I picked up an interesting book at work the other day:
Power Hungry:The Myths of "Green" Energy and the Real Fuels of the Future by Robert Bryce.
Although the book deals with all modalities of energy, fossil and renewable, for purposes of this discussion I naturally wanted to focus on alternative fuels for automotive use only so after reading this book I did some additional research. Some of you may be interested in what I discovered.
Most of our members are familiar with the joule (J) which is the derived unit of energy or work in the International System of Units (SI). It's equal to the energy expended, or work done, in applying a force of 1 newton through a distance of 1 meter (1 newton meter or one N-m). It is used as the measure of the energy density (chemical potential energy) of fuels.
Fossil carbon has been the world's predominant source of energy for the past 150 years primarily because of its intrinsic mass and volume energy densities. One kilogram of crude oil contains nearly 50 mega-joules of chemical potential energy, which is enough to lift 1 metric ton to a height of around 5,000 meters. Additionally, crude oil happens to be liquid at Earth's surface temperatures making it easy to store, transport, and convert. The energy densities of natural gas and coal, around 55 MJ/kg and 20-35 MJ/kg respectively, are similar to those of crude oil. Fossil carbon is packed with chemical energy because C and the H2 it stabilizes in a condensed form react strongly with O2 to form CO2 and H2O. As well, geologic processes have concentrated large quantities of fossil carbon into relatively small geographic areas such as coal mines and oil fields. Biofuels such as ethanol and biosynthetic diesel can have volume and mass energy densities equal to that of fossil carbon, but since they have to be harvested over large areas their real energy densities are considerably lower.
Renewable energy, unlike fossil carbon, is harnessed dynamically from the environment and therefore won't be as useful as fossil carbon until it can be stored and transported with similar ease. Although our technology is constantly attempting to improve energy storage, and progress is being made, the science of thermodynamics can be used to calculate the upper limits of what's possible for a variety of technologies. When this is done, it's clear that many technologies will never compete with fossil carbon in the realm of energy density.
Turning now to batteries, today's lead-acid types can store about .1 MJ/kg which is about 500 times less than crude oil. Although these batteries can be improved, any battery based on the standard lead-oside/sulfuric acid chemistry is limited by foundational thermodynamics to less than .7 MJ/kg.
Due to the theoretical limits of lead-acid batteries, work has progressed on other approaches such as lithium-ion batteries which involve the oxidation and reduction of carbon and a transition metal such as cobalt. These batteries have already improved upon the energy density of lead-acid types by a factor of about 6 to around .5 MJ/kg. But as currently designed, they have a theoretical energy density limit of around 2 MJ/kg. If current theoretical research regarding the substitution of silicon for carbon in the anodes is ever realized in a practical way, the theoretical limit on lithium-ion batteries might break 3 MJ/kg. Therefore, the maximum theoretical potential of advanced lithium-ion bagtteries that haven't been demonstrated to work yet is still only about 6% of crude oil. Speculating about the possibillity of an ultra-advanced lithium battery that uses lighter elements than cobalt and carbon, without considering the practicality of building such a battery and assuming it could actually be made, it's theoretical limit would be around 5 MJ/kg.
So the best batteries are currently getting 10% of the thermodynamically-determined physical upper boundary and even with improved required materials such as electrolytes, separators, current collectors and packaging, it's believed that we're unlikely to improve the energy density by more than about a factor of 2 within the next 20 years. This means that hydrocarbons, including both fossil carbon and biofuels, are still a factor of 10 better than the physical upper boundary and likely to be 25 times better than lithium batteries will ever be.
One approach that is thought to hold promise is the use of fuel cells with liquid and gaseous fuels, the two obvious choices being H2 and hydrocarbons. In terms of energy per unit mass, H2 beats crude oil and natural gas by a factor of almost 3. Unfortunately, H2 is a gas at Earth's surface so its volume density is miniscule unless it's compressed to several hundred atmospheres of pressure. At 700 bars (10,153 psi), for example, H2 has an energy volume density of around 6 MJ/liter while gasoline at 1 bar has about 34 MJ/liter. Both H2 and hydrocarbons can be produced from renewable energy sources though doing so economically and at a global scale seems an impossible dream currently. Would there be any corn left, anywhere in the world, for we and the cattle to eat?
So what conclusion can we draw from all of the foregoing? Nature's gift to us of hydrocarbons in the form of fossil carbon and biomass, and their energy-mass and energy-volume densities is superior to the thermodynamic limits of nearly all conceivable alternatives. Consequently, there's little doubt that hydrocarbons of one form or another will be humanity's primary energy storage medium for quite some time to come. Like it or not!
So much for the Volt, the Tesla, the Priapus and all the rest of their ilk.
Oh, just as an aside and for purposes of comparison, U235 in nuclear reactors contains 79 million MJ/kg.
Happy Motoring!
Power Hungry:The Myths of "Green" Energy and the Real Fuels of the Future by Robert Bryce.
Although the book deals with all modalities of energy, fossil and renewable, for purposes of this discussion I naturally wanted to focus on alternative fuels for automotive use only so after reading this book I did some additional research. Some of you may be interested in what I discovered.
Most of our members are familiar with the joule (J) which is the derived unit of energy or work in the International System of Units (SI). It's equal to the energy expended, or work done, in applying a force of 1 newton through a distance of 1 meter (1 newton meter or one N-m). It is used as the measure of the energy density (chemical potential energy) of fuels.
Fossil carbon has been the world's predominant source of energy for the past 150 years primarily because of its intrinsic mass and volume energy densities. One kilogram of crude oil contains nearly 50 mega-joules of chemical potential energy, which is enough to lift 1 metric ton to a height of around 5,000 meters. Additionally, crude oil happens to be liquid at Earth's surface temperatures making it easy to store, transport, and convert. The energy densities of natural gas and coal, around 55 MJ/kg and 20-35 MJ/kg respectively, are similar to those of crude oil. Fossil carbon is packed with chemical energy because C and the H2 it stabilizes in a condensed form react strongly with O2 to form CO2 and H2O. As well, geologic processes have concentrated large quantities of fossil carbon into relatively small geographic areas such as coal mines and oil fields. Biofuels such as ethanol and biosynthetic diesel can have volume and mass energy densities equal to that of fossil carbon, but since they have to be harvested over large areas their real energy densities are considerably lower.
Renewable energy, unlike fossil carbon, is harnessed dynamically from the environment and therefore won't be as useful as fossil carbon until it can be stored and transported with similar ease. Although our technology is constantly attempting to improve energy storage, and progress is being made, the science of thermodynamics can be used to calculate the upper limits of what's possible for a variety of technologies. When this is done, it's clear that many technologies will never compete with fossil carbon in the realm of energy density.
Turning now to batteries, today's lead-acid types can store about .1 MJ/kg which is about 500 times less than crude oil. Although these batteries can be improved, any battery based on the standard lead-oside/sulfuric acid chemistry is limited by foundational thermodynamics to less than .7 MJ/kg.
Due to the theoretical limits of lead-acid batteries, work has progressed on other approaches such as lithium-ion batteries which involve the oxidation and reduction of carbon and a transition metal such as cobalt. These batteries have already improved upon the energy density of lead-acid types by a factor of about 6 to around .5 MJ/kg. But as currently designed, they have a theoretical energy density limit of around 2 MJ/kg. If current theoretical research regarding the substitution of silicon for carbon in the anodes is ever realized in a practical way, the theoretical limit on lithium-ion batteries might break 3 MJ/kg. Therefore, the maximum theoretical potential of advanced lithium-ion bagtteries that haven't been demonstrated to work yet is still only about 6% of crude oil. Speculating about the possibillity of an ultra-advanced lithium battery that uses lighter elements than cobalt and carbon, without considering the practicality of building such a battery and assuming it could actually be made, it's theoretical limit would be around 5 MJ/kg.
So the best batteries are currently getting 10% of the thermodynamically-determined physical upper boundary and even with improved required materials such as electrolytes, separators, current collectors and packaging, it's believed that we're unlikely to improve the energy density by more than about a factor of 2 within the next 20 years. This means that hydrocarbons, including both fossil carbon and biofuels, are still a factor of 10 better than the physical upper boundary and likely to be 25 times better than lithium batteries will ever be.
One approach that is thought to hold promise is the use of fuel cells with liquid and gaseous fuels, the two obvious choices being H2 and hydrocarbons. In terms of energy per unit mass, H2 beats crude oil and natural gas by a factor of almost 3. Unfortunately, H2 is a gas at Earth's surface so its volume density is miniscule unless it's compressed to several hundred atmospheres of pressure. At 700 bars (10,153 psi), for example, H2 has an energy volume density of around 6 MJ/liter while gasoline at 1 bar has about 34 MJ/liter. Both H2 and hydrocarbons can be produced from renewable energy sources though doing so economically and at a global scale seems an impossible dream currently. Would there be any corn left, anywhere in the world, for we and the cattle to eat?
So what conclusion can we draw from all of the foregoing? Nature's gift to us of hydrocarbons in the form of fossil carbon and biomass, and their energy-mass and energy-volume densities is superior to the thermodynamic limits of nearly all conceivable alternatives. Consequently, there's little doubt that hydrocarbons of one form or another will be humanity's primary energy storage medium for quite some time to come. Like it or not!
So much for the Volt, the Tesla, the Priapus and all the rest of their ilk.
Oh, just as an aside and for purposes of comparison, U235 in nuclear reactors contains 79 million MJ/kg.
Happy Motoring!
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