Hydrogen cost could equal 50-cent gasoline, with renewable energy: study

[OKIsItJustMe]

14. Relevance to the OP

http://pubs.rsc.org/en/content/articlehtml/2015/ee/c4ee04041d

[font face=Serif][font size=5]Hydrogen or batteries for grid storage? A net energy analysis†[/font]

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Regenerative hydrogen fuel cells (RHFC's) have several characteristics that are well-suited to large-scale energy storage. They are not subject to geological requirements, which are important restrictions on pumped hydro and compressed air storage. The energy capacity and power capacity of a regenerative fuel cell can be configured independently. Storing energy in hydrogen provides a dramatically higher energy density than any other energy storage medium.^8,10 Hydrogen is also a flexible energy storage medium which can be used in stationary fuel cells (electricity only or combined heat and power),^12,14 internal combustion engines,^12,15,16 or fuel cell vehicles.^17–20 Hydrogen storage has a very low rate of self-discharge, and has therefore been proposed for seasonal storage.^8,21 The cost of energy storage in a regenerative hydrogen fuel cell is already potentially competitive with batteries in an optimized energy arbitrage system.²² Several dozen RHFC projects have already implemented hydrogen storage, spanning a wide range of energy and power capacities (Fig. 2).¹² The most common configuration among existing systems contains an alkaline water electrolyzer (AWE) and a polymer electrolyte membrane fuel cell (PEMFC).‡

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Finally, although the present analysis is restricted to systems that use hydrogen exclusively to produce electricity, there are several other possible uses for stored hydrogen. These include filling fuel cell vehicles, enriching the natural gas distribution system, local industrial consumption, and production of synthetic fuels. A flexible supply installation that can dispense hydrogen to multiple end uses may achieve a better net energy outcome than any single-use configuration. Net energy analysis of these other applications of grid-generated hydrogen, and of optimized flexible use, remains for future work.

[font size=4]5 Conclusion[/font]
Energy storage in hydrogen is a technically feasible option for grid-scale storage, and is already in pilot demonstrations. Because of its low round-trip efficiency, it may be overlooked in spite of its potential advantages, such as high energy density and low rate of self-discharge. In order to examine the potential benefits and drawbacks of hydrogen as a grid-scale energy storage technology, we apply net energy analysis to a representative hypothetical regenerative hydrogen fuel cell (RHFC) system. We introduce and apply a method to determine the energy stored on invested (ESOI_e) ratio of a reference case RHFC system.

We find that the reference case RHFC system has a higher ESOI_e 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. One reason for this is that the steel used to fabricate a compressed hydrogen storage cylinder is less energetically costly, per unit of stored energy, than the materials that store electric charge in a battery (electrode paste, electrolyte, and separator). 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%). 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 must increase before it can provide the same total energy benefit as other storage technologies. Higher RHFC round-trip efficiency relies on improved electrolyzer and fuel cell performance.

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Given what you present as the horrible inefficiency of hydrogen production and use, it seems odd that it would be attractive at all for any application, especially stationary!

The thing which some people fail to recognize (or prefer not to acknowledge) is that there are some clear advantages to hydrogen fuel cells over batteries for use in vehicles. (NASA understood this decades ago.) (PDF)

The Tesla Model S has a half ton battery to haul around. The Mirai’s “Fuel cell stack weight is 123.5 lbs (56 kg), while the hydrogen tank’s weight is 192.9 lbs (87.5 kg).” (The weight of the hydrogen itself is negligible.)

OK, so, less weight, shorter “recharge time”, with greater range… potentially, less cost. (Today, Toyota’s fuel cell is relatively expensive.)