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Science Vale UK energy event renewable energy technology - solar

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The Energy of Science Vale UK - 26 May 2011. Solar Renewable Energy Technology presentation by Nicholas Harrison (Imperial College, London). More details at www.sciencevale.com …

The Energy of Science Vale UK - 26 May 2011. Solar Renewable Energy Technology presentation by Nicholas Harrison (Imperial College, London). More details at www.sciencevale.com

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  • 1. Renewable Energy (Solar) Nicholas M Harrison Imperial College London Daresbury LaboratoryThe Rutherford Appleton Laboratory
  • 2. Scale of the Problem: Supply
  • 3. Renewables and Climate ChangeCOP-15 is widely considered a failure, as it did not result in binding CO2 - reduction targets.Nevertheless, COP-15 lead to global acceptance of the 2oC target as maximum permissible warming; more will definitely result in climate- disaster.This means, the world cannot emit more than 750 Gt of CO2 during this century; it currently emits about 35 Gt of CO2 per year (9.5 Gt C/a) !
  • 4. Renewable Capacity Solar BiomassOcean Hydroelectric Wind Geothermal
  • 5. Renewable Capacity Hydroelectric Gross: 4.6 TW Technically Feasible: 1.6 TW Economic: 0.9 TW Installed Capacity: 0.6 TW
  • 6. Mean flux at surface: 0.057 W/m2Geothermal Continental Total Potential: 11.6 TW
  • 7. Biomass 50% of all cultivatable land: 7-10 TW (gross) 1-2 TW (net)
  • 8. potential 120,000 TW;Solar practical > 600 TW ?
  • 9. Solar Land Area Requirements6 Boxes at 3.3 TW Each (graphic courtesy of Nate Lewis)
  • 10. Electricity Production Costs
  • 11. CO2 - free sources of energyNuclear energy - non-renewable feedstock, final storage ?, risks ?Clean coal technologies - requires carbon sequestration, unproven technology and energy inefficientWind - fluctuating production, limited number of suitable sites – offshore ?Hydro - can be switched on instantaneously, suitable for storage, good sites limited, production should be maximizedBiofuels – interesting liquid fuel for transport, production energy intensiveGeothermal - excellent where easily accessibleSolar energy (Photovoltaics, Solarthermal) - unlimited energy source PV: continuous price reduction through savings of scale
  • 12. Price learn-curve of crystalline Si PV- modules Slide courtesy of G Willeke
  • 14. Research LandscapeLarge international investment in researchand developmentStrong focus on optimisation of existingsystems=> The opportunity is for step change incost and / or efficiency
  • 15. STFCCurrent collaborative international projects: – High efficiency photovoltaics (inorganic) – Fundamentals of solar hydrogen production – Dye sensitised nano-oxides – Rectenna arrays
  • 16. Energy Conversion Fuel Light Electricity Fuels Electricity CO SC 2 eSugar O2 H SC SC 2 HO 2 O 2 H2O Photosynthesis Semiconductor/Liquid Photovoltaics Junctions
  • 17. Status Performance of photovoltaic and photochemical solar cells Efficiency (%)* Type of cell Research and technology needs Cell Module Higher production yields, lowering of cost Crystalline silicon 24 10-15 and energy content Multicrystalline silicon 18 9-12 Lower manufacturing cost and complexity Lower production costs, increase production Amorphous silicon 13 7 volume and stability Replace indium (too expensive and limited CuInSe2 19 12 supply), replace CdS window layer, scale up production Dye-sensitized Improve efficiency and high-temperature 10-11 7 nanostructure materials stability, scale up productionBipolar AlGaAs/Si photochemical cells 19-20 - Reduce material cost, scale up Organic solar cells 2-3 - Improve stability and efficiency M. Grätzel, Nature 415, 338 (2001)
  • 18. Ultimate Efficiency LimitsThermodynamic limit of Carnot engine: η = 1 – T0/Ts ~ 95% (100% absorption)Shockley-Queisser efficiency limit for single band semiconductor based on detail balance eq.: ~31% (1 sun: Planck low) and ~41 (max conc.)Origin of the solar cell losses:a) Light with energy below Eg will not be absorbedb) The photons with excess energy above Eg is lost in the form of heathc) Single crystal GaAs solar cell ~ 25%(AM1.5)
  • 19. Tandem solar cellsMultijunction or tandem cells:• First approach to exceed single junction efficiency• To achieve >50% efficiency need 3 or more tandems with different Eg’s No of junctions 1 sun Max conc.• Significant technological 1 30.8% 40.8% problem to relax strain 2 42.9% 55.7%• 75% efficiency achieved with 36 3 49.3% 63.8%  tandems 68.2% 86.8%
  • 20. High-efficiency ISE triple-junction solar cellsGa0.65In0.35Ptunnel diodeGa0.83In0.17Astunnel diodeGe substrate
  • 21. Intermediate band solar cellsMulti-junction solar cell Multi-band solar cell• Each junction  single gap Single junction (no lattice mismatch)• N- junctions  N- absorptions N- bands  N(N-1)/2 (gaps) Add 1 band  Add N- absorptions
  • 22. Intermediate band solar cellsIntermediate band vs multi-junction solar cell• Max. efficiency for 3 band cell ~66% (vs 55%)• Max. efficiency for 4 band cell ~72% (vs 60%)• Better performance than any other structure of similar complexity A. Luque & A. Marti, Phys. Rev. Lett 78, 5014 (1997)
  • 23. Requirements & Possible RealizationDesigning a materials system: Finite width IB to allow excitations VB-IB, IB-CB Narrow IB to reduce carrier transportPredictive simulations yield QD arraysas an excellent candidateQD arrays produce an IB with zero density of states between VB& IB & CB, which increases the radiative lifetime relative to therelaxation time within bands.
  • 24. Current technologyVertical ordering is provided by strain driven alignmentHorizontal regularity of QD’s is observed on high Miller index surfaces Q. Xie, et al., Phys. Rev. Lett. 75, 2542 (1995) S. Tomic, NMH et al., J. Appl. Phys. 99, 093522 (2006) Y. Okada, private communication
  • 25. Solar Hydrogen Detailed understanding of: – Excitation – Transport – Surface dynamics – Reduction reactionEPSRC EP/G060940/1 Nanostructured Functional Materials for Energy Efficient Refrigeration, Energy Harvestingand Production of Hydrogen from Water. Programme grant Oct 2009.
  • 26. Rectenna ArraysAn array of nanostructured antennas forsupported on metal-insulator-insulator-metaldiodes
  • 27. ConclusionsSolar energy will be a significant component of theenergy mix by 2050Significant scientific / technological breakthroughsrequired to ease the transitionVery large international research and developmenteffort – the current opportunity is in step change