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 lions share! 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. Can we supply the energy needed in the future with fossil fuel? Quite probable yes. 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). 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. Carbon dioxide sequestration 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. Light Fuel Electricity Photosynthesis Fuels Electricity Photovoltaics H O OH 2 22 sc M e sc e M CO Sugar H O O 2 2 2 Semiconductor/Liquid Junctions conversion strategies Solar 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 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 Solars 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. 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 Market share by technology 10 Prices and predictions of photovoltaic market Module efficiencyLab 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. 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 C Employment of organic materials LUMO=Lowest Unoccupied Molecular Orbital HOMO=Highest Occupied Molecular Orbital XSC : Exciton 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 state Plastic Cells: Scale-up using Roll-to-Roll Techniques 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 16 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). Silicon Si Eg = 1,1 eV Gallium Arsenide AgAs Eg = 1,5 eV Titanium Dioxide TiO2 Eg = 3,2 eV TiO2 fulfils the requirement but it absorbs only the ultraviolet radiation, that is only 3% of the available solar energy. SC semiconductor (photocatode) M metal (anode) Wat