LHV vs HHV Efficiency (LHV / HHV)
LHV vs HHV hydrogen efficiency is a choice of energy basis: 33.3 kWh/kg (lower heating value) or 39.4 kWh/kg (higher heating value), which changes one electrolyzer's quoted efficiency.
In plain terms
Burning a kilogram of hydrogen releases energy, and part of that leaves as water vapour. The lower heating value (LHV) assumes the vapour stays a gas. The higher heating value (HHV) assumes it condenses and returns its latent heat. For hydrogen, NREL gives 33.31 kWh/kg (LHV) and 39.42 kWh/kg (HHV).
Electrolyzer efficiency is that heating value divided by the specific energy consumption:
Efficiency (LHV) = 33.3 / SEC
Efficiency (HHV) = 39.4 / SEC
So one machine has two honest efficiencies, about 18 % apart.
Typical range
Take a system at 55 kWh/kg, the US DOE 2022 status for both alkaline and PEM:
| Basis | Calculation | Efficiency |
|---|---|---|
| LHV | 33.3 / 55 | 61 % (as printed by DOE) |
| HHV | 39.4 / 55 | 72 % |
The US DOE states its targets on an LHV basis. The Clean Hydrogen JU gives kWh/kg, with an LHV basis implied.
Why it moves LCOH
It doesn't, and that is the point. LCOH depends on kWh/kg, which is the same on either basis. Efficiency percentages only matter when someone converts them back into kWh/kg. If the basis is wrong, the electricity cost in the model is wrong by up to 18 %.
Common mistake
Typical range
33.3 / 39.4 kWh/kg H₂ (LHV / HHV)[1]
Related terms
Sources
- Current (2009) State-of-the-Art Hydrogen Production Cost Estimate Using Water Electrolysis (NREL/BK-6A1-46676), section 4.1.4, National Renewable Energy Laboratory, for the US DOE Hydrogen Program, 2009
- Technical Targets for Proton Exchange Membrane Electrolysis, U.S. Department of Energy, Hydrogen and Fuel Cell Technologies Office, 2022