Hydrogen

Based on CO2 emission, hydrogen production is divided into:
Green hydrogen is produced from renewable/sustainable energy sources either available in an inexhaustible supply or they renew themselves relatively quickly.
Turquoise hydrogen is produced by the thermal cracking of methane. Instead of CO2, methane pyrolysis produce solid carbon.
Grey hydrogen is obtained from fossil feedstock's. Natural gas is usually converted into hydrogen and CO2 in a combustion process. The CO2 is then released unused into the atmosphere. The production of one ton produces around 10 tons of CO2.
Blue hydrogen is produced as grey hydrogen, but the resulting CO2 is captured and stored.

Therefore this hydrogen production can be considered CO2-neutral in the balance sheet.
Brown hydrogen is obtained from the gasification of coal.

With declining costs for solar PV and wind generation, building electrolysers at locations with excellent renewable resource conditions could become a low-cost supply option for hydrogen.

Volumetric vs Gravimetric energy density. Keep in mind, hydrogen has about three times the gravimetric energy density of natural gas, but only about 1/3 of the volumetric energy density. It means, if the volumetric energy is low, more storage space will be needed.

For hydrogen the storage pressure has a big impact on the volumetric energy density: at 1 bar =0,09 kg/m3, at 350 bar = 26,1 kg/m3, at 700 bar = 42kg/m3, liquefied at -252,9°C = 71 kg/m3

Source: IKV Institue for Plastic Processing

Renewable energies fluctuate, especially solar energy, from winter to summer.

Hydrogen can provide an energy storage solution. in 2018, the energy demand in Germany was 2'500 TWh.

The German natural gas network has a total length of approximately 511.000 km.

The service lines for house connections are to a large degree made from Polyethylene (PE).

90% of pipes in the distribution network have diameters below 500mm. 75% of the distribution network is operated at pressures below 1 bar. Only 7.5% is operated at pressures over 16 bar.

Approximately 50% of the pipes in the distribution network are made from Polyethylene (PE).

Molecule size [pm]: Hydrogen: 75 vs Methane: 200

Relative density (air=1): Hydrogen: 0.07 vs Methane: 0.55

Flammability limits (lower and upper limit [%]): Hydrogen: 4.0-77 vs Methane: 4.4-17

Wobbe index [MJ/Nm3]: Hydrogen: 40.6-48.2 vs Methane: 47.9-53.3

Calorific value [MJ/m3]: Hydrogen: 11 vs Methane: 32

Ammonia is produced in vast quantities worldwide for agricultural fertilizer's but uses natural gas or other fossil fuels to provide both the hydrogen feedstock and the energy to power the synthesis process. As a result, ammonia production by these methods releases almost 1.5% of global CO₂ emissions.

Liquid ammonia has 1.5 times higher energy density than liquid hydrogen and is therefore easier to store and transport.

Green ammonia is considered the best carbon-free fuel alternative for long-haul shipping.

Fuel Cell Electric Vehicles (FCEV) will play an essential role in decarbonizing transport. Depends on the use case (average mileage per day/trip and vehicle weight, FCEV will focus on medium and large cars as well on trucks and buses. Battery Electric Vehicles will dominate the small cars and urban mobility. 

The use case has to be considered.

In stoichiometric terms, 1 kg of hydrogen requires about 9 kg of water.

The actual figures given by the manufacturers range from 10 to 22 kg of water per 1 kg of hydrogen.

Source: Australia's National Hydrogen Strategy