Doc #63 — Hydrogen: Stationary Applications

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RECOMMENDED ACTIONS

Phase 1–2 (Years 0–3): Preparation

1. Inventory existing electrolysis equipment nationally — university chemistry departments, industrial gas suppliers (BOC Gas NZ), research facilities, and water treatment plants that use electrolytic processes. Include electrode materials, power supplies, and any stored KOH.

2. Secure potassium hydroxide stocks. KOH is the standard alkaline electrolyte. Chemical suppliers, soap manufacturers (Doc #37), and laboratories hold stocks. KOH is also producible domestically, but each route has prerequisites: (a) the chlor-alkali route requires potassium chloride feedstock (not the sodium chloride used for NaOH production — Doc #112), a membrane or diaphragm cell, and a reliable DC supply; (b) the potash leaching route produces dilute potassium carbonate from wood ash, which must then be causticised with lime (requiring lime production — Doc #112) and concentrated by evaporation. Neither route is a quick substitute for stockpiled material, and both require dedicated production infrastructure before electrolysis can operate at sustained scale.

3. Identify priority stationary applications where hydrogen could replace natural gas or LPG as those fuels deplete — metal heat treatment at workshops (Doc #91), glass production (Doc #98), backup generation at hospitals and communications facilities.

4. Begin experimental electrolysis at university chemistry or engineering departments to characterize performance with NZ-fabricated electrodes and locally produced KOH. This is a research and prototyping activity, not production.

Phase 3 (Years 3–7): Pilot production

5. Construct pilot alkaline electrolyzers at 2–3 sites co-located with surplus grid power — ideally near hydroelectric stations with spare capacity or geothermal stations in the Taupo Volcanic Zone.

6. Build low-pressure hydrogen storage — gasometer-type wet storage for initial installations, progressing to welded steel tank storage at modest pressure (2–5 bar) as fabrication confidence develops.

7. Convert stationary engines to hydrogen fuel at pilot sites. Internal combustion engines designed for natural gas or LPG require modification to run on hydrogen — fuel metering changes, ignition timing adjustment, and crankcase ventilation upgrades (see Section 5 for details).

8. Develop operator training and safety protocols from pilot experience. Hydrogen safety is manageable but requires discipline — leaks, ventilation, ignition sources, and embrittlement must all be addressed.

Phase 4 (Years 7–15): Scaled deployment

9. Expand electrolyzer production using standardized designs proven at pilot sites. Distribute construction plans to workshops (Doc #91).

10. Deploy hydrogen systems at critical facilities — hospitals, water treatment plants, communications sites — as backup power where battery capacity is insufficient or degrading.

11. Supply hydrogen for industrial heat applications — workshops (Doc #91), foundries (Doc #93), glass furnaces (Doc #98) — as natural gas and LPG stocks are exhausted.

12. Begin hydrogen supply for ammonia synthesis (Doc #114) if and when the broader ammonia production dependency chain is ready — a Phase 5+ capability at the earliest.

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ECONOMIC JUSTIFICATION

Person-years for pilot hydrogen system

Construction of a pilot electrolyzer and storage system (50 kW electrolyzer, gasometer storage, engine-generator):

• Electrolyzer fabrication: approximately 1,000–2,000 person-hours (includes electrode preparation, vessel welding, electrical connections, and testing)
• Storage construction (gasometer): approximately 500–1,500 person-hours
• Engine conversion and generator setup: approximately 200–500 person-hours
• Total construction: approximately 1,700–4,000 person-hours, or roughly 1–2 person-years
• Ongoing operation: 1–2 FTE per installation (monitoring, maintenance, water and KOH supply, safety management)

What it produces

A 50 kW electrolyzer operating at 70% capacity factor (limited by surplus electricity availability) produces approximately 250–300 kg of hydrogen per month.⁷ This is enough to:

• Run a 10 kW backup generator for approximately 200–300 hours per month (partial duty — not continuous, but substantial backup capacity)
• Supply approximately 10–15 hours of high-temperature heat for metalworking per week
• Or provide chemical-grade hydrogen for laboratory and industrial processes

Comparison with alternatives

Without hydrogen, what are the alternatives for these applications?

• Backup power: Lead-acid batteries (Doc #35) serve this role but degrade over 3–5 years and depend on a lead recycling and sulfuric acid supply chain. Hydrogen provides an alternative storage pathway using different materials.
• Industrial heat: Wood and charcoal (Doc #56, Doc #102) can provide heat, but not the clean, precisely controllable flame that some metalworking and glass processes require. Natural gas and LPG stocks are finite — perhaps 5–15 years under reduced consumption, depending on field depletion and equipment condition.
• Chemical feedstock: There is no substitute for hydrogen in ammonia synthesis or certain metallurgical reductions. If NZ ever achieves domestic fertilizer production (Doc #114), it needs hydrogen.

Breakeven is difficult to define because hydrogen serves applications that have no other adequate substitute. The economic case is strongest for industrial heat (replacing depleting natural gas) and chemical feedstock (enabling ammonia synthesis). For backup power, the case depends on how well the battery supply chain (Doc #35) holds up — if lead-acid production meets demand, batteries are more efficient; if it falters, hydrogen provides a complementary pathway.

Opportunity cost

The 1–2 person-years of construction labor for a pilot system is modest. The ongoing 1–2 FTE is more significant. These workers could alternatively be building micro-hydro installations (Doc #72) or maintaining grid infrastructure (Doc #67). The hydrogen program should not begin until grid maintenance is staffed and basic manufacturing priorities (Doc #67) are met. This is a Phase 3 priority, not Phase 1.

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1. ELECTROLYSIS: HOW IT WORKS

1.1 Basic chemistry

Water electrolysis is the decomposition of water into hydrogen and oxygen using electrical energy:

2 H₂O → 2 H₂ + O₂

At the cathode (negative electrode), water is reduced to hydrogen gas:

4 H₂O + 4e⁻ → 2 H₂ + 4 OH⁻

At the anode (positive electrode), hydroxide ions are oxidized to oxygen gas:

4 OH⁻ → O₂ + 2 H₂O + 4e⁻

The theoretical minimum energy to split water is 39.4 kWh per kilogram of hydrogen produced (based on the higher heating value of hydrogen).⁸ In practice, alkaline electrolyzers consume approximately 50–70 kWh per kilogram of hydrogen, with the excess dissipated as heat.⁹ This gives an energy efficiency of roughly 55–80%, depending on current density, temperature, and electrode condition.

1.2 Alkaline electrolysis

Alkaline electrolysis is the oldest and simplest method. The cell consists of:

• Two electrodes immersed in an aqueous solution of potassium hydroxide (KOH), typically at 25–30% concentration by weight
• A diaphragm or separator between the electrodes to prevent mixing of hydrogen and oxygen gases while allowing ionic current flow
• A cell vessel to contain the electrolyte and collect the gases

When DC current passes through the cell, hydrogen bubbles form at the cathode and oxygen at the anode. The gases rise to the surface and are collected separately.

Why alkaline, not PEM or solid oxide? Proton exchange membrane (PEM) electrolyzers use expensive platinum-group metal catalysts and proprietary polymer membranes — materials NZ cannot produce and has limited stocks of. Solid oxide electrolyzers operate at 700–900°C and use complex ceramic materials. Alkaline electrolysis uses common materials: steel, nickel, and potassium hydroxide. It is the technology NZ can build.¹⁰

1.3 The diaphragm problem

The diaphragm or separator is the most technically challenging component. Its job is to allow hydroxide ions (OH⁻) to pass between cathode and anode compartments while preventing hydrogen and oxygen gases from mixing. If the gases mix, the result is an explosive mixture (hydrogen is flammable in air at concentrations of 4–75%).¹¹

Industrial separators use asbestos cloth (traditional, effective, but a health hazard), Zirfon (a proprietary zirconium oxide/polymer composite), or other specialty membranes. NZ is unlikely to produce any of these.

Workable NZ alternatives:

• Woven nickel wire cloth: Fine nickel mesh can serve as a gas-permeable, ion-permeable separator. Nickel is available from NZ recycling streams (stainless steel contains 8–10% nickel; NZ coinage contains nickel).¹²
• Porous ceramic: A thin ceramic plate with controlled porosity can serve as a diaphragm. NZ has ceramic capability (Doc #97 discusses cement; clay-based ceramics are within fabrication reach).
• Woven polyester or polypropylene fabric: Synthetic fabrics from NZ’s existing textile stocks can function as separators at moderate current densities. Durability in hot KOH is limited — replacement every few hundred to few thousand hours may be necessary.
• No separator (open-cell design): At very low current densities and with careful gas collection, electrolysis can be performed without a separator. Gas mixing is managed by physical geometry — wide electrode spacing, separate gas collection chambers — rather than a membrane. Energy consumption increases because more power is wasted and current efficiency drops; hydrogen purity is reduced to approximately 95–99% (vs. 99.5%+ with a good separator), with oxygen contamination posing a safety and quality concern at the lower end of that range.¹³ For applications where 95%+ purity hydrogen is acceptable — engine fuel and general heat applications tolerate this level — a separator-free design may suffice, though operators must monitor gas purity and maintain safe oxygen-in-hydrogen concentrations below 2% to avoid explosive mixtures.¹⁴

The separator question is the primary engineering challenge for NZ-fabricated electrolyzers. Early prototypes should test multiple approaches and select the best-performing option from available materials.

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2. ELECTROLYZER CONSTRUCTION

2.1 Electrode materials

Cathode (hydrogen electrode): Mild steel works, but corrodes slowly in hot KOH. Nickel or nickel-plated steel is preferred — nickel is stable in alkaline solutions and has good catalytic activity for hydrogen evolution. Nickel plating is within NZ’s electroplating capability (available at plating shops identified through the skills census, Doc #8). Stainless steel (grades 304 or 316) also works but is less catalytically active than nickel.¹⁵

Anode (oxygen electrode): More demanding than the cathode. Oxygen evolution in alkaline solution is corrosive, and the anode must resist oxidation while catalyzing the reaction. Options:

• Nickel: The standard industrial choice. Good corrosion resistance, adequate catalytic activity. Available from recycling.
• Nickel-plated steel: Acceptable if plating is thick enough (25–50 micrometers minimum) to resist oxygen-side corrosion.
• Stainless steel: Usable but corrodes faster on the oxygen side than nickel. May require periodic replacement.
• Nickel with added catalytic coatings: Industrial electrolyzers use nickel coated with mixed metal oxides (nickel-iron, nickel-cobalt) to reduce the voltage required. NZ could experiment with nickel-iron oxide coatings — iron is abundant and the coating can be applied by electrodeposition from a mixed nickel-iron salt solution. This is an optimization, not a requirement — uncoated nickel works, at somewhat lower efficiency.¹⁶

Electrode geometry: Flat plates are simplest to fabricate. Industrial electrolyzers use expanded metal mesh or perforated plate to increase surface area — both are within NZ metalworking capability. Plate dimensions of 300 mm x 300 mm to 500 mm x 500 mm are practical for workshop-scale fabrication.

2.2 Cell design

Two basic configurations:

Monopolar (tank-type): Multiple pairs of electrodes immersed in a single tank of electrolyte. Each pair operates at the cell voltage (~1.8–2.4 V). Pairs are connected in parallel to a common DC supply. The tank can be mild steel (with appropriate insulation from the electrodes) or stainless steel, and requires only basic welding and plumbing skills. Gas collection uses the natural buoyancy of the gases — hydrogen rises from cathodes, oxygen from anodes, collected by inverted troughs or separate collection chambers above each electrode set.

Bipolar (filter-press type): Electrodes are stacked with separators between them, like a sandwich. Each intermediate plate is a cathode on one side and an anode on the other. Cells are connected in series — the total voltage is the cell voltage multiplied by the number of cells. More compact and efficient than monopolar, but harder to fabricate (requires good sealing between cells to prevent gas mixing) and harder to maintain (the entire stack must be disassembled to replace a single failed cell).¹⁷

Recommendation for NZ: Start with monopolar tank-type electrolyzers. They are less efficient per unit of electrode area but far simpler to build, maintain, and troubleshoot. A workshop team building their first electrolyzer should not be attempting filter-press sealing. Once the simpler design is proven and operators are experienced, bipolar designs can be developed for higher-volume installations.

2.3 Electrical supply

Electrolysis requires DC current. NZ’s grid supplies AC. Conversion options:

• Rectifiers from salvaged electronics: Power supply rectifiers, welding machines (which contain high-current rectifiers), and motor drive inverters all contain the components needed. A welding rectifier outputting 50–200 A at 20–60 V DC is close to ideal for a small electrolyzer.¹⁸
• Purpose-built rectifiers: A transformer (to step down grid voltage to 20–60 V) followed by a diode bridge rectifier. Transformers and power diodes are available from NZ industrial stocks. Transformer rewinding capability exists (Doc #69).
• Direct DC from micro-hydro or solar: Some micro-hydro generators (Doc #72) can output DC directly, and solar panels (Doc #73) inherently produce DC. Electrolyzers co-located with DC generation avoid the AC-DC conversion loss.

Power requirement: Producing 1 kg of hydrogen requires approximately 50–70 kWh of electricity.¹⁹ A 50 kW electrolyzer running at full power produces roughly 0.7–1.0 kg of hydrogen per hour. For context, 1 kg of hydrogen contains approximately 33.3 kWh of energy (lower heating value), so the round-trip efficiency of electricity-to-hydrogen-to-electricity via an engine-generator is roughly 20–30%.²⁰

2.4 Water supply

Electrolysis requires reasonably pure water. Tap water contains dissolved minerals that deposit on electrodes and degrade performance. Distilled or deionized water is preferred. Rain water collection provides a good source — NZ rainfall is generally low in dissolved minerals.²¹

Water consumption: approximately 9–10 litres per kilogram of hydrogen produced (9 litres stoichiometric, plus some excess for electrolyte maintenance and evaporation losses). A 50 kW system uses roughly 6–10 litres of water per hour — approximately 50–80 litres per day, comparable to the domestic water use of one to two people. This is not a binding constraint under NZ conditions where rain collection is available, but it is a real input that must be planned for at each site, particularly in drier eastern regions or during drought periods.

2.5 Dependency chain

Input	NZ Source	Status	Constraint
Electricity	Grid (hydro, geothermal, wind)	Available, surplus under recovery conditions	Must not compete with essential grid loads
Steel plate/sheet	NZ Steel Glenbrook (Doc #89)	Available	Workshop fabrication time
Nickel (electrodes)	Recycled stainless steel, NZ coinage, imported stocks	Limited but adequate for initial scale	Finite recycled supply; trade with Australia could supplement
KOH electrolyte	Chemical suppliers; producible from potash and electrolysis	Producible domestically	Requires chlor-alkali or potash leaching capability (Doc #112)
Diaphragm material	Nickel mesh, porous ceramic, or synthetic fabric	Available from stocks or fabrication	Primary engineering challenge
Rectifier/power supply	Salvaged or fabricated from grid components	Available	Electrical engineering skill required
Water	Rain collection, municipal supply	Abundant	Minor purification needed
Piping and fittings	NZ steel; repurposed gas fittings	Available	Must be hydrogen-compatible (see Section 6)

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3. HYDROGEN STORAGE

Storage is the second major challenge after electrolyzer construction. Hydrogen has the lowest density of any gas — at atmospheric pressure, one kilogram of hydrogen occupies approximately 11 cubic metres.²² This makes storage of useful quantities bulky unless the gas is compressed, liquefied, or chemically bound.

3.1 Gasometer (wet gas holder)

The simplest storage technology. A gasometer is an inverted steel bell or drum floating in a water-filled tank. Gas is piped into the space under the bell, which rises as it fills. The water seal prevents gas from escaping. Pressure is determined by the weight of the bell — typically only a few centimetres of water column (a few hundred pascals), essentially atmospheric pressure.²³

Advantages:

• No pressure vessel metallurgy required
• Mild steel construction throughout
• Self-regulating pressure
• Proven technology — gasometers stored town gas (which contained 40–60% hydrogen) for over a century in NZ and worldwide
• Scalable from small (a few cubic metres) to enormous (historical town gas holders stored thousands of cubic metres)

Disadvantages:

• Very large for the energy stored — storing 10 kg of hydrogen (enough to run a 10 kW generator for roughly 8–10 hours at 30–40% engine efficiency²⁴) requires approximately 110–120 cubic metres of gas volume at atmospheric pressure (based on hydrogen density of 0.083–0.091 kg/m³ at 15–25°C, the typical NZ ambient temperature range)
• Water seal must be maintained (freezing is a concern under nuclear winter conditions — antifreeze additives or insulation may be necessary)
• Open to atmosphere via the water seal — some hydrogen loss through dissolution in water (minor)

Recommendation: Gasometers are the appropriate starting technology for NZ. They bypass the pressure vessel problem entirely. For applications needing more than a few hours of backup, multiple gasometers or larger construction is needed.

3.2 Low-pressure steel tanks (1–5 bar)

Welded steel tanks at modest pressure (1–5 bar, or 15–75 psi) store hydrogen at roughly 1–5 times atmospheric density. A tank storing hydrogen at 5 bar holds 5 times more gas per unit volume than a gasometer. Standard structural steel (NZ Steel product) is adequate for vessels at these pressures, with appropriate wall thickness and welded construction.

Design considerations:

• Wall thickness for a cylindrical vessel at 5 bar is modest — a 1-metre diameter vessel requires approximately 3–5 mm wall thickness depending on steel grade, well within NZ fabrication capability.²⁵
• Hydrogen embrittlement — the tendency of hydrogen to weaken steel — is a real concern but primarily affects high-strength steels at high pressures. Mild steel at low pressure is relatively resistant to embrittlement, particularly at ambient temperature. The risk is manageable with proper material selection (low-carbon steel, stress-relieved welds) and periodic inspection.²⁶
• Vessels should be hydrostatically tested (pressurized with water) before being placed in hydrogen service. This is standard pressure vessel practice.

3.3 Repurposed LPG tanks

NZ has a substantial stock of LPG cylinders and bulk tanks. Standard LPG cylinders are rated for approximately 17 bar (250 psi) — well above the low-pressure hydrogen range.²⁷ They are made from carbon steel, which is acceptable for hydrogen service at these pressures, though inspection for internal corrosion and valve compatibility is necessary.

Considerations:

• LPG fittings and regulators must be replaced or verified for hydrogen service — hydrogen’s lower viscosity and smaller molecular size mean it leaks through connections that are gas-tight for LPG.
• Internal cleaning is necessary to remove LPG residues.
• Cylinders should be inspected and hydrostatically retested before hydrogen use.
• This is a near-term solution using existing equipment, not a long-term production pathway.

3.4 What NZ cannot do: high-pressure storage

High-pressure hydrogen storage (200–700 bar) as used in modern hydrogen vehicles and industrial applications requires:

• High-strength steel or carbon fiber composite pressure vessels
• Precision pressure regulators and valves
• Metallurgical expertise to select and treat steels that resist hydrogen embrittlement at high pressure
• Testing and certification infrastructure

NZ does not have these capabilities post-event and is unlikely to develop them before Phase 5 at the earliest. This document does not recommend high-pressure hydrogen storage. The entire system design assumes low-pressure operation.²⁸

3.5 Storage sizing

Storage type	Volume for 10 kg H₂	Approximate dimensions	Energy content
Gasometer (1 bar)	~110 m³	Cylinder ~5 m diameter × 6 m tall	~333 kWh (LHV)
Steel tank (5 bar)	~22 m³	Cylinder ~2 m diameter × 7 m long	~333 kWh (LHV)
Repurposed LPG tank (10 bar)	~11 m³	Standard bulk LPG tank	~333 kWh (LHV)

For comparison, 333 kWh is enough to run a 10 kW generator for roughly 15–20 hours at 45–60% electrical conversion efficiency, or provide approximately 10–15 hours of industrial heating.

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4. STATIONARY APPLICATIONS

4.1 Backup power generation

Hydrogen burned in an internal combustion engine driving a generator provides backup electricity independent of the grid. This is functionally equivalent to a diesel generator, but fueled by hydrogen from grid electricity rather than finite petroleum.

Where this matters: Hospitals, communications facilities (Doc #48), water treatment plants (Doc #48), and other critical infrastructure need backup power. Lead-acid batteries (Doc #35) and wood gasifiers (Doc #48) are alternatives, but each has limitations — batteries degrade and depend on lead and acid supply chains; wood gasifiers require 15–30 minutes to warm up before they can supply clean gas, produce tar that fouls generators if the gas is not adequately filtered, and typically derate engine output by 30–50% compared to petrol operation because producer gas has a lower energy density than petrol vapour.²⁹ Hydrogen engines start quickly (within minutes, comparable to LPG conversion), produce clean exhaust (water vapour plus minor NOx at high load), and achieve 70–85% of petrol-rated output due to the lower energy density of the hydrogen-air mixture at atmospheric intake pressure (see Section 5.2). This output gap means a hydrogen-converted generator rated at 10 kW on petrol delivers approximately 7–8.5 kW on hydrogen — a real constraint when sizing backup systems that must cover a specific minimum load.

Realistic capacity: A 10–20 kW hydrogen-fueled generator with gasometer storage of 20–30 kg of hydrogen provides roughly 30–60 hours of backup power. This is adequate for bridging grid outages of a day or two. Longer outages require either larger storage or a continuously running electrolyzer with dedicated power supply (micro-hydro or other).

4.2 Industrial heat

NZ’s natural gas production from Taranaki fields is declining. Reserves may last 7–15 years under reduced post-event consumption, but this is uncertain and depends on well and pipeline maintenance.³⁰ LPG stocks are finite and not replenishable from domestic sources at current production rates. As these fuels deplete, applications that require combustible gas face a gap.

Applications needing clean, high-temperature combustible gas:

• Metal heat treatment: Hardening, tempering, annealing, and case-hardening of steel require precisely controlled atmosphere furnaces. Hydrogen or hydrogen-nitrogen mixtures provide a reducing atmosphere that prevents oxidation — this is the standard industrial practice. Wood or charcoal combustion produces a mixed atmosphere containing both reducing (CO) and oxidizing (CO2, H2O) species, resulting in less precise atmosphere control and visible surface oxidation (scale) on heat-treated steel.³¹
• Glass melting and working: Glass production (Doc #98) benefits from gas-fired furnaces for melting and forming. Electric furnaces are the primary option, but hydrogen provides an alternative heat source and reducing atmosphere where needed.
• Brazing and soldering: Hydrogen-atmosphere brazing produces clean joints without flux in some applications.³²
• Laboratory and analytical use: Gas chromatography, flame ionization detectors, and other analytical instruments require high-purity hydrogen.

4.3 Energy storage (grid buffering)

NZ’s electricity grid is dominated by hydro generation, which provides natural storage via reservoir management. However, some scenarios create surplus electricity that could be usefully stored as hydrogen:

• Overnight surplus: Electricity demand drops at night while hydro and geothermal generation continues. Electrolyzing water overnight and using the hydrogen during peak demand periods shifts energy from low-demand to high-demand hours.
• Seasonal surplus: In years with high rainfall and full reservoirs, NZ occasionally spills water (wastes potential energy) because generation exceeds demand plus storage. Hydrogen production from otherwise-spilled water is a use for surplus capacity.
• Micro-hydro and wind surplus: Small-scale generation systems (Doc #72) that produce more power than their local load can consume could feed surplus into electrolysis rather than wasting it.

Honest assessment of efficiency: At 20–30% round-trip efficiency (electricity to hydrogen to electricity), this is a very lossy storage mechanism compared to pumped hydro (~75–80% round-trip) or batteries (~80–90% round-trip for lead-acid).³³ Hydrogen energy storage is only justified where: (a) the alternative is wasting the surplus entirely, (b) batteries are unavailable or insufficient, or (c) the hydrogen has value for non-electrical applications (heat, chemical feedstock) in addition to or instead of reconversion to electricity.

4.4 Chemical feedstock

This is potentially the most important long-term application. Several critical industrial processes require hydrogen as a chemical input, not an energy carrier:

• Ammonia synthesis (Doc #114): The Haber-Bosch process combines hydrogen with nitrogen at high temperature and pressure to produce ammonia — the basis of synthetic fertilizer. NZ currently imports all synthetic nitrogen fertilizer. Domestic ammonia production is a multi-decade project (Feasibility [D]) with an enormous dependency chain, but hydrogen supply via electrolysis is one link in that chain that NZ can provide.³⁴
• Germanium reduction (Doc #135): The computer construction pathway requires hydrogen gas to reduce germanium dioxide to metallic germanium. Quantities are small (laboratory scale) but the purity requirement is high.³⁵
• Fat hydrogenation: Hydrogen can be used to harden vegetable oils or tallow — margarine-type products, improved candle wax hardness, or industrial lubricating greases requiring harder fats. This requires a finely divided nickel catalyst (nickel powder or Raney nickel, produced from nickel and aluminium — the latter is an additional dependency), a pressure vessel rated to 5–30 bar, temperature control at 150–200°C, and hydrogen supply at adequate purity. At the lower end of this pressure range (5–10 bar), the capability is within reach of NZ’s fabrication base, though reaction time is longer and hydrogenation may be incomplete, yielding a partially hardened product. Catalyst preparation from NZ nickel sources requires chemical processing not described here; this is a Phase 4+ capability.³⁶

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5. ENGINE CONVERSION FOR HYDROGEN

5.1 Which engines work

Hydrogen can fuel any spark-ignition (petrol-type) internal combustion engine with modification. It cannot be used in unmodified compression-ignition (diesel) engines because hydrogen’s autoignition temperature (approximately 585°C) is higher than diesel fuel’s, meaning it does not ignite reliably under compression alone.³⁷

Best candidates for conversion:

• Natural gas engines: These already run on gaseous fuel and require the least modification — mainly fuel metering adjustments. NZ has some natural gas-fueled generators and vehicles.
• LPG engines: Similar to natural gas engines in gas-handling design. Common in NZ forklifts, some vehicles, and stationary generators.
• Petrol engines: Require conversion from liquid to gaseous fuel — new fuel metering (carburetors can be adapted; fuel injection requires more work), adjusted ignition timing (hydrogen burns faster than petrol), and intake manifold modifications.

5.2 Conversion details

Fuel delivery: Hydrogen at low pressure (0.5–2 bar above atmospheric) is metered into the engine’s intake manifold through a gas mixer or venturi device. This is similar to LPG or natural gas conversion. The mixer must provide the correct air-to-fuel ratio — hydrogen’s stoichiometric air-fuel ratio is 34:1 by mass (compared to 14.7:1 for petrol), meaning much more air relative to fuel by mass, but hydrogen’s low density means the volume ratio is quite different.³⁸

Ignition timing: Hydrogen burns approximately 6–8 times faster than petrol. Ignition timing must be retarded (delayed) significantly to avoid pre-ignition and backfire — a common problem with hydrogen engines. Running lean (excess air) reduces backfire risk and improves efficiency at the cost of some power.³⁹

Power output: A hydrogen-fueled engine typically produces 70–85% of the power it achieves on petrol, due to the lower energy density of the hydrogen-air mixture at atmospheric intake pressure. Turbocharging or supercharging can recover some of this loss but adds complexity.⁴⁰

Crankcase ventilation: Hydrogen’s small molecular size means more blow-by past piston rings into the crankcase. Adequate crankcase ventilation is important to prevent hydrogen accumulation in the crankcase, which is an explosion hazard.

Exhaust: The primary combustion product is water vapour. Small amounts of NOx (nitrogen oxides) form at high combustion temperatures. No carbon emissions. Engine oil lasts longer because there is no fuel-derived carbon contamination.

5.3 What NZ cannot do with hydrogen engines

• Mobile vehicles on hydrogen: Carrying enough low-pressure hydrogen for useful range is impractical. A vehicle carrying hydrogen at 5 bar would need a tank of roughly 1,000–2,000 litres (1–2 cubic metres) for a range of 100–200 km. This is a trailer-sized tank for the range of a single petrol tank. Mobile hydrogen requires high-pressure storage (Doc #64), which NZ cannot produce. The stationary focus of this document is deliberate.

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6. SAFETY

6.1 Hydrogen properties relevant to safety

Hydrogen is flammable in air at concentrations of 4–75% by volume — an exceptionally wide flammable range compared to other fuels (methane: 5–15%; petrol vapour: 1–8%).⁴¹ It has a very low ignition energy (0.02 mJ — a static spark can ignite it). It burns with a nearly invisible flame in daylight. It is odorless and colorless. It is not toxic.

However, hydrogen also has safety advantages: it is extremely buoyant (14 times lighter than air) and disperses rapidly upward in open or ventilated spaces. Outdoor hydrogen leaks dissipate quickly rather than pooling at ground level as heavier-than-air fuels do. The rapid buoyancy makes hydrogen safer in ventilated environments and more dangerous in enclosed, unventilated spaces.⁴²

6.2 Non-negotiable safety rules

1. Never store or use hydrogen in enclosed, unventilated spaces. Any building housing hydrogen equipment must have high-level ventilation openings — hydrogen rises and accumulates at ceiling level.

2. Eliminate ignition sources near hydrogen equipment: no open flames, no smoking, no unshielded electrical contacts. Electrical equipment in hydrogen areas should be spark-proof (enclosed contacts, flameproof housings).

3. Leak detection: Hydrogen is invisible and odorless. Commercial hydrogen leak detectors are finite stock. Soap-bubble testing of all joints and connections during commissioning and maintenance is the practical approach. Consider adding a tracer odorant to stored hydrogen if a suitable compound is available.

4. Explosion prevention in electrolyzers: The electrolyzer produces both hydrogen and oxygen — the components of a potentially explosive mixture. Gas collection must keep these streams separate at all times. The separator/diaphragm is a safety-critical component. Cross-contamination above approximately 4% hydrogen in oxygen (or oxygen in hydrogen) creates an explosive hazard. Gas purity should be monitored — a simple test is burning a sample; pure hydrogen burns with a pale flame; oxygen-contaminated hydrogen pops or detonates.

5. Hydrogen embrittlement monitoring: Steel components in hydrogen service should be visually inspected for cracking at regular intervals. Any component showing cracks must be taken out of service immediately. Use low-carbon mild steel (not high-strength steel) for all hydrogen-wetted components.⁴³

6. Oxygen management: The oxygen produced as a byproduct of electrolysis is valuable (medical use, welding, chemical processes) but must be handled with its own safety precautions — oxygen enrichment dramatically increases fire risk. Store oxygen separately from hydrogen. Never allow oil or grease to contact oxygen fittings (spontaneous combustion risk).

6.3 Historical precedent

Town gas (coal gas), which was the standard domestic and industrial gas supply in NZ and worldwide from the mid-1800s through the mid-1900s, contained 40–60% hydrogen along with methane, carbon monoxide, and other gases. NZ cities operated town gas distribution networks for decades, with gasometers storing thousands of cubic metres of hydrogen-rich gas in urban areas. The safety record was imperfect — gas leaks, explosions, and CO poisoning fatalities occurred over the decades of operation — but the technology was managed at municipal scale by trained workers operating written procedures, not by specialist research engineers. The practical conclusion is that hydrogen management is achievable with adequate training, written protocols, and consistent discipline around ventilation, leak detection, and ignition-source control. It is not zero-risk, and the historical record should not be read as evidence that hydrogen is safe without these disciplines in place.⁴⁴

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7. OXYGEN: THE VALUABLE BYPRODUCT

Electrolysis produces oxygen and hydrogen in a fixed 1:2 molar ratio — 8 kg of oxygen for every 1 kg of hydrogen. This oxygen has significant value in recovery:

• Medical oxygen: Supplemental oxygen for respiratory conditions, surgical anaesthesia support, and treatment of carbon monoxide poisoning (relevant given expanded wood gasifier use — Doc #56). Medical oxygen requires high purity (99.5%+ by NZ and international pharmacopoeial standards — Medsafe Schedule 29) and dry gas; a well-designed alkaline electrolyzer can meet this standard, but achieving it consistently requires a good separator, adequate drying (silica gel or molecular sieve), and purity testing before each fill.⁴⁵
• Oxy-fuel cutting and welding: Oxy-acetylene cutting and welding consume oxygen. As acetylene from calcium carbide stocks depletes, oxy-hydrogen cutting is an alternative — but the performance gap is significant. Oxy-hydrogen flames reach approximately 2,800°C compared with oxy-acetylene at approximately 3,500°C.⁴⁶ This lower temperature means oxy-hydrogen cannot reliably cut steel plate above approximately 25–30 mm thickness, and pre-heating time is longer. Flame geometry is also broader and less concentrated, reducing precision on fine work. Oxy-hydrogen is adequate for cutting structural steel at moderate thicknesses and for welding non-ferrous metals, but is a constrained substitute for the full range of oxy-acetylene applications. Oxygen supply from electrolysis supplements finite industrial gas stocks.
• Chemical processes: Oxygen is a reagent in various chemical processes relevant to recovery.

The oxygen value can be significant enough to shift the economics of hydrogen production — if medical oxygen demand exists near the electrolyzer site, the hydrogen becomes, in effect, a byproduct of oxygen production rather than the reverse.

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8. NZ-SPECIFIC CONSIDERATIONS

8.1 Electricity surplus

NZ’s total electricity generation capacity is approximately 9,000–10,000 MW, producing roughly 42,000–44,000 GWh per year under normal conditions.⁴⁷ Normal demand is approximately 4,500–5,000 MW average. Under recovery conditions with industrial demand reduced, the surplus is substantial — potentially 1,000–3,000 MW of available capacity above essential loads, depending on the extent of industrial shutdown and grid maintenance status.

Even a small fraction of this surplus — say 50 MW dedicated to hydrogen production — would produce roughly 600–800 tonnes of hydrogen per year, far more than NZ’s stationary applications are likely to consume in the first decade.⁴⁸

The constraint is not electricity. It is the fabrication of electrolyzers, storage vessels, and converted engines — the physical equipment that turns surplus electricity into useful hydrogen. Equipment fabrication is the bottleneck, not energy supply.

8.2 Optimal siting

Hydrogen production should be co-located with:

• Surplus generation: Hydroelectric stations with surplus capacity (Benmore, Clyde, Manapouri, Waikato hydro chain), geothermal stations (Wairakei, Ohaaki, Kawerau, Ngatamariki)
• Industrial demand: Workshops and foundries needing reducing atmosphere or high-temperature heat (Hamilton/Waikato for NZ Steel proximity; Christchurch/Canterbury engineering shops)
• Critical facilities: Hospitals and communications sites needing backup power — though transporting low-pressure hydrogen any significant distance is impractical, so generation must be on-site or nearby

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9. CRITICAL UNCERTAINTIES

Uncertainty	Impact	Mitigation
Diaphragm/separator performance with NZ materials	Determines electrolyzer efficiency and hydrogen purity	Early prototyping at university labs; test multiple materials
Nickel availability for electrodes	Determines electrolyzer scale; nickel is the preferred electrode material	Inventory existing NZ nickel stocks (stainless steel recycling, coinage, industrial stocks); identify Australian trade potential
KOH production capability	Electrolyte supply determines production sustainability	Develop chlor-alkali or potash leaching process (Doc #112)
Hydrogen embrittlement in NZ-fabricated steel vessels	Determines safe operating pressure and vessel lifespan	Use low-carbon mild steel; limit pressure to 5 bar initially; inspect regularly; hydrostatically test all vessels
Actual surplus electricity availability	Recovery-condition grid load is uncertain	Monitor actual generation and demand; prioritize hydrogen only from genuine surplus
Natural gas depletion timeline	Determines urgency of hydrogen as industrial heat replacement	Monitor Taranaki field production; assess Motunui and distribution infrastructure
Engine conversion complexity for NZ fleet	Determines how quickly hydrogen-fueled backup generators can be deployed	Begin with LPG/natural gas engines (simplest conversion); develop petrol engine conversion procedures from experience
Nuclear winter impact on water supply for electrolysis	Precipitation changes affect water availability	Rain collection provides adequate supply at modest production scale

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10. CROSS-REFERENCES

• Doc #1 — National Emergency Stockpile Strategy (natural gas and LPG stock management)
• Doc #8 — National Asset and Skills Census (electroplating shops, gas industry workers, welding equipment inventory)
• Doc #135 — Computer Construction (hydrogen for germanium reduction)
• Doc #35 — Battery Management and Lead-Acid Production (complementary energy storage pathway)
• Doc #53 — Fuel Allocation and Drawdown (petroleum depletion timeline; hydrogen fills post-petroleum gap)
• Doc #56 — Wood Gasification (alternative combustible gas; competing and complementary technology)
• Doc #64 — Hydrogen for Mobile Use (mobile hydrogen applications; why high-pressure storage is hard)
• Doc #65 — Hydroelectric Maintenance (hydrogen production sites at hydro stations)
• Doc #66 — Geothermal Maintenance (hydrogen production at geothermal stations)
• Doc #67 — Transpower Grid Operations (surplus electricity availability; grid load management)
• Doc #69 — Transformer Rewinding and Fabrication (electrolyzer power supply transformers)
• Doc #72 — Micro-Hydro Design and Construction (co-located DC generation for small-scale electrolysis)
• Doc #89 — NZ Steel Glenbrook (steel plate for electrolyzers and storage vessels; hydrogen for potential direct reduction steelmaking in future)
• Doc #91 — Machine Shop Operations (electrolyzer and storage vessel fabrication)
• Doc #93 — Foundry Work (hydrogen atmosphere for clean metal casting)
• Doc #94 — Welding Consumables (welded vessel construction; oxy-hydrogen cutting)
• Doc #97 — Cement and Concrete (porous ceramic separator production)
• Doc #98 — Glass Production (hydrogen as furnace fuel)
• Doc #112 — Lime and Caustic Soda (KOH electrolyte production)
• Doc #114 — Ammonia Synthesis (hydrogen as primary feedstock)
• Doc #117 — Surgical Consumables (medical oxygen from electrolysis byproduct)
• Doc #157 — Trade Training (electrolyzer operator and safety training)

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FOOTNOTES

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1. Alkaline electrolysis fundamentals: Zeng, K. and Zhang, D., “Recent progress in alkaline water electrolysis for hydrogen production and applications,” Progress in Energy and Combustion Science, 36(3), 2010, pp. 307–326. This review covers electrode materials, electrolyte concentration, temperature effects, and cell design for alkaline systems.↩︎

2. Hydrogen energy storage concept: Gahleitner, G., “Hydrogen from renewable electricity: An international review of power-to-gas pilot plants for stationary applications,” International Journal of Hydrogen Energy, 38(5), 2013, pp. 2039–2061. Reviews operational experience from pilot plants worldwide.↩︎

3. Hydrogen combustion temperature: hydrogen-air flame temperature is approximately 2,045°C (stoichiometric, adiabatic), compared to natural gas at approximately 1,950°C. Both are adequate for most metalworking heat treatment applications. Based on standard combustion thermodynamics; see any engineering combustion text.↩︎

4. Round-trip efficiency of hydrogen energy storage: electrolysis at 55–80% efficiency, hydrogen compression/storage losses of approximately 5–10%, and engine-generator conversion at 30–40% thermal efficiency yields overall round-trip efficiency of approximately 15–30%. The wide range reflects the variation in each stage. This compares unfavorably with batteries (80–90% round-trip for lead-acid) but hydrogen storage does not degrade with cycling the way batteries do. See: Mazloomi, K. and Gomes, C., “Hydrogen as an energy carrier: Prospects and challenges,” Renewable and Sustainable Energy Reviews, 16(5), 2012, pp. 3024–3033.↩︎

5. High-pressure hydrogen storage challenges: Zheng, J. et al., “Development of high pressure gaseous hydrogen storage technologies,” International Journal of Hydrogen Energy, 37(1), 2012, pp. 1048–1057. Type III (metal-lined, carbon fiber-wrapped) and Type IV (polymer-lined, carbon fiber-wrapped) vessels require materials and manufacturing processes NZ cannot replicate. Type I (all-metal) vessels for 200+ bar require high-strength low-alloy steels with careful heat treatment and hydrogen embrittlement resistance — beyond NZ’s metallurgical capability post-event.↩︎

6. Gasometer technology: gasometers (gas holders) were standard urban infrastructure from the 1820s through the mid-20th century. NZ cities including Auckland, Wellington, Christchurch, and Dunedin operated town gas systems with gasometer storage. Auckland Gas Company operated from 1863 and held gasometers at its Newmarket works; Wellington Gas Company’s Thorndon works included large gasometers visible in historical photographs. The technology is documented in NZ municipal records and in standard gas engineering texts of the period. See: McLintock, A.H. (ed.), “Encyclopaedia of New Zealand,” R.E. Owen, Government Printer, 1966 (entry on “Gas, Manufactured”); and Chandler, D. and Lacey, A.D., “The Rise of the Gas Industry in Britain,” British Gas Council, 1949 (for technical design detail).↩︎

7. Electrolyzer production rate: at 55 kWh per kg of hydrogen (mid-range efficiency), a 50 kW electrolyzer produces approximately 0.9 kg/hour at full power. At 70% capacity factor (accounting for electricity availability, maintenance, and startup/shutdown), monthly production is approximately 0.9 × 0.7 × 24 × 30 ≈ 450 kg. The 250–300 kg estimate in the text is conservative, assuming lower capacity factor during initial operations with less reliable surplus electricity scheduling.↩︎

8. Thermodynamic minimum for water electrolysis: the standard enthalpy of water splitting is 285.8 kJ/mol (higher heating value basis) or 237.1 kJ/mol (Gibbs free energy, the minimum electrical work). For 1 kg of hydrogen (approximately 500 mol), the theoretical minimum is approximately 33 kWh (Gibbs) to 39.4 kWh (enthalpy). See: any physical chemistry text covering electrochemistry fundamentals.↩︎

9. Practical alkaline electrolyzer energy consumption: 50–70 kWh/kg H₂ is the typical range for industrial alkaline electrolyzers. The lower end (50 kWh/kg) represents modern, optimized systems; NZ-fabricated units with improvised separators and uncoated electrodes would likely be at the higher end (65–80 kWh/kg) initially, improving with experience and better materials. See: Buttler, A. and Spliethoff, H., “Current status of water electrolysis for energy storage, grid balancing and sector coupling via power-to-gas and power-to-liquids: A review,” Renewable and Sustainable Energy Reviews, 82, 2018, pp. 2440–2454.↩︎

10. Comparison of electrolysis technologies: Carmo, M. et al., “A comprehensive review on PEM water electrolysis,” International Journal of Hydrogen Energy, 38(12), 2013, pp. 4901–4934. PEM electrolyzers use iridium and platinum catalysts at loadings of 1–3 mg/cm²; these metals are not available in NZ in any meaningful quantity. Alkaline systems using nickel electrodes and KOH electrolyte are the only technology NZ can realistically fabricate.↩︎

11. Hydrogen flammability range: 4–75% in air by volume at atmospheric pressure and ambient temperature. Autoignition temperature approximately 585°C. Minimum ignition energy approximately 0.02 mJ. These are well-established values reported in standard safety references. See: NASA, “Safety Standard for Hydrogen and Hydrogen Systems,” NSS 1740.16, 2005.↩︎

12. Nickel sources in NZ: NZ does not mine nickel. Sources include: stainless steel (300-series austenitic stainless contains 8–14% nickel by weight — NZ has significant stainless steel stocks in kitchen equipment, food processing, medical equipment, and architectural fittings); NZ coinage (some NZ coins contain nickel plating or cupronickel alloy); and imported nickel stocks held by plating shops and industrial suppliers. Total available nickel is uncertain but probably sufficient for initial electrolyzer construction at modest scale.↩︎

13. Separator-free electrolysis: Gillespie, M.I. et al., “Performance evaluation of a membraneless divergent electrode-flow-through (DEFT) alkaline electrolyser based on optimisation of electrolytic flow and electrode gap,” Journal of Power Sources, 293, 2015, pp. 228–239. Demonstrates that electrolysis without a membrane is feasible at reduced efficiency and purity. Gas purity of 95–99% hydrogen is achievable with careful cell geometry.↩︎

14. Hydrogen-in-oxygen explosive limits: the explosive range for hydrogen in oxygen is approximately 4–94% by volume — far wider than hydrogen in air (4–75%). Even a separator-free electrolyzer operating at very low current density will produce some cross-contamination. The IEC/ISO 22734 standard for electrolyzer safety specifies limits; the practical safe operating threshold for hydrogen content in oxygen is generally kept below 2% to maintain adequate safety margin. Operators using separator-free designs must monitor gas composition and halt production if cross-contamination approaches this threshold. See: IEC 62282-2-100, “Fuel cell technologies — Electrolysers,” and ISO 22734:2019.↩︎

15. Electrode materials for alkaline electrolysis: Miles, M.H. and Thomason, M.A., “Periodic variations of overvoltages for water electrolysis in acid and base solutions,” Journal of the Electrochemical Society, 123(10), 1976, pp. 1459–1461. Nickel consistently outperforms iron and steel as both cathode and anode material in alkaline electrolysis, with lower overvoltage (less energy waste) at both electrodes.↩︎

16. Nickel-iron oxide catalytic coatings: Trotochaud, L. et al., “Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: the role of intentional and incidental iron incorporation,” Journal of the American Chemical Society, 136(18), 2014, pp. 6744–6753. NiFe oxide is among the most active and stable oxygen evolution catalysts in alkaline media, and both metals are available in NZ.↩︎

17. Monopolar vs. bipolar electrolyzer design: LeRoy, R.L., “Industrial water electrolysis: present and future,” International Journal of Hydrogen Energy, 8(6), 1983, pp. 401–417. Bipolar designs achieve higher current efficiency and are more compact, but monopolar designs are simpler to construct and maintain — the preferred choice for initial NZ fabrication.↩︎

18. Welding rectifiers as electrolyzer power supplies: a standard welding rectifier (e.g., Lincoln or Miller brand, widely used in NZ workshops) outputs 20–80 V DC at 50–300 A — a good match for small-scale electrolysis. Current control allows matching power input to electrolyzer capacity. Based on general electrical engineering knowledge and welding equipment specifications.↩︎

19. Practical alkaline electrolyzer energy consumption: 50–70 kWh/kg H₂ is the typical range for industrial alkaline electrolyzers. The lower end (50 kWh/kg) represents modern, optimized systems; NZ-fabricated units with improvised separators and uncoated electrodes would likely be at the higher end (65–80 kWh/kg) initially, improving with experience and better materials. See: Buttler, A. and Spliethoff, H., “Current status of water electrolysis for energy storage, grid balancing and sector coupling via power-to-gas and power-to-liquids: A review,” Renewable and Sustainable Energy Reviews, 82, 2018, pp. 2440–2454.↩︎

20. Round-trip efficiency of hydrogen energy storage: electrolysis at 55–80% efficiency, hydrogen compression/storage losses of approximately 5–10%, and engine-generator conversion at 30–40% thermal efficiency yields overall round-trip efficiency of approximately 15–30%. The wide range reflects the variation in each stage. This compares unfavorably with batteries (80–90% round-trip for lead-acid) but hydrogen storage does not degrade with cycling the way batteries do. See: Mazloomi, K. and Gomes, C., “Hydrogen as an energy carrier: Prospects and challenges,” Renewable and Sustainable Energy Reviews, 16(5), 2012, pp. 3024–3033.↩︎

21. Water purity for electrolysis: dissolved minerals (calcium, magnesium, chloride) deposit on electrodes and can contaminate gas output. Rainwater in NZ is generally low in dissolved solids (typically <20 mg/L total dissolved solids), making it suitable for electrolysis with minimal treatment. Municipal water supplies may require basic softening or distillation. See: NIWA water quality data for NZ rainfall composition.↩︎

22. Hydrogen density: at standard temperature and pressure (0°C, 1 atm), hydrogen density is 0.0899 kg/m³. At 20°C and 1 atm, approximately 0.0838 kg/m³. Therefore 1 kg of hydrogen occupies approximately 11.2–11.9 m³. This is well-established physical data; see CRC Handbook of Chemistry and Physics.↩︎

23. Gasometer technology: gasometers (gas holders) were standard urban infrastructure from the 1820s through the mid-20th century. NZ cities including Auckland, Wellington, Christchurch, and Dunedin operated town gas systems with gasometer storage. Auckland Gas Company operated from 1863 and held gasometers at its Newmarket works; Wellington Gas Company’s Thorndon works included large gasometers visible in historical photographs. The technology is documented in NZ municipal records and in standard gas engineering texts of the period. See: McLintock, A.H. (ed.), “Encyclopaedia of New Zealand,” R.E. Owen, Government Printer, 1966 (entry on “Gas, Manufactured”); and Chandler, D. and Lacey, A.D., “The Rise of the Gas Industry in Britain,” British Gas Council, 1949 (for technical design detail).↩︎

24. Generator efficiency basis: internal combustion engine-generators operating on gaseous fuels (hydrogen, natural gas, LPG) typically achieve thermal efficiencies of 25–38% at rated load under moderate temperature conditions. At partial load (50–75% of rated power), efficiency may drop to 20–30%. The “8–10 hours” figure for a 10 kW generator on 10 kg of hydrogen uses 33.3 kWh/kg hydrogen lower heating value × 10 kg = 333 kWh input energy ÷ 10 kW output ÷ 0.30 efficiency ≈ approximately 11 hours at 30% efficiency, adjusted downward to 8–10 hours to account for startup losses and partial-load operation. Based on general engine-generator performance data; actual value depends on specific engine design and operating conditions.↩︎

25. Pressure vessel wall thickness: for a cylindrical vessel, the minimum wall thickness t = (P × D) / (2 × S × E), where P is pressure, D is diameter, S is allowable stress, and E is joint efficiency. For 5 bar (0.5 MPa), 1 m diameter, Grade 250 steel (S = 165 MPa for pressure vessel service), and 0.7 joint efficiency for welded construction, t ≈ 2.2 mm. Adding corrosion allowance (1–2 mm) gives approximately 4–5 mm — standard plate thickness. Based on AS/NZS 1200 series pressure vessel standards (general principles).↩︎

26. Hydrogen embrittlement: Nelson, H.G., “Hydrogen embrittlement,” in Embrittlement of Engineering Alloys, Briant, C.L. and Banerji, S.K. (eds.), Academic Press, 1983. Low-carbon mild steel (below approximately 0.2% carbon) is relatively resistant to hydrogen embrittlement at low pressure and ambient temperature. High-strength steels (above approximately 700 MPa yield strength) are susceptible. NZ Steel’s standard structural products (Grade 250–350) are in the lower-risk category.↩︎

27. LPG cylinder specifications: NZ LPG cylinders comply with AS/NZS 3509 and are typically rated for working pressures of 1,725–2,585 kPa (approximately 17–26 bar). This exceeds the 5 bar operating range recommended for NZ hydrogen systems. Cylinders must still be inspected for condition — internal corrosion, valve integrity, and hydrostatic retest are required before repurposing. See: WorkSafe NZ, “Approved Code of Practice for the Management of Cylinders.”↩︎

28. High-pressure hydrogen storage challenges: Zheng, J. et al., “Development of high pressure gaseous hydrogen storage technologies,” International Journal of Hydrogen Energy, 37(1), 2012, pp. 1048–1057. Type III (metal-lined, carbon fiber-wrapped) and Type IV (polymer-lined, carbon fiber-wrapped) vessels require materials and manufacturing processes NZ cannot replicate. Type I (all-metal) vessels for 200+ bar require high-strength low-alloy steels with careful heat treatment and hydrogen embrittlement resistance — beyond NZ’s metallurgical capability post-event.↩︎

29. Wood gasifier performance derating: producer gas from wood gasification has a lower heating value of approximately 4–6 MJ/m³ compared with natural gas at approximately 37 MJ/m³. When substituted in petrol engines, the combined effect of lower energy density and the dilution of the intake charge typically reduces peak power output by 30–50%. The warm-up time (15–30 minutes for the gasifier to reach stable gas production) is a separate operational constraint. Tar fouling of engine components is a maintenance issue requiring regular cleaning of filters, carburettors, and valve seats. See: Reed, T.B. and Das, A., “Handbook of Biomass Downdraft Gasifier Engine Systems,” SERI/SP-271-3022, Solar Energy Research Institute, 1988.↩︎

30. NZ natural gas reserves: MBIE, “Energy in New Zealand.” NZ’s natural gas production has been declining as the Maui field depletes. Remaining reserves are concentrated in Pohokura and smaller Taranaki fields. Reserve estimates vary and depend on production rates. Under recovery conditions with sharply reduced demand, the remaining gas could last significantly longer than at pre-event consumption rates, but pipeline and well maintenance constraints may limit extraction life independently of reserve volume. See also Doc #102, footnote 13.↩︎

31. Hydrogen atmosphere for metal heat treatment: hydrogen and hydrogen-nitrogen mixtures (forming gas) are standard industrial atmospheres for bright annealing, sintering, and other processes requiring a reducing environment. See: ASM International, “ASM Handbook, Volume 4: Heat Treating,” 1991. Wood and charcoal combustion atmospheres contain CO (reducing) but also CO₂ and H₂O (oxidizing), making atmosphere control less precise.↩︎

32. Hydrogen-atmosphere brazing: hydrogen and hydrogen-nitrogen mixtures (forming gas, typically 5–15% H₂ in N₂) are used as protective atmospheres in furnace brazing of copper, stainless steel, and some other alloys. The advantage is elimination of flux, which reduces cleaning steps and enables brazing of complex joints where flux removal is difficult. The limitation is that pure hydrogen at brazing temperatures creates an explosion risk if the furnace atmosphere is disturbed; strict purge-and-inert procedures are required during startup and shutdown. See: Schwartz, M.M., “Brazing,” ASM International, 2nd edition, 2003.↩︎

33. Round-trip efficiency of hydrogen energy storage: electrolysis at 55–80% efficiency, hydrogen compression/storage losses of approximately 5–10%, and engine-generator conversion at 30–40% thermal efficiency yields overall round-trip efficiency of approximately 15–30%. The wide range reflects the variation in each stage. This compares unfavorably with batteries (80–90% round-trip for lead-acid) but hydrogen storage does not degrade with cycling the way batteries do. See: Mazloomi, K. and Gomes, C., “Hydrogen as an energy carrier: Prospects and challenges,” Renewable and Sustainable Energy Reviews, 16(5), 2012, pp. 3024–3033.↩︎

34. Haber-Bosch process for ammonia: the reaction N₂ + 3H₂ → 2NH₃ requires approximately 500°C, 150–300 bar, and an iron-based catalyst. The hydrogen feedstock has historically come from steam reforming of natural gas, but electrolytic hydrogen is chemically equivalent. The scale of hydrogen needed for meaningful fertilizer production is large — approximately 180 kg of hydrogen per tonne of ammonia. See Doc #114 for the full ammonia dependency chain.↩︎

35. Hydrogen for germanium reduction: the computer construction guide (Doc #135) describes reducing germanium dioxide (GeO₂) to metallic germanium using hydrogen gas at approximately 650°C. Quantities for initial transistor fabrication are small — perhaps 10–50 kg of hydrogen total — but the purity must be high (no oxygen contamination) to avoid re-oxidation.↩︎

36. Fat hydrogenation with nickel catalyst: the hydrogenation of unsaturated fats (oils) to saturated fats (solid fats) proceeds over a nickel catalyst at 150–200°C and 5–30 bar hydrogen. Raney nickel (produced by leaching aluminium from a nickel-aluminium alloy with sodium hydroxide) is the standard industrial catalyst. The nickel-aluminium alloy preparation requires both nickel and aluminium as feedstocks — aluminium availability in NZ is finite (imported stocks, recycling from existing aluminium goods; NZ does not smelt aluminium). Partially hydrogenated products (trans fats) form at intermediate conversion levels; the degree of hydrogenation is controlled by time and temperature. See: Bailey’s Industrial Oil and Fat Products, 6th edition, Wiley, 2005, Chapter on hydrogenation.↩︎

37. Hydrogen autoignition temperature: approximately 585°C at atmospheric pressure. This is higher than diesel fuel (~210°C) and petrol (~280°C), which is why hydrogen does not self-ignite under diesel compression ratios. Some research has explored hydrogen-diesel dual fuel (hydrogen pilot ignition), but this adds complexity without eliminating the diesel dependency. See: Verhelst, S. and Wallner, T., “Hydrogen-fueled internal combustion engines,” Progress in Energy and Combustion Science, 35(6), 2009, pp. 490–527.↩︎

38. Hydrogen engine operation: Verhelst and Wallner (note 28) provide comprehensive coverage of hydrogen ICE performance. The stoichiometric air-fuel ratio of 34:1 (mass basis) corresponds to approximately 2.4:1 by volume (because hydrogen is so light). Power output on hydrogen is typically 70–85% of petrol power due to the lower mixture energy density at atmospheric intake pressure.↩︎

39. Hydrogen pre-ignition and backfire: the high flame speed and low ignition energy of hydrogen make it susceptible to pre-ignition from hot spots in the combustion chamber (exhaust valves, spark plug electrodes, carbon deposits). Operating lean (lambda >1.5) and retarding ignition timing are the standard mitigations. See: White, C.M. et al., “The hydrogen-fueled internal combustion engine: a technical review,” International Journal of Hydrogen Energy, 31(10), 2006, pp. 1292–1305.↩︎

40. Hydrogen engine operation: Verhelst and Wallner (note 28) provide comprehensive coverage of hydrogen ICE performance. The stoichiometric air-fuel ratio of 34:1 (mass basis) corresponds to approximately 2.4:1 by volume (because hydrogen is so light). Power output on hydrogen is typically 70–85% of petrol power due to the lower mixture energy density at atmospheric intake pressure.↩︎

41. Hydrogen flammability range: 4–75% in air by volume at atmospheric pressure and ambient temperature. Autoignition temperature approximately 585°C. Minimum ignition energy approximately 0.02 mJ. These are well-established values reported in standard safety references. See: NASA, “Safety Standard for Hydrogen and Hydrogen Systems,” NSS 1740.16, 2005.↩︎

42. Hydrogen buoyancy and dispersion: hydrogen’s density is approximately 1/14 that of air. In outdoor or ventilated environments, released hydrogen rises and disperses rapidly — typically reaching safe (below 4%) concentrations within seconds to minutes for small releases. This contrasts with LPG (heavier than air, pools at ground level) and natural gas (slightly lighter than air, disperses more slowly than hydrogen). See: Swain, M.R. and Swain, M.N., “A comparison of H₂, CH₄ and C₃H₈ fuel leakage in residential settings,” International Journal of Hydrogen Energy, 17(10), 1992, pp. 807–815.↩︎

43. Hydrogen embrittlement: Nelson, H.G., “Hydrogen embrittlement,” in Embrittlement of Engineering Alloys, Briant, C.L. and Banerji, S.K. (eds.), Academic Press, 1983. Low-carbon mild steel (below approximately 0.2% carbon) is relatively resistant to hydrogen embrittlement at low pressure and ambient temperature. High-strength steels (above approximately 700 MPa yield strength) are susceptible. NZ Steel’s standard structural products (Grade 250–350) are in the lower-risk category.↩︎

44. Town gas in NZ: NZ’s major cities operated manufactured gas (town gas) systems from the mid-19th century through the 1970s–1980s, when natural gas from the Maui field replaced manufactured gas. Wellington’s gas works operated from 1872 to 1977; Auckland’s from 1863. Town gas contained approximately 50% hydrogen, 25–30% methane, 5–10% carbon monoxide, and various other gases. The safety record was imperfect — CO in town gas caused fatalities (primarily from deliberate self-harm), and gas explosions occurred — but the infrastructure was operated at scale by municipal gas departments staffed by trained workers, not specialists. See: Salmond, J., “Old New Zealand Houses 1800–1940,” Reed Publishing, 1986 (discusses gas infrastructure in NZ homes).↩︎

45. Medical oxygen from electrolysis: electrolyzer oxygen purity depends on separator quality and operating conditions. Well-designed alkaline electrolyzers with good separators produce oxygen at 99–99.9% purity. NZ medical oxygen specifications are set by Medsafe under Schedule 29 of the Medicines Regulations 1984 and align with the British Pharmacopoeia monograph for Medicinal Oxygen, requiring 99.5% minimum purity (v/v) with limits on carbon dioxide, carbon monoxide, water vapour, and nitrous oxide. Drying (silica gel or molecular sieve desiccant) is required to meet moisture limits; carbon monoxide monitoring is necessary if any gas-fired equipment is co-located. Compression into certified cylinders is required for hospital use. See: Medsafe, “Schedule 29, Medicines Regulations 1984,” https://www.medsafe.govt.nz; and WHO, “Specification for Medicinal Oxygen,” in The International Pharmacopoeia, 11th edition.↩︎

46. Oxy-hydrogen flame temperature: the stoichiometric adiabatic flame temperature for hydrogen burning in pure oxygen is approximately 2,800°C (2,977 K), compared with acetylene burning in pure oxygen at approximately 3,500°C (3,773 K). This temperature difference means oxy-hydrogen flames cannot match the cutting performance of oxy-acetylene on thick or high-carbon steel. In practice, oxy-hydrogen is used industrially for cutting glass (where lower temperature is advantageous), brazing, and welding of non-ferrous metals, but is not a full substitute for oxy-acetylene in heavy structural steel cutting. See: Baukal, C.E. (ed.), “The John Zink Combustion Handbook,” CRC Press, 2001; and standard combustion thermodynamics references (JANAF tables).↩︎

47. NZ electricity generation: Ministry of Business, Innovation and Employment (MBIE), “Energy in New Zealand” annual report. https://www.mbie.govt.nz/building-and-energy/energy-and-n... — NZ generated approximately 42,000–44,000 GWh in recent years, of which approximately 82–87% was from renewable sources (hydro, geothermal, wind). The exact renewable share varies with annual hydrology.↩︎

48. Hydrogen production from 50 MW electrolysis: at 55 kWh/kg, 50 MW continuous would produce approximately 910 kg/hour, or approximately 8,000 tonnes per year. At 70% capacity factor, approximately 5,600 tonnes per year. NZ’s stationary hydrogen demand in early recovery phases is likely well under 100 tonnes per year. Even 1 MW of dedicated electrolysis (~110 tonnes/year) would be more than adequate initially. The point is that electricity is not the binding constraint.↩︎