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Hydrogen Economy
Hydrogen Infrastructure
 One of the challenges for deployment of hydrogen fuel cell and hydrogen internal combustion engine vehicles is the lack of an established hydrogen infrastructure. This is a chicken and egg argument. There is no hydrogen refuelling infrastructure because there is no demand for hydrogen as a fuel because there are no hydrogen fuelled vehicles available because manufacturers don’t make hydrogen fuelled vehicles because there is no hydrogen refuelling infrastructure to refuel them (i.e. there isn’t a hydrogen pump at every filling station).
To break this cycle of inactivity, Comhairle nan Eilean Siar are investing in the development of a hydrogen infrastructure in the Outer Hebrides.
Production of Hydrogen from Wind by the Pure Energy Centre (Unst)
Sources of Hydrogen
Hydrogen is the most abundant element in the universe. It is estimated that 97% of atoms in the universe are hydrogen and that it accounts for 90% of the mass of the universe. However, because of it’s readiness to combine with other elements (e.g. oxygen to form water and carbon to form hydrocarbons) it is rarely found in its isolated molecular form, H2. The challenge is to separate the hydrogen.
Hydrogen is not an energy source, but an energy carrier. This means that energy is needed to separate the hydrogen from whatever it has combined with. A proportion of the energy required to achieve this is “stored” as hydrogen. Separating hydrogen can be achieved in a number of ways, the most common of which are:
- Electrolysis – A process by which water is split into its component parts, hydrogen and oxygen, using electricity.
- Reformation – A process to separate the hydrogen contained in hydrocarbon fuels. This is commonly achieved by steam reformation in which methane reacts with high pressure steam in the presence of a catalyst to produce hydrogen, carbon monoxide and a small amount of carbon dioxide. The US Department of Energy estimates that about 95% of hydrogen is produced by steam reformation. Another type is partial oxidation reformation where methane and other hydrocarbons in natural gas are reacted with a small amount of oxygen to produce carbon dioxide and hydrogen. This is typically much faster than steam reforming and is better suited to onboard reforming. Fuels suited to reformation include methanol, ethanol, natural gas, methane, propane and diesel.
Hydrogen is safe
The properties of hydrogen provide many advantages over fossil fuels in terms of safety. Hydrogen's low density and ability to rapidly disperse allow hydrogen to escape to the atmosphere should a leak occur. Propane and petrol, with their high densities and slow dispersal allow the fuels to congregate near the ground increasing the risk of explosion. Hydrogen has to reach a concentration of 4% in the surrounding atmosphere before hydrogen poses a danger. Petrol’s concentration only has to reach 1% before the danger of ignition is apparent.
Hydrogen is an odourless, colourless, non-toxic, naturally-occurring element. By comparison, all petroleum fuels are asphyxiants, and are poisonous to humans and wildlife.
Hydrogen combustion produces only water. When pure hydrogen is burned in pure oxygen, only pure water is produced. Burning hydrogen in air actually cleans the ambient air by completing combustion of the unburned hydrocarbons that surround us. Compared with the toxic compounds produced by petroleum fuels (carbon monoxide, nitrogen oxides, and hydrogen sulphide), the products of hydrogen burning are much safer.
Hydrogen can be stored safely. Compressed hydrogen gas is routinely stored in the same cylinders used for other compressed gases (e.g. oxygen, nitrogen). Such cylinders are widely used recreationally (e.g. diving), in public services (e.g. hospitals) and in industry (e.g. welding). The cylinders are subject to a robust, rigorous and well established safety procedure.
Hydrogen and Renewable Energy
The exploitation of renewable energy resources for electricity generation presents several inconveniences: • The resource is intermittent: solar panels will only function during the day; wind turbines will only function when the wind blows; • The resource may not match the demand: the availability can either exceed or fall short of the demand; • Excess resource can not be stored by the transmission network; • The best resources are often far away from where the energy is needed.
Integrating renewable generation will require significant grid reinforcement and the retention of non-renewable generation sources to ensure that “the lights stay on”.
Hydrogen provides a solution to these inconveniences. When the electricity generated exceeds the demand, the excess can be used to produce hydrogen through the process of electrolysis. The hydrogen stores the excess electrical energy. This stored energy can be used to generate additional electricity whenever the demand exceeds the supply. Also, the hydrogen can be transported to locations where the energy is needed without the requirement of a transmission grid.
Hydrogen and the Outer Hebrides
The production of hydrogen by electrolysis of water or biogas reformation is an effective means of storing renewable energy in a fuel that can then provide energy on demand for electrical generation, transportation and heating. Many of the technical constraints for integrating renewably generated electricity into the transmission networks can be resolved through the integration of hydrogen electrolysers for use as dynamic loads. This could help to reduce the need for major reinforcements of the transmission network and improve the quality of supply.
Used to best effect in the Outer Hebrides, hydrogen does not replace the electrical transmission system; rather it strengthens and complements the transmission infrastructure. Integrating hydrogen into energy systems bridges the gap between generation and demand, enabling locally produced renewable electricity to be used on demand for meeting all local energy demands including transportation. This enables the islands’ transition to a low carbon economy with high security of energy supply, and the export of high quality electricity to the mainland.
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