ReneEnergy / H2Hub Editorial

    How to Size an Electrolyzer for 10 Tonnes of Hydrogen a Day

    A buyer wants 10 tonnes of hydrogen every day. How many megawatts of electrolyzers are needed? Under an illustrative electricity-consumption assumption of 52 kWh/kg of hydrogen, the project needs 520 MWh per day. That implies roughly 24 MW at 90% full-load utilization, 31 MW at 70%, or 43 MW at 50%. These are screening calculations, not vendor quotations, and none guarantees daily delivery.

    The right approach works backward from hydrogen demand. Begin with kilograms, calculate electricity, consider the hours when that electricity is available, and only then specify nameplate electrolyzer MW, storage, and standby capacity.

    Step 1: Convert the hydrogen order into electricity

    Consider a hypothetical industrial buyer requiring 10 tonnes per day, 365 days per year. Here is the mass-and-energy balance:

    The 52 kWh/kg figure is a chosen modelling input, not a guaranteed performance specification. U.S. Department of Energy (DOE) tables report 2022 PEM and alkaline electrolyzer system energy-efficiency status of 55 kWh/kg, with 2026 technical targets of 51 kWh/kg for PEM and 52 kWh/kg for liquid alkaline systems. A target is not proof that a particular installed unit has achieved it. Source: DOE PEM targets and DOE alkaline targets.

    Check the performance boundary before comparing numbers. A stack-only figure can omit transformers, rectifiers, pumps, treatment systems or other auxiliaries. Ask if the electricity number includes hydrogen drying and compression to the buyer's required pressure; do not silently treat excluded loads as free.

    Step 2: Calculate the preliminary electrolyzer MW

    A 1 MW electrolyzer consuming power at full rating for one hour uses 1 MWh. If a unit only reaches part of its maximum power over the year, its nameplate MW must be higher than annual-average consumption.

    Nameplate electrolyzer MW = annual electricity requirement (MWh) / (8,760 hours × full-load-equivalent utilization).

    Here the average electricity demand across all calendar hours is 189,800 MWh / 8,760 h = 21.67 MW. That is not automatically the rated capacity needed.

    Illustrative utilization Full-load-equivalent hours per year Calculated electrolyzer capacity
    90% 7,884 24.1 MW
    70% 6,132 31.0 MW
    50% 4,380 43.3 MW

    These are ReneEnergy calculations from the stated 3,650 t/year demand and constant 52 kWh/kg assumption. The percentages are hypothetical scenarios, not data from an actual site. For example, at 70%, 30.95 MW × 6,132 h ≈ 189,800 MWh/year. Actual installed equipment must also accommodate available module ratings, auxiliary loads not already included, maintenance requirements, performance degradation and design margins.

    Step 3: Capacity factor, online hours and full-load hours are different

    Three measures are often mixed together:

    Renewable generation capacity factor describes solar or wind electricity output relative to the generator's own possible full-output production. It is not inherently the electrolyzer's utilization.

    Electrolyzer online hours count time when the unit is running, including operation at low power.

    Electrolyzer full-load-equivalent hours (FLEH) equal total electrical energy actually consumed divided by rated electrolyzer MW. The percentage FLEH/8,760 is the utilization assumed in our sizing equation.

    For a worked example, a 40 MW electrolyzer may be online for 6,000 hours at an average 60% load while online. It uses 40 × 6,000 × 0.60 = 144,000 MWh and has 3,600 FLEH, equal to 41.1% annual full-load utilization. Calling its utilization 6,000/8,760 = 68.5% would materially overstate the energy available for hydrogen production. At a constant illustrative 52 kWh/kg, the 144,000 MWh represents roughly 2,769 tonnes of hydrogen, before deviations from the assumed efficiency curve.

    The lesson for the equipment vendor is to provide a duty profile: starts, stops, hours at each load, operating constraints and expected degradation—not merely a single number of operating hours.

    Step 4: An annual hydrogen target does not guarantee daily delivery

    An offtake contract for 3,650 tonnes annually is not necessarily the same operational requirement as 10 tonnes delivered on every calendar day. Electricity availability can be intermittent even when annual output is sufficient.

    A steady buyer drawing 10,000 kg/day requires about 417 kg/hour. If electrolysis stops for 12 hours, the buyer still requires approximately 5,000 kg of hydrogen during that gap. Those five tonnes must come from usable hydrogen storage, another plant or contracted backup supply if deliveries cannot pause.

    That is an inventory illustration, not a finished storage design. Required nameplate inventory depends on minimum deliverable pressure, reserves, compressor capacity, maintenance, safety requirements and longer outages.

    Could a plant simply catch up by producing 10 tonnes during the other 12 hours? Under our 52 kWh/kg assumption, that means consuming 520 MWh in 12 hours = 43.3 MW average input over the producing hours, before margins. The 31 MW system from the 70% annual-utilization calculation cannot accomplish that 12-hour catch-up schedule on its own.

    Before buying equipment, ask whether the customer requires firm hourly supply, daily nominations, monthly flexibility or annual tonnage. Then price a realistic combination of electrolyzers, power, hydrogen storage and delivery capacity. Contractual reliability is not established by an annual production spreadsheet.

    Step 5: Model the actual renewable and grid-power profile

    A 31 MW electrolyzer does not imply a 31 MW solar farm, a 31 MW wind farm or a 31 MW grid connection. Renewable generators have different hourly profiles, and the plant may experience curtailment when generation exceeds the power it can use.

    Even if the annual renewable electricity total exceeds 189.8 GWh, that alone does not prove that hydrogen can be delivered daily. Too much supply may arrive in a short high-wind window, while the unit lacks power for other hours. Battery storage, grid support, hybrid solar-wind supply and larger hydrogen storage may help, but each has cost and operating consequences.

    A defensible pre-feasibility assessment runs 8,760 consecutive hourly intervals: available renewable generation; permitted grid imports; electrolyzer minimum stable load, part-load efficiency and ramp limits; shutdowns and starts; curtailment; hydrogen output; and remaining storage inventory. NREL's system-boundary research likewise considers different hydrogen production configurations rather than assuming one universal plant scope (NREL study).

    Do not assume that buying electricity from the grid automatically satisfies the low-emission or renewable certification rules in every market. Applicable eligibility depends on local rules and the particular sourcing arrangement.

    Step 6: Test energy efficiency and power-price sensitivity

    The kWh/kg assumption is not a small detail. At a fixed 70% full-load utilization, changing that input changes the required MW:

    System electricity intensity Daily consumption at 10 t/day Calculated capacity at 70%
    51 kWh/kg 510 MWh 30.4 MW
    52 kWh/kg 520 MWh 31.0 MW
    55 kWh/kg 550 MWh 32.7 MW

    These are independent mathematical scenarios, not a side-by-side comparison of quoted equipment. The 51 and 52 kWh/kg assumptions resemble DOE 2026 technical targets, not confirmed site performance.

    At 52 kWh/kg, purchased electricity at $50/MWh adds $2.60/kg to the direct electricity input cost (0.052 MWh/kg × $50/MWh). A $10/MWh increase adds $0.52/kg before any other changes. This is not the levelized cost of hydrogen: the result excludes capital recovery, water, staff, stack replacement, storage, financing, downstream compression and delivery where not captured by the stated system boundary. For a fuller explanation, see H2Hub's worked LCOH guide.

    The cheapest power strategy is not always the lowest-cost hydrogen strategy. Operating on a smaller number of cheap renewable hours may require a larger electrolyzer and greater buffering. Firm power may increase utilization but raise electricity cost and certification questions. Compare configurations on the same delivery and accounting basis.

    Step 7: Ask vendors the questions that change the answer

    A preliminary answer of 31 MW is a starting point for engineering discussions, not a purchase order. Ask shortlisted suppliers to document:

    1. Electrical boundary: Does quoted kWh/kg mean stack DC power, packaged AC input or the facility meter? Which loads are excluded?
    2. Guaranteed performance: What kWh/kg is guaranteed at beginning and end of life, at rated and partial load?
    3. Module configuration: What unit ratings, minimum operating load and turndown limits are available?
    4. Variable-duty operation: How many starts and ramp events can the equipment tolerate under warranty? How will this affect degradation?
    5. Delivered hydrogen: Which purity, moisture, pressure, cooling and compressor requirements are included?
    6. Availability and responsibility: Who supplies water treatment, rectifiers, cooling, storage and maintenance?

    The DOE-led H2NEW program studies electrolyzer durability, efficiency and cost together. That is a reminder that a low electricity-consumption number is only one part of vendor selection.

    The right development decision for a 10-tonne-per-day project

    If the buyer accepts 3,650 tonnes per year with flexible delivery, roughly 31 MW at 70% full-load utilization is a useful illustrative screening case at 52 kWh/kg. It does not establish actual renewable power availability, supplier guarantees or certification eligibility.

    If the buyer requires 10 tonnes delivered every day, nameplate MW is not enough. The developer must also establish storage or firm alternative supply, permitted operation, delivery pressure and an hourly production schedule.

    A sensible development sequence is to document the buyer's delivery obligation, set the electricity accounting boundary, calculate annual mass and GWh, compare capacity options, model 8,760 hourly operating intervals, test supply interruptions and storage, calculate delivered cost, then ask vendors to validate the duty profile.

    H2Hub's Renewable Resource Lab explains how resource profiles affect utilization. The Developer Toolbox includes a production estimator. H2Hub's workspace supports hourly analysis with assumptions labelled by evidence basis rather than treating one annual capacity factor as final design.

    Model your first hydrogen project in H2Hub

    Start your first hydrogen project in H2Hub — free. Define a site and initial capacity, examine the modelled operating year, test your utilization assumptions, and identify what data you need from suppliers and buyers.

    Scope note: H2Hub provides educational, pre-feasibility analysis. Its results do not replace engineering design, FEED, vendor guarantees, permitting, certification review, lender due diligence or professional advice.

    Sources and verification notes

    Sources

    Test your own project assumptions

    H2Hub models power, water and hydrogen costs together — every figure shows its source, date and confidence.

    Model your first hydrogen project in H2Hub

    H2Hub produces preliminary project-development analysis. It is not a substitute for licensed engineering, FEED, due diligence or investment advice.