In conclusion it appears that after end-use efficiency improvements are made, a robust carbon reduction strategy should prepare to follow a dual sector approach, making use of wind, solar, and a small but vital amount of dispatch-able electric generation. While hydrogen storage and fuel cell systems can enable carbonless electric generation, hydrogen fueled transportation, especially light-duty vehicles, can also contribute effectively to carbon reduction, especially if consumers choose to impact emissions through more flexible transportation decisions. Hydrogen transportation complements a modest sequestration effort, should it be warranted, by essentially shifting transportation emissions to large scale utility generation facilities. A strategy composed of these elements can cost-effectively eliminate the bulk of carbon emissions from these sectors, while commercializing the technologies necessary to ultimately eliminate carbon emissions. Energy storage as both cryogenic liquid and compressed hydrogen are likely to be cost effective, even more so in tandem with hydrogen vehicles. Very high efficiency utility power storage technologies (e.g. flywheels) will need to be very low cost (less than $100/kWh) in order to provide substantial benefit, although the their value is greater in solar dominated energy systems.
Looking beyond the largely linear combination of transportation and utility sectors explored in these analyses, there may be further synergies to be gained by carefully integrating energy technology and use patterns, developing a more complex and interdependent relationship between electricity and hydrogen fuel production. Excess heat from gas fired generation and perhaps hydrogen fuel cells could improve the efficiency of steam electrolysis. Pure oxygen, the byproduct of electrolytic hydrogen, would also enable improved electric generation with natural gas, in fuel cells, if not in combined cycle plants. Even further ahead, the functions of fuel cell, electrolyzer, and hydrogen compressor may be combined in a single electrochemical device, improving thermal integration and electric network topology possibilities substantially. The key technology throughout is that which links electricity and transportation fuel, efficient hydrogen production by electrolysis.
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