Maturity and costs
The alkaline electrolysis stacks have been available on a MW-scale for a long time, and a scale-up of PEM has been realized the last few years, largely driven by the drive to run electrolysis from Variable Renewable Energy (VRE) and to reduce plant footprint. Alkaline stacks are available up to 6 MW and PEM stacks up to 2MW. The SOEL is still in laboratory scale with up to 10kW.
Alkaline electrolysers have the lowest cost per kW. In commercial scale plants (2 MW +), Alkaline electrolyser plants have a capital cost of $ 800 – 1 000 /kW (or $1,8 - 2,3 MUSD per tonne of daily capacity). PEM electrolysers come in at an overall higher capital cost at 1 400 – 1 700/kW (or $3,3 - 4,2 MUSD per tonne of daily capacity). The price difference between Alkaline and PEM electrolysers is largely explained by the maturity of the technology and the use of precious metals in PEM electrolysers. There is an uncertainty regarding the investment cost due to the pre-commercial status for SOEL.
Renewable energy applications
Usage of intermittent power sources requires flexibility. A State-of-the-art PEM electrolyser can operate more flexibly than current Alkaline technology, and these characteristics are suited for variable renewable energy. Historically, the alkaline electrolyser was designed for stationary applications with grid connections and must be adapted to the new flexibility requirements.
Advancements in Alkaline technology, specifically ‘Pressurized’ Alkaline electroysers have made them once again suitable for variable renewable energy if the system components are engineered to operate with an intermittent power supply.
While PEM electrolyers offer best in class use of intermittent power sources, both PEM and (pressurized) alkaline electrolysers can offer fast load dynamics when they are in operating temperature and is suited for grid stabilizing.
The figure below compares parameters regarding the different electrolyser technologies: