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/spring17/home.html Lecture #22 April 20, 2017
Announcements Read Chapter 8 of the class notes. - I am assuming you have already read chapters 1-7. Read Chapter 12 of Richter s book. Midterm average: 93.6/112=83.6% Homework 2 will be posted today. Final: Friday, May 5th, 2pm - 5pm
Transportation: the most immediate energy problem
Weaning off of petroleum The low energy density of batteries may limit the degree to which electricity can replace petroleum. Better fuel efficiency in general, and hybrids in particular, can reduce demand for gasoline. Plug-in hybrids can shift the burden to the electric grid without issues such as range. Biofuel production can increase, at least somewhat.
Hybrid Technology Hybrids (non plug-in) derive ALL their energy from liquid fuel. Hybrids use either an engine, battery-powered electric motors, or both. Unused power from the engine charges the batteries. Engine is coupled to the power train under conditions where more power is needed, or when the engine has high efficiency. Much of the time, the engine is OFF When braking, the electric motors run backwards and generate power that is stored in the battery. Remember the bicycle demo? Fuel efficiency can be in excess of 50 miles/gallon.
Plug-in hybrids The vehicle can run solely on electricity stored in batteries under essentially all conditions. When the batteries run dry, the car fires up a liquid-fuel powered engine. The engine either runs a generator (Chevy Volt) or couples to the power train as would be the case in any hybrid (Plugin Prius), or both. Range is NOT limited by battery size because of back-up power from gasoline-powered engine.
Consider a specific example Chevy Volt Battery stores 16 kw-hrs and has mass of 175 kg. Provides around 40 miles of fully-electric range. upside-down T-shaped battery pack
Examples of all-electric cars From US News and World Report on 2017 models Make Range Starting Price Tesla Model S up to 335 miles $68K+ Chevy Bolt EV 238 miles $36,620 BMW i3 114 miles $42,400 Nissan Leaf 107 miles $30,680
The impact of plug-in hybrids From a study, undertaken by the American Physical Society (APS), on the potential impacts of greater energy efficiency.
Incremental Progress Reduce the need for liquid fuels - - - Corn-based ethanol - Cellulosic ethanol - Biodiesel with improved production (algae?) Improve mileage standards (overall efficiency and hybrids) Shift toward the grid using all-electric and plug-in hybrids. Increase the production of biofuels Make up the difference with petroleum based fuel. - Consumption of oil for transportation has been relatively flat despite growth in both GDP and population
How far could today s technology take us in weaning us off of petroleum? In 2015, around 143 billion gallons of gasoline were consumed, with an average fuel efficiency of about 25 mpg. With better fuel efficiency, perhaps with more widespread use of hybrids, it is reasonable to aim for 35 mpg, which would bring consumption down to roughly 102 billion gallons. With plug-in hybrids and all-electrics, this could be brought down to roughly 41 billion gallons (or maybe even less?). The U.S. produced around 15 billion gallons of ethanol in 2015. Imagine this increasing to 20 billion. This would reduce gasoline consumption to around 20 billion gallons, around 14% of what was used in 2015.
Energy Elsewhere
Energy Elsewhere Can space help us with energy on Earth? What are some of the energy issues related to colonizing space? How can we use the available energy in our solar system? How do we get started? What are some of the big issues?
Think Big There is a lot of energy that one could in principle use within the solar system This number is just what hits the earth alone!
Suggestion from Peter Glaser Put huge solar-power collectors in space where they will be illuminated (nearly) 24/7. Beam the power to Earth using microwaves. Earth-based receiving antenna feeds power into the grid Use (at least) two stations so that one is always outside of the Earth s shadow.
O Neill further developed the idea Manufacture the solar power stations in space. This saves the energy of lifting everything off the surface of the Earth. O Neill further suggested that space habitats were, for many reasons, a natural next step for humanity. Among the advantages: nearly free energy and helps alleviate booming population. Clearly saw the habitats as the beginning of humanity spreading beyond the confines of Earth.
O Neill envisioned solar-power generation plants in space Idea first introduced by Peter Glaser around 1968 Electricity is generated in orbit. Electricity is beamed down to Earth using microwaves. Power station is manufactured in space to save energy
Gerard O Neill invented the modern collider used in particle physics Fermilab, near Chicago, the Large Hadron Collider, or LHC at CERN are both examples
From NYT in 2009
If we manufacture things in space, the people doing it will need someplace to live
More recent plans to build space-based solar power stations Note date of 24 April 2014. IEEE is a main-stream organization for electrical engineers. Just because they have plans does not mean they will follow through. Even so, it shows the ideas are alive and well.
But what does the future hold. really? O Neill s vision may well be right. Eventually, I believe he will be seen as a true visionary. In the short to medium term, however, there are probably cheaper ways to get stuff up into orbit, and cheaper ways to produce electricity. Elon Musk, founder of SpaceX, believes the immediate answer to getting things into space more cheaply is reusable rockets. Musk, not a fan of space-based power stations, is focused simply on opening up space travel. In particular, he wants to colonize Mars - no joke!
Elon Musk on reusable rockets Uploaded on January 12, 2012
Test of the Grasshopper on 7 October 2013 Single-engine test rocket rose to 744 meters before making a soft landing. I showed this to my class in 2013, describing it as a turning point in the history of space travel.