There is a strong momentum of utilizing renewable energy in electrolysis technologies for H₂ and other green chemicals. As renewable energy emerges and penetrates further into the energy market, the storage of surplus “off peak” electricity has received widespread considerations. An electrolyzer (ELX) can utilize “off peak” electricity from solar or wind farms to produce hydrogen or other fuels (e.g., ammonia, methanol, ethylene). These chemicals can subsequently be operated in a fuel cell mode to generate electricity or used as intermediates for other industrial applications. Compared to conventional batteries, the chemical storage of renewable energy has advantages of high energy density, long duration, and more flexibility. The covered technologies can include water electrolysis, CO₂ conversion, NH₃ synthesis, or other new electrolysis technologies.

This work will provide perspectives of how the electrolysis and reversible fuel cells can be used as a means for long-duration energy storage, in a comparison with other energy storage technologies like batteries, flow batteries, pumped water and compressed air. In particular, this "chemical" storage will be compared with "electronic" storage by Li-ion battery in term of energy efficiency, capital and operating cost, and easy integration with the intermittency of renewable energy.