: As discussed in Section 2.2, hydrogen degrades many common steels and alloys over time. All hydrogen-wetted components must be fabricated from compatible materials and inspected regularly.

4.2 Safety protocols for farm vehicle use

• Never refuel or operate hydrogen vehicles in enclosed buildings without forced ventilation
• Hydrogen sensors at ceiling level in any building where hydrogen vehicles are stored or maintained
• All fuel connections leak-tested after any maintenance
• Fuel system shutoff valve accessible to the operator, clearly marked
• Fire extinguisher (dry powder — water is ineffective on hydrogen fires and unnecessary since hydrogen fires produce no secondary combustion products) available at all refuelling points
• Operator training must cover hydrogen-specific hazards, not generic fuel safety — the differences from petrol and diesel behaviour are the dangerous part

4.3 Comparison with wood gas safety

Both hydrogen and wood gas (Doc #56) present serious safety risks. Carbon monoxide from wood gas is an asphyxiation hazard (colourless, odourless, lethal); hydrogen is an explosion and fire hazard. Neither is inherently safer than the other — both require trained operators and appropriate safety protocols. The NZ workforce will need specific training for each fuel type.

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5. THE FUEL CELL ALTERNATIVE

5.1 Why fuel cells are mentioned

Proton exchange membrane (PEM) fuel cells convert hydrogen directly to electricity at 40–60% efficiency — roughly double the thermal efficiency of a hydrogen ICE.³⁷ A fuel cell vehicle uses an electric motor, avoiding the mechanical complexity and power loss of combustion. If fuel cells were available, they would be the preferred hydrogen-to-motion pathway.

5.2 Why NZ cannot build them

PEM fuel cells require:

• Platinum catalyst: Approximately 10–30 grams per vehicle fuel cell stack. NZ has no platinum production. Global platinum supply is concentrated in South Africa (~70%) and Russia (~12%).³⁸ Post-event platinum availability is effectively zero.
• Perfluorosulfonic acid membrane (Nafion): A fluoropolymer membrane that NZ cannot produce. Requires advanced fluorine chemistry.
• Carbon-based gas diffusion layers: Precision-manufactured porous carbon materials.
• Bipolar plates: Machined graphite or coated stainless steel with micro-channel flow fields.

None of these are producible in NZ. Fuel cells are mentioned here to explain why this document focuses on hydrogen ICE rather than fuel cells — it is not an oversight but a materials constraint.

5.3 Existing fuel cells in NZ

NZ may have a small number of fuel cell systems in research institutions, a few hydrogen fuel cell vehicles, and some portable/backup fuel cell units. These are a finite resource. If they exist, they should be inventoried as part of the national census (Doc #8) and allocated to the highest-value applications — probably stationary power for critical communications equipment where their high efficiency and silent operation are most valuable, not for vehicles.

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6. DEPENDENCY CHAINS

6.1 Production dependencies

Alkaline electrolysis requires:

Grid electricity (Doc #67, #65)
  → Rectifier (transformer + diodes — NZ fabricable)
    → Electrolyser cell stack
      → Nickel electrodes (NZ stocks, recycling, Australian trade)
      → KOH electrolyte (from potash or KCl electrolysis)
      → Separator membrane (development needed — zirconia, porous nickel, or polymer)
      → Steel cell frames (NZ Steel, Doc #89)
    → Water purification (deionised water required — ion exchange or distillation)

6.2 Storage dependencies

Low-pressure gaseous (achievable):

NZ Steel plate or pipe (Doc #89)
  → Pressure vessel fabrication (NZ workshops, Doc #89)
    → Hydrostatic pressure testing (NZ capability exists)
      → Valve and fitting fabrication (limited by hydrogen-compatible seal materials)

Metal hydride (requires imports):

Alloy powder (FeTi or LaNi₅)
  → Titanium (Australian import via Tasman trade, Doc #151)
  → Nickel (Australian import or NZ recycled stocks)
  → Alloy fabrication (arc melting, milling — NZ capable if materials available)
    → Activation treatment (heating/cycling under hydrogen)
      → Containment vessel with heat exchanger (NZ fabricable)

6.3 Engine conversion dependencies

Donor engine (petrol or diesel from NZ vehicle fleet)
  → Fuel injection/mixing system
    → Regulators (adapted from LPG components — NZ stocks)
    → Hydrogen-compatible seals (PTFE, specific elastomers — finite imported stock)
    → Stainless steel fuel lines (NZ stocks, finite)
  → Ignition modification (workshop capability, Doc #91)
  → Backfire prevention (fabricable from steel mesh)
  → Operator training (Doc #157)

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7. CRITICAL UNCERTAINTIES

Uncertainty	Impact	How to resolve
NZ’s existing electrolyser equipment and hydrogen experience	Determines starting point for development	National asset census (Doc #8)
Electrolyser separator membrane fabrication	A potential showstopper for domestic electrolyser production	Materials science experimentation in Phase 2
Hydrogen embrittlement rates in NZ-available steels	Determines safe operating pressure for NZ-fabricated vessels	Systematic testing programme using NZ Steel products
Actual range and productivity of low-pressure hydrogen farm vehicles	Determines whether the niche is practical or only theoretical	Prototype deployment in Phase 3
Tasman trade development for titanium, nickel, rare earths	Determines whether metal hydride storage becomes available	Dependent on Doc #151 outcomes
LPG component suitability for hydrogen service	Affects conversion cost and complexity	Testing NZ LPG components with hydrogen
Diesel dual-fuel calibration for NZ engine types	Determines whether NZ’s diesel tractor fleet can use hydrogen	Engine testing programme
Farmer adoption and safety compliance	Determines real-world deployment success	Training and demonstration programmes

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CROSS-REFERENCES

Document	Relationship
Doc #8 (National Asset and Skills Census)	Identifies electrolyser equipment, pressure vessel capability, workshop capacity
Doc #33 (Tires)	Hydrogen vehicles face the same tire constraint as all vehicles
Doc #34 (Lubricants)	Hydrogen engines require lubricants; hydrogen combustion produces water that may affect oil life
Doc #35 (Batteries)	Battery-electric is the competing and generally superior electrification pathway
Doc #53 (Fuel Allocation)	Hydrogen fits within the national fuel transition strategy
Doc #54 (Vehicle Electrification)	The primary vehicle electrification pathway; hydrogen is complementary, not alternative
Doc #56 (Wood Gasification)	The primary combustion fuel substitute; hydrogen competes for the same vehicle niche
Doc #57 (Biodiesel)	Another competing fuel pathway for farm vehicles
Doc #63 (Hydrogen: Stationary)	The prerequisite — stationary hydrogen production must work before mobile applications
Doc #65 (Hydro Maintenance)	Grid electricity powers electrolysis
Doc #67 (Transpower Grid)	Grid reliability determines electrolyser operation
Doc #89 (NZ Steel)	Steel supply for pressure vessels, electrolyser components, and vehicle modifications
Doc #91 (Machine Shop Operations)	Fabrication capability for all hydrogen hardware
Doc #113 (Sulfuric Acid)	Nickel processing and some electrolyser component treatments require acid
Doc #151 (Trans-Tasman Relations)	Australian trade route for titanium, nickel, and potentially other hydrogen-relevant materials
Doc #157 (Trade Training)	Operator and technician training for hydrogen systems

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FOOTNOTES

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1. High-pressure hydrogen storage vessels for vehicles: SAE International, “J2579 — Technical Information Report for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles,” multiple editions. Type IV vessels (polymer-lined, carbon fibre overwrap) are used in Toyota Mirai and Hyundai Nexo at 700 bar. Type III (aluminium-lined, carbon fibre overwrap) are common at 350 bar. See also: US Department of Energy, Hydrogen and Fuel Cells Program, “Hydrogen Storage” technical pages. https://www.energy.gov/eere/fuelcells/hydrogen-storage↩︎

2. Hydrogen embrittlement of steels is extensively documented. See: Gangloff, R.P. and Somerday, B.P. (eds), “Gaseous Hydrogen Embrittlement of Materials in Energy Technologies,” Woodhead Publishing, 2012. For practical guidelines on materials selection for hydrogen service: ASME B31.12, “Hydrogen Piping and Pipelines.” The susceptibility threshold depends on steel type, stress state, and hydrogen pressure — as a general guideline, carbon and low-alloy steels require careful evaluation above ~50 bar hydrogen pressure, and many common structural steels should not be used in high-pressure hydrogen service.↩︎

3. Metal hydride storage: Züttel, A., “Materials for hydrogen storage,” Materials Today, 2003, 6(9), 24–33. https://doi.org/10.1016/S1369-7021(03)00922-2. Also: Sakintuna, B., Lamari-Darkrim, F., and Hirscher, M., “Metal hydride materials for solid hydrogen storage: A review,” International Journal of Hydrogen Energy, 2007, 32(9), 1121–1140.↩︎

4. NZ tractor and agricultural vehicle numbers are estimated from NZ Transport Agency registration data and industry sources. The exact figure of registered tractors is not readily available from public sources; the Motor Trade Association or Federated Farmers may have more precise data. Figure requires verification.↩︎

5. Electrolyser construction time estimate is based on documented small-scale alkaline electrolyser builds in research and maker communities. The actual time depends heavily on design complexity, materials preparation, and fabricator experience. This figure should be treated as a rough order-of-magnitude estimate.↩︎

6. Hydrogen ICE conversion: Verhelst, S. and Wallner, T., “Hydrogen-fueled internal combustion engines,” Progress in Energy and Combustion Science, 2009, 35(6), 490–527. https://doi.org/10.1016/j.pecs.2009.08.001. This is the standard reference for hydrogen ICE engineering. Also: White, C.M., Steeper, R.R., and Lutz, A.E., “The hydrogen-fueled internal combustion engine: a technical review,” International Journal of Hydrogen Energy, 2006, 31(10), 1292–1305.↩︎

7. Person-year estimate derived from the per-unit estimates in this document: 50 engine conversions at 40–100 person-hours each (2,000–5,000 hours), plus electrolyser construction for 5–10 installations at 200–400 hours each (1,000–4,000 hours), plus storage vessel fabrication, infrastructure, and training. Total: approximately 5,000–15,000 person-hours, or roughly 3–8 person-years at 1,800 hours/year. The 5–10 person-year range accounts for additional overhead, design iteration, and unforeseen difficulties. This is a rough planning estimate.↩︎

8. Electrolyser energy consumption: Ursua, A., Gandia, L.M., and Sanchis, P., “Hydrogen Production From Water Electrolysis: Current Status and Future Trends,” Proceedings of the IEEE, 2012, 100(2), 410–426. Practical alkaline electrolysis consumes 50–55 kWh per kg H₂ at the cell stack; system-level consumption is typically 55–65 kWh/kg including pumps, controls, and balance of plant.↩︎

9. Hydrogen lower heating value: 120.0 MJ/kg (standard thermodynamic value). Internal combustion engine thermal efficiency for hydrogen is typically 25–38% depending on operating conditions and compression ratio. See Verhelst and Wallner (note 6).↩︎

10. Electric vehicle well-to-wheel efficiency comparison: for grid electricity to battery to motor, overall efficiency is approximately 75–85%. For grid electricity to electrolysis to hydrogen to ICE, overall efficiency is approximately 15–25%. This comparison is standard in energy systems analysis. See: Bossel, U., “Does a Hydrogen Economy Make Sense?” Proceedings of the IEEE, 2006, 94(10), 1826–1837.↩︎

11. NZ electricity generation: approximately 42,000–44,000 GWh per year, of which ~82–87% is from renewable sources (hydro ~55%, geothermal ~18%, wind ~7%, other renewables ~5%). Source: MBIE, “Energy in New Zealand” annual reports. https://www.mbie.govt.nz/building-and-energy/energy-and-n... Under post-event conditions with reduced industrial demand, significant surplus generation capacity would be available.↩︎

12. Alkaline electrolyser operating parameters: see Ursua et al. (note 7). Operating temperature of 60–90°C improves electrode kinetics and ionic conductivity. Pressurised operation up to 30 bar is achievable in well-designed cells, reducing downstream compression requirements. Traditional separators were asbestos cloth; modern systems use zirconium oxide–coated polymers (Zirfon) or similar materials.↩︎

13. PEM electrolysis requires iridium oxide anode catalysts and platinum cathode catalysts, plus Nafion (perfluorosulfonic acid) membranes manufactured by DuPont or equivalent producers. None of these materials are producible in NZ. See: Carmo, M. et al., “A comprehensive review on PEM water electrolysis,” International Journal of Hydrogen Energy, 2013, 38(12), 4901–4934.↩︎

14. Electrolyser energy consumption: Ursua, A., Gandia, L.M., and Sanchis, P., “Hydrogen Production From Water Electrolysis: Current Status and Future Trends,” Proceedings of the IEEE, 2012, 100(2), 410–426. Practical alkaline electrolysis consumes 50–55 kWh per kg H₂ at the cell stack; system-level consumption is typically 55–65 kWh/kg including pumps, controls, and balance of plant.↩︎

15. Hydrogen consumption for farm tractor operations is estimated from engine power output, thermal efficiency, and typical duty cycles. A 50 kW engine at 30% efficiency consuming hydrogen at 120 MJ/kg would consume approximately 1.0–1.5 kg/hr at moderate load. This figure requires validation against actual hydrogen tractor operating data, which is limited.↩︎

16. Hydrogen gas density at standard temperature and pressure (STP, 0°C, 1 atm): 0.0899 kg/m³. One kilogram therefore occupies approximately 11.1 m³. This is a basic physical property.↩︎

17. Low-pressure storage calculation: at 20 bar and 20°C, hydrogen density is approximately 1.6 kg/m³ (using ideal gas law with compressibility correction). Storing 5 kg requires ~3.1 m³ of gas volume. Vessel volume is slightly larger to account for wall thickness and internal fittings. The vessel weight estimate assumes mild steel at a design pressure of 20 bar with appropriate safety factor (typically 3:1 for pressure vessels) and standard cylindrical geometry.↩︎

18. Range and work output estimate: 5 kg H₂ × 120 MJ/kg × 0.30 (engine efficiency) = 180 MJ mechanical work. Diesel energy content is ~38.6 MJ/litre, with engine efficiency ~35%, giving ~13.5 MJ/litre of mechanical work. So 180 MJ ÷ 13.5 MJ/litre ≈ 13 diesel-equivalent litres. However, the comparison is approximate because duty cycles and engine loading patterns differ. The “few hours” estimate assumes moderate tractor workload.↩︎

19. At 200 bar and 20°C, hydrogen density is approximately 14–16 kg/m³ (ideal gas law significantly overpredicts at this pressure; real-gas compressibility factor Z ≈ 1.10–1.13 must be applied). Storing 5 kg therefore requires approximately 310–360 litres of internal vessel volume. The range reflects uncertainty in temperature and compressibility correction. See: NIST Chemistry WebBook, Thermophysical Properties of Hydrogen, https://webbook.nist.gov/chemistry/fluid/↩︎

20. Hydrogen embrittlement of steels is extensively documented. See: Gangloff, R.P. and Somerday, B.P. (eds), “Gaseous Hydrogen Embrittlement of Materials in Energy Technologies,” Woodhead Publishing, 2012. For practical guidelines on materials selection for hydrogen service: ASME B31.12, “Hydrogen Piping and Pipelines.” The susceptibility threshold depends on steel type, stress state, and hydrogen pressure — as a general guideline, carbon and low-alloy steels require careful evaluation above ~50 bar hydrogen pressure, and many common structural steels should not be used in high-pressure hydrogen service.↩︎

21. High-pressure hydrogen storage vessels for vehicles: SAE International, “J2579 — Technical Information Report for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles,” multiple editions. Type IV vessels (polymer-lined, carbon fibre overwrap) are used in Toyota Mirai and Hyundai Nexo at 700 bar. Type III (aluminium-lined, carbon fibre overwrap) are common at 350 bar. See also: US Department of Energy, Hydrogen and Fuel Cells Program, “Hydrogen Storage” technical pages. https://www.energy.gov/eere/fuelcells/hydrogen-storage↩︎

22. Carbon fibre production requires polyacrylonitrile (PAN) fibre, which is drawn, oxidised at 200–300°C, and then carbonised at 1,000–3,000°C in an inert atmosphere. The PAN precursor itself requires acrylonitrile, produced from propylene and ammonia (the Sohio process). This represents a multi-step petrochemical/industrial chemistry chain that NZ does not have. See: Huang, X., “Fabrication and Properties of Carbon Fibers,” Materials, 2009, 2(4), 2369–2403.↩︎

23. Liquid hydrogen: boiling point -252.87°C. Liquefaction consumes approximately 30–40% of the hydrogen’s energy content. Boil-off from vehicle-scale cryogenic tanks is typically 1–3% per day even with vacuum-insulated multi-layer insulation. Source: Züttel, A. (note 3) and US DOE Hydrogen Storage technical resources.↩︎

24. Liquid hydrogen: boiling point -252.87°C. Liquefaction consumes approximately 30–40% of the hydrogen’s energy content. Boil-off from vehicle-scale cryogenic tanks is typically 1–3% per day even with vacuum-insulated multi-layer insulation. Source: Züttel, A. (note 3) and US DOE Hydrogen Storage technical resources.↩︎

25. Metal hydride storage: Züttel, A., “Materials for hydrogen storage,” Materials Today, 2003, 6(9), 24–33. https://doi.org/10.1016/S1369-7021(03)00922-2. Also: Sakintuna, B., Lamari-Darkrim, F., and Hirscher, M., “Metal hydride materials for solid hydrogen storage: A review,” International Journal of Hydrogen Energy, 2007, 32(9), 1121–1140.↩︎

26. Metal hydride storage: Züttel, A., “Materials for hydrogen storage,” Materials Today, 2003, 6(9), 24–33. https://doi.org/10.1016/S1369-7021(03)00922-2. Also: Sakintuna, B., Lamari-Darkrim, F., and Hirscher, M., “Metal hydride materials for solid hydrogen storage: A review,” International Journal of Hydrogen Energy, 2007, 32(9), 1121–1140.↩︎

27. Range estimate for metal hydride hydrogen vehicles is extrapolated from the FeTi system capacity (~1.8 wt% hydrogen), assuming a 350–500 kg hydride system storing 6–9 kg of usable hydrogen, and a converted engine achieving 25–35% thermal efficiency. At an estimated fuel consumption of 0.05–0.08 kg H₂/km for a light utility vehicle, this gives approximately 80–150 km. This is a rough estimate; actual range depends heavily on vehicle weight, terrain, driving pattern, and engine calibration. No NZ-specific field data exists.↩︎

28. Hydrogen ICE conversion: Verhelst, S. and Wallner, T., “Hydrogen-fueled internal combustion engines,” Progress in Energy and Combustion Science, 2009, 35(6), 490–527. https://doi.org/10.1016/j.pecs.2009.08.001. This is the standard reference for hydrogen ICE engineering. Also: White, C.M., Steeper, R.R., and Lutz, A.E., “The hydrogen-fueled internal combustion engine: a technical review,” International Journal of Hydrogen Energy, 2006, 31(10), 1292–1305.↩︎

29. NZ’s LPG vehicle conversion industry: NZ has an established industry converting vehicles to run on LPG (liquefied petroleum gas), with accredited installers and a regulatory framework (NZS 5425). The gas handling, regulator, and injection system technologies are directly relevant to hydrogen conversion, though hydrogen’s different properties (smaller molecule, wider flammability range, higher flame speed) require specific modifications. The exact number of accredited LPG installers in NZ should be verified through the Motor Industry Association or relevant trade bodies.↩︎

30. Hydrogen ICE conversion: Verhelst, S. and Wallner, T., “Hydrogen-fueled internal combustion engines,” Progress in Energy and Combustion Science, 2009, 35(6), 490–527. https://doi.org/10.1016/j.pecs.2009.08.001. This is the standard reference for hydrogen ICE engineering. Also: White, C.M., Steeper, R.R., and Lutz, A.E., “The hydrogen-fueled internal combustion engine: a technical review,” International Journal of Hydrogen Energy, 2006, 31(10), 1292–1305.↩︎

31. Hydrogen ICE conversion: Verhelst, S. and Wallner, T., “Hydrogen-fueled internal combustion engines,” Progress in Energy and Combustion Science, 2009, 35(6), 490–527. https://doi.org/10.1016/j.pecs.2009.08.001. This is the standard reference for hydrogen ICE engineering. Also: White, C.M., Steeper, R.R., and Lutz, A.E., “The hydrogen-fueled internal combustion engine: a technical review,” International Journal of Hydrogen Energy, 2006, 31(10), 1292–1305.↩︎

32. Hydrogen-diesel dual fuel: Saravanan, N. et al., “Combustion analysis on a DI diesel engine with hydrogen in dual fuel mode,” Fuel, 2008, 87(17–18), 3591–3599. Also: Shin, B. et al., “Hydrogen combustion in a diesel engine,” International Journal of Hydrogen Energy, multiple publications. Diesel substitution rates of 60–80% are reported in research literature, but optimal calibration varies significantly by engine type.↩︎

33. Hydrogen-diesel dual fuel: Saravanan, N. et al., “Combustion analysis on a DI diesel engine with hydrogen in dual fuel mode,” Fuel, 2008, 87(17–18), 3591–3599. Also: Shin, B. et al., “Hydrogen combustion in a diesel engine,” International Journal of Hydrogen Energy, multiple publications. Diesel substitution rates of 60–80% are reported in research literature, but optimal calibration varies significantly by engine type.↩︎

34. Dual-fuel hydrogen-diesel performance: at low loads, the diesel pilot fraction is higher (30–40% of total energy input) because a minimum diesel quantity is needed for reliable ignition. At higher loads, hydrogen can supply 60–80% of total energy. Peak torque reduction of 5–15% is reported due to the lower volumetric energy density of the hydrogen-air charge displacing some intake air. See: Saravanan et al. (note 20) and Lata, D.B. and Misra, A., “Theoretical and experimental investigations on the performance of dual fuel diesel engine with hydrogen and LPG as secondary fuels,” International Journal of Hydrogen Energy, 2010, 35(21), 11918–11931.↩︎

35. Hydrogen safety properties: Molnarne, M. et al., “Safety analysis of hydrogen vehicles and infrastructure,” published by European Integrated Hydrogen Project (EIHP). Also: Rigas, F. and Amyotte, P., “Hydrogen Safety,” CRC Press, 2012. The nearly invisible flame is a distinctive hazard of hydrogen — thermal imaging can detect hydrogen fires that are invisible to the naked eye.↩︎

36. Hydrogen safety properties: Molnarne, M. et al., “Safety analysis of hydrogen vehicles and infrastructure,” published by European Integrated Hydrogen Project (EIHP). Also: Rigas, F. and Amyotte, P., “Hydrogen Safety,” CRC Press, 2012. The nearly invisible flame is a distinctive hazard of hydrogen — thermal imaging can detect hydrogen fires that are invisible to the naked eye.↩︎

37. PEM fuel cell efficiency: US DOE, “Fuel Cell Technologies Office Multi-Year Research, Development, and Demonstration Plan,” Section 3.4 — Fuel Cells. Stack efficiency of 50–60% at rated power; system efficiency (including parasitic losses for air supply, cooling, and control) of 40–55%. This compares to 25–38% for hydrogen ICE.↩︎

38. Global platinum supply: approximately 75% from South Africa (Bushveld Complex), ~12% from Russia (Norilsk), remainder from Zimbabwe, Canada, and others. US Geological Survey, Mineral Commodity Summaries, “Platinum-Group Metals,” annual. https://www.usgs.gov/centers/national-minerals-informatio...↩︎