Analyzing the cost of electrolytic water for hydrogen production

Proton exchange membrane electrolyzer (PEM) hydrogen production cost analysis

Alkaline electrolyzer has low electrolytic efficiency, requires the use of strong caustic alkali, requires the removal of water and alkali from the hydrogen. That is difficult to start and change the load quickly, and cannot adjust the speed of hydrogen production quickly. So it is poorly adapted to renewable energy generation.

Figure 4 Cross-sectional diagram of PEM electrolyzer

1-proton exchange membrane, 2/2′-catalytic layer, 3/3′-porous transfer layer 4/4′-spacer and flow channel, 5/5′-end plate

Proton exchange membrane electrolyzer uses polymeric proton exchange membrane to replace the diaphragm and liquid electrolyte in alkaline electrolyzer. It has the dual function of ion conduction and gas isolation. The structure of PEM electrolyzer is similar to fuel cell, which consists of membrane electrode, bipolar plate and other components. The membrane electrode provides the reaction site and consists of a proton exchange membrane and a cathode catalyst.

Cost components of a PEM electrolysis tank

Compared with alkaline electrolyzer, PEM electrolyzer has the advantages of non-polluting reaction, no need to separate alkali for hydrogen, high conversion efficiency, low energy consumption, compact tank structure, more flexible operation (load range 0-150%). And more suitable for the volatility of renewable energy, etc. Many new electrolytic hydrogen production projects have started to choose PEM electrolyzer technology. However, due to the short time of commercialization of PEM electrolysis technology and the high cost of key components such as proton exchange membrane and platinum electrode catalyst. The manufacturing cost of PEM electrolyzer is high, which is three to five times of that of alkaline electrolyzer of the same scope.

To calculate the cost of hydrogen production in a PEM tank, the following assumptions are made:
(1) The cost of a 1000 Nm3 /h PEM electrolyzer is 30 RMB million, including land cost, civil construction and equipment installation of 2 RMB million;
(2) Each 1 m3 of hydrogen consumes 0.001 t of raw water and 0.001 t of cooling water, and the water cost is 5 RMB/ t;
(3) Depreciation period of equipment 10 a, civil construction and installation 20 a, using straight line depreciation, no salvage value, equipment depreciation 10% per year, civil construction and installation 5% per year;
(4) The price of industrial electricity is 0.4 RMB/kWh, and each 1 m3 of hydrogen consumes 4.5 kWh of electricity;
(5) Working 2,000 h per year, producing 2 million m3 of hydrogen per year;
(6) Labor cost and maintenance cost is 400,000 RMB per year.

According to the same calculation principle, the cost of hydrogen production in PEM electrolyzer is higher than that in alkaline electrolyzer. Mainly because the purchase cost of PEM electrolyzer is too high and the annual depreciation cost is too high. The depreciation cost of equipment accounts for 44% of the total cost, and the cost of electricity accounts for 50%, so the cost reduction still has to start from these two aspects.

As the electricity cost decreases, the share of electricity cost in total cost gradually decreases. And the hydrogen cost also gradually decreases. When the electricity cost is 0.13 RMB/kWh and 0.2 RMB/kWh, the hydrogen cost is 2.4 RMB/Nm3 and 2. 71 RMB/Nm3, which is 24% and 33% of the cost, respectively. Compared with the cost of hydrogen production by alkaline electrolyzer, there is still a certain gap. Mainly because the PEM electrolyzer is too expensive and the depreciation cost is too high.

Under the combination of different electricity prices and different electrolyzer costs, i.e.

1.electricity price 0.4 RMB/kWh, electrolyzer cost 30 RMB million

2.electricity price 0.3 RMB/kWh, electrolyzer cost 20 RMB million

3.electricity price 0 2 RMB/kWh, electrolyzer cost 15 RMB million

4.electricity price 0.13 RMB/kWh, electrolyzer cost 5 RMB million

Figure 7 shows the effect of operation time on the cost of hydrogen production detailed.

Relationship between hydrogen production cost and electrolyzer working time under different conditions

1-0. 13 RMB/kWh-5 million; 2-0. 2 RMB/kWh-15 million;
3-0. 3 RMB/kWh-20 million; 4-0. 4 RMB/kWh-30 million

As we can see from Fig. 7, the hydrogen cost gradually decreases as the electrolyzer operating time increases and the hydrogen production increases. Among them, the higher the cost of electricity and fixed cost, the more obvious the decreasing trend. By 2030 and 2050, They estimate the electricity cost will be 0.2RMB/kWh and 0.13 RMB/kWh. And the working time is 4,000 h / a and 8,000 h / a, corresponding to the PEM electrolyzer cost of 15 RMB million and 5 RMB million. Then the corresponding hydrogen production cost is 1.41 RMB/Nm3 and 0.72 RMB/Nm3, comparing with the current hydrogen production cost. The cost of hydrogen production is greatly reduced.

Compared with alkaline electrolyzer, the hydrogen cost of PEM electrolysis is still high. But it is expected to be gradually lower than the hydrogen production cost of alkaline electrolyzer after 2030. And lower than that of fossil fuel hydrogen production after 2040 as the procurement cost of PEM electrolyzer decreases.

From the above analysis, We can see that the cost of hydrogen production in PEM electrolyzer is quite high compared with alkaline electrolyzer due to the high cost of equipment. But with the increase of hydrogen demand and the progress of technology, the cost of PEM electrolyzer will decrease, and with the decrease of renewable power cost and the increase of hydrogen production. The cost of hydrogen production in PEM electrolyzer will be lower than that in alkaline electrolyzer eventually.

If we consider the area of land, i.e. land cost, PEM electrolyzer is more compact. While the area of PEM is almost half of that of alkaline plant in the same scale. And the advantage of PEM electrolyzer is more obvious in the area where land is expensive, combined with its advantages of high efficiency, low energy consumption, fast response and high load. They estimated PEM electrolyzer will become the mainstream direction of electrolytic hydrogen production in the future.

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