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Challenges in the incoming energy scenario: role of chemical sciences SERGIO CARRA’
Mean global energy consumptions Total 13.8 TW, US 3.3 TW, Italy 0.25 TW The less expensive fossil sources represent the lion’s share!
Can we supply the energy needed in the future with fossil fuel? Quite probable yes. Than it appears that renewable resources will not play a large role in primary power generation 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 energy.
Current global energy consumption = 13.8 TW • By 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 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).
Carbon dioxide sequestration The employment of geological reservoirs is potentially feasible but it arises problems for maintaining 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.
Renewable The total rate (TW) is 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.
Solar energy appears to be the only source able to supply 10-20 TW carbon-free power needed at 2050. CO H O 2 2 2 e Sugar sc M H O 2 H O 2 O 2 Fuel Light Electricity Fuels Electricity e sc M Semiconductor/Liquid Junctions Photosynthesis Photovoltaics conversion strategies
What is the area needed to generate the required power? • The full energy consumed in the world can 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 expensive Typical levelized cost by source Solar’s typical range of 25-50 cents/kWh is much higher than other sources
It competes with grid price not generator cost Average residential grid price (US cents/kWh) Much easier to compete with grid price than generation cost.
Market share by technology 10 Silicon technology dominates the market: 93% for crystalline Si (single-, multi-, poly-, nano-) Market share for Si and thin film technologies were continuously decreasing during last 10 years Prices and predictions of photovoltaic market
Module efficiency Lab scale Max efficiency HIT heterojunction intrinsic thin film Many different technologies on the market rushing for high efficiency & low costs
Shockley-Queisser analysis (1961) It is based on four assumptions: 1- single p-n junction 2- one electron-hole pair excited for incoming photon 3- thermal relaxation of the electron-hole pair energy in excess of the bandgap 4- illumination with unconcentrated sunlight Maximum yield of 31% is obtained.
C S-Q limit can be exceeded by violating one or more of its premises. A- Intermediate-band solar cells B- Quantum-well solar cellsl C-Multiple junctions cells
Employment of organic materials XSC : Exciton Solar Cells LUMO=Lowest Unoccupied Molecular Orbital HOMO=Highest Occupied Molecular Orbital Unsaturated Molecoles and fullerenes for : - harvesting solar radiations -to give rise to a fast charge transfer -to limit the return to the ground state
Plastic Cells: Scale-up using Roll-to-Roll Techniques 16 Printed or coated inexpensively on flexible materials using roll-to-roll manufacturing Can be produced with varying degrees of translucency so that it is customized for specific markets Environmentally friendly Easily scaled up Utilizes wide spectrum of light
Solar electricity cost as a function of module efficiency . I- Wafers of silicon. II- Thin films of amorphous silicon , tellurides, selenides III- Research goals: carrier multiplication, multiple junctions, sun light concentration, new materials (organic).
Photoelectrochemistry SC semiconductor (photocatode) M metal (anode) Water photodissociation occurs if hν>2.97 eV (Photo)chemical Water Splitting: 2 H2O → O2 + 2H+ + 2e- +H2 Silicon SiEg= 1,1 eV Gallium Arsenide AgAsEg = 1,5 eV Titanium Dioxide TiO2Eg = 3,2 eV TiO2 fulfils the requirement but it absorbs only the ultraviolet radiation, that is only 3% of the available solar energy.
Operation principles of a dye-sensitized mesoporous heterojunction solar cell. (Gratzel) Gray dots : 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 burning 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 production, such as. • .Activation of methane to methanol • CH4 + (1/2)O2 → CH3OH • .Photoreduction of CO2 to methanol • CO2 + 6H+ +6e- → CH3OH • .Improvement of the slow catodic processes reactions • .Fuel cells operating with metanol • CH3OH + H2O → CO2 + 6H+ + 6e-
Methane CH4 Existing routes via syngas Prospective direct routes being researched CO+2H2 (Synthesis gas) Methanol Hydrogen Syncrude Fuels Chemicals Lubricants Olefins Refinery products Ammonia Jet Fuel Dimethhyether (DME) Diesel Naphta “Gas to chemicals” “Gas to hydrogen” “Gas to liquids” The discover of new catalytic systems 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 .
Photosynthesis Two massive protein complexes split water and carbon dioxide and forge new energy-storing bonds in sugar molecules. Photosyntesis has immense appeal for the closed cycle capture of energy from the sun. The prospect of non biological photosyntesis , that is through bio-inspired chemical reactions , deserves new research.
How to design photosyntetic systems with artificial reaction centers? Biominspired approach (BP) • Chemical Antenna for harvesting solar energy • Chemical Structure able to transfer the excited electron at fast speed.(0,1-1 ns) photosyntesis BP ET Gas-solid (PV) interfaces Liquid-solid Relevance of electron transfer processes ET
Syntetic Biology Interdisciplinary approach including physics,chemistry ,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 isolated and connected directly to produce fuels such as hydrogen, methane and alcohols. Post petroleum economy.
Craig Venter : Science on line, july 2007 The genome of one bacterium has been succesfully replaced with that of a different bacterium. Then synthetic biology seems to make possible 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.
Though it be honest, it is never good to bring bad news. (Shakespeare) • From the analysis of the carbon free options it comes out that: • Fossil fuels are penalized by carbon dioxide 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 • Solar energy is promising but it requires a deep transformation of the energy system
Stabilization triangle divided in sectors each of one corresponding to an advisable reduction of the emitted carbon. Big importance is attributed to the improvement of efficiency!
Conclusions External 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, …..)
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