Personal Rapid Transit and Driverless Cars

An ULTra PRT vehicle on a test track. (Wikimedia Commons)

As a teenager in the 1970s I remember reading about Personal Rapid Transit in a number of places including this Popular Science article. Unlike conventional transit like light rail or bus systems, a PRT system uses small, individually switched cars on a specially designed guideway. Upon entering a station, you select your destination on a console. Within a few seconds a 3-6 passenger car arrives and whisks you directly to your destination. At least that was the dream.

Of the dozens of proposals and prototypes, the Morgantown PRT that links WVU campuses is the only one of that era ever to be deployed at scale. The rest were either cancelled entirely or were defeatured into automated people mover systems like you find at many airports.

In 2011 two new systems opened, ULTra PRT at London's Heathrow Airport and the 2getthere system in Masdar UAE. Both are relatively small systems each with fewer than five passenger stations and fewer than 25 vehicles. But the new systems also represent an important departure from previous PRT designs. Both use battery powered vehicles with autonomous control. They run on rubber tires and steer themselves so there's no switching gear on the guideway. They are powered by batteries that automatically recharge when the cars wait at stations. This contrasts with previous PRT designs that used powered guiderails and a central control and switching system.

The primary barrier to PRT systems has been the cost of the tracks or "guideways." It's estimated that it would cost beween $30 million and $40 million a mile to expand the Morgantown system. That's because the guideway has to incorporate precision guide curbs, power transmission, track switches and even a heating system to melt snow and ice to keep it safe in bad weather.

In contrast, the ULTra guideway is estimated to cost between $7 and $15 million per mile. That's because it's a simple concrete pathway with no active systems.

Which brings me to Driverless Cars.

In essence, the ULTra and 2getthere systems are self-driving electric cars in which the environment has been constrained enough to simplify the self-guidance problem. High curbs make it easier for the cars to center themselves in lanes, dedicated roadways minimize pedestrian and obstacle avoidance. Strategically placed charging stations let them be electrically powered using batteries of modest capacity.

Meanwhile, Google's self-driving cars have driven themselves more than 300,000 miles accident-free, on conventional roads, without special infrastructure. Like many, I've wondered why Google is building such cars. They're in the information business, not transportation. A talk by Big Data guru, Ed Lazowska clued me in. Before the Google people let a car drive a route by itself, they first have a human drive the car over the same route. During the trip, its sensors scan the environment, picking out landmarks and obstacles, measuring road conditions and fine-tuning its GPS map of the roadway. Google is interested in supplying data to enable driverless cars and they're doing research to determine what data is needed.

A recent Freakonomics post on the subject suggested that driverless cars will arrive incrementally starting with the already common cruise control, adding adaptive cruise control, collision avoidance and self-parking before fully driverless operation arrives.

But I'm afraid that calling these "driverless cars" is the 21st Century equivalent of calling automobiles "horseless carriages". In each case the focus is on what's missing (the driver or the horse) instead of what new capacity has been introduced. "Horseless carriage" doesn't exactly describe a vehicle capable of sustaining 65 miles per hour with a range of over 300 miles. Nor does it conjure images of the megacities it enables or the endless parking lots it requires.

Consider this possibility: driverless technology enables the PRT dream on existing infrastructure. Instead of dedicated guideways costing tens to hundreds of millions, a PRT system built on driverless technology would rely on GPS and 3G data networks, both of which are already in place. Initial deployments can be restricted to certain neighborhoods that meet high standards of traffic signals, lane markings and crosswalk protection. Even a system restricted to certain lanes and certain streets would offer PRT of greater scale and capacity than anything yet deployed. Yet the investment to get started is regulatory permission, a few vehicles and some signage.

Fancy stations aren't required – only some curb space. Cars would be summoned using smartphones. And it wouldn't just be a peoplemover. Cargo, also, could be sent unattended. Grocery stores could use the same infrastructure for home (or corner) delivery. In the long run, even mail delivery and garbage collection could be automated.

We can learn something from this:

There are some fundamental principles at work here that can be applied to other large-scale problems:

• Infrastructure is usually the most expensive component. Whenever possible, use infrastructure that's already in place and share infrastructure with other projects.
• Push control (or decision making) as close as possible to the application or beneficiary.
• Inform the distributed control with global data.
• Build systems that can be scaled incrementally; where adding capacity is a matter of buying more of the same rather than periodic large investments to get to the next capacity threshold.

Consider the above principles applied to education. (You know I can't resist.) Existing infrastructure includes the internet, inexpensive computers and tablets, content development tools, video standards and so forth. Personalized learning relies on giving more control to the student and teacher to adapt learning to individual needs while being informed by common standards. And web-scale technologies are required if systems are to grow to support millions of students.

The "Wouldn't it be Cool" Department

Walt Disney World has the most heavily used monorail system in the world. They also have a well-maintained private road system connecting their resorts and theme parks. Wouldn't it be cool if Disney deployed a PRT system (based on driverless car technology) to connect their resorts and parks together? Such an attraction would enhance the Disney experience while proving the viability of the concept to the world.

Learning from Data - An Automotive Example

Monday saw me driving 800 miles home from a family Thanksgiving celebration. Due to my wife's change in plans, my only companion for the drive was our small dog (who had a narrow escape the day before). I needed something to keep my attention. So I decided to perform an experiment in data collection. I learned a lot even from a small data sample.

The vehicle I was driving was a 2010 Subaru Forester. Some friends have the same vehicle and have been pleased with getting around 27 MPG on the highway. We typically get only 23-24 MPG on the highway and I had been wondering why.

Among the features of this car is an average gas mileage display that's tied to the trip odometer. So, sampling the gas mileage is as simple as setting the cruise control, resetting the trip odometer, driving a set distance and reading out the result. As I was crossing the relatively flat plains of Idaho (speed limit 75) this seemed to be a good opportunity to gather some data.

Over a period of several hours, I took a bunch of samples following the above method and using my GPS to track altitude changes. I abandoned samples where the altitude change was more than a few hundred feet. The result is 27 good samples. I've posted the raw data here in case you want to play with them. Most of the samples are for 20 mile segments but some are as long as 40 and some are as short as 5 miles.

As you can imagine, the lower-speed samples got a bit tedious. But I was curious enough that I even took a side trip on a remote road (off the freeway) to get samples below 45 MPH. There's considerable variability in those results as you can see in the plot below. Halfway through the trip I refilled with fuel. I switched from regular (87 octane) to premium (92 octane) to see how that might affect mileage.

2010 Subaru Forester Fuel Economy vs. Speed

The results certainly aren't what I expected. EPA city and highway ratings have always led me to expect relatively flat miles per gallon with city being much poorer due to stop-and-go driving. Instead, I got a nearly linear downward slope. Using Excel's curve-fitting feature and found that a polynomial curve worked better than a line. The formula is embedded in the graph above.

More data points would be required to really validate this curve but it certainly fits within the margin of error of my samples. Therefore we can make some cost estimates using this formula. Notable is that peak economy is between 40 and 45 MPH – much slower than I had expected. From this I was able calculate the cost of each hour saved on this long drive.

Here's a table of results for a 800 mile drive in a 2010 Subaru Forester with average fuel cost of $3.759 per gallon. Time saved and additional cost are from a baseline speed of 55 MPH. Note that the distance is cancelled out in the Cost Per Hour Saved so those numbers are accurate regardless of the length of the trip.

Speed	MPG	FuelCost	Time	Hrs Saved	Addl Cost	Cost Per Hr Saved
55	33.1	$90.83	14.55
60	32.1	$93.71	13:33	1.21	$2.89	$2.38
65	30.7	$97.88	12.31	2.24	$7.05	$3.15
70	29.0	$103.65	11.43	3.12	$12.82	$4.11
75	27.0	$111.55	10.67	3.88	$20.72	$5.34
80	24.6	$122.45	10.00	4.55	$31.62	$6.96
84	22.4	$134.31	9.52	5.02	$43.48	$8.66

Here are a few things I've learned from this:

• My friend with the other Forester drives slower on the highway than I do.
• I had not known how sensitive vehicle gas mileage is to speed.
• Everything I have read led me to expect no benefit from higher octane fuel once the vehicle's requirements have been met. In the case of the Forester, higher octane actually reduced fuel economy. This observation is confirmed by the official EPA ratings.
• I would love to see tables like the one above before purchasing my next car.

I learned a lot from this tiny data sample and my future driving habits will be changed accordingly. Now imagine what we could learn if there were a large public database of fuel economy data. Car manufacturers could optimize for specific driving patterns. Consumers would be better informed about fuel economies to expect. There are fleet tracking devices like this one that are already reporting that data but it's locked up in private databases. If anonymous fuel economy data (speed, distance, altitude and MPG) were released there's a lot we could learn about fuel economy under a variety of conditions.

I can't wrap this post up without relating it to education. A relatively small data sample taught me a lot and will impact my future driving behavior. In the same way, it doesn't take a lot of data fed back to students and teachers before they see opportunities to improve. And when we grow from little data to big data, revolutionary changes are on the horizon.

Quote: Peter Sandman on Climate Change Outrage

If you’re talking to a room full of people who hate the idea of the set of remedies you have proposed for climate change and instead of trying to reduce their outrage about the remedies, you’re busy trying to increase their outrage about climate change, you’re fighting the wrong fight.

(Peter Sandman, Quoted on Freakonomics)

We Need an Energy Breakthrough

I haven't yet read The Quest by Daniel Yergin -- only this review. But it's nice to know that someone who has spent a career studying energy issues agrees with my conclusions. We need a breakthrough in energy technology. The environmental burden caused by fossil fuels is too great for us to rely on that source as we try to elevate the standard of living for the world's populations.

Update: The Cost of Solar Energy

Nearly a year ago I wrote a three-part series on energy. At the time, I calculated a cost of $83.33 per gigajoule for solar power. That compares to $1.42 per gigajoule from nuclear power.

Google is investing $168 million in the Ivanpah Solar Farm in the California Desert. As far as I can tell, the total investment will be approximately $2.068 billion. It will be capable of generating 392 gross megawatts of electricity and should last at least 25 years.

In order to convert these numbers to a cost per gigajoule, we have to make some assumptions. I'll use some very generous ones. The solar array cannot generate energy at night and will only generate peak output for part of the day. Not surprisingly, the California desert location chosen for the Ivanpah project happens to be the most favorable in the entire United States. The approach used with solarvoltaics is to multiply peak output by 6 hours per day in that region. Lower numbers are used in other regions. I'll assume that the Ivanpah project is engineered to collect excess solar energy compared to its peak output and so I'm using an 8 hour multiplier instead of 6. Since a net megawatt figure isn't offered, I'll use assume 100% delivery efficiency and use the gross figure. These, of course, are unrealistically favorable assumptions.

It works out to 392 megawatts * 8 hours * 365 days *  3,600 joules/watt-hour = 4,120,704,000 megajoules/year or 4,120,704 gigajoules per year.

Assuming a lifetime of 25 years, construction cost of $2.068 billion and no maintenance costs we get $2.068 billion / (25 years * 4,120,704 gigajoules / year)  = $20.07 per gigajoule. That's an improvement of four times over my previous calculation for solar power. It starts to approach the $13.89 per gigajoule cost of wind power.

It's a huge improvement over solar panels but this still remains the most expensive way in the world to generate electricity. It's an order of magnitude more expensive than conventional energy sources which have the added advantage of delivering power 24 hours a day regardless of the weather.

I'm glad to see this happening but it won't spark a revolution in energy production.

How Much Daylight Do You Save?

Shortcut: Click Here for the Daylight Saving Calculator

Tonight most of us in North America get to sleep an extra hour as we go off of Daylight Saving Time. Before 2007 the shift would already happened. The US Energy Policy Act of 2005 added four weeks to Daylight Saving time. The end of daylight savings was delayed by one week in the fall (possibly to keep it lighter for trick or treaters) and it now starts three weeks earlier in the spring. These changes took effect in 2007.

I've always been skeptical of the value of Daylight Saving Time. Though I'm not great at it, I still subscribe to Benjamin Franklin's admonishment, "Early to bed and early to rise makes a man healthy, wealthy and wise. Having the sun rise and set later reduces the incentive to rise and retire early. Ironically, Franklin is widely credited with inventing daylight savings time. In fact, his writings on the subject were satirical.

Three years ago, when the new daylight rules took effect, I decided to find out how much daylight is really saved. The theory of Daylight Saving is that any daylight before you rise from bed is daylight "lost." Therefore, the amount of daylight you "save" will depend on three things: your latitude, your longitude and the time you wake up in the morning. Here's why:

• Latitude: The higher your latitude -- the further you are from the equator -- the more dramatically the length of the day changes between winter and summer. Above the arctic circle, the sun says up for days or weeks in the summer and sets for the same amount if time in midwinter.
• Longitude: If you are at the Eastern edge of your timezone the sun will rise approximately an hour earlier than on the Western edge.
• Rise Time: If you rise before the sun and retire after it sets then there is no daylight to be saved. Any daylight to be saved is between sunrise and "you rise."

With that in mind, I put on my programmer hat and wrote my Daylight Savings Calculator. This calculator takes the city you live in and your rise time and calculates how much daylight is saved under the old and new US rules. If your city isn't listed, you can choose one nearby or enter your latitude, longitude and timezone. It has a few limitations: If you enter a latitude above the Arctic Circle it does strange things. Also, it follows US rules for daylight saving regardless of your location. So, if you enter a latitude in the Southern hemisphere it will accurately plot the length of the days but the calculations of daylight to be saved will be really wrong.

Click here to try it out!

With my recent move to Seattle it's interesting to see how much more dramatic the lay-length shifts are. Using a rise time of 6:30am, I saved 149 hours of daylight in Provo and save 181 hours of daylight in Seattle.

Despite these savings of daylight, I'm still skeptical about whether the savings result in a net benefit or liability. The Wikipedia article on the subject discusses energy use, economic effects, public safety and health. Overall, there's more controversy than conclusion. 

Energy: The Future is Nuclear

In my first blog post on energy I calculated that worldwide energy production must increase to about 734 exajoules per year in order to raise the standard of living for most people to a reasonable level of comfort. This compares with current energy production of around 474 exajoules per year. It also assumes massive reductions in energy consumption in countries like the United States and Canada.
My second post on energy detailed the cost of energy from existing sources and the prospects of using each to meet the energy needs of the developing. Notably, wind and solar are by far the most expensive sources of energy and their environmental impact isn't as neutral as they've been portrayed.
The least expensive source of energy is nuclear — beating even hydroelectric power. But we need some changes to the nuclear economy based on technology improvements. We can't continue using the predominant form of nuclear fission without a long-term waste storage plan and safer reactor designs.
I'm following four innovative approaches to nuclear energy. Any one of these, if proven viable, promises to offer abundant, cheap and clean energy that can be sustained for millennia.

Fast-Neutron Nuclear Fission Credit: TerraPower	Nearly all nuclear reactors presently used for energy production are thermal reactors which use slow-moving or "thermal" neutrons. The advantages of these reactors are that they can use low-grade nuclear fuel (moderately enriched uranium), they can use water as a coolant and it is difficult to misuse them to create nuclear weapons. Many design variations exist from those of questionable safety like Chernobyl to reliable designs that have operated for many decades. The trouble with thermal reactors is that they require enrichment of uranium ore and they produce nuclear waste that remains dangerously radioactive for thousands of years. In contrast, fast-neutron reactors require more highly-enriched fuel (increasing the risk of weaponization) and more exotic coolants like liquid sodium. However, they have three big advantages. First, the waste from a fast-neutron reactor has a much shorter half-life and requires storage for only a few hundred years. Second, the fast neutrons can be used to enrich uranium to produce more fuel than the reactor consumes. Third, the fast neutrons can be used to reprocess the nasty waste from thermal reactors resulting in a mix of new nuclear fuel and short half-life waste. Many research groups are pursuing variations on the fast-neutron design that capitalize on these advantages while managing the problems of weaponization and exotic coolants. One approach is to have most reactors of the thermal design while a few fast-neutron reactors reprocess and produce fuel for the rest. However, such a nuclear economy requires a lot of transportation and processing of radioactive materials. A traveling wave reactor is a variation on the fast-neutron design that is pre-loaded with a small amount of enriched fuel to get it going and filled the rest of the way with unenriched feedstock. The reaction starts in the enriched section with the fast neutrons enriching the neighboring fuel. The "wave" of the reaction moves from the pre-enriched section through the newly-enriched area until all fuel has been consumed. TerraPower is working on a traveling wave design that could be pre-loaded with enough fuel to last 60 to 100 years. A small amount of enriched fuel (the dangerous stuff) would be loaded with a large quantity of depleted uranium (plentiful and safe to transport) and the whole system buried. When the reactor eventually "burns out" the short half-life waste might be left buried in place while a new reactor takes over.
Polywell Fusion Credit: EMC2 Fusion	Nuclear Fusion has long been the holy grail of energy production. It's the primary reaction fueling our sun and the stars. For fusion you take two hydrogen atoms and fuse them using high temperature and pressure to create helium and a lot of energy. The advantages of fusion over fission is that the fuel is plentiful -- hydrogen extracted from seawater being one option -- and the waste is inert helium. It should be noted, however, that most fusion reactions release radiation so the reactor itself must still be shielded. The trouble is that maintaining a controlled reaction has proven to be very difficult. IEC Fusion is one of several approaches that is gaining attention over the more conventional and extremely expensive tokamak. Inertial Electrostatic Confinement Fusion was invented by Philo T. Farnsworth who also invented television. Farnsworth's idea was to place a grid in a vacuum chamber with a strong negative charge. When hydrogen ions are released into the chamber they are accelerated toward the grid and some percentage of them collide in the center with sufficient energy to fuse into helium. The Fusor, as Farnsworth called his device, has been proven to generate fusion. Building one is relatively simple and inexpensive. Many hobbyists have built their own. However, current designs consume considerably more energy than they produce. The main energy leak is that many of the ions collide with the grid itself consuming some of the charge and contaminating the plasma with the products of the (non-nuclear) grid collision. For a little more than a decade, Dr. Robert Bussard quietly researched ways to overcome problems with the fusor. His device, called the Polywell, makes the grid out of coils. An electrical current in the coils creates a magnetic field that guides the ions around it and prevents collisions. He and his team made several important breakthroughs shortly before their U.S. Navy funding ran out. At that point he gave a famous talk at Google in which he detailed the progress they had made and sought funding to continue the research. Unfortunatly, Dr. Bussard died of natural causes before funding was renewed. Thankfully, Dr. Richard Nebel, has obtained funding and continued the work. So far the results are promising and he expects to have proven whether the concept is viable within two years.
Focus Fusion Credit: Lawrenceville Plasma Physics	The Dense Plasma Focus device creates a toroidal plasma by discharging a high voltage arc in a near-vacuum. The electrical and magnetic fields in the plasma torus cause it to collapse into a very dense-hot formation called a plasmoid. Under the right conditions, the plasmoid is dense and hot enough to create nuclear fusion. The fusion reaction releases heat, x-rays and high-velocity ions. The trick is to capture all three of these products in such a way as to generate electricity. Lawrenceville Plasma Physics claims that they have a reactor design that will effectively capture sufficient energy to be a viable clean source of nuclear energy. Most fusion research focuses on the Deuterium-Tritium reaction (Deuterium and Tritium are both isotopes of Hydrogen). That's because it's the easiest fusion reaction to achieve because it requires the least energy. However, both IEC Fusion and Focus Fusion have potential to work with other reactions because increasing the heat is mostly a matter of raising the voltage. This raises the possibility of using a Hydrogen Boron reaction. The advantage of this is that when Hydrogen and Boron fuse they release three Helium atoms and a bunch of energy but no neutron radiation. Thus, a hydrogen-boron reactor wouldn't require heavy shielding.
Steam Fusion Credit: General Fusion	General Fusion proposes to inject a small amount of deuterium-tritium mixture at the center of a sphere of liquid metal. The outside of the sphere is simultaneously struck by hundreds of rams which create a spherical shock wave. When the wave reaches the center it compresses and heats the D-T mix sufficiently to generate fusion. When I first read about the idea, the researchers proposed to use mercury for the liquid metal and steam to drive the pistons. Hence the moniker, "Steam Fusion." The current General Fusion design uses pneumatic pistons and a hot lead-lithium mix for the metal. They call it MTF Fusion but I think Steam Fusion is more catchy.

If proven viable, any of these approaches might deliver plentiful, clean, safe and inexpensive energy. And that combination could bring about societal changes rivaling the Industrial Revolution. All four appear viable on paper which means that there is a very good chance that one or two can be proven viable. The Nuclear Age has been long in coming but I think it's almost here.
Other posts in this series:
Scotty, We Need More Power!
Increasing Energy Production

Increasing Energy Production

In my last post in this energy series I determined that in order to alleviate world poverty we need to increase worldwide annual energy production from 474 exajoules (total production in 2008) to 734 exajoules (108 gigajoules per person per year). That's a difference of 260 exajoules.
This number is probably low because it assumes a 50% reduction in energy consumption in the U.S and Canada and it is based on today's population. The U.S. may not be able to achieve such efficiencies and worldwide population is certainly going to increase. For the sake of the following calculations I chose a target of producing an additional 350 exajoules.
The U.S. Energy Information Administration offers the following breakdown of worldwide energy production in 2006 (the latest year for which they've published data).

I've converted from BTUs to Joules. The total comes to 495 exajoules which is a little higher than the 474 cited in my previous post but the numbers are close enough to work with.
So, here are the prospects for generating an additional 350 exajoules from various sources:

Petroleum and Natural Gas One gigajoule from oil costs $13.56. One gigajoule from gas costs $4.74.	The Peak Oil theory dates back to 1956. It suggests that there will come a day where the remaining oil reserves are too expensive to extract and worldwide petroleum production will be forced to decline. Current projections are that peak oil will be reached on or before 2020. But the peak oil year has been moved back several times and there is good evidence that it's still a long way off. Regardless of whether oil and gas reserves are nearing exhaustion, there are other problems with petroleum. Foremost is pollution. I'll defer debate about carbon dioxide as a pollutant to other authors. There still remain other pollutants including sulfur oxides, nitrous oxides, carbon monoxide and so forth. Natural gas burns more cleanly than crude oil products but it still generates pollutants. New automotive technology has reduced oil emissions to a fraction of their former levels. But these gains have been achieved in industrialized countries where regulations have encouraged such developments. In the developing world, emissions are much worse though the extent isn't accurately measured. The other problem with petroleum and natural gas is opportunity cost. Presently we have no good alternative energy source for transportation. If we consume petroleum to generate electricity and heat, the cost of transportation will be driven up. Due to the transportation link, petroleum use will be around for a long time. But, it's hard to consider massive increases in oil and gas consumption as a sustainable solution for meeting poverty's energy needs.
Coal One gigajoule from coal costs $3.24.	Among fossil fuels, coal is the low-price leader. For this reason, coal supplies 49% of electricity in the United States, 69% in China and 40% worldwide. In the United States it is estimated that enough coal is recoverable to last 146 years at current growth rates. So, there is enough coal to last for quite a while and it is inexpensive. But as with Oil and Gas, pollution is a problem. For those concerned about carbon dioxide emissions, coal releases about 35% more CO2 than gas or oil for the same amount of energy. More concerning to me are emissions of soot and sulfur dioxides. In the United States, scrubbers, are used to keep emissions relatively clean. However, most Chinese plants lack such scrubbers and China burns more coal than the United States, the European Union and Japan combined.
Hydroelectric One gigajoule from hydropower costs $2.36.	Hydroelectric power is a nearly perfect solution. It's renewable, non-polluting, extremely efficient and it can be stored (in the form of reservoirs) until needed. However, though they don't pollute, dams and reservoirs have considerable environmental impact. In the United States, we've already harnessed just about all the hydropower available. More might be available in the developing world but not enough to deliver the needed 350 exajoules.
Wind One gigajoule from a wind farm costs $13.89.	With new technology, the cost of wind power has dropped by more than 80% in the last two decades. Despite that improvement, it's the second most expensive source of energy on this list. The amount of wind energy that can be generated per acre varies tremendously with the amount and consistency of wind in that area. A representative example is the mega windfarm proposed by T. Boone Pickens which would produce 4,000 megawatts from 200,000 acres. That works out to approximately 630 gigajoules per acre per year (assuming that the 4,000 megawatts is average production). Unfortunately I suspect that 4,000 megawatts is peak production during ideal wind conditions. Giving the benefit of the doubt and assuming 4,000 megawatts is average, this kind of wind energy density can supply the total energy needs of six people per acre. To be clear, I'm using the total energy need per person, not just electricity. It includes lighting, heat, cooling, transportation and the energy required to manufacture and produce all goods used by that individual. While wind will make important contributions to overall energy production, the cost of production and low energy density per acre prevent it from being more than a small contributor to the overall solution.
Solar One gigajoule from solar-voltaic panels costs $83.33.	Direct Insolation is the amount of solar energy delivered per square meter per day. In my city of Provo, Utah it averages 4.64 kWh/m^2*day. That works out to 6.1 gigajoules per square meter per year. The best solar cells ever tested achieve 41.6% efficiency in the laboratory. However, using solar cells of practical cost without tracking or concentration systems, the best efficiency to be expected is about 5%. Assuming these parameters, it would take 354 square meters of solar panels to supply the energy needs of one person. The roof of a typical suburban home is about 150 square meters. This shows that the energy density of solar power starts to approach practicality. Presently, the big barrier is the cost of manufacture. At Today's Prices, a 354 square meter solar array would cost approximately $1.4 Million. This explains why solar power is far and away the most expensive source. Solar-voltaic technology is advancing rapidly. The cost of manufacture is dropping and the efficiency is climbing. There are other solar technologies such as passive solar heating, solar water heating and solar concentrators which may cost less than solar-voltaic systems. There are also problems. Solar power is not consistent which means energy storage or alternative sources are needed for night and cloudy days. Solar power--particularly solar-voltaic panels--is ideally suited to urban rooftops. Not only do panels deliver peak power during peak electrical demand (for air conditioning) but by converting light into electricity they reduce heat uptake on the roof thereby reducing the air conditioning load in the summer. However, for this to be practical, cost of manufacture would have to be reduced to about 5% of current costs. That's a tall order.
Nuclear One gigajoule from nuclear power costs $1.42.	Nuclear power is the least expensive energy source available. The amount of energy that can be produced is tremendous, there is enough fuel to last millennia and the environmental impact is the least of all the energy sources cited. The problem with nuclear power is that while the actual environmental impact is very small the perceived environmental impact is large and, in an accident like Chernobyl, the potential impact is tremendous. Clearly the perception of environmental impact is due to the potential for disaster. This has resulted in a political atmosphere that has severely limited the construction of new power plants since the Three Mile Island incident. Another problem with nuclear power is the prospect of repurposing a power plant or its waste products into nuclear weapons. New technologies for nuclear power are emerging that address the potential for disaster as well as limiting the prospects for repurposing. Those will be the subject of my next post on energy.

Energy prices were obtained from the following sites. Each was converted into dollars per gigajoule As prices fluctuate with the market the numbers you see as you follow the links may not be the same ones I used. Likewise, prices or some sources like coal can vary by as much as 60% depending on region. In each case, I selected prices that seemed to represent the majority of the market.
Energy Content of Fuels
Spot Price of Oil
Spot Price of Natural Gas
Spot Price of Coal
Hydroelectric Energy Cost
Wind Energy Cost
Solar Energy Cost
Nuclear Energy Cost (In Europe)

Other posts in this series:
Scotty, We Need More Power!
Energy: The Future is Nuclear

Scotty, We Need More Power!

Energy production and standard of living are directly connected. My neighbor, Dr. L. Douglas Smoot has a presentation (as yet unpublished) that he's made to various audiences in the last year. His thesis is that in order to raise the standard of living for impoverished nations we have to raise the corresponding energy production. That's because energy is required for the production of food, for manufacture of goods, for the treatment of illness, for the management of indoor temperature and for the transportation of everything.

The graph above, extracted from this excellent Department of Energy study shows the correlation between the Human Development Index (a measure of standard of living) and per-capita energy use. It's arguable that the energy consumption of U.S. citizens could be reduced while still maintaining a comfortable lifestyle. Nevertheless, per-capita energy production of developing countries would have to be increased to somewhere around U.K. levels if poverty and disease are to be reduced to levels seen in industrialized countries

The DOE study indicates the threshold is about 4,000 kWh per person which is somewhere between Spain and South Korea on the the graph. Of course, electricity is only a fraction of total energy use. The same DOE study indicates a ratio of total energy to electricity use of 7.5 should be used for standard-of-living calculations. Therefore we need approximately 30,000 kWh or 108 gigajoules per-person.

There is a lot to be gained through improving energy efficiency. Insulation, hybrid cars, smaller vehicles, public transit, high-density housing and so forth are all important pieces of the solution. However, the initial figures I have used here are less than half of U.S. energy consumption. So, efficiency gains are more likely to reign in high-consumption populations like U.S., Canada and Japan then they are to reduce the needs of developing countries. Besides, it costs energy to manufacture all of these efficiency improvements.

The current world population is estimated at 6.8 Billion. So, in order to eliminate poverty, increase freedom and improve the human condition we need approximately 734 exajoules (734 * 10^18 J) of net energy production per year in addition to massive improvements in energy efficiency. In 2008, worldwide net energy production was 474 exajoules. Given that population continues to grow, we should be seeking to more than double worldwide energy production while still seeking to improve energy efficiency.

If energy production is increased at the cost of environmental damage, we'll miss the goal. Clean air, clear water and wild spaces are just as important to quality of life as good health, nutritious food and a comfortable home. In future posts I'll look into where that energy might come from.

Other posts in this series:
Increasing Energy Production
Energy: The Future is Nuclear