Tuesday, March 1, 2016

Flexible Inputs to Hydrogen Energy Storage

Previous posts introduced Isotherm’s energy storage system architecture and the reasons why hydrogen is a compelling solution for consideration.  To get a better understanding of where and how the architecture can be applied, let’s take a look at the major subsystems and functions starting with the system inputs.

Energy Inputs

Electrical power system scenarios where energy storage is needed include: over-generation, variable generation, off-grid/microgrid, and other applications where power generation and electrical demand are out of phase in time.  Any source of electrical energy can be stored for later use subject to the inefficiency losses of the system.  In cases where these losses are economically preferable to shutting down a generating unit due to insufficient demand, for example, energy storage improves overall power generation performance.

Energy storage is particularly suited to renewable energy to offset the inherent fluctuations in generation from solar, wind and other variable sources.  Storage capability is necessary for most off-grid renewable power systems, and critically enabling to the trend of increasing renewable sources on the grid.  Using hydrogen storage technology for solar and wind energy sources also provides an end-to-end power system that produces no carbon emissions.

Transportation and other mobile applications can make use of hydrogen for fueling capability or onboard energy storage.  Vehicle systems face challenges with the need for a hydrogen fueling infrastructure, and the competitive advantages of battery technologies for onboard energy storage.  At larger scales and more limited route options (e.g. trains, ships, airplanes, etc.), these challenges begin to wane.  For these larger scale mobile applications, energy input can come from a variety of sources and can be set up at key refueling locations.  Alternatively, a hydrogen storage system can be integrated onboard and driven by the propulsion system to provide auxiliary power when needed.

Water Sources

Water in a hydrogen energy storage system can be recirculated from electrical generation output (e.g. fuel cell) to hydrogen generation input (e.g. electrolyzer) requiring limited water input.  However, if potable water production is a needed function, various water inputs can be provided in an open loop configuration.  Electrolyzers using saltwater have been demonstrated, and other water sources are possible (e.g. urine, wastewater, etc.).

This unique capability of potable water production in parallel with energy storage opens up many intriguing possibilities along the water-energy spectrum.  For example, the system could operate from solar and/or wind power to provide desalination in coastal regions and also provide electricity at night or when the wind dies down.  This system would also produce oxygen, sodium hydroxide and chlorine as byproducts of the saltwater electrolysis process that can be used locally or sold. 

For a remote location in a developing region, a microgrid could incorporate urine as the water input to the system.  In addition to potable water, oxygen and energy storage; the system would also produce nitrogen for crop fertilization.  In any of these configurations, the system design, operation and maintenance could be optimized for the application.

Other Inputs

An optional input to the system is the use of other potential sources of hydrogen such as biomass.  Various feedstocks can be used, and could replace the need for water inputs if desired.  In this case, potable water production and energy storage would be provided without any access to a water source.

Another possible input to the system is natural gas that can be converted to hydrogen via steam-methane reforming.  This is a mature process that has been used for decades for most of the hydrogen commercially produced.  However, it results in carbon monoxide and carbon dioxide that would need to be sequestered to maintain a zero carbon emission system.  This may be a viable transition option for using natural gas without the release of carbon by combustion.

Matt Moran is the Managing Member at Moran Innovation, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems since 1982. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been involved in seven technology based start-ups; and provided R&D and engineering support to many industrial, government and research organizations.  More about Matt here