Available Engineering tool

Electrolyser spec normaliser

Are these electrolyser quotes comparable once they are on the same basis?

Comparison basis

Every vendor gets converted to this. Change it any time — the table recomputes instantly, nothing re-enters.

Boundary

Current

Display unit

Outlet pressure (bar)

Process scope

Fill in at least two vendors above and click Normalize.

Method, assumptions and limits

This tool does not touch the number a vendor gave you — it converts it. Every conversion is one of five independent steps, applied in a fixed order, and every step that required an assumption (because the vendor didn't state that part of the basis) is logged in the assumption ledger under your results, not hidden inside the total.

1. Efficiency % → kWh/kg (only if a vendor gave you a percentage, not a direct figure)

A percentage has no meaning without a denominator. The same 66% efficiency claim means 50.5 kWh/kg on an LHV basis (33.32 kWh/kg ÷ 0.66) or 59.7 kWh/kg on an HHV basis (39.39 kWh/kg ÷ 0.66) — an 18.2% gap from the same stated percentage. If the vendor didn't say which, this tool shows both as a range rather than picking one for you.

kWh/kg = (LHV or HHV, 33.32 or 39.39) / (efficiency % / 100)

2. kWh/Nm³ or kWh/Sm³ → kWh/kg

Volumetric hydrogen density depends on the reference temperature used to define "normal" or "standard" conditions — a real, unresolved convention split in the industry (0°C, 15°C and 20°C are all in active use). The difference between the 0°C and 15°C conventions alone is ~5.5%. If a vendor states Nm³ without a reference temperature, this tool shows the full band across all three conventions instead of guessing which one they meant.

3. Current: DC ↔ AC

Electrolyzers run on DC; grid power is AC. The rectifier that bridges them is not lossless.

kWh/kg (AC) = kWh/kg (DC) / rectifier efficiency [default 0.96, typical range 0.95–0.98]

4. Boundary: stack ↔ system

A "stack" number excludes everything the stack needs to actually run. This tool applies that gap in two separate, non-overlapping steps: the rectifier step above (step 3, power electronics only), then a balance-of-plant fraction here covering everything else the rectifier doesn't — water treatment, cooling, pumps, controls. The BoP fraction explicitly excludes rectification, which is already accounted for in step 3; applying both was a real ambiguity risk (whether a "typical system/stack ratio" already includes rectifier losses varies by source), so this tool defines the boundary explicitly rather than leaving it to guesswork.

kWh/kg (system) = kWh/kg (stack) × (1 + balance-of-plant fraction) [default 12%, typical range 8–15%, rectification excluded]

5. Process scope: compression, drying, purification

Whether the quoted number includes getting hydrogen to delivery pressure and dry/pure enough to use. Compression energy is the closed-form isothermal-work formula divided by an isothermal efficiency, not a lookup table — see the equation below. Drying (TSA) and purification to ISO 14687 grade adds a further ~0.4 kWh/kg by default. SOEC's high-temperature steam heat input (~7 kWh-thermal/kg) is shown as a separate line — it is not electricity and is never added into the electrical kWh/kg figure.

W_compression = (R / M_H2) · T · ln(P_out / P_in) / 3600 / η_isothermal [kWh/kg, default η=50%, typical range 45–65%]

What this tool deliberately does not do

It does not adjust for degradation or end-of-life performance — every figure here is BOL (beginning-of-life) unless you're comparing figures the vendor already labeled as EOL. Use the Degradation-Adjusted LCOH tool for lifetime economics.
It does not validate that a vendor's number is physically achievable — only that it's expressed on a comparable basis to the others. A normalized number that still looks too good is a due-diligence question, not something this tool resolves for you.
The 20-year energy cost comparison is a simple undiscounted multiplication, meant only to translate a kWh/kg gap into a dollar magnitude you can feel. It is not a financial model — use the LCOH tool for that.

Sources for default coefficients

HHV 39.39 kWh/kg, LHV 33.32 kWh/kg — standard thermochemical values (141.79 / 119.96 MJ/kg).
H2 density 0°C/15°C/20°C reference conditions — DIN 1343 and common industry "standard cubic meter" conventions.
Rectifier efficiency 95–98% — typical for modern thyristor/IGBT electrolyzer power supplies.
Balance-of-plant fraction 8–15% — auxiliary equipment only (pumps, water treatment, cooling, controls), rectification excluded — see step 4 above.
Compression: closed-form isothermal work (R/M·T·ln(P₂/P₁)) divided by a 45–65% isothermal efficiency typical of real multi-stage mechanical H2 compressors — not a fitted or looked-up figure.
All defaults are editable in the advanced fields on each vendor card and shown, not hidden, in every normalized result.

FAQ

Why do electrolyzer vendor specs disagree so much on kWh/kg?+

Usually because they're not on the same basis: stack-only vs. full system (8–15% difference), DC vs. AC (2–5% from rectifier losses), LHV vs. HHV (18.2% if the number came from a quoted efficiency percentage), and whether compression, drying and purification energy is included. None of these differences mean a vendor is lying — they mean the numbers were never comparable to begin with.

What's the difference between kWh/kg and kWh/Nm³ for hydrogen?+

kWh/kg is energy per unit mass; kWh/Nm³ is energy per unit volume at a stated reference temperature and pressure (commonly 0°C or 15°C at 1 atm). Converting between them requires knowing which reference temperature was used — 0°C vs. 15°C alone changes volumetric density by about 5.5%.

Is a lower kWh/kg always a better electrolyzer?+

Only if the basis is identical. A stack-only DC number will always look better than a system AC number for the same physical machine, because it excludes losses every real installation has to pay for. Compare on system, AC, and matched process scope before drawing a conclusion.

Worked example

Three vendors, three units, three boundaries — the argument this tool was built for. Normalized onto one basis: system boundary, AC input, 30 bar delivery, compression and drying included.

As quoted on the datasheet

Vendor A: 52 kWh/kg — system, AC, 30 bar, compression + drying included
Vendor B: 4.3 kWh/Nm³ — stack, DC, 1 bar, nothing included
Vendor C: 70 % LHV — stack, DC, 30 bar, nothing included

Normalized to one basis

Vendor A: 52.00 kWh/kg
Vendor B: 58.54 kWh/kg
Vendor C: 55.93 kWh/kg

Converted to kWh/kg but left on its own basis, Vendor B reads 47.8 kWh/kg — the best of the three. Put on the same basis as the others it is 58.5 kWh/kg, the worst by 6.5 kWh/kg. The ranking inverts entirely.

Where Vendor B's 10.7 kWh/kg went, in the order the tool applies it: DC → AC costs 1.99 kWh/kg at a 0.96 rectifier efficiency; stack → system costs 5.98 kWh/kg at a 0.12 balance-of-plant fraction; compressing 1 → 30 bar costs 2.32 kWh/kg at 50% isothermal efficiency; drying and purification cost 0.40 kWh/kg. Every one of those four is an assumption the tool made because the datasheet did not state it, and every one is listed as such in the tool's own assumption ledger next to the number. At $50/MWh and 1,000 kg/day, the 6.5 kWh/kg gap between Vendor A and Vendor B is roughly $107,000 a year in electricity that the datasheet comparison hid.

References

NIST Chemistry WebBook, hydrogen thermochemical data (HHV/LHV basis). Source

Engine v0.3.0Last reviewed 27 September 2026 Changelog Report an error

Cite this tool

Polestar Technology (2026). Electrolyser spec normaliser. HYDRA engine v0.3.0. https://polestartech.co/tools/electrolyzer-spec-normalizer.html

HYDRA Review: Comparing quotes for a real project? HYDRA Review normalises them with your own boundary assumptions.