Energy on this world and elsewhere Instructor: Gordon D. Cates Office: Physics 106a, Phone: (434) 924-4792 email: cates@virginia.edu Course web site available at www.phys.virginia.edu, click on classes and find Physics 1110. or at http://people.virginia.edu/~gdc4k/phys111/fall13 November 12, 2013
Announcements Quiz grades are on collab. - Office hours Wednesday, 6-8 pm. Midterm November 21. Homework will be posted tomorrow Homework will be due on November 14. You are allowed a 1-page cheat sheet, 8.5x11 or equivalent. ONE SIDE ONLY, and it must be HAND WRITTEN.
Solar Energy
The price of solar cells The price of the modules themselves, not counting the other stuff that would be needed, is around $2/Watt, roughly the same as the the price of similar peak capacity using wind.
Shipments of solar cells 2009 saw domestic shipment of around 1.3 GW, which can be contrasted to around 10 GW for wind. Still, it is really beginning to grow.
The concept of intensity In the context of sunlight: Intensity of sunlight = Incident power of sunlight area over which it falls
Intensity of sunlight hitting the earth Above the atmosphere: about 1.4 kw/m2 - This is for a surface FACING the sun. On the Earth s surface: about 1.0 kw/m2 Averaged over day and night, all the seasons, for the 48 contiguous states in the U.S.: around 200 W/m 2
Area needed to generate electricity using solar power Power = efficiency x Intensity x Area Area = Power efficiency x Intensity
Area needed to generate electricity using solar power 83.4 mi. x 83.4 mi., area needed to produce (on average) all electricity currently used (assuming 200 W/m 2 ).
Area needed to generate electricity using solar power 83.4 mi. x 83.4 mi., area needed to produce (on average) all electricity currently used (assuming 200 W/m 2 ). 118 mi. x 118 mi. (twice the above mentioned land area).
Area needed to generate electricity using solar power 441 million acres devoted to cropland (for comparison). 83.4 mi. x 83.4 mi., area needed to produce (on average) all electricity currently used (assuming 200 W/m 2 ). 118 mi. x 118 mi. (twice the above mentioned land area).
Solar thermal generation of electricity
Types of Solar Thermal Parabolic Trough - Most existing facilities, and currently approved facilities in California are of this variety. Solar-tracking dish-based collectors with Sterling Engines This is the SES design, and their are currently 1 or 2 proposed large-scale facilities in California. Power-tower design. - Several have been built, but in the tens of Megawatt range.
The Solar Power Tower Design Multiple mirrors called heliostats track the sun and reflect light onto a central collector. Temperatures are so high that molten salt is used as the liquid that get heated. The molten salt, in turn, is used to produce steam that drives turbines to make electricity. The molten salt stores heat so well that the plant can produce electricity for several days without sunlight.
Solar Two - 10 MW demonstration project
Solar Two - 10 MW demonstration project This system is no longer in operation for the production of electricity.
20 Megawatt System near Seville Spain
Solar Two - 10 MW demonstration project
Solar Thermal The Ivanpah Solar Plant: 377 MW facility nearing completion in the Mojave desert in California.
Solar-thermal technology: one example
Solar-thermal technology: one example
Solar-thermal technology: one example
Solar thermal, power production using a heat engine where sunlight provides the heat Long (very long) mirrors forming a trough with a parabolic shape focus sunlight onto pipes, typically containing oil. Temperatures of around 400 degrees C are achievable. The efficiency with which sunlight is converted to electricity is around 25%, extremely good compared to economical photovoltaics.
A solar thermal plant was constructed by the Luz corporation in California. Shown are examples of the collectors in the Luz Corporations facility. Luz eventually went bankrupt. Investors who subsequently bought the facility, however, are able to sell electricity at a very competitive price.
Part of the 350 Megawatt Solar Electric Generating System or SEGS facility in California originally built by Luz
Nuclear Power
Nuclear Reactor driven power generating facility Just as illustrated in the previous slide, a source of heat (the nuclear reactor) is used to create steam, which then drives an electrical generator. Efficiency is in the mid 30% range.
Nuclear energy: pros No emission of greenhouse gases. Relatively abundant resources are available Potentially quite economical? (It is at least true that operating existing plants is quite economical.) Some aspects of the technology are quite mature. Advanced (less mature) technology could make the resources truly vast.
Nuclear energy: cons Meltdowns can potentially release large amounts of radioactivity. The storage of waste is not a settled issue. Reactors produce plutonium which can be made into nuclear weapons. Terrorist attacks on nuclear reactors could change the equation of what is and is not safe. Is the release of radioactivity during routine operation a problem?
Existing sources of radioactivity Radon Cosmic rays Medical procedures Coal plants
Existing sources of radioactivity Radon Cosmic rays Medical procedures Coal plants Fallout from above-ground testing