Hydrogen and its competitors, 2004

10Risø Energy Report 3Hydrogen in European and global energy systems3development to store hydrogen as a cryogenic liquid ininsulated tanks or within solid materials, includingmetal hydrides and nanoporous materials such as activatedcarbon or organometallic compounds.Applications for hydrogen as a fuel include portableequipment, transport, power generation (centralised ordispersed) and industrial processes. For power generationand industrial applications, hydrogen can be burned as asubstitute for natural gas. For transport, hydrogen can beused in a gasoline engine with only minor modifications.High-purity hydrogen, however, is used to best advantagein high-efficiency technologies such as fuel cells. 2 Afuel cell produces electricity, heat and water through anelectrochemical process whose inputs are oxygen fromthe air and a fuel such as hydrogen. Fuel cells have manyuseful characteristics, including modularity, good loadfollowingability, almost no noise and, when usinghydrogen, almost no emissions.Fuel cells come in many varieties. Low-temperaturedesigns such as proton exchange membrane fuel cells(PEMFCs, also known as polymer electrolyte membranefuel cells) are mostly aimed at portable and transportapplications. High-temperature designs such as solidoxide fuel cells (SOFCs) are better for stationary powerplants.At the point of use, burning hydrogen as a fuel has verylittle impact on the environment. There are no emissionsof greenhouse gases, nor of most other pollutants. If airis used as the oxygen source, nitrous oxide will bepresent in the exhaust gases and may need to becontrolled, as with any other combustion technology.The total environmental impact of hydrogen thereforedepends almost entirely on the way the hydrogen isproduced. Hydrogen energy systems based on renewableenergy sources such as wind or solar power are amongthe most environmentally-benign systems known today.The transport and distribution of hydrogen is an importantissue that does not always get the attention itdeserves. The use of large amounts of hydrogen worldwidewill require a comprehensive and very costly infrastructure,which only can be developed in a long timeperspective. To keep costs at a reasonable level, thisinfrastructure will have to be used at close to fullcapacity, making the smooth transition to hydrogen animportant challenge for society and industry [5].Once in place, however, a hydrogen infrastructure wouldhave several advantages. Working alongside the existinggrids for electricity, natural gas and district heating, ahydrogen grid could act as a fourth “backbone” thatwould link the other three energy sources as well asproviding energy in its own right (figure 1). Hydrogencould be distributed locally, regionally or nationally, andcould even be carried by the existing natural gas grid,with some modifications. 3 Alternatively, a proportion ofhydrogen could simply be blended with the supply ofnatural gas.Hydrogen is easy to use because of its versatility, in termsof both manufacture and end-use. Hydrogen couldprovide the link between renewable energy and thetransport sector, transforming biomass, solar and windenergy into transport fuel and reducing dependence onoil. A hydrogen economy is expected to substantiallyimprove the security of energy supply for the transportsector.Besides its potential as a fuel or energy transport mediumin the transport and power generation sectors, hydrogencould have an important role as a way to store surplusenergy. Fuel cells normally used to produce electricityfrom hydrogen can be designed to switch into reverseand produce hydrogen from electricity. At periods whenelectricity is cheap – when the wind is blowing strongly,for instance, so that wind farms are producing morepower than the grid requires – this surplus electricity canbe used to make hydrogen, which is then stored forfuture use. This “buffer” principle could be used at allscales, from centralised power stations right down tosmall fuel cells in private cars.However, especially with regard to complex energysystems, the overall efficiency from primary energy toend use has to be considered carefully and considerabledrawbacks are here identified for a hydrogen system,because of its long energy conversion chain. Whenhydrogen is produced out of electricity and then reversedback into electricity again, there are great losses andtherefore additional advantages and added values shouldbe observed to justify such a system from an energy-efficientpoint of view.One of the most important advantages of hydrogen is itspotential to replace gasoline and diesel as transport fuels,and thus to eliminate air pollution directly from vehicles.However it is produced, hydrogen cannot atpresent compete with conventional transport fuels inpurely economic terms. However, within 10-20 years thesupply of oil is expected to peak, while demand willprobably continue to grow, so in the medium to longterm the price of oil is expected to increase. Nevertheless,the introduction of a hydrogen system has to be seen asa long-term option. Although hydrogen will becomecheaper as technology improves and demand increases,hydrogen is not expected to become cost-competitive asa transport fuel in another 10-30 years time. Even if thedevelopment of a hydrogen infrastructure is given a highpriority in terms of costs and political willingness, itcannot be expected to be in place before 20-40 yearsfrom now.2. Not all the hydrogen production methods discussed here provide high-purity hydrogen. Expensive purification processes may be needed to purifyhydrogen made by reforming processes, for instance. On the other hand, some types of fuel cells do not require high-purity hydrogen.3. Most conventional natural gas pipelines are able to carry hydrogen, though compressors and valves may have to be adapted or replaced.