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Like fossil fuelsMaterials containing carbon, formed long ago by geological processes acting on the remains of living organisms. Examples include coal and natural gas, hydrogen is often produced far away from where it will be used, and must be transported over long distances to homes, factories or refuelling stations. It is less dense than air, so it will escape and quickly disperse if there are any leaks in a container or pipe. Additionally, hydrogen is not very energy dense by volume when compared to traditional fuels like petrol. For example, to match the energy stored in one litre of petrol, you would need over 18 litres of hydrogen at high pressure (200 barA metric unit of pressure, 1 bar is roughly equal to air pressure at sea level). Part of the challenge of transporting hydrogen is finding ways of increasing its energy density The amount of energy stored in a substance per unit volume – this could mean moving it around as a liquid or a high pressure gas, safely and cheaply.


Gas pipelines

For long-distance transport, hydrogen can be pumped through gas pipelines. There are hundreds of kilometres of hydrogen pipes in the world already, for example in the USA, Germany and Belgium. Maintaining a system of pipes requires constant work; hydrogen gas leaks from small gaps, so there must be regular checks for wear and tear, particularly at valves and joints. Some countries already have wide networks of natural gas pipes linked up to homes and businesses, which could be converted to carry hydrogen. See Home heating and cooking for more.

Compressed gas and liquid hydrogen

One way of increasing the amount of energy stored by hydrogen is to compressUsing pressure to squeeze a gas into a small space a lot of gas into a small container, usually made of aluminium reinforced with plastic, fibreglass or carbon fibre. The containers can then be loaded onto trucks and delivered to where they are needed – no hydrogen is lost as long as the container is secure.

At extremely low temperatures (below -253°C) hydrogen becomes a liquid. Liquid hydrogen is 800 times denser than hydrogen gas in the atmosphere, so liquefactionThe process of making a substance into a liquid is an attractive option for storing a lot of energy in a small space. Liquefaction technology has been used since the 1960s to transport natural gas, but for hydrogen the process is more expensive and energy intensive, as the temperatures required are much lower (-253°C compared to -162°C).

Liquid hydrogen is transported by road, rail or ship, depending upon the distance and the amount needed. Over time heat will gradually leak into the cold store, converting the liquid to gas and causing some of the hydrogen to be lost.


Future options for moving hydrogen around

Research is ongoing to create solids or liquids that can absorb large volumes of hydrogen, for easy transportation. One option is to convert hydrogen into liquid ammoniaA toxic industrial chemical made of hydrogen and nitrogen, often used to make fertilisers. Chemical formula NH3  for the duration of travel – this comes with a different set of hazards to hydrogen, as ammonia is toxic. The hope is that these future options can address many of the cost and safety concerns surrounding current methods of high-pressure or liquid storage.