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Solar Hydrogen Energy 2

Sep 25, 2015

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Energy

  • 1Introduction

    The decreasing availability and the negative externalities of the fossil fuels haveposed a prominent risk to our ecosystem. Hydrogen can replace these traditionalfuels as one of the most promising energy carriers for the future energy economy.This chapter discusses the sustainability of energy sources and demonstrates how anew energy system based on hydrogen and renewable sources can be technically andeconomically feasible.

    1.1 The Current Situation

    Nearly 88% of the current energy economy relies on fossil fuels which are not onlydiminishing rapidly in quantity but also damaging the ecosystem signicantly. It isnecessary to adopt a fresh mindset to nd solutions to the problems and to devise afuture with a more secure and sustainable energy supply. To achieve this requires adifferent energy system based on natural renewable energy sources or safe and cleannuclear technologies.

    Since it takes hundreds of millions of years to generate fossil fuels, it is impos-sible to expect that, at the current consumption rate, such resources will replenishthemselves rapidly enough for utilization. Such energy sources therefore cannot beconsidered renewable as they cannot regenerate in a reasonable time frame. On thecontrary, the sources that are dened as renewable energies come from a naturalprocess that constantly repeats itself over a short period of time. Among many ofthese renewable sources, for example, is the electromagnetic energy from the Sunthat reaches our planet every day. Other examples include the gravitational forcesbetween the Moon and the Earth, and the geothermal energy inside our planet.

    Energy can also be provided by nuclear technology, particularly through fusionpower plants that try to recreate on Earth the process that takes place inside thestars. This however still poses formidable technological challenges that will prob-ably not be solved in time before the nal depletion of fossil fuel, let alone the dam-ages the fuels continue to bring to the environment in the interim. Meanwhile, the

    Zini G., Tartarini P.: Solar Hydrogen Energy Systems. Science and Technology for theHydrogen Economy.DOI 10.1007/978-88-470-1998-0 1, Springer-Verlag Italia 2012

  • 2 1 Introduction

    current nuclear fusion technology still presents many disadvantages and safety risksthat many consider to outweigh its benets. For these reasons, at the moment themain attention is focusing on better developing and exploiting the renewable energysources. There are still vast technical and economic challenges to overcome before anew energy regime is established to fully replace the current fossil fuel-based econ-omy. Besides, this transfer will also bring about major institutional changes as wellas a complete and utter paradigm shift in our life style and in the international powerequilibrium in the next few decades.

    1.2 The Peak Oil Theory

    Since fossil fuels are bound to be exhausted, it is essential to have a clear under-standing on the current extraction and consumption pattern of this resource beforediscussing new energy sources that can stand for replacement.

    In the 1950s, the American geologist M.K. Hubbert developed a theory namedPeak Oil, which states that the extraction pattern of the petroleum and other com-bustibles follows a bell-shaped curve. The trend of the curve shows that the quantityof the discovered and extracted oil increases over the years and reaches a maximumamount, before declining gradually with a symmetrically mirrored trajectory. Theconcept behind this model is that the availability of fossil fuels is limited, either dueto the decreasing new oil reserve discoveries or to the increasing costs of extractingremaining few oil in the existing elds.

    The curve is described by the logistic growth model equation as:

    Q(t) = Qmax1+ a exp(bt) (1.1)

    where Qmax represents the total amount of available sources, Q(t) is the amount ofthe production accumulated so far and a and b are the constants obtained from themodel of crude oil production decrease in the USA from 1911 to 1961.

    Many different research data all indicate that Hubberts model indeed matchesclosely with the actual production pattern in many oil producing countries over theyears. In Figure 1.1, the model is superimposed to the actual recorded oil productiontrend in the USA between 1910 and 2005 and it is evident how these two curvesfollow closely one after the other. Other countries have also demonstrated the sameproduction tendency over the years. For example, Indonesia as an OPEC membercountry has shifted from being an oil-exporting country to an importing one, with aproduction curve equally similar to Hubberts model.

    At the moment, the forecast based on a static consumption1 of oil predicts a lifecycle of another 50 years for this fuel. This estimate, however, just like others, suf-fers from a great deal of inaccuracy due to the fact that the actual quantity of the1 Static consumption is intended as a xed consumption remaining at the current level, inde-pendent from the variable world consumptions which are expected to have a net increase andexclude the possibility of discovering new exploitable reserves.

  • 1.2 The Peak Oil Theory 3

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    Fig. 1.1. The Hubberts model and the USA oil production curves

    oil reserves is protected in fear of causing global nancial panics. Even many statis-tics provided by international organizations tend to be incorrect for the lack of com-plete data.

    There are also other concerns to consider regarding the efforts invested in dis-covering new oil reserves. The major oil companies in the world have stated that theever-increasing rate of consumption will not be sustained even by the nding of newsources. Such reserves are not only difcult to locate, but also require much higherextraction investment, such as building longer pipelines across politically unstablecountries with the risks of undergoing terrorist attacks, or sustaining higher reningcosts if the reserves contain oil of lower quality. The continuous speculation of theworld market on the prize of the crude oil does not help stabilising the situation either.Furthermore, when the oil production begins to decrease according to the decline inthe Hubberts curve, the marginal costs of extraction will start to rise and render theproduction highly undesirable even before the last drop of oil is exploited. This willforce the oil companies to run the risks of less certain investment returns and theywill shift the burden to the nal users with higher market prices.

    The approximation of the Hubberts curve is also valid for other types of com-bustibles apart from petroleum. For example, if the life cycle of methane gas accord-ing to the current consumption is estimated to be around 65 years, for carbon fossilit is longer than 200 years before its exhaustion. Although it is true that there is noimmediate danger for the traditional combustible sources to run out, it is importantto take into consideration that most of the fossil fuel reserves are located in politi-cally and socially unstable countries, which results in a situation very similar to an

  • 4 1 Introduction

    oligopoly with the problems inherent in this type of market. This means that severesupply shortage is more likely caused by political turbulences than by actual fuelunavailability.

    Apart from the concerns of reserve availability, an even more pressing problemis the destruction on the global ecosystem caused by the thermodynamics of carbon-based fuel combustion. This will be discussed in the next section.

    1.3 Forms of Energy Sources and Environmental Impact

    The Sun provides energy to the Earth in the form of electromagnetic radiation. Suchenergy interacts with the Earths ecosystem and is transformed into different forms,such as biochemical energy accumulated in the organic systems and the potentialenergy stored in the movements of air or water masses. Other types of energy areavailable from the planet itself or from the gravitational interaction with the Moon(see Table 1.1).

    Table 1.1. Origins of types of renewable energy available on Earth

    Origin Energy Type

    Sun Electromagnetic Radiation (thermal and photovoltaic)Potential (water cycles)Potential (wind, waves)Biochemical (biomasses)

    Earth Radioactivity ThermalMoon Gravitational Potential (tides)

    From a thermodynamic point of view, the sources that produce minimum entropyper energy unit are gravitational forces, nuclear fusion and solar radiation. Theseenergies are manifested on Earth in the forms of electromagnetic energy, wind andtidal movements, oceanic thermal exchanges, marine currents, water cycles, geother-mal sources, biomass and nuclear fusion. All of them generate limited environmentalimpact and possess considerable potential which has not yet been fully exploited ona large scale.

    In the meantime, up until now the world has obtained most of its energy fromthe combustion of fossil fuels. Such combustion produces by-products which causesevere pollutions of air, soil and water sources. It also emits billion tons of CO2 intothe air per year, together with other harmful substances like nitrogen and sulphuroxides. CO2, when freed in the atmosphere, prevents the heat accumulated on theEarths surface from being released int

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