How to size an electrolyzer from hydrogen demand
For 1,000 t of hydrogen per year, 50 kWh/kg system electricity use and a 50% annual capacity factor imply about 11.42 MW of electrolyzer input.
Put the demand on a clear time basis
Use tonnes per year directly. For an operating-day target, multiply by scheduled operating days: 4 t/day × 250 days = 1,000 t/year. A calendar-day average uses calendar days, so label which target you have.
A daily amount alone cannot determine MW. Specify operating hours or an annual capacity factor that represents the same schedule.
Convert annual tonnes into required input power
Convert annual tonnes to kg, multiply by system electricity use (kWh/kg), then divide by 8,760 hours × annual capacity factor to obtain kW. Divide by 1,000 for MW.
For 1,000 t/year, demand is 1,000,000 kg/year. At 50 kWh/kg, annual electricity is 50,000,000 kWh. A 50% factor gives 4,380 equivalent full-load hours: 50,000,000 ÷ 4,380 ÷ 1,000 = 11.4155 MW, or 11.42 MW. This is an illustrative H2Prism calculation.
Est. required power (MW) = annual hydrogen demand (kg/year) × system electricity use (kWh/kg) ÷ (8,760 h/year × capacity factor × 1,000 kW/MW)
Apply capacity factor once
In the annual formula, capacity factor appears once in equivalent hours. Do not also reduce annual demand by that same factor.
The 4 t/day target over 250 days is 1,000 t/year; at 50% annual capacity factor it needs 11.42 MW. If instead 4 t must be made over 24 full-load hours on each operating day, the schedule gives 4,000 × 50 ÷ 24 ÷ 1,000 = 8.33 MW. Those 6,000 hours equal 68.5% of a calendar year. These are alternate schedules; do not combine their utilization figures.
Est. required power (MW) = daily hydrogen target (kg/operating day) × system electricity use (kWh/kg) ÷ operating hours per operating day ÷ 1,000
Match the electricity boundary and check the inverse
Match SEC to the MW boundary; stack-only use may exclude balance-of-plant loads. DOE's 2024 PEM analysis reports 55.2 kWh/kg beginning-of-life system use, including stack and balance of plant, and 57.5 kWh/kg lifetime-average system use in its case. These are study values, not universal defaults. The 50 kWh/kg here is illustrative.
The inverse estimates annual tonnes by multiplying MW × annual hours × capacity factor, then dividing by SEC. Open Target production → power in the Electrolyzer Output calculator to check a demand-based case.
Est. hydrogen output (t/year) = electrolyzer input (MW) × 8,760 h/year × capacity factor ÷ system electricity use (kWh/kg H₂)
Sources
DOE Hydrogen Program
Clean Hydrogen Production Cost Scenarios with PEM Electrolyzer Technology, Record 24005
Page 8, System Electricity Usage and Lifetime: 55.2 kWh/kg beginning-of-life system use, including stack and balance of plant; 57.5 kWh/kg modeled lifetime-average system use
As of: 2024-05-20
Last confirmed: 2026-10-21
Common questions
How much electrolyzer power is needed for 1,000 t/year?
About 11.42 MW at 50 kWh/kg and 50% annual capacity factor over 8,760 hours.
Should I apply capacity factor to annual hydrogen demand?
Apply it once through annual equivalent hours; do not also reduce the annual target by it.
Can I size an electrolyzer from tonnes per operating day alone?
No. Specify operating days and hours, or an annual capacity factor tied to that schedule.