The relationship between work required and the compression of a gas is logarithmic so only 30% more energy is required to compress a gas to 700 bar from 100. This extra work plus the potential inherent in the gas at 100 bar is recovered when the pressure is dropped back to the 6 bar used in the fuel cell.
In a fuel cell hydrogen is combined with oxygen to produce electrical energy, heat and water in a process that is thermodynamically the opposite of electrolysis - the fuel cell produces the same amount of energy as is consumed in 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.
Hydrogen is the ideal energy because it produces over 3 times the amount of energy as an equal weight of gasoline and when burned or is converted to electricity in fuel cells, water and heat are the only outputs.
Hydrogen's drawbacks are the energy required to compress it to the 350 to 700 bar (atmospheres) needed for volume and range considerations in most transportation applications and the CO2 produced by steam reforming of natural gas, which is the principal way the gas is produced commercially.
Steam reforming is used because electrolysis is between 3 and 10 times more costly but the CO2 negates much of the environmental potential of hydrogen when both are produced by this process.
High-pressure electrolysis is the cheapest form of electrolysis because it eliminates the need for further compression of the gas.
At 1000 meters, the deepest extent of an OTEC system, the water pressure is 100 bar and electrolysis performed there would bring hydrogen to the surface at that pressure.
If climate catastrophe is as imminent as has been suggested, we should be prepared to address the problem regardless of the cost. That is the primal human response to existential threats but as has been pointed out by an MIT thesis, heat pipe OTEC is the renewable energy with the lowest levelized capital cost and therefore should be transitioned to on that basis alone.
Safety is often raised as a problem with hydrogen. According to the Electronic Library of Construction Occupational Safety and Health however, electrocutions kill on average 143 construction workers each year in the United States. According to federal data, incidents related to natural gas pipelines are not uncommon, occurring nearly every other day, causing millions of dollars in property damage and several deaths each year. Gasoline fires are also a common cause of death in vehicle accidents.
The California Fuel Cell Partnership notes, that "For more than 50 years, hydrogen has been produced and used for commercial and industrial purposes with an exemplary safety record. Like all fuels, hydrogen is flammable and has to be handled with care--just as we handle gasoline with care today. Unlike other fuels, it is very buoyant. With proper ventilation, hydrogen dissipates rapidly into the air, greatly reducing the chance of fire. Hydrogen is non-toxic, so if released it does not present a health hazard to humans and its effect on the environment is benign."
A recent Citibank report "Energy Darwinism" says slowing global warming would save tens of trillions of dollars.
The study shows that the difference in climate damage costs between a low 1.5 degree C warming scenario and a high 4.5 degrees C scenarios is as high as $50 trillion. And even a 2.5 degrees C scenario costs $30 trillion less the 4.5 degrees C business-as-usual scenario.
A group from the Applied Physics Laboratory of Johns Hopkins University was one of the earliest proponents of OTEC. The concern they had at the time was it could start a new ice age. It was determined that 5 terawatts would reduce surface ocean temperatures, and therefore atmospheric temperatures, by 1C each decade.
Nature has demonstrated we could attain zero warming at zero cost because OTEC platforms
would pay for themselves out of the $6 trillion/year the world pays
for the energy it currently consumes.
OTEC could produce 86 percent of that current production.