REVISTA MEXICANA DE FISICA S59 (2) 85–92 OCTOBER 2013

Hydrogen and Fuel Cells: Potential Elements in the Energy Transition Scenario

U. Cano-CastilloInstituto de Investigaciones Electricas,

Reforma 113, col. Palmira, Cuernavaca, Mor. 62490, Mexico.

Received 7 April 2013; accepted 20 April 2013

Hydrogen as a clean and sustainable fuel, as well as fuel cells as the means to efficiently generate clean electricity for many applications, aretwo most relevant elements that should not be overlooked in the new international energy scenario. The technologies associated to hydrogenand fuel cells have reported tremendous advances in the last 20 years, regarding both their performance and their reduction in cost. Althoughsome technical challenges remain to accelerate their commercial use, there is no question regarding their important role they will play in thesoon-to-be energy new international scene. This is a reality particularly for developing countries which may play an important part in theintroduction of these new forms of harvesting and using energy. These regions have normally the largest growing demand rate for electricity,they are going through a modernization stage needing more electricity and they usually enjoy plenty of primary renewable energy resources.

Keywords:Hydrogen cells, fuel cells, renewable energy.

PACS: 89.20.-a; 89.30.-g; 87.20.-n.

1. Why hydrogen?

Hydrogen has the greatest energy content per unit weight,that is 1kg of hydrogen has a LHV=119.9MJ and aHHV=141.8MJ [1]. This feature makes this gas a very at-tractive fuel for the replacement of more conventional fuels,particularly fossil fuels. When this fuel is used to generateelectricity using fuel cells, the only byproduct will be water,often with a high heat content, which can be used to increasethe overall energy conversion efficiency.

As other fuels such as gasoline or liquefied petroleum(LP) gas, hydrogen needs energy to be available, and it shouldbe seen as a value-added product, just like gasoline. Whenthis energy is harvested from renewable resources the produc-tion of hydrogen gets an extra appeal as hydrogen generationcosts can be reduced and become a sustainable fuel. But be-sides energy, the production of hydrogen needs a feedstockthat contains this element. And that is what makes hydro-gen a flexible fuel. Hydrogen can be obtained by a methodknown as reforming, which uses different feedstock sources,for example hydrocarbons like natural gas, which containplenty of hydrogen besides other components. Other none-fossil organic compounds also contain hydrogen atoms, suchas biomass, biogas, alcohol from fermented glucose, etc. Allthese compounds can be converted into hydrogen, thereforeif energy and feedstock for hydrogen generation are renew-able, hydrogen can be considered a true sustainable fuel, justwhat our society is looking for to guarantee our energy de-mand. But when organic compounds, fossil or not, are con-verted into hydrogen, other atoms like carbon, nitrogen, oxy-gen, etc. are converted to oxidized compounds. Carbon andoxygen will form carbon dioxide which is a green-house gas(GHG). When this occurs, biomass will normally be consid-ered carbon neutral fuels as they come from converted CO2 inthe first place, for example trees and crops capture CO2, theyform organic compounds that again release CO2 when used.Besides, when hydrogen is extracted from such hydrogen-

containing sources and is used in efficient devices such asfuel cells to generate electricity, the kWh produced will gen-erate less CO2 for the same extracted energy when burningthe organic compound.

In the case of fossil fuels, for example compressed naturalgas (CNG), the CO2 generated per kWh of electricity will addto GHG in the atmosphere but to a lesser extent, compared tothe burning of CNG directly. Therefore using fossil fuels ashydrogen source can already contribute to lower GHG emis-sions helping to the gradual less-fossil-fuels dependency ofour societies, where the ultimate goal will be to let fossil fuelsaside. Using efficiently a clean fuel like hydrogen will bringadditional benefits like a decrease in the amount of fuels usedto generate the electricity we consume today. By soon chang-ing to hydrogen use, the duration of fossil fuel reserves willincrease and will give the opportunity of using these fuels forother more beneficial purposes.

There is another mature technology for hydrogen produc-tion that can be combined with renewable energy resourcesbut that avoids the use of carbon containing compounds, thatis, water electrolysis. The electrolysis of water operates bypassing an electrical current through water, decomposing itsmolecule in hydrogen and oxygen. Clearly this hydrogenproduction path offers a 100% sustainable energy system forthe production of a clean fuel with renewable energy sourcesand renewable feedstock that abound on our planet. Manyother new methods, like photoelectrolysis that directly usesthe sunlight to breakdown water molecules or like microor-ganisms generating hydrogen from their life cycle, are thesubject of many R&D activities around the world but havenot reach commercial status like reforming and electrolysis.

All of these reasons as well as the availability of fuel celltechnologies, a device to efficiently extract the energy con-tained in hydrogen, make of this gas a very attractive alter-native fuel for our ever-growing electricity needs. Better yet,they offer a renewable, clean and sustainable path for the use

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of energy. As mentioned above, those regions enjoying theavailability of primary energy sources such as solar, wind en-ergy, hydro, etc. may become energy powers.

2. Fuel cells: efficient electrochemical energyconverters

Fuel cells are electrochemical devices that are capable of pro-moting reactions that extract electricity from a fuel, ideallyhydrogen. These devices have a similar operating principleto that of batteries. A chemical compound reacts chemicallyin a reaction involving electrons transfer,i.e. electrochemicalreactions occur. Such reactions take place in a device withtwo electrodes one for an oxidation reaction, fuel oxidation,and another for a reduction reaction, typically the reductionof oxygen from air. Both reactions exchange an electricalcurrent that is collected outside the device and used to carryout work. As opposed to batteries which need recharging orreplacement to continue giving electricity, a fuel cell receivesthe chemical compound continuously; therefore it will notdischarge as long as a fuel is fed. This gives fuel cells greatadvantage over batteries especially when recharge is expectedto be immediate as in transportation applications.

What makes fuel cells even more attractive is the high ef-ficiency at which they operate converting chemical energy ofa chemical fuel, like hydrogen, directly into electricity. Ac-cording to theory, the conversion energy efficiency of con-ventional electricity generators,i.e. a heat engine convertingthermal energy, depends strongly on the relationship knownas the Carnot Cycle. In practice the thermal energy is ex-tracted from a fuel by combustion and the efficiency to con-vert this energy into work will depend on a temperature dif-ference. In fuel cells the energy conversion occurs directlyvia electrochemical reactions as described above. Thermo-dynamically low temperature fuel cells could achieve effi-ciencies of up to 83% but in practice there exists some volt-age losses. Yet these devices operate at greater efficienciescompared to conventional thermal energy converters. It isworth mention that there are different types of fuel cells buta broad classification determines their more suitable appli-

cation. High temperature fuel cells (such as solid oxide andmolten carbonate fuel cells, SOFC and MCFC respectively),are normally related to stationary and high power applica-tions like commercial and industrial, while low and interme-diate temperature fuel cells (e.g.proton exchange membrane,direct alcohol, alkaline and phosphoric acid fuel cells and fuelcells, PEMFC, DAFC, AFC and PAFC respectively) are nor-mally related to low power stationary and mobile and trans-portation applications, like cars and electronics.

Now a days, there are global well known companies(Coca Cola Co., WalMart, Google, among others) that haveincorporated hydrogen fuel cells technology to fulfill theirenergy needs and possibly to show their commitment to envi-ronmental concerns. This clearly shows how these technolo-gies are gaining a more mature commercial status.

3. Applications

Early application markets detected so far, are more related tothe technological status, and the economics of the technol-ogy than the markets themselves. Although any applicationrequiring electricity translates to an endless range of potentialmarkets for fuel cells, not all markets are suitable for the useof fuel cell technology. Important challenges still remain andthey typically relate to durability and costs, but other insti-tutional and infrastructure-related barriers do exist, althoughthey are being tackled from different angles.

In mobile applications such as fuel cell cars in electrictransportation, fuel cells should at least last 5,000 hours to betechnologically competitive regarding durability. Other pa-rameters for competitiveness in this application are relatedto other practical issues including costs. Table I is a ta-ble adapted from a figure reporting fuel cells vehicle perfor-mance at the end of stage 2010 by the Japan Hydrogen FuelCells Demonstration project or JHFC [2], that describes themain features fuel cells for transportation need to accomplishbefore they are commercially competitive.

In 2009, an agreement among some car manufacturers tomake commercial fuel cell cars available for the year 2015was signed in Berlin. In recent weeks Toyota confirmed this

TABLE I. Fuel cell vehicle’s performance past and present status.

Competitive Feature 2002 2005 2010 2015

Actual technology Technology Target

Vehicle efficiency 50% 50% 60% 60%

Low Temperature performance 0◦C -25◦C -30◦C 30◦C

Hydrogen

Refueling time 3 kg/3 min 3 kg/3 min 5 kg/3 min 5 kg/3 min

Durability 5 years 5 years 10 years 15 years

Vehicle Price 100 million yen - 10 million yen Several*

Driving Range - 300 km - 500 km

*Although the cited reference does not mention a specific cost target, the US Department of Energy established a target cost of US$30/kW for 2017 [3]

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target. Besides such car industry effort, a group of companiesinterested in the fuel infrastructure associated to this trans-portation sector, and of course in the business opportunitiesfrom that, also signed an agreement to fulfill the infrastruc-ture needs for those cars. Both acts are clear commitmentsfrom industry and a sign of confidence not only on the tech-nological status of fuel cell cars but also confidence on thecommercial aspects associated to this market.

Other markets that have identified benefits from the useof fuel cells are the water treatment industries. For example,in 2007 a Wastewater Treatment Plant (WWTP) [4], the Tu-lare in California, started using its anaerobic digester biogas,which in the past they use to flare, in a fuel cell for electricitygeneration. Approximately 500,000 cubic feet of pretreatedbiogas per day are used in the plant. The plant claims to havereduced its electricity bill by over $1 million per year, as theygenerate 45% (1.2MW) of their electricity requirements. Inthis project they installed 1.2MW on-site molten carbonatefuel cells, a high temperature stationary generator with anavailability of 99.45% in 2010. In this project they report anelectrical efficiency of 47% and a combined heat and powerefficiency of 90%. Second cycles are an advantage of hightemperature fuel cells. On emissions reduction by the use offuel cells they report 6,200 tons of CO2 avoided per year.

3.1. Stationary Power

Residential applications have been an attractive market fordistributed generation appealing fuel cells developers, mainlyseeking electrical network independence. Different ap-proaches have been tried to test business models, as well asto test technical performance. One challenge that has beenaround for many years in this applications has to do withfuel cells durability, as stationary power requires 40 thou-sand hours of life expectancy. Nevertheless, many developershave been testing this market as is one of the most energy de-manding worldwide. For example, in Japan there are morethan 20,000 fuel cell residential units installed, testing dif-ferent configurations and technologies. Such tests combinesdifferent paths for the production of hydrogen fuel, includ-ing hydrocarbon and bio-waste external processing, internalfuel processing, water electrolysis including renewable en-ergy sources like solar photovoltaic systems, direct hydro-gen use, etc. Regarding the fuel cell technology employed,PEMFC domain the low power capacities (< 5 kW) of thesesystems, but other fuel cells technologies are being also testedwith emphasis on the possibility of having waste heat increas-ing the overall efficiency of the energy system. Such config-urations therefore include combined heat and power (CHP)systems with higher temperature fuel cells. Electrical config-urations consider distributed generation (DG) in both modes,connected to the grid and independent of the main electri-cal network where systems are also tested as backup power.Among Japanese efforts to promote the use of fuel cells at thecommercial level, a household fuel cell system called ENE-

FARM was launched in 2009, including the cooperation withprivate companies [5].

Other goals in different programs such as the US hydro-gen and Fuel Cells Program include the development of dis-tributed generation and micro-CHP fuel cell systems (5 kW)operating on natural gas (NG) or liquefied petroleum gas(LPG) by 2020, achieving 45% electrical efficiency and adurability goal of 60,000 hours. The cost by 2020 is expectedat a level of $1,500/kW. Also for medium-scale CHP fuel cellsystems, 100 kW to 3 MW, are expected to be developed at50% electrical efficiency but a 90% CHP efficiency. Durabil-ity and costs goals are 80,000 hours and $1,500/kW operatingon NG and $2,100/kW operating on biogas.

By May 2012 over 250 fuel cell systems were installedunder the Callux field test program in Germany. Combinedthese systems they added one million hours of operation. TheCallux program is one of the several residential micro-CHPdemonstration initiatives of the National Innovation Program(NIP) in that country.

3.1.1. More on Combined Heat and Power

Whenever heat is produced there is always the possibility ofincreasing the energy efficiency in generation systems. Asmany countries consume heat especially during winter it isonly natural to make use of the byproduct hot water or vaporwater to fulfill heat needs in some applications. In this waycombined heat and power is the main goal of developers in-tending to gain clients in this market. The Japanese programENEFARM has already put in place 13,500 such systems inhouseholds [6].

3.1.2. Prime and Premium Power

Prime and Premium Power are stationary applications wherelarge fuel cells can provide many advantages over grid power.In the first case, fuel cells can bring continuous power toplaces where the grid is not available. Examples of this isthe mining industry, which presents several power needs thatare often temporary or need to move locations. In the miningindustry there is an extra appeal for fuel cells as that sectorestablishes hard requirements as workplaces making this in-dustry invest heavily in clean air and other environment con-ditioning systems. In these conditions mobility is not the onlyrequirement for electricity generator. Low noise and zeroemissions make of fuel cells the ideal technologies for suchenvironments. As it is mentioned elsewhere in this paper,niche markets based on focus economies can take advantageof fuel cell generators features without economic concernsassociated to emerging technologies.

3.1.3. Backup and Remote Power

These markets are already enjoying certain commercial suc-cess in particular on the telecomm industry, where fuelcells backup systems offer certain advantages over traditionalbackup power systems based on batteries or gensets. Cell

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towers have been the subject of fuel cells niche markets dueto their suitability for the technology, which offers longerperiods between “charges”. Batteries need to be constantlyrecharged to avoid the natural self discharge they suffer from.Fuel cells do not discharge as the energy carrier is not part ofthe fuel cell. Fuel cells are said to be more predictable [7]in terms of their performance as battery capacity diminisheswith time and they can be ruined if their charge is drawntoo often. Fuel cells on the other hand can operate duringten years without losing power capacity. When fuel cellsare compared with generators, they offer a silent, cleanerand more energy efficient means to provide the importantbackup power. Also fuel cells require little on-site mainte-nance. Many of the known features and benefits associatedto fuel cells technology apply to this application: they offeroperating efficiencies of around 50%, fuel cells are scalableand modular to operate in parallel if needed, fuel cells havea wider operating environment temperature range (-40◦F to122◦F), they can be used indoor or outdoor with a minimalfootprint and they offer longer life with no moving parts. Ac-cording to the US Hydrogen and Fuel Cells Program [8],telecommunications companies had purchased an estimated300-500 fuel cell systems by 2008 (initial sales of fuel cellsfor telecommunications backup power began in late 2004).When installing a fuel cell backup power system in this typeof application, 6 cylinders of compressed hydrogen are typ-ically used with approximately 4 m3 or 7.4 m3 of hydrogenat a pressure of about 165 bars and an approximate weightof 63 kg. This results on a combined capacity of electricalpower to attend 24-96 hours of main power outage.

3.2. Transportation

Transportation has been perhaps the application that has at-tracted the largest investment for the development of vehi-cles based on hydrogen fuel cells technology. The reason:every year millions of cars are sold around the world. Ac-cording to the International Organization of Motor VehicleManufacturers (OICA), in 2012 more than 60 million carswere sold internationally. No wonder why basically all au-tomotive manufacturers have fuel cell cars being tested andfor some, this technology represents the ultimate goal of thefuture transport. Despite that yet many refer to fuel cell carsas something for the future, there has been recent confirma-tion by many car manufacturers of their commercializationplans for the next few years. Some major automakers haveannounced to sell fuel cell cars by the year 2015. For exam-ple, Hyundai’s ix35 exposed at the Yeosu World Expo 2012 isexpected to sell 1,000 units by 2015. Also Toyota and Hondahave sustained their plans and commitment to commerciallymake available fuel cell cars. In January 2011, 13 automakersand hydrogen suppliers signed a joint statement to introduceby 2015 fuel cell electric vehicles as well as to develop hydro-gen infrastructure in Japan. A similar agreement was signedin Europe including European car manufacturers and gas sup-pliers. Daimler for example plans to begin commercialization

in 2014. Such commitment shows that car manufacturers aretruly convinced that hydrogen fuel cell cars can compete inthe markets and not only be a wishful thinking technology.

According to the German Hydrogen and Fuel Cells Asso-ciation [9], the existent cooperation between BMW and Toy-ota has been extended to the field of fuel cells, with emphasison fuel cell system, hybridized electric drive train and hydro-gen storage. This cooperation aims at entering the mass mar-ket around 2020. The same source of information let us knowof the national programs from Germany and France for elec-tric vehicles, where government support in France,vehiculeselectriques, is dedicated to pure battery electric individualmobility, while in Germany hydrogen mobility,H2-Mobility,supports electric fuel cell vehicles. Both cases are foreseenby 2020 in terms of mass roll-out including the supportingdedicated fuel supply infrastructure. These programs hope toreach or surpass 1 million vehicles on the road by then.

Not only fuel cell cars are intended for the conventionalcar market, but they can also compete with other traditionalenergy technologies. For example, Honda’s FCX Clarity hasbeen equipped with a power supply function with a capacityof 9 kW which could also be used to supply approximatelysix days of electricity to the average Japanese home or used asa power supply for emergencies. This way the same productcan provide transportation service and electrify your home. Itsounds very interesting. This very same 2013, Hyundai an-nounced that it will become the first car company to initiatemass production of fuel cell cars with its FCEV Probably oneof the most ambitious programs for hydrogen and fuel cells isthe Japanese program, which intends to initiate the commer-cialization stage of fuel cells vehicles and hydrogen stationsin 2015. Such program is in line with the Japanese govern-ment goal of 80% reduction of CO2 in the transportation sec-tor by 2050. This commercialization stage is expected to takeabout 10 years, after which full commercialization and prof-itability of involved business should be achieved,i.e. marketdriven scenario. Also by the end of the commercializationstage the number of hydrogen stations is expected to be in

FIGURE 1. Schematics of the fuel cell system in the HyundaiFCEV intended to initiate mass production.

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the order of 1,000 while fuel cell vehicles are expected to bearound 2 million cars, which means around 2,000 cars perstation.

For the auto industry, by 2017 one of the expected goalsis the development of a 60% peak-efficient hydrogen fuel cellpower system, with the 5,000 hours durability demanded bythis industry and a mass production cost of $30/kW.

3.3. Other transport systems: Fuel cell Buses, MaterialsHandling Equipment and Locomotives

Fuel cell buses were the first transportation systems to be onthe road for technology testing in the sector. There are stillmany advantages about the use of fuel cells in utility vehi-cles and buses, as well as other similar niche markets. Oneof the main advantages relates to the fact that these servicesnormally have well defined routes and therefore well knownload profiles. On top of that, such driving profiles are nor-mally repetitive, therefore predictable, which makes systemdesign and control a lot easier than personal vehicles. Thehydrogen storage systems are also easier to design and withthis, the range for each fuel tank charge, easy to predict. Thisalso helps to develop fuel infrastructure as the fuel needs canbe satisfied on site where the fleet has its base, which alsogives flexibility to the choice of hydrogen generation path andtherefore the fuel cost. For the case of fuel cell buses, fuelcells are now advantageous only for urban services as properfuel infrastructure is not yet developed. Also there is somesocial obligation for authorities to provide transport serviceswhich may be taken as a platform to help cover the initialcosts of the vehicles. Although the market size is smaller thanpersonal cars, utility vehicles and other fleets, including fuelcell buses are early markets that can afford the initial highercosts of emerging technologies. Not only the latter is true buteven some niche markets could be facing competition fromhydrogen fuel cell technologies, as prices are getting closedepending on the specific market characteristics (need for alarger range, emission restrictions, etc.)

FIGURE 2. Fuel cell materials handling system. One of the manypresent in development and on site testing (From Ref. [6]).

FIGURE 3. Fuel cell-hybrid switcher platform vehicle in prepara-tion to receive a PEMFC power plant and hydrogen storage system.

Among the early markets capable of accepting the tech-nologies features including its costs, materials handlingequipment is one of the interesting applications for hydro-gen fuel cells. The US Department of Energy includes thedevelopment and testing of this type of equipment but as op-posed to some developers, the main interest is on the use ofDFFC, particularly direct methanol technology. Among thegoals within the program, system performance, its operationand safety are of great importance, as well as the evaluationof market viability. The main reason for this approach is thefact that direct liquid alcohol fuel may offer reduced infras-tructure costs, high energy density, and low overall fuelingcosts.

There are specialty applications in the transport indus-trial sector, for example last May 2012 [10], AMPLATS An-glo American Platinum, the world’s top producer of the pre-cious metal, launched what is said to be the first fuel cell-powered mining locomotive. The locomotive was developedin collaboration with Vehicle Projects, Trident South Africaand Battery Electric. In a similar project, Vehicle ProjectsInc partnered with BNSF Railway Company and the USArmy Corps of Engineers, to develop a prototype hydrogen-fueled fuel cell-battery hybrid shunt locomotive for urbanand military-base rail applications. The power plant uses a250 kW PEMFC but is expected to be increased to 500 kWcapacity.

3.4. Other uses: Military, Portable/Micro

The military industry has always been a promoter or an earlyuser of emerging technologies. This is true for mobile fuelcell power systems. In particular, there has been great inter-est in increasing the electricity capacity (KWh) that soldierscarry on during their missions, as the electronic equipmentand other devices they use, also increase. A typical soldierwill carry batteries for their energy needs but as fuel cellshave promised comparatively speaking extended ranges, the

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interest on these technologies has prompted various projectsthan include: the use of hydrogen and direct alcohol PEMfuel cells, the conversion of military fuels into hydrogenfor fuel cells as on-site fuel generation. Other applicationsinclude the use of fuel cells in aerial unmanned vehicles(UAV’s) which combines the advantages of extended rangesof battery-based electrical UAV’s with the low acoustic andthermal footprints associated to fuel cell systems, providingthese solutions with an additional interest for users.

On portable power applications fuel cell systems,i.e. ca-pacities of< 250 W, an energy density of 900 Wh/L is ex-pected by 2015. This target does not necessarily apply to themilitary as top priority is not the cost but the mission accom-plishment.

In the portable application sector for auxiliary powerunits in the capacity range of 1 to 10 kW, fuel cell systemsare expected to achieve a specific power of 45 W/kg and apower density of 40 W/L at a cost of $1,000/kW.

3.5. Hydrogen Infrastructure and Delivery

As it is mentioned in the following sections, hydrogen stillfaces challenges for its practical storage especially in mobileapplication, including transport. But the availability of hy-drogen depends on the whole value chain associated to thisfuel, that is, its generation, its transportations, its storage andits delivery or transfer to the final use devices, including theregulations associated to safety and other concerns along theway. This value chain also represents the infrastructure nec-essary to put into practice an economy that holds hydrogenfuel as one relevant component based on the advantages men-tioned so far.

3.6. Energy Storage and Renewable Energy Sources

Hydrogen has been thought of as an energy vector just likeelectricity. This means that energy can be conveniently gen-erated, transported, stored and eventually transformed intoelectricity through the use of this fuel. There is also anotherattribute to hydrogen gas and is the fact that once is gener-ated it can be stored for long periods of time without losingany significant value, which clearly competes against the tra-ditional energy storage technologies like batteries and others.This feature can contribute to leverage the intermittency ofsome renewable energy sources like wind and solar and ofcourse their economy. It has been reported that in Germany(see Fig. 4), where wind energy has been growing fast in thelast years, hydrogen could be used to store future wind en-ergy that the national network will not be able to take dueto its limited capacity and the expected wind generation for2020. This also includes solar and off-shore wind technolo-gies growth, where the latter is the main contributor.

On the other hand fluctuating renewable resources makeit difficult to match production with demand even with thenew trend of network injection of the produced electricity, as

FIGURE 4. Projected renewable electricity in Germany.

FIGURE 5. Difference between electricity generated by windpower and demand profile, shows a surplus of energy.

the available infrastructure is limited in its capacity and maysuffer from various fluctuations that potentially may harm theexisting electrical equipment.

If hydrogen is to enter the new energy scenario there willbe the need for certain degree of restructure in the electri-cal system, as hydrogen technologies may include electri-cal loads like electrolyzers and their compressors (high en-ergy devices), electrical generators represented by fuel cells,both stationary and potentially mobile fuel cells such as carsturned into residential generators. There will also be the needfor fuel dispatch in fuel stations as well as other new electri-cal systems connected to the network.

If primary renewable energy sources consider hydrogenfor distributed generation using fuel cells, it will contributeto save losses when central generation of electricity trans-mits and distributes electricity, a value often considered to bearound 7%. If DG increases in new electricity systems, thiswill give them network independence advantages.

4. What challenges remain?

4.1. Hydrogen storage

Probable one of the most limiting technical barriers that holdhydrogen from being the ideal expected energy route or atleast an important player of the future energy scenario, relatesto its storage. Despite the fact that it has been mentioned thathydrogen can be thought of as a way to levering intermittent

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energy sources, such as wind and solar energy, storing thisgas imposes additional energy needs with the actual storagetechnologies. Hydrogen is a gas at ambient conditions andwhen stored, this gas is pressurized and stored typically ataround 150 bar in very heavy tanks which are impractical formobile applications. Hydrogen has a very high energy den-sity per mass unit, but it is also true that its compressibility isvery low making its energy content per volume small, need-ing then large spaces to store sufficient amounts of hydrogenfor some applications, adding weight and volume. Neverthe-less, in the last few years high pressure tanks for hydrogenstorage up to 700 bar have been developed based on muchlighter composite materials,i.e. carbon fibers around alu-minum tanks. Cryogenic storage of hydrogen does increaseits volumetric energy density but also increases its cost as lowtemperatures of around -250◦C together with compression at350 bar are needed. Besides that and, most importantly isthat very efficient insulation storage systems are needed tomaintain the hydrogen stored for large periods.

Transportation applications, like hydrogen fuel cell carsface technical goals that require a range of 500 km with onefuel tank charge. Depending on the technology, this meansat least something like about 4 kg of hydrogen. Besidesthe mass content that guarantees sufficient competitive au-tonomy, safety and conformability of the hydrogen storagetanks, are compelling requisites that need to be fulfilled. Allof these factors clearly affect the final cost of the technology.

New methods to store hydrogen are being developed in-cluding the cryo-pressurized method, which requires lesslow temperatures than the traditional cryogenic technologies.Also some interesting ways to store hydrogen include mate-rials that can hold hydrogen atoms in the solid state at verysmall distances, making it possible to increase volumetric en-ergy density. These methods include adsorption and desorp-tion of hydrogen, and the formation of complex, chemicaland intermetallic hydrides. Yet due to the nature that ofteninvolves the exchange of heat from physical processes, forexample during adsorption and desorption, some methods re-quire specific dynamics that can be considered practical to beimplemented in real energy systems; a challenge not alwayseasy to achieve.

4.2. More Figures on Technology Costs

The success of any new technology cannot ignore the impor-tance of costs as users will ultimately make decisions amongtheir technology options based on the economy besides theenergy solution they represent. For new and emerging tech-nologies such costs have a strong dependence on manufactur-ing routes, which for hydrogen and fuel cells are still under“refinement”.

Manufacturing of fuel cells at laboratory scale is a verylabor-intensive activity which results in high costs of the tech-nology, but such processes are being transferred to automaticmanufacturing processes that improve their manufacturingcosts.

FIGURE 6. Manufacturing of PEMFC at Instituto de Investiga-ciones Electricas, requires several stages.

As seen above, the costs for hydrogen storage relatesstrongly on the technology used and most importantly on theenergy costs involved in both the fuel production and its stor-age. If storing hydrogen has high costs, only those appli-cation markets that can afford the benefits of hydrogen usewill be willing to pay. Other markets will not. To exemplifythis let us take the cost per kWh stored in lithium ion batter-ies which could be around USD$500 to USD$600 per kWh(present commercial batteries) while stored hydrogen pro-jected cost (at 500 thousand manufactured units) is now aboutUSD$15/kWh with a goal cost established at USD$8/kWhfor 2017. An application that can benefit from a fast rechargeas offered by pressurize hydrogen may be willing to pay thecosts, at higher values, against the burden of having to waithours for the recharging of batteries if paying increases pro-ductivity.

Although several systems are still under testing and im-provement stages, such as hydrogen storage in solid forms(e.g. metal hydrides, chemical compounds, hydrogen sorp-tion), hydrogen stored in its pressurized conditions still re-mains the most achievable goal in applications like auto-motive. The US sub-program on hydrogen storage hasestablished onboard automotive hydrogen storage systemsachieving 1.8 kWh/kg system (5.5 wt%), 1.3 kWh/L sys-tem (0.040 kg hydrogen/L) and $12/kWh ($400/kg H2) inorder to reach commercial competitiveness, by 2017. Nev-ertheless, ultimate targets of 2.5 kWh/kg system (7.5 wt%),2.3 kWh/L system (0.070 kg hydrogen/L), and $8/kWh($266/kg H2) should facilitate the introduction of hydrogenfuel cell propulsion systems for most vehicle classes andmodels.

As mentioned earlier, there exist some institutional chal-lenges associated mainly with safety issues, including manu-facturing, installing permit and operation system stages. Al-though this is true, hydrogen fuel technologies have benefitedfrom the long lasting experience of the special gasses industrywhere the commercialization of hydrogen has seen the devel-opment of many codes and standards already in place for the

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production, transport, storage and use of this element. Otherinstruments have been and are being developed for the use offuel cell systems in many different applications and sectors.

5. Conclusiones

Hydrogen and fuel cells technology have not entered a fullcommercial stage as promised a decade ago. The latter mightbe due to some technical remaining challenges as well assome institutional decisions around the planet. Despite thedrop in R&D budgets for these technologies in the last fewyears particularly in North America, hydrogen and fuel celltechnologies did not stop from advancing toward the publicuse. The shipment of these technologies has recovered itsgrowth rate to values previously expected. Global auto com-panies have countersigned their commitment to initiate massproduction and sale of fuel cells vehicles. Governments ofcountries like the USA, Japan, Germany and Korea keep their

conviction of supporting the advancement of these technolo-gies and their conviction on the possibility of having cleanand efficient technologies, as well as the promise of energyefficient systems using an alternative and sustainable fuel, hy-drogen. As the commercial introduction of hydrogen and fuelcells products smoothly advances, a parallel but to some ex-tent similar advancement takes place with renewable energytechnologies. Both progress lines are expected to coincideat several points, one for sure will be on the hydrogen pro-duction size but hybridity of advanced energy systems willbe looking at fuel cell generators sharing distributed energyloads or micro network configurations built in the near future.Those economies and regions that will be able to notice thecoming opportunities not only for growth but also for the ful-fillment of energy needs and environmental pressures, shouldnot forget hydrogen and fuel cell technologies in the energyequation.

1. LHV and HHV refer to the low heating value and high heatingvalue of hydrogen respectively.

2. JHFC Status Report on Fuel Cell Electric Vehicle Performance,2010.

3. DOE Hydrogen and Fuel Cells Program, ANNUALPROGRESS REPORT 2012c1.

4. http://www.ci.tulare.ca.us/default.asp

5. Fuel Cells Commercialization Conference of Japan - FCCJ,April 2012.

6. The Fuel Cell Industry Review 2012, Fuel Cell Today.

7. Fuel Cells for Backup Power in Telecommunications Facilities,Providing a constant, reliable electric power supply, DOE/GO-102009-2709, April 2009.

8. http://www.hydrogen.energy.gov/permitting/telecommunications.cfm

9. Deutsche Wasserstoff und Brennstoffzellen Verband e.V.(DWV).

10. Vehicle Projects website (http://www.vehicleprojects.com/index.htm) news and events section.

Rev. Mex. Fis. S59 (2) 85–92