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Electrolyzer

Alkaline Electrolyser (AE)

Introduction

For the creation of carbon-free hydrogen from nuclear and renewable sources, electrolysis is a potential alternative. The process of separating water into hydrogen and oxygen is known as electrolysis. This reaction occurs in a device known as an electrolyzer. Electrolyzers come in a variety of sizes, from little appliances that are ideal for small-scale dispersed hydrogen generation to massive central production plants that might be connected directly to non-greenhouse gas generating sources of energy.

The electrolyser used for the ROBINSON project's cases is an Alkaline Electrolyser (AE).

Alkaline Electrolyser (AE)

Technical Description

Within the ROBINSON project, the electrolysis technology is applied via an Alkaline electrolyzer (AE) (or a polymer electrolyte membrane-based (PEM)). PEM electrolyzers are preferred because of their operational flexibility, which includes quick start-up and reaction times as well as relatively cheap investment costs (Bauer et. al, 2021). PEM electrolyzers have an efficiency of roughly 60%, corresponding to a specific power consumption of 56 kWh/kg hydrogen generation. Although the investment costs for this more established electrolyzer technology are much cheaper, alkaline electrolyzers offer less operating flexibility than PEM. Furthermore, AEs have a 67% efficiency, equating to a particular power consumption of 50 kWh/kg hydrogen generation (Bauer et. al, 2021). The cost data of the two types of the electrolyzers are presented below.

 Summary of the technical characteristics of the PEM electrolysers 

Main Characteristic 

H2B2 – ELN200

NEL – MC250

Max nominal H2 production [Nm3/h] 

207

246

Production range [%] 

10 - 100

10 - 100

Operating pressure [barg] 

15 – 40

30

H2 Purity [%] 

99.99 -> 99.999

99.95 – 99.9995

Input voltage [VAC] 

3 x 400

3 x 6600 – 35000 (lower optional)

Frequency [HZ] 

50 ± 5%

50

Power (BOP+Stack) [kW] 

1 055.7 kW

1 250 kW

Controls system communication 

Modbus TCP/IP or Profinet (RJ45 port)

-

Ambient temperature range [oC] 

+5 – +45

-20 - +40

Ambient humidity [%] 

0 – 95 (non-condensing)

-

Air ventilation 

Available from a non-hazardous area

-

Duty cycle 

24/7

  

Dynamics 

<1 sec start-up time from stand by

<10 sec ramp up time minimum to full load

≥15% ramp rate (% of full scale)

Cold start time [min] 

<5

<5

Nitrogen for purge 

For each purge, consumption is <0.2 kg at 3 barg

-

Instrumentation air system 

Consumption 7 Nm3/h at 10 barg

-

The CAPEX for the PEM has an average cost of 1182€/kWe, while the CAPEX for the AE ones is 988€/kWe, on average (Herenčić et al., 2021). Their lifetimes are 60,000 and 75,000 hours, respectively. Currently, a possible supplier is being evaluated, and bids for units with a production rate of up to 200 kg/day or 500 kg/day are being considered (assuming full load operation of the electrolyzer).

Economic parameters of the electrolyzer

Cost parameter

Value (PEM)

Value (AE)

Unit

CAPEX

385-2068 (Avg: 1182)

571-1268 (Avg: 988)

[euro/kWe]

REPEX

385-2068 (Avg: 1182)

571-1268 (Avg: 988)

[euro/kWe]

OPEX

19

 

[euro/kWe]

Lifetime

60,000

75,000

[hours]

An alkaline electrolyzer from Green Hydrogen Systems is being assessed as an alternative installation in Denmark. Installing two A90-type electrolyzers is necessary to produce the same amount of hydrogen as the two previously stated PEM units. There is little supplier-specific information on system dynamics available. These values are simply approximations based on the Danish Energy Agency data.

Summary of technical specifications of the examined alkaline electrolyzers of Green Hydrogen Systems

Main Characteristic 

A90

Max nominal H2 production [Nm3/h] 

90

Production range [%] 

16% – 100%

Operating pressure [barg] 

35

H2 Purity [%] 

> 99.998

Input voltage [VAC] 

3 x 400

Frequency [HZ] 

50 ± 10%

Duty cycle 

24/7

Dynamics 

5 Sec from hot standby to operation (16%-100%)

Cold start time [min] 

15

Technology Flowchart

 

 Schematic view of a PEM electrolyser

Technology requirements and operating conditions

The operational conditions of the two PEM electrolyzers are presented below. Ambient temperature is the main parameter taken into account that the application of the MC250 is possible in freezing climates; at the same time, the ELN200 can operate only in favourable conditions.

 Summary of operational specifications of the examined alkaline of the PEM electrolyzers in evaluation

Main Characteristic 

H2B2 – ELN200

NEL – MC250

Stack consumption [kWh/Nm3 H2] 

4.7

4.5

AC power consumption (BOP+Stack) [kWh/Nm3 H2] 

5.1 [kWh/Nm3 H2]

50.4 [kWh/kg H2]

Feedwater (might be tap water if water treatment is included) consumption [l/h] 

295.7

222

Feedwater conductivity at 25 oC [uS/cm] 

< 2000

-

Feedwater pressure [barg] 

2 – 6

-

Ambient temperature range [oC] 

+5 to 45

-20 to +40

Ambient humidity [%] 

0 – 95 (non-condensing)

-

Feedwater temperature [oC] 

5 – 40

5 - 40

 

 

 Summary of the operational specifications of the examined alkaline electrolyzers of Green Hydrogen Systems

Main Characteristic 

A90

Stack consumption [kWh/Nm3 H2] 

4.33

Feedwater consumption [l/h]

81 (90 Nm3/h*0,9 L/Nm3)

Feedwater conductivity [uS/cm] 

< 5

Controls system communication 

Ethernet/Modbus

Ambient temperature range [oC] 

+5 – +35

Ambient humidity [%] 

0 – 90

 

Documentation