Pass a current through water and two gases come off. The reaction is 2H₂O → 2H₂ + O₂, and it has not changed since 1800. What has changed is the question of who controls the current. The word green describes the electricity, not the molecule. Hydrogen from a dam is chemically the same as hydrogen from fossil gas. The difference is its history, and that history is mostly grey. According to the IEA’s Global Hydrogen Review 2024, low-emission hydrogen was under 1% of global output, and only part of that came from electrolysers running on renewable power. For anyone planning a building or a district, the hard part of this technology is not the chemistry. It is provenance: which kilowatt-hour, in which hour, under which contract.

The live signal makes the point at utility scale. On 10 October 2026, Tech Times reported that EWE and Verbund will develop CHC Electrolysis JadeWeser. It is a 500 MW electrolyser in Nordenham, Lower Saxony, aiming at about 50,000 tonnes of green hydrogen a year by 2032 and built next to cavern storage. According to Tech Times, putting the plant beside storage cuts the cost penalty of the EU’s hourly-matching rule from about 20% to single digits. The site is doing the work of the control mechanism.

What it is

What it is: An electrolyser is a sandwich: an anode, a cathode, and a separator between them. The separator lets charge through and keeps hydrogen and oxygen apart. Direct current goes in, and hydrogen leaves on one side and oxygen on the other. The three industrial families differ in what carries the charge. Alkaline cells move hydroxide ions (OH⁻) through a porous diaphragm soaked in 25–30% potassium hydroxide, between nickel electrodes, at roughly 60–90 °C. They use no precious metals and have the longest industrial record. PEM (proton-exchange membrane) cells move protons across a thin acidic polymer membrane, with iridium on the oxygen side and platinum on the hydrogen side. They are compact and can ramp in seconds. SOEC (solid-oxide) cells move oxide ions through a ceramic electrolyte, typically yttria-stabilised zirconia, at 700–850 °C. They split steam rather than liquid water.

The hydrogen counts as green only when the power behind it can be shown to be renewable. In the EU, that proof is written into law. Delegated Regulation (EU) 2023/1184 sets the conditions for renewable hydrogen: additional generation, geographic correlation, and time correlation that tightens from monthly to hourly matching from 2030. That is the governance layer underneath the chemistry. A plant is green when its paperwork can prove it, hour by hour.

Why it works

Why it works: Every hydrogen molecule needs two electrons. Faraday’s law, n = I·t / 2F with F = 96,485 C/mol, turns that into site units. One kilogram of hydrogen is 496 mol and takes about 26,600 ampere-hours of charge. Multiply by the cell voltage and you have the energy bill. At 1.23 V, the reversible voltage, the floor is about 33 kWh/kg. At 1.48 V, the thermoneutral voltage, it is 39.4 kWh/kg, the full higher heating value of the gas. The gap between those two numbers has to arrive as heat. Low-temperature cells run nearer 1.8–2.0 V and cover the gap with their own losses. Add pumps, rectifiers and gas drying, and a real system lands around 50–55 kWh/kg. SOEC can take that heat from a neighbour’s furnace instead, which is why its electricity demand can sit near 40 kWh/kg.

Load range is where physics turns into urban planning. At low current, a little hydrogen diffuses through an alkaline diaphragm into the oxygen side. Hydrogen becomes flammable in oxygen at about 4%, and plants shut down well before that point, often at around 20% load. PEM membranes are dense and thin, so they can follow a wind or solar curve down to a few percent. SOEC ceramics wear out under heating and cooling cycles, so they want a hot, steady neighbour. Choose a technology and you have chosen a load profile. Choose a load profile and you have chosen the site.

Then come the balances. Each kilogram of hydrogen consumes 9 kg of water by stoichiometry, and more once purification losses are counted. It also releases 8 kg of oxygen. A low-temperature system turns roughly 70–75% of its electricity into hydrogen, and most of the rest leaves as heat at 60–80 °C. A 10 MW PEM hall therefore sheds on the order of 2–3 MW of low-grade heat, which is district-heating scale. Electricity dominates the cost: every 10 CHF/MWh on the power price adds about 0.55 CHF to each kilogram. Capital is the other large cost, and it is due whether the stack runs or not. The plain trade-off: PEM buys flexibility with iridium, a metal mined mostly as a by-product of South African platinum. That is a supply dependency you sign at procurement, not one you can renegotiate later.

Origins

Origins: In 1789 two Dutchmen, Adriaan Paets van Troostwijk and Jan Rudolph Deiman, split water with electrostatic sparks, eleven years before the battery existed. In 1800, weeks after Alessandro Volta’s letter about his pile reached London, William Nicholson and Anthony Carlisle repeated the experiment with a steady current, and anyone could reproduce it. By about 1900, alkaline electrolysis was an industrial process, and it went where power was cheap: waterfalls. At Vemork, near Rjukan in Norway, Norsk Hydro’s 1911 power station, usually credited to the architect Olaf Nordhagen, gained an electrolysis plant beside it around 1929 to feed ammonia production. The people of that history are mostly unnamed: the shift workers who tended thousands of cells in a cell hall that made fertiliser for half a continent. Their plant also concentrated heavy water, which made it a target of Allied sabotage in 1943. Since 2015 it has been part of the Rjukan–Notodden UNESCO Industrial Heritage Site.

PEM electrolysis grew out of General Electric’s membrane work in the 1960s, first aimed at spacecraft and submarines. SOEC came from German research in the 1970s and 80s, where Dornier’s HOT ELLY programme split steam in ceramic cells at furnace temperatures. In 1992, Fraunhofer ISE’s Energieautarkes Solarhaus in Freiburg, with architecture credited to Planerwerkstatt Hölken + Berghoff, put the electrolyser inside the house itself. It stored summer sun as hydrogen and turned it back into power in winter. According to PAZ’s own concept panel on this topic, green hydrogen is more than two hundred years old as an experiment and very young as an industry.

←TODAY: In 2026 low-emission hydrogen is still under 1% of output, and EU law moves its proof from monthly to hourly matching in 2030. →3012: The cell hall is ordinary district infrastructure, as unremarkable as a substation, sited by its heat and oxygen buyers. Fulcrum: The molecule never changes; the contract that proves its origin is the part architects actually design around.

In practice

In practice: Switzerland’s reference is small on purpose. At the Gösgen run-of-river station on the Aare in Niedergösgen, Alpiq, H2 Energy and Linde put a 2 MW PEM electrolyser to work in 2020. It runs on river power and supplies hydrogen to the Hydrospider network that fuels Switzerland’s fleet of fuel-cell trucks. Hydropower gives the stack what solar alone cannot: steady baseload and a high capacity factor. Gösgen fits in one sentence: small, patient, and tied to a real buyer. The people who made it work are mostly engineers whose names appear on no plaque. They solved grid connection, water treatment and refuelling logistics, the unglamorous pieces that decide whether a stack earns its capital.

For an architecture or planning office, electrolysis shows up as a building brief. You need a transformer and rectifier yard to turn grid AC into stack DC, drawn from the first sketch. Gas halls are vented at the ridge, zoned for explosive atmospheres and fitted with pressure-relief panels. The stack is itself structural: dozens to hundreds of cells clamped between steel end plates by tie rods, a filter press held in compression much like a post-tensioned element. The neighbours are the brief too: the steelworks, the glass plant, the cement kiln, the concrete batching yard, and a thermal network that can take the 60–80 °C heat. A Swiss office working on an industrial-district masterplan, or a feasibility study for a thermal network, is now designing the provenance, not just the shed.

Atelier: The risk for an office is accepting “hydrogen-ready” as a vendor label and drawing the hall before anyone has checked where the power comes from. AI-assisted feasibility tools make it faster to produce a polished plant layout before the 8,760-hour supply profile exists. That speed hides the decision that matters. Monday move: put two rows into your district feasibility template, minimum stack load (%) and heat offtake (MW per 10 MW of electrolysis), and refuse to fix a footprint until the energy engineer has filled both from an hourly supply profile.

Hack

Hack: Trace a cell’s voltage all the way to the energy bill per kilogram, so the next “high-efficiency” claim on your desk can be checked against Faraday in seconds. The constant kwh_per_V is Faraday’s law in site units, about 26.6 kWh for every volt across the cell per kilogram of hydrogen. Run it in plain Python or inside a GhPython component in Grasshopper next to a Rhino site plan. Any vendor figure below 1.23 V × 26.6 ≈ 33 kWh/kg of electricity has to be importing heat, as SOEC does, or the claim is wrong.

F, M_H2 = 96485.0, 2.016e-3               # C/mol, kg/mol
kwh_per_V = 2 * F / M_H2 / 3.6e6          # ~26.6 kWh/kg per volt
for V in (1.23, 1.48, 1.9):               # reversible, thermoneutral, real cell
    print(V, 'V ->', round(V * kwh_per_V, 1), 'kWh/kg')
print('CHF/kg per +10 CHF/MWh at 55 kWh/kg:', 55 * 10 / 1000)

The output gives 32.7, 39.4 and 50.5 kWh/kg, plus 0.55 CHF/kg of price sensitivity. Those four numbers are enough to question a feasibility deck.

From where I write, the hydrogen plants that hurt districts were not the ones that failed. They were the ones locked into a stack supplier and an offtake contract nobody had standing to reopen when the power mix changed. If your office is drafting a brief that includes electrolysis, write the exit clause — stack replacement, iridium recovery, heat-offtake renegotiation — before the entry contract. Run the five lines above on the next hydrogen number that lands on your desk, and ask for the hourly profile behind it.