1Today we will discuss and analyze the article on “A Grand Solar Plan”from Scientific American 2008.• Homework #6 posted and due next Wednesday• Reading Chapters 4 and 5 from E&E• Make sure to identify your sources for your research projectA Grand Solar Plan“[Many] have proposed various steps that could slightly reduce fossil-fuel use and emissions. These steps are not enough.”A) Strongly AgreeB) Somewhat AgreeC) NeutralD) Somewhat DisagreeE) Strongly Disagree“Solar energy’s potential is off the chart.”Sunlight striking the earth in 40 minutes is equivalent to the global energy consumption in one year.Does that seem right?We found sunlight was ~ 5000 times more than we use.So what is 40 minutes out of one year?40 / (365 x 24 x 60) = 1 / 13,000What might be the factor of ~ 2 difference? Perhaps they are counting “striking the earth” as hitting the upper atmosphere.“We present a grand plan that could provide 69% of the U.S.’s electricity and 35% of its total energy with solar power by 2050.”What fraction of the U.S.’s total energy is electricity?We currently use ~ 100 QBtu total. Solar would provide 35 QBtu total.So 25 QBtu for electricity and 10 QBtu for other (?)“The plan would effectively eliminate all imported oil….”Oil accounts for roughly 40 QBtu of U.S. usage. How much oil do we import today?A) 10%B) 30%C) 60%D) 90%Thus, that means 0.6 x 40 QBtu = 24 QBtu provided from solar (but not for electricity!). Seems like a problem. Maybe they meant by 2100 when 90% of U.S. energy would be from solar?2“Photovoltaic Farms”30,000 square miles of PV arrays at 14% efficiencyHow much average power provided if 300 Watt/m2?1 mile ~ 5280 feet ~ 1600 metersNote that Arizona is 114,000 square miles total.30,000 square miles x (1600*1600 m2/ mile2) = 8 x 1010m2300 W/m2x 0.14 x (8 x 1010m2) = 3 x 1012Watts Exactly what they claim Æ 3000 GigaWatts or 3 TeraWattsHow much energy is that in one year?A) 1 QBtuB) 10 QBtuC) 35 QBtuD) 80 QBtuE) 1000 QBtu3000 GigaWatts x (3 x 107seconds) = 9 x 1019Joules1055 Joules/BtuÆ 8 x 1016Btu = 80 QBtuThis is almost 3 x what they claimed to provide by 2050?Why might that be?3000 GigaWattsBut, lots of electricity in the day (but not at night).More capacity in the summer, but not the winter.Storage Ideas:“Pressurized Caverns”“Hot Salt”Is the hot salt for night/day or summer/winter?“A 50-MW plant with seven hours of molten salt storage – is being constructed in Spain… For our plan 16 hours of storage would be needed.”Perhaps the factor of 3 from before is to account for winter?“ … and the Electric Power Research Institute shows that suitable geologic formations exist in 75% of the country.”What is the EPRI?“Direct Current, Too”Needs to have major infrastructure to transport the electricity from the Southwest around the entire country. This is highly non-trivial.Timeline and Costs:Present Æ 2020:$420 billion in cumulative subsidy (for 2020 or 2050?)84 GigaWatts of plants, partial transmission backbone.2020 Æ 2050Key part of oil offset must be the 344 million plug-in hybrid vehicles. That means by 2050, a completely new fleet of all U.S. cars…What did you understand the $420 billion is for?3Area of solar panels: 8 x 1010m2Dollar amount mentioned: 420 x 109dollars19 cents per square meter of PVThis is not the cost Æ no where close.The cost must come from private industry, investments, etc.The federal government is only providing a small subsidy.It would help if they included the total costs and pay-back times.Some idea?They aim for $1 / Watt capacity. Thus, the PV alone is 3000 GigaWatts Æ 3 Trillion Dollars capital investment.“In 2050 U.S. carbon dioxide emissions would be 62% below 2005 levels, putting a major brake on global warming.”What do you think?What do you think about the overall
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