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alkaline electrolyzers require a mixing tank for KOH, which the polymer electrolyzers do not. In
the comparison of hydrogen production methods described below, adjustments in efficiency and
cost numbers must be made for these differences.
State of the Technology
The state of the technology in electrolytic systems is summarized in Table 3, where the
performance characteristics are listed for a representative array of commercial electrolysis
systems (NRC and NAE 2004). The data in this table have been derived from Ivy 2004, and
NRC and NAE 2004. The daily production of H2 for these systems ranges from 10 kg to
1,000 kg. With the exception of the Proton product, all of the electrolyzers shown are alkaline
systems.
In the Proton HOGON 380 PEM system, the highest conversion efficiency of electricity to
molecular hydrogen is attained: 95% of the current flow results in the production of hydrogen
from water. In the alkaline systems, a lower figure near 80% holds. The balance goes to side
reactions. The overall system energy required to produce hydrogen ranges from 53.4 to
72.4 kWh/kg. These figures include the entire energy requirement for hydrogen production,
including the electrolyzer, compressor, and the other ancillary equipment depicted in the process
diagram shown in Figure 70. For the Stuart and the Norsk examples, the fraction of the system
energy attributable to the electrolyzer is seen to run about 83–89%. The overall system efficiency
is the energy stored as hydrogen per unit input of energy expended. This result utilizes the higher
heating value for hydrogen of 39 kWh/kg.
Table 3 Performance Characteristics of Commercial Electrolyzers
Electrolyzer
Brand and Model
H2
Production
(kg/day)
H2/H2O
Product/
Reactant
(%)
System
Energy*
(kWh/kg)
206
Electrolyzer
Portion of
System
Energy (%)
Overall
System
Efficiency†
(%)
System Power
Requirement
(kW)
Stuart IMET 1000 130 80 55.7 83 70 288
Teledyne EC –750 91 80 64.6 - 60 235
Proton: HOGON 380
(PEM)
22 95 72.4 - 54 63
Norsk Hydro type
5040
1040 80 53.5 89 73 2330
Avalence: Hydrofiller 11 89 62.8 - 62 25
* Includes a 2.3 kWh/kg adjustment for compression of the H2 to 6,000 psi (NRC and NAE 2004).
† Assumes a higher heating value (HHV) of 39 kWh/kg for H2.