Energy storage in hydrogen is a technically feasible option for grid-scale storage, and is already in pilot demonstrations. In order to examine the potential benefits and drawbacks of hydrogen as a grid-scale energy storage technology, through a collaborative study, scientists from Imperial College, Stanford University and Western Washington University have looked at the energy efficiency characteristics of storing energy in a regenerative hydrogen fuel cell (RHFC) using net energy analysis.
The study, which compares RHFC configuration, containing an alkaline water electrolyzer and a PEM fuel cell, to other storage technologies, concludes that the reference case RHFC system has a higher energy stored on invested (ESOIe) ratio than lithium ion battery storage. This indicates that the hydrogen storage system makes more efficient use of manufacturing energy inputs to provide energy storage. However, lithium ion batteries remain energetically preferable when considering the operation of the system, as well as its manufacture, due to their higher round-trip efficiency (90%). The scientist report that this is reflected in the overall energy efficiencies of the two storage technologies: the overall energy efficiency of a typical lithium ion battery system is 0.83, compared to 0.30 for the reference case RHFC system.This highlights that in spite of its relatively efficient use of manufacturing energy inputs, the round-trip efficiency of a RHFC system needs to be improved before it can provide the same total energy benefit as other storage technologies. The authors report that improving the RHFC round-trip efficiency relies on electrolyzer and fuel cell performance.
“When storing excess power from wind turbines, energy storage in hydrogen provides an energy return similar to batteries, in spite of its lower round-trip efficiency. The aggregate energy return on investment (EROI) of wind generation augmented with RHFC storage is reported to be equal to that of the same wind facility augmented with lithium ion battery storage, when up to 25% of the electricity output passes through the storage system.”
The study concludes that in the case of excess power from solar photovoltaics, storage in hydrogen provides an EROI that is slightly higher than curtailment, though lower than batteries. As with other storage technologies, energy storage in hydrogen coupled to wind generation is said to provide an overall EROI that is well above the EROI of fossil electricity generation.