Battolyser (nickel-iron battery-electrolyser)

Protects divisions; far below any physical value of the model.

Market range Not applicable.

Unit multiplier used in the CRF, the BOP divisor and the guards.

Market range Exact by definition.

Turns a percent input (0-100) into a fraction.

Market range Exact conversion, no range.

Turns a fraction into a percent for display, and caps the discount rate guard at 100 %.

Market range Exact conversion factor.

Length of the year used by the time-budget check (charge + discharge + electrolysis hours).

Market range Exact convention.

Converts MWh to kWh.

Market range Exact conversion factor.

Converts kWh of storage to Wh for the volume estimate.

Market range Exact conversion factor.

Converts litres to cubic metres.

Market range Exact conversion factor.

Converts kilograms to tonnes.

Market range Exact conversion factor.

Energy content used for the specific energy, the H2 thermal output and the LCOH = LCOWB x HHV conversion.

Market range No independent range cited; HHV basis throughout the calculator.

Voltage at which electrolysis efficiency is 100 % on an HHV basis; the implied cell voltage is 1.48 V divided by the voltage efficiency.

Market range No independent range cited; thermodynamic value.

Fully charged battery potential; the electrolysis cell voltage is shown as a margin above it.

Market range No independent range cited.

Charge-to-gas yield; multiplies the voltage efficiency in the stack specific consumption.

Market range 87 % (Barton 2020) to 100 % (Mulder 2017).

Lower end of the lab overall efficiency; reference only, shown for comparison with the annual output efficiency.

Upper end of the lab overall efficiency; reference only.

Mulder's lab round trip, kept for reference only: the model uses Barton's 70 % (battery_rte_pct) so that the reference case comes from one cell.

Market range 70 % (Barton 2020, C/5) to 83 % (Mulder 2017, lab).

Upper limit of the battery round-trip efficiency.

Barton's C/5 round trip: the value the model uses (battery_rte_pct).

Lower limit of the input guard: below it the round-trip efficiency is outside anything published for Ni-Fe.

Reference only: conventional Ni-Fe upper end.

Lower end of the standby loss shown for a full battery; not part of the annual balance.

Upper end of the standby loss shown for a full battery; not part of the annual balance.

Barton's 70 % operating point (2.11 V, 83 mA/cm2): the value the model uses (elec_efficiency_hhv_pct), since the modelled current density sits below it.

Market range 50 % (Barton typical) to 90 % (Mulder max).

Mulder's lab maximum: top of the specific-energy bound (45 kWh/kg); reference only, the efficiency is no longer an input.

Reference only: lab efficiency at the highest tested current density.

Barton's typical electrolysis efficiency, tied to no current density: reference only and the low end of the specific-energy bound. The model uses the 70 % point (elec_efficiency_hhv_pct).

Reference cell voltage; the implied cell voltage of the model is compared with it.

Market range No independent range cited.

Balance-of-plant divisor on the stack specific consumption (the load penalty of the electrolysis mode).

Market range No independent range cited.

Reference specific energy; the model's deviation from it is shown.

Default storage duration (C/5).

Market range Duration of at least 1 h (charge rate below 1C).

Input guard: a duration below 1 h would mean charging faster than 1C.

Market range No independent range cited.

Default number of full battery cycles a year.

Market range No independent range cited.

Default electrolysis hours a year.

Market range No independent range cited.

Source of the default battery capital cost, before conversion to EUR.

Market range No independent range cited.

Converts Barton's 2020 GBP battery price to EUR 2020: 440 / 0.8897 = 494.5 EUR/kWh.

Market range Exact published average.

Converts IRENA's 2020 USD electrolyser costs to EUR 2020, the same year as the battery part.

Market range Exact published average.

Low end of the entire alkaline system cost; minus the stack it gives the low end of the electrolysis-part cost used in the Customized CAPEX lower bound.

Market range USD 500-1 000/kW (IRENA 2020, > 10 MW).

High end of the entire alkaline system cost; taken whole (stack included) it gives the high end used in the Customized CAPEX upper bound.

Market range USD 500-1 000/kW (IRENA 2020, > 10 MW).

Removed from the system cost because the battolyser's Ni-Fe electrodes are its stack and are already costed in the battery part (Barton 2020: the battery price as an electrolyser stack excludes gas collection and compression).

Market range No independent range cited.

Low end of the electrolysis-part cost (balance of plant only, the stack being the battery electrodes); enters the lower bound of the Customized CAPEX (494.5 x 2 h + 201.4 = 1,190.4 EUR/kW).

High end of the electrolysis-part cost (the whole alkaline system, none of the stack in the battery price); enters the upper bound of the Customized CAPEX (494.5 x 6 h + 875.5 = 3,842.5 EUR/kW).

Source of the model's fixed O&M rate. The IEA figure is used rather than NREL's because NREL's 2.5 % is meant to cover capacity additions or replacements, which this calculator costs in its own electrode replacement line.

Market range 1.5 %/year (IEA 2019, electrolysis) to 2.5 %/year (NREL 2021, 4-hour battery incl. augmentation).

Cost of one electrode and electrolyte set as a share of the battery-part CAPEX: electrodes and KOH electrolyte are replaced, cell casings, terminals, racking and the electrolysis-part balance of plant are kept.

Market range No independent range cited.

Floor of the electrode life slider (lower values are refused) and the denominator of the lifetime-wear ratio.

Market range No independent range cited.

Charge throughput of Mulder's test; divided by its 500 cycles it converts a charge throughput into equivalent deep cycles of wear.

Market range No independent range cited.

Sets the top of the electrode life slider: 20 years x 365 cycles = 7,300 equivalent cycles.

Floor of the replacement count and of the O&M guard.

Market range Not applicable.

Active nickel per kWh of storage.

Market range No independent range cited.

Active iron per kWh of storage.

Market range No independent range cited.

Energy density used for the indicative cell volume.

Market range 100 Wh/L now, 130-250 Wh/L practical limit (Mulder).

Oxygen co-produced per kg of hydrogen.

Market range Exact stoichiometry.

Water consumed by electrolysis per kg of hydrogen (minimum, before purification reject).

Market range Exact stoichiometric minimum.

Reference size of the CAPEX scaling law, at the bottom of the 1-5 MW design range (RWE press release 2023).

Market range Not applicable.

Exponent of the CAPEX scaling law, kept at 1: the battolyser is modular, scaled by module count (2.5 MW skids, 5 MW modules), and the Ni-Fe cells that carry about 85 % of the CAPEX are priced per kWh with no published size effect. The balance of plant could scale at 0.6-0.75 (IRENA 2020 after Bohm et al.), so the linear law is prudent on that 15 % (it may overstate the CAPEX at 5 MW), not neutral. The size slider is held to 1-5 MW, the range the cells are designed for.

Market range 1 (modular numbering-up); 0.6-0.75 for a conventional electrolyser balance of plant (IRENA 2020 p.71).

Lower guard of the specific CAPEX clamp; never binds inside the declared domain (checked at the box corners).

Market range Not applicable.

Upper guard of the specific CAPEX clamp; never binds inside the declared domain (checked at the box corners).

Market range Not applicable.

Default of the electricity price input, for both charging and electrolysis.

Market range No independent range cited; the slider runs 30-120 EUR/MWh as a sensitivity.

Model value of the battery round-trip efficiency (reference case Barton 2020, tested 3 Ah cell). No longer an input: the reference case sets it.

Model value of the electrolysis efficiency, HHV (reference case Barton 2020, tested 3 Ah cell, at the 2.11 V point printed by Barton). Its use at the model's lower current density is derived (evidence medium), not read. No longer an input: the reference case sets it. At Barton's typical 50 % (2.96 V, a high-current regime the cell does not reach at rated power) the LCOH would be 8.71 EUR/kg instead of 7.63.

Market range 50 % (Barton typical) to 90 % (Mulder lab maximum).

REFERENCE CASE. 'Barton 2020 (Loughborough, 3 Ah cell) on a common cost base': round trip 70 %, electrolysis 70 % HHV (2.11 V) and the battery-part price (GBP 440/kWh = 494.5 EUR/kWh) come from Barton 2020, measured on one cell, except the faradaic efficiency (Mulder's 100 % rather than Barton's measured 87 %, declared as a modelling assumption); the electrolysis part (IRENA 2020, 420.2 EUR/kW) and the fixed O&M (IEA 2019, 1.5 %/year) are not in Barton and form a common cost base, named as such. It replaces the former default (RTE 80 % from Mulder, electrolysis 70 % from Barton's 2.11 V point, Barton's price), itself a mix of two cells: the nominal LCOH moves from 7.49 to 7.63 EUR/kg. Barton's price is a UK retail price of conventional Ni-Fe batteries, distribution margin included, so it leans high. battery_limit stays 'exfactory': Barton's is a purchase price before installation and IRENA's system cost excludes shipping, civil works and site preparation.

Market range Not applicable.

Default 0: the model value (Barton 2020 on a common cost base).

Market range Not applicable.

Customized CAPEX per kW of rated power, EUR 2020, equipment price level (ex-works). Applied as entered at every size, with no scale law. The battery/electrolysis split, the electrode set and the fixed O&M follow it.

Market range 1,190.4-3,842.5 EUR/kW (see the two bound entries).

Lower bound of the Customized CAPEX, identical in the guard, the slider and the help.

Market range Not applicable.

Upper bound of the Customized CAPEX, identical in the guard, the slider and the help.

Market range Not applicable.

Model value of the battery-part capital cost (reference case Barton 2020): equipment purchase price, EUR 2020; installation, indirects and contingency excluded. No longer an input: a different price goes through the Customized CAPEX.

Market range No independent range cited.

Model value of the electrolysis-part CAPEX (common cost base): rectifier, gas treatment and drying, water purification, cooling and commissioning of a conventional alkaline system, without the stack (the Ni-Fe electrodes, costed in the battery part). No longer an input.

Model value of the fixed O&M (common cost base), applied to the CAPEX used, model or Customized; purchased electricity and electrode replacement are separate lines. No longer an input.

Market range 1.5 %/year (IEA 2019) to 2.5 %/year (NREL 2021, 4-hour battery incl. augmentation).

Default electrode and electrolyte life in equivalent deep cycles; drives the number of replacements paid over the economic life.

Market range 500 (Mulder, demonstrated floor) to 7,300 (Barton, conventional Ni-Fe).

Default discount rate of the annuity.

Market range No independent range cited; slider 0-10 %.

Default annuity horizon.

Market range No independent range cited; slider 10-20 years.

STATUS. Pre-commercial technology with no current vendor offer. As of October 2026 no vendor sells a battolyser: there is no datasheet, no vendor price, and no vendor cost data exists. Battolyser Systems merged into Alquion, whose only product, the Flexolyser, is a flexible alkaline electrolyser with no battery function and no printed specifications (vendor status taken from the commissioning brief, not re-verified here). The physics comes from lab cells (Mulder 2017, 10 Ah, 18 months; Barton 2020, 3 Ah). The costs are declared approximations: a retail Ni-Fe battery price (Barton 2020), a conventional alkaline electrolyser (IRENA 2020), an electrolysis O&M rate (IEA 2019) and a declared electrode replacement share.

Market range Not applicable.

DEVICE. One Ni-Fe cell in KOH with a Zirfon diaphragm. Charging converts Fe(OH)2 to Fe and Ni(OH)2 to NiOOH; once charged, the same electrodes evolve H2 and O2. Efficiencies follow Mulder's definitions (eq. 5-7): battery efficiency = energy discharged / energy in; electrolysis efficiency = 1.48 V x charge to gas / energy in, i.e. 1.48 V divided by the cell voltage.

Market range Not applicable.

SCHEDULE. Annual steady state, no hourly dispatch. Battery mode: cycles x usable kWh discharged, divided by the round-trip efficiency for the energy charged, both at rated power. Electrolysis mode: rated power x electrolysis hours. Charge + discharge + electrolysis hours must fit in 8,760 h; above it the inputs are refused. At the defaults the year holds 8,432 h.

Market range Not applicable.

ALLOCATION. Adapted from Jenkins 2022 eq. 7 (LCOWB): one levelised cost per MWh of useful output, electricity discharged plus hydrogen HHV. Two departures from Jenkins: eq. 7 leaves the charging electricity out (free energy from the wind farm) and puts the wind farm in the capital cost; here bought electricity is in the annual cost and no generator capital is. The cost per MWh discharged equals this LCOWB: it is a joint allocation, not Jenkins' LCOS (eq. 5 divides by electricity discharged only) and not a stand-alone battery LCOS. LCOH = LCOWB x 39.37/1000 per kg. End-of-life cost and residual value are not modelled (0): Jenkins sets end of life to 0 because it assumes a lead-acid battolyser feeding the lead-acid recycling chain, which is not established for Ni-Fe. The annual cost is CRF x CAPEX + fixed O&M + electrode replacement provision + electricity, the structure of the Hydrogen Observatory LCOH manual eq. 1, 8-14 (other OPEX and stack replacement as a share of CAPEX), with replacements paid pro-rata rather than as the manual's rounded-down count.

Market range Not applicable.

REPLACEMENT. Electrode wear per year = the larger of the battery cycles and the charge throughput divided by 2, the capacities of charge per deep cycle in Mulder's test (1000/500). Electrolysis charge counts in battery capacities as hours x C-rate x 1.37 V / cell voltage (current at rated power = power / cell voltage; capacity in Ah taken at the 1.37 V OCV). Sets used over the life = lifetime x wear / electrode life; the first set is in the CAPEX and the rest are paid pro-rata, the last one only for the part used, with no lump at the end of life. One set costs 50 % of the battery-part CAPEX (declared), itself the model's battery share of the CAPEX used. The provision is the replacements used x set cost / lifetime, a constant EUR 2020 cash amount per year, never discounted, so it does not move with the discount rate. Project mode does not replace the set (it replaces only the whole asset), so this line is what a project figure omits. At the defaults: 442 equivalent cycles a year, a set lasts 4.5 years, 2.3 replacements, 190,602 EUR/year. It rises with battery cycles and electrolysis hours: over the cycles slider (200 to 365 at the defaults) it goes from 139,607 to 190,602 EUR/year, 1.50 to 1.67 EUR/kg. The total LCOH still falls there (8.16 to 7.63 EUR/kg) because each extra cycle spreads the capital over more output, but less than with no replacement (6.66 to 5.96 in the 7,300-cycle case); with 500-cycle electrodes and 1,000 electrolysis hours the wear wins and it rises slightly (20.75 to 21.28).

Market range Not applicable.

CAPEX BOUNDARY. The CAPEX is an equipment price level: retail Ni-Fe battery price (Barton 2020) plus the alkaline electrolysis balance of plant (IRENA 2020 system cost minus stack). IRENA's system figure excludes shipping, civil works and site preparation, and the retail battery price excludes installation; indirects, owner's costs and contingency are in neither. costs.capex.battery_limit is therefore 'exfactory' and project mode adds its cost layers and contingency. A bidirectional converter for battery discharge is not costed separately; IRENA's rectifier stands in for the power electronics. The calculator's own LCOH carries no uplift, so it is a screening figure that project mode will raise. Electrode replacements are not in the CAPEX: they are a separate annual provision. A Customized CAPEX must sit at the same level and in EUR 2020: Barton's figure is a retail price (distribution margin included, so it leans high), and a quote at another year or an installed price would be escalated and marked up a second time by project mode.

Market range Not applicable.

COST YEAR. CAPEX in EUR 2020: battery part from Barton's 2020 GBP at the ECB 2020 rate, electrolysis part from IRENA's 2020 USD at the ECB 2020 rate; fixed O&M and the replacement set are shares of that CAPEX. Electricity is EUR 2023 (Observatory, ENTSO-E 2023), not indexed. The meta declares 2020, and a Customized CAPEX must be entered in EUR 2020 ex-works for the same reason. No escalation applies to any line, so the discount rate is used as a real rate.

Market range Not applicable.

LIMITS. Not modelled: hourly prices and arbitrage (discharged electricity is not credited at a different price), efficiency drift between electrode replacements, end-of-life cost or residual value (Jenkins' zero is for a lead-acid battolyser), self-discharge in the balance (shown as a standby figure), Barton's 87 % faradaic efficiency (Mulder's 100 % kept), water and oxygen values, grid fees, and land. The default price is the 4,000-cheapest-hours average while the model buys power for 6,607 h, so it leans low. Lifetime 15 years at the default duty means about 6,600 equivalent deep cycles, 13 times the 500+ shown in the lab: the electrode life input is the least grounded number and the replacement provision follows it. Size is held to 1-5 MW, the range the cells are designed for (RWE 2023); the CAPEX is linear in size (modular numbering-up), while IRENA 2020 (p.71, after Bohm et al. 2020) gives 0.6-0.75 for a conventional electrolyser balance of plant, so at 5 MW the electrolysis part may be overstated. The 70 % round trip was measured at C/5 (5 h) and is applied unchanged over the 2-6 h slider: at 2 h (C/2) it is optimistic, as Ni-Fe losses rise with current.

Market range Not applicable.

BOUNDS. LCOH bound 4.5-10.5 EUR/kg = lowest (4.51) and highest (10.23) Total LCOH printed in the Hydrogen Observatory manual use cases with default 2024 data (p.37, 40), conventional low-temperature electrolysis transposed to a battolyser: evidence medium. The reference case (Barton 2020 cell, 7.63 EUR/kg) sits inside it, just above its mid-point. Specific energy bound 45-85 kWh/kg = 39.37/(efficiency x 0.95) over 90 % to 50 %: a domain statement from the model's own formula, not an external check. Both hold on the nominal case and on every charted sweep; the reference case leaves the band above about 100 EUR/MWh or below about 1,050 electrolysis hours, and the charts (price 40-75 EUR/MWh, hours 2,000-4,300 h) stay well inside it. They do not hold across the whole input box, and the bound was not widened to fit: over its 192 valid corners with the model CAPEX the LCOH runs from about 3.0 to 29.0 EUR/kg and 24 % of corners sit inside the band (2.8 to 53.4 EUR/kg over the 384 valid corners with a Customized CAPEX). The cheap end combines 2 h, 365 cycles, 6,000 electrolysis hours, 30 EUR/MWh, 7,300-cycle electrodes, 0 % and 20 years; the dear end combines 6 h, 200 cycles, 1,000 electrolysis hours, 120 EUR/MWh, 500-cycle electrodes, 10 % and 10 years. The cost per MWh discharged has no market bound: no accessible source prints a Ni-Fe battolyser LCOS.

Market range Not applicable.

CHAINING. Electricity appears on both sides of this asset. The inlet 'Electricity (charging and electrolysis)' (annual_electricity_input_mwh / 8760) takes upstream generation, PV, wind or a grid supply, and pays for both battery charging and electrolysis. The outlet 'Electricity discharged (battery mode)' (annual_discharged_mwh / 8760) may feed a downstream electricity load, or stay unlinked as a by-product. The two are never netted against each other: never link the discharged outlet back to this asset's own inlet, nor to the upstream source that charges it, or the netting cancels charge against discharge and the levelised cost loses its meaning. Hydrogen, the main product, is linked downstream on its own.

Market range Not applicable (chaining rule).