Electrolyzer Stack Degradation: What It Does to Your Hydrogen Cost Over 10 Years

An electrolyzer gets less efficient every hour it runs. The stack needs a little more voltage to make the same hydrogen, so each kilogram takes more electricity. Eventually the stack has to be replaced, and that bill often lands in the middle of the project's life, not at the end.

Most early hydrogen models treat this as a footnote: a fixed efficiency and a stack swap 'around year seven'. This guide puts numbers on it. A worked 100 MW example shows how degradation and stack replacement change hydrogen cost over 10 years, then sets out six things to check in your model and your supply contract.

This is general pre-feasibility guidance, not engineering, legal or financial advice. Confirm degradation rates, warranties and replacement costs with your equipment supplier and independent engineer.

What stack degradation means

An electrolyzer stack is a pile of cells that split water using electricity. As the cells age, catalysts lose activity, membranes thin and contaminants build up. The visible symptom is a rising cell voltage. Higher voltage at the same current means more kilowatt-hours for every kilogram of hydrogen.

Degradation is usually quoted in one of two ways:

• Millivolts per thousand hours (mV/kh), or microvolts per hour (µV/h) per cell. The two are the same number: 4.8 mV/kh equals 4.8 µV/h.

• Percent per thousand hours (%/kh). The voltage rise as a share of the starting voltage.

End of life is a convention, not a failure. The U.S. Department of Energy's PEM targets are consistent with a 10% performance loss at end of life. Its alkaline table works out lifetime as the hours it takes the voltage to rise 10% at the average degradation rate.

How fast stacks degrade

Published figures vary widely, and the gap between targets and real operation matters:

• PEM, DOE 2022 status: an average of 4.8 mV/kh (0.25%/kh) and a 40,000-hour lifetime. The 2026 target is 2.3 mV/kh and 80,000 hours.

• Liquid alkaline, DOE 2022 status: 3.2 mV/kh (0.17%/kh), which by DOE's own formula gives roughly 60,000 hours to end of life.

• Industry expectation: EPRI puts current expected stack life at 7 to 10 years, or 60,000 to 80,000 operating hours, for both PEM and alkaline, against a plant life of 20 to 40 years. Several replacements are therefore normal.

• Test results under stress: an NREL-led study measured 28 µV/h in a 4,000-hour test of a low-catalyst PEM cell at high current density, nearly six times the DOE status average. A 7,800-hour test of a nine-cell PEM stack measured 35.5 µV/h per cell, mostly from contamination that could be reversed.

The lesson is not that one number is right. It is that the rate depends on the design, the operating regime and the water, and that a model should test a range.

Worked example: the same plant, four degradation rates

Take the hypothetical 100 MW plant from our hydrogen PPA guide, now on firmed power so the stack accumulates hours quickly. All inputs are illustrative assumptions, not supplier quotes, data about a real project or H2Hub outputs.

• Power: $50/MWh delivered, 7,000 full-load hours a year, input held constant

• System electricity use: 55 kWh/kg at beginning of life, of which 50 kWh/kg is drawn by the stack and rises with degradation

• Fixed costs: $1,800/kW installed and $45/kW-year, annualized at 8% over 20 years, about $22.8 million a year

• Stack replacement: $500/kW ($50 million), triggered when stack voltage is 10% above new

• Cost per kilogram levelized over the first 10 years at 8%

Because power input is fixed, a degrading stack does not use more electricity in total. It makes less hydrogen from the same electricity, so every cost is spread across fewer kilograms.

Case	Rate	Stack swaps in 10 years	10-year cost	Change	From lost efficiency	From replacement
No degradation	0	None	$4.54/kg	-	-	-
Low (DOE 2026 target)	0.13%/kh	None	$4.71/kg	+$0.16	+$0.16	$0
Typical (DOE 2022 status)	0.25%/kh	Year 6	$5.10/kg	+$0.56	+$0.17	+$0.38
Stressed	0.50%/kh	Years 3, 6, 9	$5.90/kg	+$1.36	+$0.19	+$1.17

Calculation for the typical case: at 0.25%/kh, voltage reaches 10% above new after 40,000 hours, which is 5.7 years at 7,000 hours a year. Before the swap, electricity use climbs from 55.4 to 58.9 kWh/kg and annual output falls from about 12,630 to 11,880 tonnes. The $50 million replacement in year 6 alone pushes that year's cost to about $9/kg.

Three points stand out:

1. The replacement, not the efficiency loss, drives the difference. Lost efficiency costs between $0.16 and $0.19/kg in every case, because stacks are replaced before efficiency falls further. Replacement frequency is what separates the cases.

2. Ten years can flatter a slow stack. The low case shows no replacement, but its stack ends year 10 about 9% above its starting voltage. The swap is due shortly after the window closes, so a 20-year model would show it.

3. Doubling the degradation rate more than doubles the cost. Going from 0.25%/kh to 0.50%/kh adds two extra replacements in the decade and raises the penalty from $0.56/kg to $1.36/kg.

Components may not add exactly because of rounding. These are simplified screening figures. They exclude replacement downtime, balance-of-plant wear, water, compression, storage, taxes and any change in stack prices over time. A real model should run the actual operating profile hour by hour.

Six things to check before you commit

1. The basis of the degradation figure

Ask whether the quoted rate was measured at steady load or under the start-stops and ramping your power supply will impose. DOE notes that its status figure is based on continuous operation, and that progress against targets must also consider dynamic operation. A rate from a steady-state lab test may not survive solar or wind operation.

2. The end-of-life definition

Confirm what 'end of life' means in the contract: a 10% voltage rise, a 10% efficiency loss or a production shortfall. Each triggers a replacement at a different time, and they are not interchangeable.

3. Replacement cost and who pays

A Columbia University review found that stacks make up 19% to 60% of upfront electrolyzer capital cost, depending on technology, with lifetimes of 3.5 to 11.5 years. Get a firm replacement price or a price formula, and check whether a long-term service agreement covers it.

4. Operating regime and water quality

Load cycling, high current density and poor water purity all accelerate degradation. The 7,800-hour test above traced most of its losses to metal impurities from the feed water and system components. Budget for water treatment and monitoring, and model degradation for the profile you will actually run.

5. Balance-of-plant sizing for end of life

A degraded stack makes more heat, and the cooling system and power electronics must handle the worst case, not just day one. The EU-funded ENDURE project notes that degradation forces electrolyzer components to be significantly oversized. Check that the quoted balance of plant is sized for end-of-life conditions.

6. Performance guarantees and downtime

Look for guaranteed efficiency over time, not just at handover, and for remedies if the stack degrades faster than promised. Plan the replacement outage too: our PPA guide shows how take-or-pay terms can turn plant downtime into a direct cost.

A short pre-investment test

Before choosing a supplier, a developer should be able to answer five questions from one model:

1. What hydrogen cost results at the supplier's degradation rate, and at double that rate?

2. In which years do stack replacements fall, over the full project life?

3. What does each replacement cost, and is the price fixed or indexed?

4. Is the guaranteed degradation rate measured under our real operating profile?

5. Do the offtake contract and power contract tolerate the output loss and replacement downtime?

If the project only works at the lowest degradation rate, it is carrying a technology bet and should say so.

Test degradation cases with H2Hub

Start your first H2Hub project free to compare operating and cost cases for a candidate site. The current free entry includes one project and its PDF report, with no credit card. The LCOH Lab explains the cost inputs behind the result, and our LCOH explainer walks through the basic calculation.

H2Hub is a screening and learning tool. Its outputs are estimates, not supplier quotations, engineering opinions or investment advice.

Frequently asked questions

What is electrolyzer stack degradation?

It is the gradual rise in cell voltage as an electrolyzer ages. The stack needs more electricity for each kilogram of hydrogen, and it is replaced when performance falls past an agreed limit, often a 10% voltage rise.

How long does an electrolyzer stack last?

Current expectations are roughly 60,000 to 80,000 operating hours, or 7 to 10 years, for PEM and alkaline stacks. Real life depends on operating conditions, and lab and field results vary widely.

How much does stack degradation add to hydrogen cost?

In our illustrative 100 MW example, between $0.16 and $1.36/kg over 10 years, depending on the degradation rate. Most of the difference comes from how often the stack must be replaced.

Does flexible operation with solar or wind speed up degradation?

It can. Start-stops, ramping and partial load stress the cells differently from steady operation, so ask suppliers for degradation data measured under a profile like yours.

Primary sources and further reading

1. U.S. Department of Energy — Technical Targets for Proton Exchange Membrane Electrolysis. 2022 status and 2026 targets for degradation and lifetime.

2. U.S. Department of Energy — Technical Targets for Liquid Alkaline Electrolysis. Degradation status and the lifetime formula.

3. EPRI — Technology Brief: Water Electrolyzer Stack Degradation. Expected stack and plant lifetimes.

4. Columbia University Center on Global Energy Policy — Demystifying Electrolyzer Production Costs. Stack share of capital cost and lifetime range.

5. Padgett et al., Journal of the Electrochemical Society, 2025 — Quantifying Sources of Voltage Decay in Long-Term Durability Testing for PEM Water Electrolysis.

6. Sun et al., Journal of Power Sources, 2014 — Investigations on degradation of the long-term proton exchange membrane water electrolysis stack.

7. UCLouvain — ENDURE: alkaline electrolysers with enhanced durability.

Editorial verification: 6 November 2026. Worked examples are calculations from stated assumptions, not forecasts, market prices or H2Hub-generated results.