Power-to-Gas Efficiency Calculator
Power-to-gas converts electricity into hydrogen via electrolysis, stores it, then converts it back to electricity through a fuel cell — a full power-to-power round trip. This calculator takes the electricity you put in, the electrolyzer's specific energy consumption, and the fuel cell's electrical efficiency, then reports the hydrogen produced, the electricity that comes back out, and the round-trip efficiency of the whole chain. For the upstream efficiency of the electrolysis step on its own, see our Electrolyzer Efficiency Calculator, and for how a fuel cell turns hydrogen back into electricity in detail, see the Hydrogen Fuel Cell Output Calculator.
Total electricity fed into the electrolyzer over the period you are evaluating.
Typical alkaline/PEM electrolyzers consume 52-58 kWh/kg -- see the Electrolyzer Efficiency Calculator for technology-specific values.
Typical PEM fuel cell electrical efficiency (LHV basis).
electricity input ÷ electrolyzer specific energy consumption
hydrogen produced × 33.3 kWh/kg (LHV) × fuel cell efficiency
(electricity output ÷ electricity input) × 100
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →Converting electricity to hydrogen and back to electricity is expensive in efficiency terms: a full power-to-gas-to-power round trip lands around 33% in this example -- meaning two-thirds of the original electricity is lost along the way. That's roughly half the round-trip efficiency of a lithium-ion battery (85-92%). Hydrogen's advantage isn't round-trip efficiency -- it's the ability to store enormous quantities of energy for weeks or months, something batteries can't do economically at any efficiency.
How power-to-gas round-trip efficiency is calculated
This calculator traces electricity through a full power-to-gas-to-power round trip: into an electrolyzer that makes hydrogen, then back out through a fuel cell that converts that hydrogen into electricity again. Three quantities tie the calculation together.
Hydrogen Produced (kg) = Electricity Input (kWh) ÷ Electrolyzer Specific Energy Consumption (kWh/kg H₂). The electrolyzer splits water into hydrogen and oxygen, and its specific energy consumption says how many kilowatt-hours it takes to produce one kilogram of hydrogen; at 1,000 kWh of input and 55.2 kWh/kg (a typical PEM system), that is 1,000 ÷ 55.2 = 18.12 kg of hydrogen. For technology-specific electrolyzer efficiency values, see our Electrolyzer Efficiency Calculator.
Electricity Output (kWh) = Hydrogen Produced (kg) × 33.3 kWh/kg (LHV) × (Fuel Cell Efficiency (%) ÷ 100). The 33.3 kWh/kg figure is hydrogen’s lower heating value (LHV) -- the usable energy content of a kilogram of hydrogen when the water vapor produced leaves the fuel cell without condensing, which reflects how most fuel cells actually operate. At 18.12 kg, 33.3 kWh/kg, and 55% efficiency, that is 18.12 × 33.3 × 0.55 = 331 kWh of electricity delivered back out. For a detailed breakdown of the fuel-cell step, see our Hydrogen Fuel Cell Output Calculator.
Round-Trip Efficiency, Power-to-Power (%) = (Electricity Output (kWh) ÷ Electricity Input (kWh)) × 100. This is the share of the original electricity that survives the full round trip; at 331 kWh out and 1,000 kWh in, that is (331 ÷ 1,000) × 100 = 33.1%. Each conversion step loses energy -- electrolysis typically operates around 70% efficiency, and fuel cells convert hydrogen back to electricity at only about 50-60% efficiency -- so multiplying those losses together (roughly 0.70 × 0.55) lands the combined round trip around 30-40%, well below a lithium-ion battery’s single-conversion-step efficiency of 85-92%. Hydrogen’s case is not round-trip efficiency but storage duration: it can store enormous quantities of energy economically for weeks, months, or even seasonally, something batteries cannot do cost-effectively at scale. Capturing and using the waste heat from both the electrolyzer and the fuel cell (combined heat and power) can meaningfully improve the overall system’s effective efficiency even when the pure electrical round-trip efficiency stays similar. Data sources: Electrolyzer efficiency data from NREL hydrogen production studies; PEM fuel cell efficiency from fuel cell technology assessments; hydrogen LHV energy content (33.3 kWh/kg); lithium-ion battery round-trip efficiency from battery storage research; power-to-gas system modeling from IEA and DOE hydrogen storage analyses.