How Hydrogen Numbers Stack Up — Part I — USES

Hydrogen by Numbers — image by Author

This article is Part I in a series of articles where we attempt to understand how Hydrogen stacks up using numbers, formulas, units and conversions

The Hydrogen Economy is almost upon us. The global energy mix is set to change. Green Hydrogen — Hydrogen produced using renewable energy — is absolutely central to this. With so many uses and applications that cut across the entire economy it is vital to understand how Hydrogen stacks up

The most important uses of Hydrogen are dealt with in this article. Later articles will deal with Production of Hydrogen (Part II), detailed uses and Case Studies of Hydrogen in Transportation (Part III), Power Generation (Part IV) and Gas Grid/Building/Heating (Part V)

Hydrogen Uses

FUEL CELL

Fuel Cell is a key pillar that will help to realize the utility of Hydrogen. As long as Hydrogen is fed into a fuel cell, electric current is produced. This happens via an electrochemical reaction that is the basis of a Fuel Cell. In this reaction, latent energy within Hydrogen is extracted and converted into current by oxidizing it

To oxidize 1 kg of Hydrogen completely, 8 kg of Oxygen is required. The final outcome is 9 kg of water vapor and a lot of energy. See later article Hydrogen by Numbers — Part II — Production for calculation of these quantities

Energy associated with 1 kg of H2 is equivalent to 120–142 MJ of energy

The two related values are — Lower Heating Value (LHV) and Higher Heating Value (HHV) — also referred to as Net Calorific Value and Gross Calorific Value respectively.

If the Fuel Cell is able to harness the latent energy contained in the produced water vapor, during the transaction itself, then HHV is used, else LHV is used

For the sake of this article let us be conservative and confine ourselves to LHV throughout. So,

1 kg of H2 is equivalent to 120 MJ of energy

This is a good equation to remember for those in the gas industry and for those who compare Hydrogen with common fuels like propane, LPG, etc for cooking, heating and hot-water as those fuels and gas bills are accounted for in mega joules or MJ. Compared to Propane, Hydrogen is 2.6 x times more packed with energy per kg (see Plot below)

Since 1 KWH = 3.6 MJ, (1000 w x 3600 s = 3.6 x 106)

1 kg of H2 is equivalent to 33.4 KWH of energy

This is a good equation to remember for those in the power industry and for those who compare Hydrogen with lithium-ion batteries for drawing energy for lighting, electric appliances, etc as those bills are accounted for in kilo watt-hours. However, since conversions are not perfect, this needs to be adjusted using relevant efficiency

Produced energy is thermal energy. Before a Fuel Cell can be useful, this thermal energy must be converted into electrical energy (and then kinetic energy) depending upon the application. So for Power Generation (converting into electrical energy only) this must be adjusted by Fuel Cell efficiency.

For driving an FCEV (converting into electrical and then kinetic energy), the final outcome will depend upon both Fuel Cell efficiency and Motor efficiency

For Power generation, current maximum electrical efficiency observed is 60%, so

1 kg of H2 will produce 33.4 KWH x 60% = 20.04 KWH of electrical energy

For driving an FCEV, current maximum kinetic efficiency observed is 75%, so

1 kg of H2 will produce 33.4 KWH x 60% x 75% = 15.03 KWH of kinetic energy

For an FCEV, there is no transmission system so no gears and therefore no Gear Efficiency enters into the equation. How this translates into range (distance) for a Hydrogen-powered FCEV, we will see in the next article on Hydrogen by Numbers — Part III — Transportation

At this stage, it is worth examining how Hydrogen compares with other fuels. Below is a plot showing Energy Density both in MJ / kg (x-axis) and MJ/liter (y-axis). It is important to note a kg of Hydrogen has more than 142 x times more energy than a kg of Lithium-ion battery!

Other uses of Hydrogen at the point of production are:

· Storage of Hydrogen — in situ reservoirs

· Conversion into Green Ammonia

· Conversion into Green Methanol

· Uses in Transportation, Power Gen, Buildings & Gas Grid — covered in separate articles in this Series

STORAGE IN RESERVOIRS

UHS or Underground Hydrogen Storage is use of a depleted gas reservoir or an aquifer for seasonal storage of Hydrogen produced from electrolysis during periods of excess renewable energy production. This is shown to be is technically feasible with be no insurmountable technical barrier

From an economic point of view, gas and petroleum drillers who have depleted gas reservoirs and other depleted legacy petroleum assets sitting on their balance sheets, this presents an excellent avenue for them to either use these for Hydrogen storage free of cost themselves by becoming Hydrogen producers or enter into business of renting out these storage reservoirs to willing Hydrogen producers

Big advantages of UHS (Underground Hydrogen Storage):

· it is underground and out-of-sight

· in terms of capacity can beat batteries in sheer energy storage capacity by several magnitudes

· energy density does not deteriorate over time as it does for batteries

Currently, the world’s largest battery system is South Australia’s Tesla Big Battery at 100 MW / 129 MWh. Same amount of energy can be extracted from 129,000 / 20.04 KWH = 6,437 kg of H2. This is equivalent to (refer volume in next section) = 6,437 x 12.02 m3 = 77,372 Nm3 of H2 (’N’ indicates at normal temperature and pressure) = 221 m3 at 350 bar. Finding this space within reservoirs that run into 000s of m3 is trivial!

Stored Hydrogen can be relieved and converted into electricity when required in peak periods or in winter seasons when heating demand is at a high and energy prices are at their peak. However there is a drawback that the round-trip efficiency — that is — water + electricity → Hydrogen → electricity + water = 50% only. So it makes sense for a Hydrogen storage facility to sell Hydrogen only when the price differential is favorable

GREEN AMMONIA — NH3

Another highly popular use is converting Hydrogen into Ammonia, producing green Ammonia. Ammonia has similar properties to Natural Gas in terms of storage and transportation so poses no new challenges as it can be easily shipped to destination of end use

Compared to the existing Haber-Bosch process of Ammonia production where natural gas is used for heating, this method using renewable Hydrogen as a replacement fuel is a lot cleaner and greener and will reduce GHG emissions overall

A new method for Ammonia production invented by CSIRO, Australia, enables production of Ammonia at much lower pressures (10–35 bar) using directly sourced Hydrogen from an electrolyser and nitrogen from an air separation unit (ASU) eliminating much of the balance of plant. The technology thus reduces the required energy input per ton of Ammonia and is less capital intensive

Ammonia can be used as an energy vector to extract Hydrogen at commercial or grid-scale to drive Fuel Cells. Or, Ammonia can also be used directly as a fuel in gas turbines and propulsion systems to generate power and drive vehicles

GREEN METHANOL — CH3OH

Methanol is also shaping up as a viable Hydrogen storage option because it is now possible to extract Hydrogen from it at room temperature and normal pressure

Two recent research trials have demonstrated the generation of Hydrogen from Methanol — one in Curtin University, Queensland, Australia and the other in Berkeley, California

Even though carbon is part of methanol, upon extracting Hydrogen using above methods, the other byproducts produced are GHG friendly eg formaldehyde, so overall this process is net zero emissions.

Methanol is an easy fuel to handle for storage and transportation. As a comparison, a 40-ton transport truck can carry 3,600 kg of Methanol (H2 as green methanol) compared to 500 kg of H2 at 200-bar (H2 as pressurized gas)

Conclusion

In this article we have demonstrated how Hydrogen is used and what it is worth in terms of energy capacity. Given the positives associated with Hydrogen and its impeccable green credentials, renewable Hydrogen is destined to be a key pillar in the coming global economy

In future articles we explain using numbers and Case Studies for Hydrogen Production and other Uses in Transportation, Power Generation, Injection in to Gas Grid for domestic uses

NOTE: For consultation please contact at www.hydrozen2050.com