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The modern grid, electricity or hydrogen?

For the most abundant of these, a hydrogen grid is better suited to conveying power from the producer to consumer than an electrical grid that can also be more hazardous. Furthermore, unlike an electricity grid, hydrogen is a water as well as an energy carrier. And water is arguably even more vital than energy.

As shown in the following graphic, deep water electrolysis produces hydrogen with the potential to produce mechanical, electrical and gravitational energy as well as water.

Compressed hydrogen has the highest energy potential by weight of the non-nuclear materials.  The most efficient way to produce compressed hydrogen is to perform electrolysis in deep water where at a depth of 1000 meters the pressure is 100 bar. At the surface therefore the gas arrives logarithmically about 70 percent of the way towards the 700-bar required for modern transport hydrogen tanks. 

The optimal operating pressure of PEM fuel cell systems in automotive or stationary applications is about two orders less than this.

In a fuel cell hydrogen is combined with oxygen to produce electrical energy and water in a process that is thermodynamically the mirror image of electrolysis.

Water produced by fuel cells on average would have a hydrological head of 840 meters or about four times the current potential of the Hoover Dam. Hydrogen and water can be combined in a stationary installation at any elevation however to produce energy and water and the head between where it is produced and where it is needed can be used either to augment the system's energy output or to facilitate water distribution.

Volkswagen, the world’s largest automaker, has come down firmly on the side of batteries, therefore electricity, as opposed to fuel cells and hydrogen, and it explained why in a recent, well-illustrated press release per the following.

The automaker cited a study by management consultancy Horváth & Partners that found that battery-electric cars have an efficiency of 70% to 80% compared to 25% to 35% for the fuel cell vehicles. Yet Horváth & Partners claims, “The use of green hydrogen will be a crucial contributor to the decarbonization of the economy and our society.”  And that, “Achieving the climate protection targets requires all sectors to make a contribution, and green hydrogen based on regenerative energy – one of the most important emerging technologies – plays a key role here. Whether in transport, industry or the heat sector, our experts will support you in the course of the green transformation with green hydrogen.”

Jim Baird's picture

Thank Jim for the Post!

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Discussions

Bob Meinetz's picture
Bob Meinetz on Jul 3, 2020 3:04 pm GMT

"In a fuel cell hydrogen is combined with oxygen to produce electrical energy and water in a process that is thermodynamically the mirror image of electrolysis."

Love the comparison of thermodynamic energy conversion to reflection in a mirror - what goes in, must come out. Or gravity: what goes up, must come down. We might torture the metaphor a bit, and liken a dirty mirror to inefficient conversion? Maybe not.

Jim, I'm confused about where the energy to electrolyze water would come from, at depth. Is not the energy derived from OTEC dependent on the temperature differential between deep/surface water? 

 

Sbu Ntshalintshali's picture
Sbu Ntshalintshali on Jul 7, 2020 1:23 pm GMT

I appreciate your deep technical analysis. It seems the process is more complex than appears in most studies. However, Hydrogen is still more important in decarbonizing both electrical and transport industry. I live in Durban, South Africa. Durban is a coastal city with largest port in Southern Africa. I will be closely monitoring the deleopment of Hydrogen as fuel source for shipping industry. Thanks once again!

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