Storage of Renewable Energy as Hydrogen on the Gas Grid. Is It a Workable Proposition?
Earlier this year an article appeared in Renewable Energy World quoting a report from Bloomberg which suggested that hydrogen produced from “surplus” electricity can be stored in the gas grid. This proposal is one of many which purports to provide an energy storage solution for “surplus” electricity generated by renewable sources. The driver for this proposal comes as the result of the non-dispatchability of renewable electricity generation as a method to accommodate the variability of, for example, wind power. While this proposal may appear to furnish a simple solution to the renewable hydrogen storage dilemma, it has quite a few hidden pitfalls.
The storage of renewable generated hydrogen in the gas grid is not a new idea. The concept has been proposed in Germany, reported by Florian Leucht at ICEPAG in 2014 at UC Irvine, and more recently in the Polish literature. These references are not to meant to an exhaustive recounting of the literature but to serve as gateway starting points for further investigation.
Many legal jurisdictions around the world, e.g., California and Germany, have legislated mandatory renewables content for their energy portfolios. California has an ambitious schedule of 25% by 2016 (end of & met) and 33% by 2020. Germany’s portfolio standards are just as aggressive with 33% renewable content for electricity and 20% renewable content for all energy components in place by 2020.
In the mix of capital equipment used for generation of renewable energy, wind power has garnered the lowest cost per kW of generation capacity. However, wind power is not dispatchable owing to the capricious nature of “every which way the wind blows”. The variance in wind energy production as a function of time of day can be seen in the figure below. The data are from the Tehachapi wind farm with a 5200 MW nameplate capacity and were recorded in 2010. The other phenomenon of note in this figure is the timing of the peak production of the wind power in California. Invariably, it occurs at night, in a pattern almost exactly opposed to the daily electricity demand curve.
Figure: Catalog of observed wind velocities over one month at the 5,200 MW wind farm in Tehachapi California
(See PDF Link for Figures.)
Owing to the mandated renewable’s acceptance requirements, the grid operator in CA, CA ISO, is required to purchase this wind generated energy. As the wind energy component is not dispatchable, the CA ISO must have some fossil fuel plants on standby in order to maintain the grid integrity, if and (surely) when the wind sources fade, as they will. Full integration of this wind resource should have some storage capability for the wind energy and/or more sophisticated weather (wind) forecasting ability to provide at least a 5-10 minute prediction window for wind performance to allow for initiation of the backup generation sources.
Storage Possibilities for Non-dispatchable Renewables
Of course, when ever the question of electricity storage arises, one’s immediate thoughts go to batteries. However, batteries will not be considered here as they are not yet ready for wide scale deployment as an economical grid scale storage solution, they are still too costly. Another grid scale storage solution is afforded by pumped storage. While an attractive solution to the problem, pumped storage is constrained by geographical constraints and is not considered here. Beginning in 2013 several companies in Germany, most notably, E.ON, proposed to use electrolytic hydrogen as a storage vehicle for this excess renewable energy. Energy storage built upon electrolytic hydrogen was the premise of the Bloomberg report and the main driver for this paper.
Hydrogen Generation for Storage of Excess Renewable Energy
The concept of excess renewable electricity is meant to describe the generation of renewable electricity in quantities that are unable to be used by the utility owing to lack of demand on its grid. One solution that has been used is that the utility offers this surplus power to other energy users outside of its own grid at often negative pricing, “Take my electricity, please”. Here we’ll look at electrolytic hydrogen generation, storage options, and, some applications.
See PDF link for full text.