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Solar FAQs and Global Renewable Energy

This document compiles a comprehensive set of analyses and references to address frequently asked questions about solar energy and its potential to meet our future energy needs sustainably. It discusses the assumptions, theoretical potentials, and estimation of extractable and technical potentials of various renewable energy sources, including solar, wind, waves, and geothermal. With the increasing need for carbon-neutral power, this document emphasizes the importance of transitioning to renewable energy sources to mitigate the risks associated with greenhouse gas emissions.

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Solar FAQs and Global Renewable Energy

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  1. Solar FAQs and Global Renewable Energy Premise: The Sun is a singular C-neutral solution to our future energy needs, one whose capacity dwarfs fossil, nuclear, wind, … Purpose of Solar FAQs document: Compile self-consistent set of supporting analyses and references

  2. Overarching Assumptions • By 2050 we’ll need 15 TW, by 2100 30 TW, of new power • Ė = N · (GDP/N) · (Ė/GDP) • Even if N saturates and Ė/GDP continues to decrease, GDP/N will increase • All or most of this new power should be C-neutral • 1-2 GtC/yr emissions (1940’s level) implies 550 ppmv atmospheric C and ΔT~2°C, and is already considered risky • 6-7 GtC/yr emissions (2000’s level) is (perhaps nonlinearly) riskier • All of most of this new C-neutral power must be chemical • 80% of energy consumed at point-of-use is chemical

  3. Estimating Theoretical Potentials 1-3 ms/century lengthening of the day ~ 0 TW human harvesting Pfill (constant) pharvest (variable) 2.4 TW tidal friction E/tdiss (variable) Steady State: Pfill = E/tdiss + pharvest No harvesting: Pfill = E/tdiss Max harvesting: Pfill = pharvest

  4. Heat (TWt) Thermodynamic limit (1-Tl/Th) Mechanical (TWm) Theoretical ~1/2 of Betz (16/27=59%) limit (33%) Electrical (TWe) 2010 EERE H2O electrolysis efficiency target (75%) Chemical (TWc) Extractable Fraction allowed by known technology Chemical (TWc) Technical Estimating Extractable & Technical Potentials

  5. Table of Results

  6. Artic Circle Tropic of Cancer Tropic of Capricorn Antarctic Circle Solar 15 TWe = 0.17% of the earth’s surface (~ Venezuela) at 10% efficiency Photons 89,000 TWp Theoretical 100% Heat Thermodynamic limit for concentrated sunlight (87%) 170,000 TWp Thermodynamic limit for concentrated sunlight (87%) Thermodynamic limit for un-concentrated sunlight (68%) Mechanical 33% Electrical Electrical 75% 75% Average solar energy density W/m2 40% Torrid 225 52% Temperate 150 8% Frigid 75 Average 175 Chemical 58,000 TWc Chemical 61,000 TWc Chemical 19,000 TWc Extractable Land only (29%) and Temperate+Torrid only (97%) Current best PV efficiency (40%/87%) Current photo-electrolysis efficiency (10%/68%) [Note: switchgrass efficiency is 0.38%] Current best steam engine efficiency (30%/28.7%) Nelson 2003 Fig 2.3 Chemical 7,500 TWc Chemical 2,500 TWc Chemical 5,600 TWc Technical Chemical 0.15 GWc Chemical 190 GWc Chemical 0.6 GWc 2001 Actual IEA PVPS 2004 (1/5 of peak capacity) WEA 2004 (sustainable only) WEA 2004 (active only)

  7. Wind National Renewable Energy Laboratory http://rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html ≥ Class 3 (~400 W/m2) @ 50m Photons 110,000 TWp 100% Heat Thermodynamics 1-Tl/Th (~0.84%) Mechanical 1,000 TWm Theoretical 33% Average wind energy density: 2 W/m2 Electrical Wallace 1977 75% Chemical 250 TWc Extractable Land only (29%) > Class 3 only (~20-27% x 2) Lateral replenishment from over oceans? Vertical replenishment from jet stream? Chemical 14 TWc Energy dissipation time ~ 8-9 days Cell circulation time ~ 2-5 days Technical WEA 2000 Wallace 1977 Chemical 5 GWc 2001 Actual Hodell and Thomas (U Florida atmospheric circulation website) http://ess.geology.ufl.edu/ess/Notes/AtmosphericCirculation/atmosphere.html WEA 2004

  8. Artic Circle Tropic of Cancer Tropic of Capricorn Antarctic Circle Ocean Waves 6 kW/m 20 knots 50 km 1 m 6 s Mechanical 34 TWm Theoretical Wick 1977 http://www.seafriends.org.nz/oceano/waves.htm 33% Electrical TWe 75% Average wave energy density in ice-free oceans: 0.114 Wm/m2 Chemical 8.5 TWc Extractable Wick 1977 Near-shore only (7%) Chemical 0.62 TWc Technical Isaacs 1976 Chemical ~0 GWc 2001 Actual WEA 2004

  9. Geothermal ~2/3 Radiogenic ~1/3 Conduction through or cooling of lithosphere http://www.mantleplumes.org/Energetics.html Heat 44 TWt Mantle 1000-4000°C Theoretical Thermodynamic limit for ΔT~75°C (1-Tl/Th ~ 25%) Outer core Mechanical TWm Inner core 33% IGA 2004 Electrical TWe 80 km thick lithosphere 75% Chemical 2.8 TWc Average geothermal power density W/m2 39% Land + Continental Shelves 0.065 61% Ocean 0.101 Average 0.087 Extractable Land only (29% x 0.065/0.087) High-temperature (>150°C) only (?%) Thermodynamic limit for ΔT~150°C (50%/25%) Lowrie 1997 Chemical 1.9 TWc Technical IGA 2004 Chemical 5 GWc 2001 Actual WEA 2004 (includes heat with conversion)

  10. 106 103 1 10-3 10-6 Sources with > 15 TW extractable and technical potential Solar Electricity Solar Thermal Solar Fuel Wind Geothermal Hydropower Technical Potential (TWc) Ocean Wave Ocean Salinity Gradient Ocean Surface Currents Ocean Tidal Ocean Thermal Gradient 2001 Supply 10-6 10-3 1 103 106 Extractable Potential (TWc) Summary Theoretical Potentials > 15 TWc: Solar, Wind, Waves, Geothermal Extractable Potentials > 15 TWc: Solar, Wind, maybe Waves Technical Potentials > 15 TW: Solar, maybe Wind 2001 Actual > 15 TW: None even close

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