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1、Challenges in the incoming energy scenario: role of chemical sciencesSERGIO CARRAMean global energy consumptionsTotal 13.8 TW, US 3.3 TW, Italy 0.25 TWThe less expensive fossil sources represent the lions share!Than it appears that renewable resources will not play a large role in primary power gene
2、ration unless, or until:. Cost breakthroughs in carbon-free technologies are achieved. Externalities are introduced , such as environmentally driven carbon taxes. Actually also if there are reassuring resources of fossil fuels, geopolitical and regional factors can affect significantly the price of
3、energy. Can we supply the energy needed in the future with fossil fuel?Quite probable yes.Current global energy consumption = 13.8 TWBy 2050 consumption = 25 TW. Need abot 10 TW.Fossil fuels: Can produce extra 10 TW only at risk to environment.Wind/Geothermal/Biomass/Hydroelectric: Cannot produce 10
4、 TW. (But should be implemented where appropriate: energy is extensive)Nuclear: Requires massive investment today to provide power plant infrastructure (10 TW = 10,000 new 1 GW reactors, in 50 years).The employment of geological reservoirs is potentially feasible but it arises problems for maintaini
5、ng a low rate of of CO2 leaking.Besides for the cost of plants and infrastructures an increase of expences of 15% is predicted. In conclusion it appears to be a promising option with uncertainties in his : technical and economical ASPECTS. Carbon dioxide sequestration RenewableThe total rate (TW) is
6、 shared between different categories:-hydroelectric 0.3 pv=1.5-geothermal 0.03 pv=12 -eolic 0.074 pv=7-biomass 1.3 (+)-solar 0.03 pv= 600(+) due to the low efficiency of photosynthesis about 17% of the of the terrestrial area land is required to produce 10TW.LightFuelElectricityPhotosynthesisFuels E
7、lectricityPhotovoltaicsH OOH222scMesceMCOSugarH OO222Semiconductor/LiquidJunctions conversion strategiesSolar energy appears to be the only source able to supply 10-20 TW carbon-free power needed at 2050.What is the area needed to generate the required power?-The full energy consumed in the world ca
8、n be produced in a tropical land with a squared area with a side of 500 Km .-The present energy employed in Italy can be produced in a land area with a side of 60 Km -It is sufficient to cover about 0.17 % of the territory. Solar is expensiveTypical levelized cost by sourceSolars typical range of 25
9、-50 cents/kWh is much higher than other sourcesIt competes with grid price not generator costAverage residential grid price (US cents/kWh) Much easier to compete with grid price than generation cost.Silicon technology dominates the market:93% for crystalline Si (single-, multi-, poly-, nano-)Market
10、share for Si and thin film technologies were continuously decreasing during last 10 yearsMarket share by technology10Prices and predictions of photovoltaic marketModule efficiencyLab scale Max efficiencyHIT heterojunction intrinsic thin filmMany different technologies on the market rushing for high
11、efficiency & low costs Shockley-Queisser analysis (1961)It is based on four assumptions:1- single p-n junction2- one electron-hole pair excited for incoming photon 3- thermal relaxation of the electron-hole pair energy in excess of the bandgap4- illumination with unconcentrated sunlight Maximum yiel
12、d of 31% is obtained.S-Q limit can be exceeded by violating one or more of its premises.A- Intermediate-band solar cells B- Quantum-well solar cellslC-Multiple junctions cellsC Employment of organic materialsLUMO=Lowest Unoccupied Molecular OrbitalHOMO=Highest Occupied Molecular Orbital XSC : Excito
13、n Solar Cells Unsaturated Molecoles and fullerenes for :- harvesting solar radiations-to give rise to a fast charge transfer-to limit the return to the ground statePlastic Cells: Scale-up using Roll-to-Roll TechniquesPrinted or coated inexpensively on flexible materials using roll-to-roll manufactur
14、ingCan be produced with varying degrees of translucency so that it is customized for specific marketsEnvironmentally friendlyEasily scaled upUtilizes wide spectrum of light16Solar electricity cost as a function of module efficiency .I- Wafers of silicon.II- Thin films of amorphous silicon , tellurid
15、es, selenidesIII- Research goals: carrier multiplication, multiple junctions, sun light concentration, new materials (organic).Silicon Si Eg = 1,1 eV Gallium Arsenide AgAs Eg = 1,5 eV Titanium Dioxide TiO2 Eg = 3,2 eVTiO2 fulfils the requirement but it absorbs only the ultraviolet radiation, that is
16、 only 3% of the available solar energy. SC semiconductor (photocatode)M metal (anode)Water photodissociation occurs if h2.97 eVPhotoelectrochemistry(Photo)chemical Water Splitting: 2 H2O O2 + 2H+ + 2e- +H2Operation principles of a dye-sensitized mesoporous heterojunction solar cell. (Gratzel) Gray d
17、ots : mesoscopic oxide particles covered with a monolayer of dye. The development of energetic technologies arises new and stimulating challenges for chemical sciences :-Complex systems including many degrees of freedom .What is the real cost of the silicon solar energy?.How important will the burni
18、ng of coal be to global warming?- Chemistry of small molecules, implied in: . Atmospheric chemistry . Combustion .New fuel synthesis. .Excitaction and transfer of electrons.- Chemistry of CO2 involving: .New applications on large scale processes-Design of new catalytic systems , involved in energy p
19、roduction, such as.Activation of methane to methanol CH4 + (1/2)O2 CH3OH.Photoreduction of CO2 to methanolCO2 + 6H+ +6e- CH3OH .Improvement of the slow catodic processes reactions.Fuel cells operating with metanolCH3OH + H2O CO2 + 6H+ + 6e- “Gas “Gas toto liquidsliquids” ”HydrogenMethanolSyncrudeOle
20、finsChemicalsDimethhyether(DME)FuelsNaphtaDieselJet FuelLubricantsAmmoniaRefineryproducts“Gas “Gas toto hydrogenhydrogen” ”“Gas “Gas toto chemicalschemicals” ”CO+2H2(Synthesis gas)MethaneMethaneCHCH4 4Existing routes via syngasProspective direct routes being researchedThe discover of new catalytic s
21、ystems opens important perspective in the synthesis of new fuels.A secure energy future depends on wether chemists will discover efficient catalysts for the production of alternative fuels .Photosyntesis has immense appeal for the closed cycle capture of energy from the sun.The prospect of non biolo
22、gical photosyntesis , that is through bio-inspired chemical reactions , deserves new research.Photosynthesis Two massive protein complexes split water and carbon dioxide and forge new energy-storing bonds in sugar molecules. How to design photosyntetic systems with artificial reaction centers? Biomi
23、nspired approach (BP)-Chemical Antenna for harvesting solar energy-Chemical Structure able to transfer the excited electron at fast speed.(0,1-1 ns)ETphotosyntesisBPinterfacesGas-solid (PV)Liquid-solid Relevance of electron transfer processes ETInterdisciplinary approach including physics,chemistry
24、,biology and engineering, aimed to design and build simplified biological catalytic systems with high efficiency. In nature the metabolic pathways are connected in complicated networks that have evolved for organisms survival and reproduction and not for fuel production. The relevant steps might be
25、isolated and connected directly to produce fuels such as hydrogen, methane and alcohols.Post petroleum economy.Syntetic BiologyCraig Venter : Science on line, july 2007The genome of one bacterium has been succesfully replaced with that of a different bacterium.Then synthetic biology seems to make po
26、ssible new cell functions by fusing existing genomes.Fall out on energy problems:To develop an anaerobic species that will digest cellulose into ethanol , thus generating a fuel from biomass.From the analysis of the carbon free options it comes out that:-Fossil fuels are penalized by carbon dioxide
27、sequestration-Nuclear fission requires high investiments and nevertheless it does not yet represent an alternative to fossil fuels, unless new technological breakthrogh will emerge -Eolic, geothermic and biomass energies can only give an integrating support to the wide incoming energy requirements-S
28、olar energy is promising but it requires a deep transformation of the energy system Though it be honest, it is never good to bring bad news. (Shakespeare) Stabilization triangle divided in sectors each of one corresponding to an advisable reduction of the emitted carbon. Big importance is attributed
29、 to the improvement of efficiency! ConclusionsExternal limitations on carbon dioxide emissions imply the adoption of precautions that will be introduced through the adoption at local level of a mix of different carbon free technologies in a mutual integrated system ( energy saving, increase in the employment of natural gas instead of carbon, increase of renewable sources, nuclear, .) THE ENDTHE END THANK YOUTHANK YOU
