November 2008 Archives
Biofuels and petroleum-based fuels have a common origin. They both arise from the photosynthesis of solar energy that causes carbon and hydrogen to combine in a way that raises their energy level. The primary difference between them is their age. In the case of biofuels, their age is typically just a year or two from the time the energy was collected by some living plant, but in the case of petroleum, it's measured in tens of millions of years from the time the carbon was part of a living organism.
Much of the oil produced over geological time formed at depths of roughly 1.5 to 3 miles below the earth's surface. This is called the 'oil window' where the temperatures and pressures are just right to convert carbon-based materials into oil. If you go much deeper than that, the temperatures and pressures convert the organic compounds into methane, the primary constituent of natural gas. Nearly all of the oil and methane that formed over the years has simply escaped into the environment through natural oil seeps and leaks in the earth's surface. Because oil and gas are less dense than the earth that compresses them, they have a tendency to rise to the top. In rare instances, oil got trapped under impervious rock structures that kept it from escaping for millions of years. This geological formation creates an oil field. Much of the world's oil was found under large rock structures that can cover many square miles in area. These are known as the super giant oil fields and they have been a major source of the oil that we have been using over the past 60 years. As far as we know, every super giant oil field that exists has already been discovered has been producing oil for several decades and most, if not all, have started to peak. The pure oil that came up under its own pressure is now gone, and to keep these fields producing, it's necessary to inject millions of barrels of water per day into the fields to help maintain pressure. Most giant oil fields today produce a mixture of oil, water, and dissolved gas that takes significant capital and effort to separate from each other. Despite incessant exploration in the most remote corners of the earth, no super giant oil fields have been discovered in more than four decades and the rate of even giant oil fields has tapered off considerably in the past two decades. As the production volume from these giant oil fields drops off, there appears to be only one potential alternative for producing transportation fuels, and it will be to use feedstocks derived from recently living plants.
It would be great if this transition from petroleum to biofuels could occur over a period of decades and an orderly manner, but because the world's year-over-year demand for oil continues to increase, it's likely that we will have much less time to make this conversion unless demand can be curtailed to get by on the diminished yearly output from existing oil supplies while ramping up alternative sources of biofuels. The only way for demand to be curtailed is for its price to rise significantly, and it's not inconceivable that it could reach $500/barrel when the production peak arrives. This is the kind of increase that would direct more effort into finding a substitute for oil when additional drilling can't keep up.
A price range of $500 a barrel would mean that the cost of gasoline would approach $20 a gallon and that would likely to cause the average American to become apoplectic. The most recent wild price gyrations of oil indicate that we could very well be on the cusp of a long-awaited decrease in world oil production accompanied by a significant increase of oil prices. In other words, it would be the onset of Peak Oil. Just in case you haven't been paying attention, gasoline prices in the U.S. were relatively flat from the period between 1980 and 2002 at around $1.50-$2.00 per gallon. Since 2002, gasoline prices have been going up at a rate between 10 to 15 percent per year. When supply and demand of a commodity are evenly matched, a minor change of either supply or demand tends to create wild price swings. In the case of oil, neither supply nor demand can be quickly adjusted to match each other, so extreme pricing swings are inevitable when no excess production capacity exists. I mention that so that you don't feel that the recent price of gas falling under $2/gallon in the U.S. is an indication that we should expect to see lower gas prices in the future and that it's time to trade in your hybrid for a Hummer.
The global consumption rate of oil is approximately 83 million barrels per day. The equipment that handles this oil has very little storage capacity relatively speaking and, to pay for its enormous capital cost, it needs to stay busy 24 hours a day, 7 days a week. In other words, you don't build in extra capacity to the system just in case you might need it. And when you realize you don't have enough capacity to meet demand, you can't just add more capacity over night. When peak oil really does occur and yearly global output starts to decline, we'll know for sure only in hindsight when we see an upward price trend and year over year decline in output without any price decrease other than a few brief price spikes.
An ironic side effect of rising oil prices is that it will please both the oil companies and environmentalists. Oil companies will be able to wring record profits from selling what little they can produce of a precious resource and it will please the environmentalists concerned with climate change because it will reduce carbon emissions, something they have been trying to do for many years without much success.
Prior to the discovery of methods to extract and utilize coal, the early industrial societies of Europe were in danger of denuding local forests in the pursuit of heating fuel. Will this environmental disaster revisit us when all the earth's fossil fuels become depleted and we have only what grows on the earth's surface to burn as fuel? This time, in addition to heating homes and businesses, we have a new need that didn't exist a hundred years ago, namely the need for liquid fuels for transportation. And we also have 6 times as many people on the earth as we had 100 years ago. Will transportation simply be curtailed while we focus on the more immediate needs of food production and shelter from the cold? What about the transportation of goods around the world? Is globalism over? Will we need to get by on only products that can be obtained locally and no longer have our salad ingredients transported at high speed from an average distance of 1500 miles?
There has been no shortage of books written on the topic of an upcoming societal collapse which will presumably be triggered by a world-wide shortage of traditional fossil fuels, starting with oil. Other books have also been written to refute arguments about the coming oil crisis. Are the prophets of doom just like Chicken Little telling us the sky is falling or are they helpful Cassandras warning us to prepare ourselves for a major change in the way we'll need to live? Critics of this 'scarcity thinking' are referred to as the 'Cornucopians' who believe in energy abundance and humanity's collective imagination to engineer its way out of any problem nature can throw at us. There are some of these Cornucopians who are obviously deluded, believing that the earth manufactures oil through some mysterious process in real time and the oil fields are quietly replenishing themselves as we look elsewhere for new ones. Some even believe that there is some form of free zero-point energy technology that our governments and the oil companies have been collectively hiding from us, which no doubt that can be traced to alien visitors. But there are people on the Cornucopian side of the argument that appear to be rational too, who don't believe in the tooth fairy, and so after you've read a few books on each side of this issue, it's hard to know which side is right and which side is clinging to a flawed analysis of the subject.
There are very few authors who write about this topic who haven't taken a side on the issue and the unfortunate effect of that is that it's very difficult to get an unbiased opinion. The authors tend to collect and present evidence that supports their world view and dismiss or gloss over any contradicting viewpoints. I guess that makes for more sensationalistic reporting, but at the same time, you don't know who to believe. When an author has an axe to grind, he will sometimes use vague and sweeping statements like, "The sun provides the earth with more energy in 40 minutes than all humanity uses in a year". Or, "It takes more energy to make a gallon of ethanol than you get out of it". Or, "The amount of land it takes to grow biofuels would exceed all the farm land in the world just to fuel the American's gasoline addiction". Even proponents of biofuels who are aligned on principle will sometimes attack each other with a "My biofuel's better than your biofuel" attack, often adopting the arguments of their mutual enemies.
So, will we experience a cataclysm brought on by the sudden depletion of petroleum-based fuels or will a substitute fuel come to our aid? Usually, when I'm faced with such a conundrum, I try to rely on math to cut through the shrill voices of those trying to persuade me to adopt their pre-conceived world view.
Humanity collectively consumes about 400 quadrillion BTUs or 'quads' (10^15 BTU) per year in energy, most of it in the form of non-renewable fossil fuels. Can this amount of energy be replaced with renewables without severely disrupting the world economy or, as the pessimists are predicting, will failure of the oil supply to meet demand ignite a cataclysmic collapse of modern society followed by mass starvation which will ultimately lead to a die off of most of humanity? And, if a collapse is the unfortunate course we're on, is it too late to do anything about it?
Of the 400 quads used by humanity, the U.S. uses about 1/4 of that amount, or 100 quads, despite having only 5% of the world's population. Usually, Americans are profoundly ashamed when they learn of this, thinking that our citizens are profligate wasters of energy, so I sometimes temper it with the fact that the average Canadian uses even more energy per capita than the average American. Everyone loves Canadians. I've yet to find an exception. They are frugal and responsible people, and so knowing they use more energy per capita than Americans helps us to focus on the real issue and that is that when a society is spread out geographically and lives far from the equator, its per capita energy use tends to be higher due to transportation and heating costs. You really can't compare a modern society surviving in an environment where temperatures routinely drop below freezing with a society scratching out an existence near the equator and jump to the conclusion that one culture is wasteful and the other is enlightened. We can't just round up the world's population and put them in mud huts lined up close to the equator, although I don't doubt that there are those who think we should consider that as an option. It's possible that primitive third world societies will be the only survivors of a societal collapse that a few groups seem to be looking forward to with a sort of giddy anticipation as modern society gets its just deserts. I don't subscribe to that philosophy myself, and am often dismayed that some people would choose to be gleeful about anticipating a collapse of society just to have their predictions of doom proven to be correct, even as they themselves prepare to suffer and perish in the event.
To figure out how close to the precipice we are, it's helpful to see how far beyond our potential energy budget we're living. While we're enjoying the inheritance of cheap fossil fuels, few people doubt that we'll eventually need to live on what's provided to us daily from the sun. The sun's irradiation of the earth's surface is approximately 1000 watts per square meter when shining at full intensity. The average amount of solar radiation varies according to the relative position from the equator and local weather patterns. The number of equivalent hours per year of full intensity sunlight ranges from about 900 in Norway to nearly 3000 in some of the desert regions of the earth. For most of the U.S., an average number for solar radiation is around 1400 hours per year. An acre of land, or approximately 4047 sq. meters, therefore receives about 5.7 M kWh of sunlight per year in the U.S. If you could convert this solar energy into electricity at 100% efficiency, it would be enough to supply about 650 U.S. households with all of their electricity.
The most obvious issue with that calculation is that nothing converts 100% of the solar energy that irradiates it into usable energy. Even the best laboratory solar cells under development are in the 40% range. The solar panels you can buy today are in the 12-18% range. Assuming we're at the low end of that range, say 13%, 7 acres of solar panels would supply 650 households, or about 480 sq. ft. per household. By the way, 480 sq. feet is an array only 22' x 22' which would fit on most roof tops or backyards in the U.S.. So solar panels could provide enough energy to provide electricity for our households, provided one can grid tie or store the energy for use when the sun wasn't shining. How about fuel for transportation? Is there enough sun energy to make biofuels based on our consumption rate? And are biofuels efficient at converting solar energy into fuel?
In the U.S., the most popular biomass for producing ethanol today is corn. It has an average yield of 140 bushels an acre and produces 2.7 gallons of ethanol per bushel. Each gallon of ethanol contains about 84,000 BTU of energy. After running those numbers through a few calculations, it means that we get 2.3 kWh per square meter per year in ethanol energy from corn. Since growing corn and converting it to ethanol also requires energy inputs, the overall increase is only about 30% of the 2.3 kWh per square meter of the ethanol. This comes out to a net of .7 kWh per sq. meter per year. Compared to the theoretical insolation of 1400 kWh/sq. m/yr, this energy conversion efficiency is .05%. That's pretty low compared to conventional solar panels which, at 13% efficiency extract 260 times more energy from the sun than corn ethanol. It's even a long way from typical photosynthetic conversion efficiencies of 2%-6%. Part of the reason for this is because I've subtracted out the energy inputs (thus losing 77%) and took no account of the other biomass produced in the form of corn stover which accounts for as much as 50% of the biomass produced in each corn plant. Also, corn's 4 month growing season means that for about 8 months out of the year, the sun reaching a cornfield is not being converted into carbohydrates.
There are a number of other proposed energy crop fuel sources that take fewer fossil fuel inputs and provide higher biomass output, but the processes to convert the biomass to ethanol are still in the developmental stages. For example, switchgrass requires very little fertilizer, herbicides, or pesticides and can produce about 1/3 of its dry weight in ethanol. It also has some side benefits in restoring the soil fertility and reducing soil erosion where it's grown. Since even marginal land not suitable for other crops can produce as much as 15 tons of switchgrass per acre, this would translate to 1500 gallons of ethanol per acre (compared to 322 gallons per acre in the case of corn in the previous example) and so the efficiency, because of higher biomass output and fewer energy inputs, gives an effective energy output of 7.3 kWh per square meter per year. This translates to .5% efficiency in terms of solar energy conversion. This is about 10 times better than corn per acre.
Conventional solar panels with 13% efficiency are still 26 times more efficient than even switchgrass. So why are biofuels still even considered viable? One reason is that the capital costs of solar panels today are on the order of $4M per acre, and it would take a long time to pay that cost back considering it would only generate about 2% of that capital cost in energy per year at today's prices. I realize that 2% sounds like a pretty abysmal payback, but if energy prices double, or go up by factor of 10 times like some think is possible, then solar panels will look very attractive. Also, solar panels are likely to come down in price as the manufacturing capacity for them ramps up. On the other hand, electricity is not as practical for transportation because you generally have to carry transportation fuel on board the vehicle. You could use batteries, of course, but the energy density of batteries is much, much lower than that of liquid hydrocarbon fuels. A typical battery can hold less than 1% of the energy per pound compared with hydrocarbon fuels. Also, it takes many hours to charge up a battery so you have to plan its use more carefully and can't really conveniently take it on a long road trip like you can a car that runs conventional fuels. But if you could get by on an electric vehicle powered by the sun for local commuting, it certainly would be a lot better from an energy efficiency standpoint. If you could use an electric bicycle, the efficiency improvement is even more impressive because the energy to move something around is mostly determined by its weight. A car with one occupant weighs about 10 times as much as an electric bike with one occupant and thus uses about 10 times the energy per mile driven.
So, let's do another calculation. If we can achieve a .5% solar energy extraction value from biofuels and use it just to cover our transportation needs, assuming other renewables like solar and wind power can make up the difference for heating and electricity, how much land would it take to grow the feedstocks? According to the EIA, the U.S. uses 29% of its energy for transportation needs, or about 29 quads. To grow 29 quads of biomass per year, assuming we can get a net average increase of 100 MBTU/acre/year as in the switchgrass example above, it would take 290,000,000 acres. Unfortunately, this is a good portion of the 400,000,000 acres of arable land in the U.S.. So even switchgrass with its favorable energy balance would not be able to keep up with the current U.S. transportation fuel demand, let alone any future energy demand increases, and still leave enough land on which to grow our food.
What about algae? We hear a lot of about algae because it can be grown in an enclosed environment so you can avoid the evaporative effect of normal crops which can require as much as 1000 gallons of water per gallon of biofuel they produce. With an enclosed system, we might even be able to take advantage of non-arable desert land. But what would the BTU per acre yield be? According to some studies done by NREL for the Aquatic Species Act during the 1970's through the 1990's, it appears to be possible to produce as much as 15,000 gallons of biodiesel per acre in very specialize enclosed growing environments. Because biodiesel has a higher BTU content compared to ethanol (about 135,000 BTU/gal for biodiesel vs. 84,000 BTU/gal for ethanol), this would yield about 2,000 MBTU per acre per year. That's about 20 times more output than switchgrass which means that its efficiency would approach a 10% conversion of sunlight into energy. However, it's not clear how much capital expenditure would be required to build and operate the enclosed algae raceways. And there's little information about the required energy inputs, so in reality the conversion efficiency is likely to be much less than 10%. The calculations also assume a sunny desert-like environment with a year-round growing capability. However, these environments are usually short of local water resources. Even though growing algae in enclosed raceways reduces evaporation of the water, some water would necessarily be lost in the oil extraction process. Therefore, water would have to be brought in from elsewhere, which is likely to be expensive and controversial since much of the water in the desert southwest of the U.S. is already spoken for or is otherwise being fiercely contested.
At the time the algae work was done, it was estimated that it would cost twice as much to produce fuel from algae as it did from petroleum. But in the intervening years, petroleum prices have more than doubled and so biofuel from algae is being considered again by many startup companies. How much land would it take? According to the research, about 1 quad could be produced on 200,000 hectares (about 500,000 acres) so the 29 quads we'd need for transportation fuels would be around 15 million acres which is much less than the 290M acres we calculated for switchgrass. Still, 15 million acres is nothing to sneeze at. It's about .7% of the land mass of the U.S.. It would take up about 20% of the land in a state the size of Arizona or New Mexico.
Frequently when people talk about creating biofuels with algae, they bring up the topic of using CO2 from coal-fired electric plant's flue gas to help stimulate the growth of the algae. This, of course, would require co-locating a fossil fuel electric plant next to the algae production plant. I feel this is a bad approach. First of all, the biofuel made from the algae generally would be used within a few months of its production, releasing this previously sequestered carbon into the atmosphere, so it's not really a carbon sequestration scheme by any means, and secondly, it's not a sustainable solution if the process depends on fossil fuel as one of its inputs. The eventual goal of renewable energy is to get us out of the habit of putting ancient carbon into the atmosphere, so it makes no sense to use fossil fuel as an input to the process. To be carbon neutral, the carbon dioxide input should be coming from the atmosphere, not from fossil fuels. I realize that there are those who would claim that it would be a sort of 'stepping stone', and has the potential to reduce carbon emissions by up to 50% by, in essence, recycling the ancient carbon one more time before releasing it. However, it feels like "green washing" the burning of coal by temporarily converting it into biofuel and I find it to be counterproductive to the cause of getting us off of fossil fuels completely.
Another possibility would be to have algae-based biofuel plants small enough to generate fuels near where the fuel would be used so as not to lose efficiency by having to transport the fuels all over the world from centralized production facilities located in some desert location. Could this be done? A typical car uses about 500 gallons of fuel per year. Assuming that you can produce 15,000 gallons of algae based biofuel per acre per year, this means a car would require about 1500 square feet of growing area. That would take up about a 40' square area in one's back yard, not much more than a swimming pool and its associated decking.
But how would growing your own biofuel compare with generating solar electricity for an electric or plug-in hybrid car? A Tesla roadster can drive 12,500 miles annually with the energy produced by 240 square feet of solar panels. You can buy that much solar capacity for around $15,000 today. I'm guessing that a 1500 sq. foot algae-based bioreactor would be more expensive than that, but perhaps not. The solar panel providing a similar amount of energy takes up 1/6 the amount space of the algae bioreactor and has no moving parts or liquids and thus is likely to take much less maintenance to keep it running.
In the future, just about all local travel and commuting (say, distances under 80 miles a day) could be done using solar-generated electricity and plug-in hybrid vehicles. For distances greater than that, liquid hydrocarbon fuels would still be necessary. Of course, for powering aircraft, ships, trucks, and trains, liquid biofuels would be required far into the forseeable future. And those modes of transportation will require liquid fuels on very large scales, so the biofuels for them will necessarily need to be made in large production facilities. It would make sense to distribute the large scale plants along transportation routes so that the fuel could be produced in close proximity to refueling stations. There may be opportunities for 'back yard' sized facilities because when the oil production eventually peaks, liquid fuels will continue to rise in cost. It may be more profitable to grow an acre of biofuel than it would be to grow tomatoes or corn.
If algae looks like it has the most potential to have the highest solar conversion efficiency and won't compete with food for growing locations, should we even be messing around with corn-based ethanol? I think that corn ethanol serves a useful purpose. It will take many years to replace current vehicles with any fuel that requires a new engine, such as would be required by biodiesel. Ethanol in high concentrations can be burned in all flex fuel vehicles as well as in most of non-flex fuel cars in the U.S. today with only minor changes. All of the cars today are already burning ethanol in low concentrations. The potential to turn cellulosic waste biomass into ethanol has already been proven and is currently coming on line. Algae-based fuels have yet to be proven beyond pilot scale production. This will require more time and so I think it would be unwise to jump to the conclusion that the solution is at hand for algae-based biofuel production and abandon efforts for biofuels that we can produce today.
Will biofuels save us from the coming cataclysm that some are predicting? It's hard to say with confidence. The only thing that is holding up biofuels at this point is the low cost of oil, which, with every downward price excursion shakes the confidence that the time is here to finally break ourselves of our oil addiction. The time will come, and when it does, there will be a few biofuel companies poised to take advantage of it, provided their investors have the fortitude to stick with it.
Much of the oil produced over geological time formed at depths of roughly 1.5 to 3 miles below the earth's surface. This is called the 'oil window' where the temperatures and pressures are just right to convert carbon-based materials into oil. If you go much deeper than that, the temperatures and pressures convert the organic compounds into methane, the primary constituent of natural gas. Nearly all of the oil and methane that formed over the years has simply escaped into the environment through natural oil seeps and leaks in the earth's surface. Because oil and gas are less dense than the earth that compresses them, they have a tendency to rise to the top. In rare instances, oil got trapped under impervious rock structures that kept it from escaping for millions of years. This geological formation creates an oil field. Much of the world's oil was found under large rock structures that can cover many square miles in area. These are known as the super giant oil fields and they have been a major source of the oil that we have been using over the past 60 years. As far as we know, every super giant oil field that exists has already been discovered has been producing oil for several decades and most, if not all, have started to peak. The pure oil that came up under its own pressure is now gone, and to keep these fields producing, it's necessary to inject millions of barrels of water per day into the fields to help maintain pressure. Most giant oil fields today produce a mixture of oil, water, and dissolved gas that takes significant capital and effort to separate from each other. Despite incessant exploration in the most remote corners of the earth, no super giant oil fields have been discovered in more than four decades and the rate of even giant oil fields has tapered off considerably in the past two decades. As the production volume from these giant oil fields drops off, there appears to be only one potential alternative for producing transportation fuels, and it will be to use feedstocks derived from recently living plants.
It would be great if this transition from petroleum to biofuels could occur over a period of decades and an orderly manner, but because the world's year-over-year demand for oil continues to increase, it's likely that we will have much less time to make this conversion unless demand can be curtailed to get by on the diminished yearly output from existing oil supplies while ramping up alternative sources of biofuels. The only way for demand to be curtailed is for its price to rise significantly, and it's not inconceivable that it could reach $500/barrel when the production peak arrives. This is the kind of increase that would direct more effort into finding a substitute for oil when additional drilling can't keep up.
A price range of $500 a barrel would mean that the cost of gasoline would approach $20 a gallon and that would likely to cause the average American to become apoplectic. The most recent wild price gyrations of oil indicate that we could very well be on the cusp of a long-awaited decrease in world oil production accompanied by a significant increase of oil prices. In other words, it would be the onset of Peak Oil. Just in case you haven't been paying attention, gasoline prices in the U.S. were relatively flat from the period between 1980 and 2002 at around $1.50-$2.00 per gallon. Since 2002, gasoline prices have been going up at a rate between 10 to 15 percent per year. When supply and demand of a commodity are evenly matched, a minor change of either supply or demand tends to create wild price swings. In the case of oil, neither supply nor demand can be quickly adjusted to match each other, so extreme pricing swings are inevitable when no excess production capacity exists. I mention that so that you don't feel that the recent price of gas falling under $2/gallon in the U.S. is an indication that we should expect to see lower gas prices in the future and that it's time to trade in your hybrid for a Hummer.
The global consumption rate of oil is approximately 83 million barrels per day. The equipment that handles this oil has very little storage capacity relatively speaking and, to pay for its enormous capital cost, it needs to stay busy 24 hours a day, 7 days a week. In other words, you don't build in extra capacity to the system just in case you might need it. And when you realize you don't have enough capacity to meet demand, you can't just add more capacity over night. When peak oil really does occur and yearly global output starts to decline, we'll know for sure only in hindsight when we see an upward price trend and year over year decline in output without any price decrease other than a few brief price spikes.
An ironic side effect of rising oil prices is that it will please both the oil companies and environmentalists. Oil companies will be able to wring record profits from selling what little they can produce of a precious resource and it will please the environmentalists concerned with climate change because it will reduce carbon emissions, something they have been trying to do for many years without much success.
Prior to the discovery of methods to extract and utilize coal, the early industrial societies of Europe were in danger of denuding local forests in the pursuit of heating fuel. Will this environmental disaster revisit us when all the earth's fossil fuels become depleted and we have only what grows on the earth's surface to burn as fuel? This time, in addition to heating homes and businesses, we have a new need that didn't exist a hundred years ago, namely the need for liquid fuels for transportation. And we also have 6 times as many people on the earth as we had 100 years ago. Will transportation simply be curtailed while we focus on the more immediate needs of food production and shelter from the cold? What about the transportation of goods around the world? Is globalism over? Will we need to get by on only products that can be obtained locally and no longer have our salad ingredients transported at high speed from an average distance of 1500 miles?
There has been no shortage of books written on the topic of an upcoming societal collapse which will presumably be triggered by a world-wide shortage of traditional fossil fuels, starting with oil. Other books have also been written to refute arguments about the coming oil crisis. Are the prophets of doom just like Chicken Little telling us the sky is falling or are they helpful Cassandras warning us to prepare ourselves for a major change in the way we'll need to live? Critics of this 'scarcity thinking' are referred to as the 'Cornucopians' who believe in energy abundance and humanity's collective imagination to engineer its way out of any problem nature can throw at us. There are some of these Cornucopians who are obviously deluded, believing that the earth manufactures oil through some mysterious process in real time and the oil fields are quietly replenishing themselves as we look elsewhere for new ones. Some even believe that there is some form of free zero-point energy technology that our governments and the oil companies have been collectively hiding from us, which no doubt that can be traced to alien visitors. But there are people on the Cornucopian side of the argument that appear to be rational too, who don't believe in the tooth fairy, and so after you've read a few books on each side of this issue, it's hard to know which side is right and which side is clinging to a flawed analysis of the subject.
There are very few authors who write about this topic who haven't taken a side on the issue and the unfortunate effect of that is that it's very difficult to get an unbiased opinion. The authors tend to collect and present evidence that supports their world view and dismiss or gloss over any contradicting viewpoints. I guess that makes for more sensationalistic reporting, but at the same time, you don't know who to believe. When an author has an axe to grind, he will sometimes use vague and sweeping statements like, "The sun provides the earth with more energy in 40 minutes than all humanity uses in a year". Or, "It takes more energy to make a gallon of ethanol than you get out of it". Or, "The amount of land it takes to grow biofuels would exceed all the farm land in the world just to fuel the American's gasoline addiction". Even proponents of biofuels who are aligned on principle will sometimes attack each other with a "My biofuel's better than your biofuel" attack, often adopting the arguments of their mutual enemies.
So, will we experience a cataclysm brought on by the sudden depletion of petroleum-based fuels or will a substitute fuel come to our aid? Usually, when I'm faced with such a conundrum, I try to rely on math to cut through the shrill voices of those trying to persuade me to adopt their pre-conceived world view.
Humanity collectively consumes about 400 quadrillion BTUs or 'quads' (10^15 BTU) per year in energy, most of it in the form of non-renewable fossil fuels. Can this amount of energy be replaced with renewables without severely disrupting the world economy or, as the pessimists are predicting, will failure of the oil supply to meet demand ignite a cataclysmic collapse of modern society followed by mass starvation which will ultimately lead to a die off of most of humanity? And, if a collapse is the unfortunate course we're on, is it too late to do anything about it?
Of the 400 quads used by humanity, the U.S. uses about 1/4 of that amount, or 100 quads, despite having only 5% of the world's population. Usually, Americans are profoundly ashamed when they learn of this, thinking that our citizens are profligate wasters of energy, so I sometimes temper it with the fact that the average Canadian uses even more energy per capita than the average American. Everyone loves Canadians. I've yet to find an exception. They are frugal and responsible people, and so knowing they use more energy per capita than Americans helps us to focus on the real issue and that is that when a society is spread out geographically and lives far from the equator, its per capita energy use tends to be higher due to transportation and heating costs. You really can't compare a modern society surviving in an environment where temperatures routinely drop below freezing with a society scratching out an existence near the equator and jump to the conclusion that one culture is wasteful and the other is enlightened. We can't just round up the world's population and put them in mud huts lined up close to the equator, although I don't doubt that there are those who think we should consider that as an option. It's possible that primitive third world societies will be the only survivors of a societal collapse that a few groups seem to be looking forward to with a sort of giddy anticipation as modern society gets its just deserts. I don't subscribe to that philosophy myself, and am often dismayed that some people would choose to be gleeful about anticipating a collapse of society just to have their predictions of doom proven to be correct, even as they themselves prepare to suffer and perish in the event.
To figure out how close to the precipice we are, it's helpful to see how far beyond our potential energy budget we're living. While we're enjoying the inheritance of cheap fossil fuels, few people doubt that we'll eventually need to live on what's provided to us daily from the sun. The sun's irradiation of the earth's surface is approximately 1000 watts per square meter when shining at full intensity. The average amount of solar radiation varies according to the relative position from the equator and local weather patterns. The number of equivalent hours per year of full intensity sunlight ranges from about 900 in Norway to nearly 3000 in some of the desert regions of the earth. For most of the U.S., an average number for solar radiation is around 1400 hours per year. An acre of land, or approximately 4047 sq. meters, therefore receives about 5.7 M kWh of sunlight per year in the U.S. If you could convert this solar energy into electricity at 100% efficiency, it would be enough to supply about 650 U.S. households with all of their electricity.
The most obvious issue with that calculation is that nothing converts 100% of the solar energy that irradiates it into usable energy. Even the best laboratory solar cells under development are in the 40% range. The solar panels you can buy today are in the 12-18% range. Assuming we're at the low end of that range, say 13%, 7 acres of solar panels would supply 650 households, or about 480 sq. ft. per household. By the way, 480 sq. feet is an array only 22' x 22' which would fit on most roof tops or backyards in the U.S.. So solar panels could provide enough energy to provide electricity for our households, provided one can grid tie or store the energy for use when the sun wasn't shining. How about fuel for transportation? Is there enough sun energy to make biofuels based on our consumption rate? And are biofuels efficient at converting solar energy into fuel?
In the U.S., the most popular biomass for producing ethanol today is corn. It has an average yield of 140 bushels an acre and produces 2.7 gallons of ethanol per bushel. Each gallon of ethanol contains about 84,000 BTU of energy. After running those numbers through a few calculations, it means that we get 2.3 kWh per square meter per year in ethanol energy from corn. Since growing corn and converting it to ethanol also requires energy inputs, the overall increase is only about 30% of the 2.3 kWh per square meter of the ethanol. This comes out to a net of .7 kWh per sq. meter per year. Compared to the theoretical insolation of 1400 kWh/sq. m/yr, this energy conversion efficiency is .05%. That's pretty low compared to conventional solar panels which, at 13% efficiency extract 260 times more energy from the sun than corn ethanol. It's even a long way from typical photosynthetic conversion efficiencies of 2%-6%. Part of the reason for this is because I've subtracted out the energy inputs (thus losing 77%) and took no account of the other biomass produced in the form of corn stover which accounts for as much as 50% of the biomass produced in each corn plant. Also, corn's 4 month growing season means that for about 8 months out of the year, the sun reaching a cornfield is not being converted into carbohydrates.
There are a number of other proposed energy crop fuel sources that take fewer fossil fuel inputs and provide higher biomass output, but the processes to convert the biomass to ethanol are still in the developmental stages. For example, switchgrass requires very little fertilizer, herbicides, or pesticides and can produce about 1/3 of its dry weight in ethanol. It also has some side benefits in restoring the soil fertility and reducing soil erosion where it's grown. Since even marginal land not suitable for other crops can produce as much as 15 tons of switchgrass per acre, this would translate to 1500 gallons of ethanol per acre (compared to 322 gallons per acre in the case of corn in the previous example) and so the efficiency, because of higher biomass output and fewer energy inputs, gives an effective energy output of 7.3 kWh per square meter per year. This translates to .5% efficiency in terms of solar energy conversion. This is about 10 times better than corn per acre.
Conventional solar panels with 13% efficiency are still 26 times more efficient than even switchgrass. So why are biofuels still even considered viable? One reason is that the capital costs of solar panels today are on the order of $4M per acre, and it would take a long time to pay that cost back considering it would only generate about 2% of that capital cost in energy per year at today's prices. I realize that 2% sounds like a pretty abysmal payback, but if energy prices double, or go up by factor of 10 times like some think is possible, then solar panels will look very attractive. Also, solar panels are likely to come down in price as the manufacturing capacity for them ramps up. On the other hand, electricity is not as practical for transportation because you generally have to carry transportation fuel on board the vehicle. You could use batteries, of course, but the energy density of batteries is much, much lower than that of liquid hydrocarbon fuels. A typical battery can hold less than 1% of the energy per pound compared with hydrocarbon fuels. Also, it takes many hours to charge up a battery so you have to plan its use more carefully and can't really conveniently take it on a long road trip like you can a car that runs conventional fuels. But if you could get by on an electric vehicle powered by the sun for local commuting, it certainly would be a lot better from an energy efficiency standpoint. If you could use an electric bicycle, the efficiency improvement is even more impressive because the energy to move something around is mostly determined by its weight. A car with one occupant weighs about 10 times as much as an electric bike with one occupant and thus uses about 10 times the energy per mile driven.
So, let's do another calculation. If we can achieve a .5% solar energy extraction value from biofuels and use it just to cover our transportation needs, assuming other renewables like solar and wind power can make up the difference for heating and electricity, how much land would it take to grow the feedstocks? According to the EIA, the U.S. uses 29% of its energy for transportation needs, or about 29 quads. To grow 29 quads of biomass per year, assuming we can get a net average increase of 100 MBTU/acre/year as in the switchgrass example above, it would take 290,000,000 acres. Unfortunately, this is a good portion of the 400,000,000 acres of arable land in the U.S.. So even switchgrass with its favorable energy balance would not be able to keep up with the current U.S. transportation fuel demand, let alone any future energy demand increases, and still leave enough land on which to grow our food.
What about algae? We hear a lot of about algae because it can be grown in an enclosed environment so you can avoid the evaporative effect of normal crops which can require as much as 1000 gallons of water per gallon of biofuel they produce. With an enclosed system, we might even be able to take advantage of non-arable desert land. But what would the BTU per acre yield be? According to some studies done by NREL for the Aquatic Species Act during the 1970's through the 1990's, it appears to be possible to produce as much as 15,000 gallons of biodiesel per acre in very specialize enclosed growing environments. Because biodiesel has a higher BTU content compared to ethanol (about 135,000 BTU/gal for biodiesel vs. 84,000 BTU/gal for ethanol), this would yield about 2,000 MBTU per acre per year. That's about 20 times more output than switchgrass which means that its efficiency would approach a 10% conversion of sunlight into energy. However, it's not clear how much capital expenditure would be required to build and operate the enclosed algae raceways. And there's little information about the required energy inputs, so in reality the conversion efficiency is likely to be much less than 10%. The calculations also assume a sunny desert-like environment with a year-round growing capability. However, these environments are usually short of local water resources. Even though growing algae in enclosed raceways reduces evaporation of the water, some water would necessarily be lost in the oil extraction process. Therefore, water would have to be brought in from elsewhere, which is likely to be expensive and controversial since much of the water in the desert southwest of the U.S. is already spoken for or is otherwise being fiercely contested.
At the time the algae work was done, it was estimated that it would cost twice as much to produce fuel from algae as it did from petroleum. But in the intervening years, petroleum prices have more than doubled and so biofuel from algae is being considered again by many startup companies. How much land would it take? According to the research, about 1 quad could be produced on 200,000 hectares (about 500,000 acres) so the 29 quads we'd need for transportation fuels would be around 15 million acres which is much less than the 290M acres we calculated for switchgrass. Still, 15 million acres is nothing to sneeze at. It's about .7% of the land mass of the U.S.. It would take up about 20% of the land in a state the size of Arizona or New Mexico.
Frequently when people talk about creating biofuels with algae, they bring up the topic of using CO2 from coal-fired electric plant's flue gas to help stimulate the growth of the algae. This, of course, would require co-locating a fossil fuel electric plant next to the algae production plant. I feel this is a bad approach. First of all, the biofuel made from the algae generally would be used within a few months of its production, releasing this previously sequestered carbon into the atmosphere, so it's not really a carbon sequestration scheme by any means, and secondly, it's not a sustainable solution if the process depends on fossil fuel as one of its inputs. The eventual goal of renewable energy is to get us out of the habit of putting ancient carbon into the atmosphere, so it makes no sense to use fossil fuel as an input to the process. To be carbon neutral, the carbon dioxide input should be coming from the atmosphere, not from fossil fuels. I realize that there are those who would claim that it would be a sort of 'stepping stone', and has the potential to reduce carbon emissions by up to 50% by, in essence, recycling the ancient carbon one more time before releasing it. However, it feels like "green washing" the burning of coal by temporarily converting it into biofuel and I find it to be counterproductive to the cause of getting us off of fossil fuels completely.
Another possibility would be to have algae-based biofuel plants small enough to generate fuels near where the fuel would be used so as not to lose efficiency by having to transport the fuels all over the world from centralized production facilities located in some desert location. Could this be done? A typical car uses about 500 gallons of fuel per year. Assuming that you can produce 15,000 gallons of algae based biofuel per acre per year, this means a car would require about 1500 square feet of growing area. That would take up about a 40' square area in one's back yard, not much more than a swimming pool and its associated decking.
But how would growing your own biofuel compare with generating solar electricity for an electric or plug-in hybrid car? A Tesla roadster can drive 12,500 miles annually with the energy produced by 240 square feet of solar panels. You can buy that much solar capacity for around $15,000 today. I'm guessing that a 1500 sq. foot algae-based bioreactor would be more expensive than that, but perhaps not. The solar panel providing a similar amount of energy takes up 1/6 the amount space of the algae bioreactor and has no moving parts or liquids and thus is likely to take much less maintenance to keep it running.
In the future, just about all local travel and commuting (say, distances under 80 miles a day) could be done using solar-generated electricity and plug-in hybrid vehicles. For distances greater than that, liquid hydrocarbon fuels would still be necessary. Of course, for powering aircraft, ships, trucks, and trains, liquid biofuels would be required far into the forseeable future. And those modes of transportation will require liquid fuels on very large scales, so the biofuels for them will necessarily need to be made in large production facilities. It would make sense to distribute the large scale plants along transportation routes so that the fuel could be produced in close proximity to refueling stations. There may be opportunities for 'back yard' sized facilities because when the oil production eventually peaks, liquid fuels will continue to rise in cost. It may be more profitable to grow an acre of biofuel than it would be to grow tomatoes or corn.
If algae looks like it has the most potential to have the highest solar conversion efficiency and won't compete with food for growing locations, should we even be messing around with corn-based ethanol? I think that corn ethanol serves a useful purpose. It will take many years to replace current vehicles with any fuel that requires a new engine, such as would be required by biodiesel. Ethanol in high concentrations can be burned in all flex fuel vehicles as well as in most of non-flex fuel cars in the U.S. today with only minor changes. All of the cars today are already burning ethanol in low concentrations. The potential to turn cellulosic waste biomass into ethanol has already been proven and is currently coming on line. Algae-based fuels have yet to be proven beyond pilot scale production. This will require more time and so I think it would be unwise to jump to the conclusion that the solution is at hand for algae-based biofuel production and abandon efforts for biofuels that we can produce today.
Will biofuels save us from the coming cataclysm that some are predicting? It's hard to say with confidence. The only thing that is holding up biofuels at this point is the low cost of oil, which, with every downward price excursion shakes the confidence that the time is here to finally break ourselves of our oil addiction. The time will come, and when it does, there will be a few biofuel companies poised to take advantage of it, provided their investors have the fortitude to stick with it.
Biofuels made from biomass, such as corn and soybeans, have been getting criticism lately for their impact on world food prices. Opponents of the alternative fuels say that using a portion of the world's farmland and the associated crop yields for the production of fuel will add to the pressure developing countries face in supplying their populations with adequate food supplies. To address these concerns, countries have started creating biofuels from crops that are either inedible or of low demand, such as sugarcane and rapeseed, or on land that is unarable for traditional food crops. While these may provide answers to questions about the impact on food supplies, there are many other questions to address.Many scientists are beginning to question whether biofuels will actually be able to help slow global warming, due to the indirect impact on land use worldwide required for the production of biofuels. The Wall Street Journal provided an example to illustrate this situation. If farmers in Brazil slash and burn more rainforest to grow food because land in the US is being used to grow grain for fuel, carbon dioxide emissions may actually increase overall. Corn-based ethanol has already been shown to increase greenhouse-gas emissions by 93% over using gasoline. Even biofuel made from switch grass grown on land that would otherwise have been used for growing corn would increase emissions by 50%. As a result, the Environmental Protection Agency is taking steps to measure each biofuel's actual lifetime emissions to help determine which may have a positive impact on the environment, and weed out those that may be detrimental.
The emissions in question extend beyond carbon dioxide, however. A new study in Chemistry & Industry suggests that increasing the use of biodiesel worldwide may actually increase the amount of greenhouse gas emissions produced. The study compared petroleum-based diesel to biodiesel made from rapeseed over the entire lifecycle of each fuel, from production to consumption. Surprisingly, both fuels emit about the same amount of carbon dioxide, the main greenhouse gas biofuels are meant to address. However, the release of nitrous oxide, a greenhouse gas 200 times more potent than carbon dioxide, is not released equally. Petroleum fuels release 85% of their greenhouse gases when burned in the engine, while over 60% of the emissions from biodiesel occur during farming of the crop. This is because agricultural fields release a large amount of nitrous oxide, something that is not a problem with petroleum. The study concluded that by running cars on traditional diesel and planting trees on the land that was intended to be used to grow the biodiesel crop, overall greenhouse gas emissions could be reduced by one-third. A joint study between the University of California - Berkeley and Cornell University was done to determine whether distilling ethanol from corn, switch grass or wood biomass, and making biodiesel from soybean or sunflower plants can produce more energy output in the fuel than is consumed during production. The results:
However, this isn't the whole story. Yes, there are many situations where creating biofuel from biomass does not make sense, but who said it was necessary to turn everything we see into biofuels? It makes a lot more sense to have biofuels compete from an economic standpoint, being farmed from areas of land where nothing else will grow, and from plants that cannot be eaten anyway. Many of the early biofuel adopters have also discovered another ready source of biodiesel: fast food restaurants. While this certainly will never provide enough biofuel to make a dent in worldwide demand, it also doesn't have any negative impact on the environment. The fuel is sustainably grown and is used for food initially. Only after that utility is used up do we transform it into something that can power a vehicle as well.And there is plenty of room for other forms of biomass, as seen in the wood pellet-powered Precer Bioracer. The problem comes when we try to adapt our environment - in this case our farmland and rainforests - to meet the needs of our current technology - the internal combustion engine. If we adopted our current technology to suit our environment, we would create a situation that is much more sustainable. Another great example of this is the Woodgas Solar Camp Stove. iEnergy created the stove that can create the heat of a blast furnace using dead twigs gathered off the ground, and powered by a small solar panel. This innovative device doesn't even require planting new crops, and instead uses ambient biomass - fuel that otherwise would stay on the ground and create a greater risk of wildfires - in a safe and productive manner. What could be more sustainable than that? This article was produced by, and originally appeared on Biomass Authority here.
The emissions in question extend beyond carbon dioxide, however. A new study in Chemistry & Industry suggests that increasing the use of biodiesel worldwide may actually increase the amount of greenhouse gas emissions produced. The study compared petroleum-based diesel to biodiesel made from rapeseed over the entire lifecycle of each fuel, from production to consumption. Surprisingly, both fuels emit about the same amount of carbon dioxide, the main greenhouse gas biofuels are meant to address. However, the release of nitrous oxide, a greenhouse gas 200 times more potent than carbon dioxide, is not released equally. Petroleum fuels release 85% of their greenhouse gases when burned in the engine, while over 60% of the emissions from biodiesel occur during farming of the crop. This is because agricultural fields release a large amount of nitrous oxide, something that is not a problem with petroleum. The study concluded that by running cars on traditional diesel and planting trees on the land that was intended to be used to grow the biodiesel crop, overall greenhouse gas emissions could be reduced by one-third. A joint study between the University of California - Berkeley and Cornell University was done to determine whether distilling ethanol from corn, switch grass or wood biomass, and making biodiesel from soybean or sunflower plants can produce more energy output in the fuel than is consumed during production. The results:- Corn requires 29% more energy than is produced
- Switch grass requires 45% more energy than is produced
- Wood biomass requires 57% more energy than is produced
- Soybeans require 27% more energy than is produced
- Sunflower seeds require 118% more energy than is produced
However, this isn't the whole story. Yes, there are many situations where creating biofuel from biomass does not make sense, but who said it was necessary to turn everything we see into biofuels? It makes a lot more sense to have biofuels compete from an economic standpoint, being farmed from areas of land where nothing else will grow, and from plants that cannot be eaten anyway. Many of the early biofuel adopters have also discovered another ready source of biodiesel: fast food restaurants. While this certainly will never provide enough biofuel to make a dent in worldwide demand, it also doesn't have any negative impact on the environment. The fuel is sustainably grown and is used for food initially. Only after that utility is used up do we transform it into something that can power a vehicle as well.And there is plenty of room for other forms of biomass, as seen in the wood pellet-powered Precer Bioracer. The problem comes when we try to adapt our environment - in this case our farmland and rainforests - to meet the needs of our current technology - the internal combustion engine. If we adopted our current technology to suit our environment, we would create a situation that is much more sustainable. Another great example of this is the Woodgas Solar Camp Stove. iEnergy created the stove that can create the heat of a blast furnace using dead twigs gathered off the ground, and powered by a small solar panel. This innovative device doesn't even require planting new crops, and instead uses ambient biomass - fuel that otherwise would stay on the ground and create a greater risk of wildfires - in a safe and productive manner. What could be more sustainable than that? This article was produced by, and originally appeared on Biomass Authority here.
A new breed of multi-fuel stoves are making their way onto the market, harvesting biomass fuels at the household level like never before. While wood stoves have long been a staple of indoor heating (especially in log cabins or romantic restaurants) they often lack consistency in burning temperature and are a challenge to power. For anyone who has ever visited his or her grandparen'ts farm you'll know wood doesn't exactly chop itself... furthermore, wood logs don't pack as easily as other smaller consistent units of fuel such as wood pellets or corn.
This new wave of biomass stoves and biomass heaters has opened up the opportunity for multiple biomass fuel sources to compete. In some circles they are even raising the question of whether energy sources such as corn should really be used for heat instead of food. The concern is that food prices will go up as corn becomes a competitive fuel product as ethanol and biomass.
Pictured below, the 52,300 BTU multifuel heater from American Harvest can hold up to 63 pounds of fuel and burns corn, wood pellets, soy beans, olive pits, cherry pits, bio mass fuel grains, and processed silage. With features such as an automatic circulation exhaust blower, digital control board with built in diagnostics, and nine heat settings with heat and draft control this ain't you're grandma's stove. This particular model has received mixed reviews and while the technology is still new we encourage you to share your tips about other models below.
This new wave of biomass stoves and biomass heaters has opened up the opportunity for multiple biomass fuel sources to compete. In some circles they are even raising the question of whether energy sources such as corn should really be used for heat instead of food. The concern is that food prices will go up as corn becomes a competitive fuel product as ethanol and biomass.
Pictured below, the 52,300 BTU multifuel heater from American Harvest can hold up to 63 pounds of fuel and burns corn, wood pellets, soy beans, olive pits, cherry pits, bio mass fuel grains, and processed silage. With features such as an automatic circulation exhaust blower, digital control board with built in diagnostics, and nine heat settings with heat and draft control this ain't you're grandma's stove. This particular model has received mixed reviews and while the technology is still new we encourage you to share your tips about other models below.
Biomass is a hot topic in Canada where many cars and boats use partial biofuel mixtures and heating systems are designed with sustainability in mind. In fact, many types of forest produced biomass, including wood chips and vegetation, are in high demand for use as fuel in specially designed power generation stations. This large scale demand for forest produced biomass has lead to the first ever biomass legal policy in New Brunswick.
This new policy was developed over the course of two years from research conducted at the University of New Brunswick and will apply to eight million acres of Crown forest land; total Crown land is shown on the map below. The studies were focused on determining how much forest biomass material defined as "tree tops, branches, foliage, non-merchantable woody stems of trees and shrubs, pre-existing dead woody material and flail chipping residue" could be removed without harming the forest. Under the new policy over 600 cubic miles of tree tops, twigs, and branches will be available every year as fuel for power generation.
This is a landmark international decision as other nations look to alternative fuels and harvesting techniques. New Brunswick Canada has lead the way with this new policy and future impact studies will shed more light on the topic; the full story including Canadian metrics can be found here.
This new policy was developed over the course of two years from research conducted at the University of New Brunswick and will apply to eight million acres of Crown forest land; total Crown land is shown on the map below. The studies were focused on determining how much forest biomass material defined as "tree tops, branches, foliage, non-merchantable woody stems of trees and shrubs, pre-existing dead woody material and flail chipping residue" could be removed without harming the forest. Under the new policy over 600 cubic miles of tree tops, twigs, and branches will be available every year as fuel for power generation.
This is a landmark international decision as other nations look to alternative fuels and harvesting techniques. New Brunswick Canada has lead the way with this new policy and future impact studies will shed more light on the topic; the full story including Canadian metrics can be found here.
While driving around Palo Alto last week I spotted one of the Stanford University bio diesel buses (part of the Marguirite public transit system) making it's rounds. Stanford currently uses B5 biodiesel for these busses, a blend of conventional petroleum diesel with 5% vegetable derived diesel fuel. While this may not sound like much, especially compared with the programs at the University of Colorado which have had buses running on 100% biodiesel since 2003, it does represent progress.
The Stanford program began in June 2005 with the 5% B5 grade fuel described above and has since begun transitioning to a higher and higher percentage of biofuels. As the busses progressively green their fuel the stickers on the side of each bus will evolve to show more and more yellow within the black droplet (representing conventional diesel). As of October 28th 2008 however, when we took the pictures posted below, the busses are still at 5% as shown in the sticker. Keep your eye out for these busses and read more about the Stanford program here.
The Stanford program began in June 2005 with the 5% B5 grade fuel described above and has since begun transitioning to a higher and higher percentage of biofuels. As the busses progressively green their fuel the stickers on the side of each bus will evolve to show more and more yellow within the black droplet (representing conventional diesel). As of October 28th 2008 however, when we took the pictures posted below, the busses are still at 5% as shown in the sticker. Keep your eye out for these busses and read more about the Stanford program here.
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