Coal gasification is the conversion of coal into gases that can be used directly as fuel or as feedstocks for the creation of liquid fuels (e.g. hydrocarbons) or for commercial processes such as the production of fertilizers and other chemicals, including pharmaceuticals. As oil stocks begin to run short and an inexorable demand is placed on natural gas to substitute for it, either to be burned per se or indeed turned into synthetic oil, we face an energy supply crisis which will hit civilization across the board, with soaring prices of all goods including food, and even food shortages, since modern agriculture is now entirely underpinned by oil and gas: e.g. oil to run farm machinery and gas to produce hydrogen which is combined with nitrogen to make ammonia, the mainstay raw material for synthetic fertilizers.
If this crisis will begin to bite within a decade following the arrival of Peak Oil, and then grip humankind more determinedly in subsequent decades, what is there that might be implemented to take the place of oil and gas? The only other carbon-based material in substantial abundance is coal, and so we need to dig more of it. There are estimated to be upward of six trillion tonnes of coal available for extraction on earth, and probably much more in locations that are hard to access. For example, some three trillion tonnes of coal have been identified under the sea off the coast of Norway, but this is not amenable to conventional mining and extraction. The UK has around 220 million tonnes of coal (to be compared with the 60 million tonnes or so we use each year, two thirds of which is imported) in known mines and it is thought that a total of 1.5 billion tonnes could be got by extending the existing mining infrastructure - i.e. just keep digging the seams that are already underway. Indeed, some mines that were closed in the 1980's in Yorkshire and in South Wales are now being re-opened, and so there are efforts ongoing in this respect.
It was however, estimated that there are some 190 billion tonnes of coal altogether underlying the UK, particularly if regions under the southern part of the North Sea are included in the tally, as I commented in a previous posting ("Coal May be Crowned King after all!", Monday December 4th, 2006). However, while this would amount apparently to nearly 700 years worth of supply, not all of that is readily accessible, and to dig it out by conventional means, covering an underground area of probably around one third that of the UK mainland, is not a realistic option unless some extremely efficient new technology were devised and implemented by the industry.
As an alternative strategy, the conversion of coal to gas in situ is being considered. The putative process is called Underground Coal Gasification (UCG). In UCG, two boreholes are drilled into a coal-seam underground, one to introduce oxygen and water (to provide steam), and the second to bring the gaseous products of the partial combustion/steam reforming of the coal to the surface. The gas will consist principally of hydrogen and carbon monoxide along with smaller amounts of methane and other flammable hydrocarbons that are formed by in situ pyrolysis of the coal itself in consequence of the high temperatures incurred.
There are many potential advantages to the UCG approach, namely that actual coal extraction is unnecessary, along with the usual detritus of coal mining, e.g. slag-heaps of rock and coal waste (such as engulfed a school at Aberfan, in South Wales, forty years ago, killing 129 children). Furthermore, the process would make available a clean fuel/chemical feedstock gas, and on our own shores. As noted, there is the considerable appeal too that it might be thus possible to utilise huge stocks of coal that would otherwise remain inaccessible. The essential premise of UCG has been shown to work in trials e.g. in Russia, but it is mandatory to evaluate the controllability of the process over sustained periods of operation (we are talking about hundreds of years), and any negative environmental impact on underground aquifers (i.e. groundwater pollution) and on any adjacent strata, such as subsidence. The latter is of particular concern since coal often intersperses rock layers and provides a supporting medium for them and so, if the coal is dug out, either literally, or by conversion from solid to gas, will not the overlying rock simply collapse into the "hole" that has been created?
The gasification of coal seams in situ was first done by the Russians in the 1930's and processes have been in operation since WWII. One, ongoing in Uzbekistan, is still in operation now, and experimental UCG technology is being undertaken in Australia, as advised by experts on the subject from Uzbekistan. In the 1950's, Britain established its own UCG trial in shallow mines in Derbyshire with success, but the National Coal Board later abandoned the project on economic grounds. In the US, technology from the oil and gas industries was adapted in the 1970's to make UCG a more readily controllable process, while in Europe UCG has been applied to work both shallow and deep seams; the latter in Spain during 1992 - 1999, and funded by the British DTI, the EU and Spanish and Belgian organisations.
Hence the overall vista for UCG appears optimistic, and a six-year project has been inaugurated in the UK at a cost of $15 - 20 million, with the following aims:
(1) To improve the accuracy of in-seam drilling.
(2) To examine the implications of burning UCG gas in electricity-generating turbines.
(3) To evaluate the real land-reserve capacity for UCG.
(4) To identify a semi-commercial site to undertake the process.
(5) To work-out the likely costs.
(6) To carry-out a feasibility study of offshore coal-exploitation by UCG methods.
It sounds great, so let's get started! What are our realistic alternatives? Nuclear, renewables on a gargantuan scale, or increasingly vulnerable imports of natural gas from unstable regions of the world. If it works, UCG answers some questions about security of supply, and with carbon-capture technology it could also cut our CO2 emissions. It still doesn't mean we can readily match our current requirements of imported fuel (although UCG gas could be converted into some synthetic fuel using Fisher-Tropsch technology) and so transportation remains almost certain to be curbed on a substantial scale, hence forging local communities/economies, if people need to stay put and it is less feasible to transport food/goods over significant distances.
Related Reading.
http://www.coal.gov.uk/resources/cleanercoaltechnologies/ucgoverview.cfm
Wednesday, October 17, 2007
Saturday, October 13, 2007
Ulf Bossel, Platinum and the Hydrogen Economy?
Ulf Bossel put the cat among the pigeons a while ago, by suggesting that the establishment of a Hydrogen Economy is a non-starter, compared with simply using the electrons directly that would be employed to split water into its constituent elements, oxygen and hydrogen. The European Cell Forum, which is committed to the creation of a future based on sustainable and safe sources of energy, has decided to carry on its promotion of fuel cells for sustainably produced fuels, but that it will no longer support the development of fuel cells that require "hypothetical" supplies of fuel such as hydrogen.
This may appear odd, since we hear about hydrogen all the time and to the degree that it is easy to think that when the oil "runs-out" hydrogen will simply be tapped into as a substitute for it. The problem is that hydrogen does not occur free in nature but must be freed from other elements, such as oxygen in water, with which it is naturally combined, and the separation of elements requires other forms of energy. Almost all the hydrogen used currently in the world - as a chemical feedstock e.g. for oil refining and making artificial fertilizers - is made by steam-reforming natural gas, and there is a CO2 budget that must be costed-in, hence hydrogen from this source is not clean but contributes to CO2 emissions. Furthermore, it consumes natural gas, and so there is a pressure placed on another resource in accord with the indisputable fact that it takes resources to extract resources. Ideally therefore, that hydrogen should be produced by e.g. water electrolysis using electricity made from renewable sources.
However, Bossel's argument is that the electrons produced from e.g. wind, hydro, wave or whatever sources could be used directly say to charge batteries or to make hydrocarbon fuels, even methanol, as George Olah is promulgating, at an efficiency of about three times that which would be obtained by converting them into hydrogen and processing and distributing the material to "burn" it in fuel cells. Bossel's argument goes along the lines that there are energy losses incurred at each step in the necessary chain of actions, in accord with the incontrovertible Second Law of Thermodynamics - basically, entropy.
He points-out that there are three principal loss-makers in the chain, namely production, storage and distribution. There is obviously a loss of 50 - 60% incurred when the material is burned in the fuel cell, but in its favour is the fact that an efficiency of even 40 - 50% is substantially above the Carnot-cycle limit (Thermodynamics again) of around 35% for a typical internal combustion engine. The losses may be summarised as follows: 90% efficiency for rectifying alternating current to DC to run the electrolyzer; 75% overall efficiency (ideal) for the electrolyzer itself; and then the storage of the bulky hydrogen gas either as a highly compressed gas, which takes about 20% of the energy content of the hydrogen to compress it (or as a cryogenic liquid, which takes 30 - 40% to produce); 10% for distribution and say 50% efficiency for the fuel cell itself, which amounts to about a 25% efficiency overall.
There are electrolyzer units that can produce high pressure hydrogen and if each gas-station were to make its own hydrogen by electrolysis, much of the distribution losses (probably 30%) might be recovered. A report has been published by a firm of independent analysts in Germany which is critical of some of Bossel's figures especially in regard to storage and transmission, particularly across large distances say from sunny north Africa (if the hydrogen were produced using PV technology which would be much more efficient there) by pipeline to Europe. However, an in-situ arrangement as I allude to would surely get around that, presuming we could make enough renewable electricity, or if there were a grid of electrons (rather than of hydrogen) including north African PV, European wind-power, North Sea wave energy and so on, such power might be supplied to run local electrolysis equipment, which would avoid actual hydrogen transmission. But if Bossel is right, why not use these electrons in a more direct manner?
On a tit-for tat basis, we can make the following calculation:
The heat of combustion of hydrogen is -285 kJ/mol, and so 1 kg of hydrogen = 1000 g/2 g/mol x -285 kJ= -142,500 kJ = 1.425 x 10^8 J.
We get through 82 million tonnes of oil altogether annually in the UK and we use 60 million tonnes of that for fuel. The energy content of oil is rated at 42 GJ/tonne and so that 60 million tonnes "contains" 60 x 10^6 x 42 x 10^9 Joules = 2.52 x 10^18 J of energy.
Hydrogen can be produced at a pressure of up to 10,000 psi by electrolysis at a rate of 60.5 kW/kg of H2. Hence the equivalent H2 to match that amount of oil is:
2.52 x 10^18 J/1.425 x 10^8 J/kg = 1.768 x 10^10 kg H2. Bossel has used the conversion factor of 1.5, i.e. that H2 can be used with 1.5 times the recoverable energy efficiency of gasoline. Since gasoline gives an approximately 14% well-to-wheel efficiency that would make about 21% overall for hydrogen, which seems a bit low and I would think that say 59% for the electrolysis system x 90% for rectification x 50% for the fuel cell = 26.6% is more like it.
However, let's consider the generating capacity the whole enterprise would need. To make 1.768 x 10^10 kg of H2 over a year, i.e. 8760 hours, would require:
1.768 x 10^10 kg x 60.5 x 10^3 (W/kg H2)/8760 = 122.1 GW. But this figure is mitigated according to the efficiency with which hydrogen may be used. If Bossel is right, this becomes 81.4 GW or let's call it a factor of two (which seems more reasonable), making it 61.0 GW.
Either way, we would need a colossal installation of renewables, e.g. 2 MW wind-turbines, with a rated capacity of 2 MW - but an actual output of say 30% if placed offshore, which amounts to 0.6 MW per unit. Hence we would need 61 GW/0.6 MW = 100,000 of them. Probably these could be accommodated in the North Sea in a square of turbines 316 x 316 and at an average spacing of 0.5 km we are talking about an area of 160 km^2, which doesn't sound too bad, albeit that the weather in the North Sea is some of the roughest in the world, and so maintenance might prove a problem.
As an alternative, around 60 new nuclear reactors could be installed to make the electricity for hydrogen, and on top of the new generation required to replace the decommissioned current 31 reactors, actually equal in output to about 14 1 GW reactors, and so it would be necessary to quadruple this capacity by which means to install a "Hydrogen Economy" in the UK. I have been told that hydrogen could be made more efficiently using the thermal power from a nuclear reactor to run the iodine-sulphur cycle, rather than by electrolyzing water (50% compared to 35%) , but the installation capacity needed remains huge. If Bossel is right and electrons can be used with three times the efficiency than will be recovered (hydrogen actually re-generates electrons in the fuel cell, to turn wheels, in a chemically-fuelled electric car) by turning them into hydrogen, the installation capacity immediately falls to 20 new nuclear power stations, or about 33,000 turbines, which is still enormous but appears more achievable.
I am not ruling out hydrogen altogether but simply making the point that when oil supplies begin to wane, it is not a simple matter of switching from oil to hydrogen, but a new and vast infrastructure must be implemented first, to both produce and use hydrogen. The question looms: is it worth it, or might there not be better ways to deal with our impending transportation problems, such as relocalising society to use less transport? Even those who are profound advocates of the "Hydrogen Economy" need to address the problem that the PEM (Proton Exchange Membrane) cell relies on an electrode consisting partly of platinum (about 50 - 100 g worth), which is a metal so rare than only 150 tonnes of new platinum are produced each year, and well below the current and growing demand for it.
Admittedly, the 40% of world platinum that is presently put into catalytic converters could be fabricated into PEM cells, were the putative conversion from oil-power to H2-power to be made, but this is only sufficient to put around:
150 tonnes x 1000 kg/tonne x 1000 g/kg x 0.4/50 g/cell = 1.2 million new "vehicles" on the road each year, out of a world total of about 700 million. Hence in 15 years we could replace just 3% of the current number. Thus, unless more platinum is recovered on a huge scale (from sources as yet unknown to geology), or some alternative fuel cell technology is brought to a commercial level of development on some similarly immediate timescale, the enterprise looks set to fall at the last fence, in this, the last race that humankind will ever have to place bets on.
Related Reading.
(1) http://www.memagazine.org/backissues/membersonly/june02
(2) NREL National Renewable Energy Technology Laboratory, "Technology Brief: Analysis of Current-Day Commercial Electrolyzers."
(3) Ulf Bossel, Proceedings of the IEEE, Vol. 94, 2006, 1826.
(4) W.Weindorf, U.Buenger and J.Schindler, LBST, "Comments on the paper by Eliasson and Bossel 'The Future of the Hydrogen economy: Bright or Bleak. July 2003. www.efec.com/reports
This may appear odd, since we hear about hydrogen all the time and to the degree that it is easy to think that when the oil "runs-out" hydrogen will simply be tapped into as a substitute for it. The problem is that hydrogen does not occur free in nature but must be freed from other elements, such as oxygen in water, with which it is naturally combined, and the separation of elements requires other forms of energy. Almost all the hydrogen used currently in the world - as a chemical feedstock e.g. for oil refining and making artificial fertilizers - is made by steam-reforming natural gas, and there is a CO2 budget that must be costed-in, hence hydrogen from this source is not clean but contributes to CO2 emissions. Furthermore, it consumes natural gas, and so there is a pressure placed on another resource in accord with the indisputable fact that it takes resources to extract resources. Ideally therefore, that hydrogen should be produced by e.g. water electrolysis using electricity made from renewable sources.
However, Bossel's argument is that the electrons produced from e.g. wind, hydro, wave or whatever sources could be used directly say to charge batteries or to make hydrocarbon fuels, even methanol, as George Olah is promulgating, at an efficiency of about three times that which would be obtained by converting them into hydrogen and processing and distributing the material to "burn" it in fuel cells. Bossel's argument goes along the lines that there are energy losses incurred at each step in the necessary chain of actions, in accord with the incontrovertible Second Law of Thermodynamics - basically, entropy.
He points-out that there are three principal loss-makers in the chain, namely production, storage and distribution. There is obviously a loss of 50 - 60% incurred when the material is burned in the fuel cell, but in its favour is the fact that an efficiency of even 40 - 50% is substantially above the Carnot-cycle limit (Thermodynamics again) of around 35% for a typical internal combustion engine. The losses may be summarised as follows: 90% efficiency for rectifying alternating current to DC to run the electrolyzer; 75% overall efficiency (ideal) for the electrolyzer itself; and then the storage of the bulky hydrogen gas either as a highly compressed gas, which takes about 20% of the energy content of the hydrogen to compress it (or as a cryogenic liquid, which takes 30 - 40% to produce); 10% for distribution and say 50% efficiency for the fuel cell itself, which amounts to about a 25% efficiency overall.
There are electrolyzer units that can produce high pressure hydrogen and if each gas-station were to make its own hydrogen by electrolysis, much of the distribution losses (probably 30%) might be recovered. A report has been published by a firm of independent analysts in Germany which is critical of some of Bossel's figures especially in regard to storage and transmission, particularly across large distances say from sunny north Africa (if the hydrogen were produced using PV technology which would be much more efficient there) by pipeline to Europe. However, an in-situ arrangement as I allude to would surely get around that, presuming we could make enough renewable electricity, or if there were a grid of electrons (rather than of hydrogen) including north African PV, European wind-power, North Sea wave energy and so on, such power might be supplied to run local electrolysis equipment, which would avoid actual hydrogen transmission. But if Bossel is right, why not use these electrons in a more direct manner?
On a tit-for tat basis, we can make the following calculation:
The heat of combustion of hydrogen is -285 kJ/mol, and so 1 kg of hydrogen = 1000 g/2 g/mol x -285 kJ= -142,500 kJ = 1.425 x 10^8 J.
We get through 82 million tonnes of oil altogether annually in the UK and we use 60 million tonnes of that for fuel. The energy content of oil is rated at 42 GJ/tonne and so that 60 million tonnes "contains" 60 x 10^6 x 42 x 10^9 Joules = 2.52 x 10^18 J of energy.
Hydrogen can be produced at a pressure of up to 10,000 psi by electrolysis at a rate of 60.5 kW/kg of H2. Hence the equivalent H2 to match that amount of oil is:
2.52 x 10^18 J/1.425 x 10^8 J/kg = 1.768 x 10^10 kg H2. Bossel has used the conversion factor of 1.5, i.e. that H2 can be used with 1.5 times the recoverable energy efficiency of gasoline. Since gasoline gives an approximately 14% well-to-wheel efficiency that would make about 21% overall for hydrogen, which seems a bit low and I would think that say 59% for the electrolysis system x 90% for rectification x 50% for the fuel cell = 26.6% is more like it.
However, let's consider the generating capacity the whole enterprise would need. To make 1.768 x 10^10 kg of H2 over a year, i.e. 8760 hours, would require:
1.768 x 10^10 kg x 60.5 x 10^3 (W/kg H2)/8760 = 122.1 GW. But this figure is mitigated according to the efficiency with which hydrogen may be used. If Bossel is right, this becomes 81.4 GW or let's call it a factor of two (which seems more reasonable), making it 61.0 GW.
Either way, we would need a colossal installation of renewables, e.g. 2 MW wind-turbines, with a rated capacity of 2 MW - but an actual output of say 30% if placed offshore, which amounts to 0.6 MW per unit. Hence we would need 61 GW/0.6 MW = 100,000 of them. Probably these could be accommodated in the North Sea in a square of turbines 316 x 316 and at an average spacing of 0.5 km we are talking about an area of 160 km^2, which doesn't sound too bad, albeit that the weather in the North Sea is some of the roughest in the world, and so maintenance might prove a problem.
As an alternative, around 60 new nuclear reactors could be installed to make the electricity for hydrogen, and on top of the new generation required to replace the decommissioned current 31 reactors, actually equal in output to about 14 1 GW reactors, and so it would be necessary to quadruple this capacity by which means to install a "Hydrogen Economy" in the UK. I have been told that hydrogen could be made more efficiently using the thermal power from a nuclear reactor to run the iodine-sulphur cycle, rather than by electrolyzing water (50% compared to 35%) , but the installation capacity needed remains huge. If Bossel is right and electrons can be used with three times the efficiency than will be recovered (hydrogen actually re-generates electrons in the fuel cell, to turn wheels, in a chemically-fuelled electric car) by turning them into hydrogen, the installation capacity immediately falls to 20 new nuclear power stations, or about 33,000 turbines, which is still enormous but appears more achievable.
I am not ruling out hydrogen altogether but simply making the point that when oil supplies begin to wane, it is not a simple matter of switching from oil to hydrogen, but a new and vast infrastructure must be implemented first, to both produce and use hydrogen. The question looms: is it worth it, or might there not be better ways to deal with our impending transportation problems, such as relocalising society to use less transport? Even those who are profound advocates of the "Hydrogen Economy" need to address the problem that the PEM (Proton Exchange Membrane) cell relies on an electrode consisting partly of platinum (about 50 - 100 g worth), which is a metal so rare than only 150 tonnes of new platinum are produced each year, and well below the current and growing demand for it.
Admittedly, the 40% of world platinum that is presently put into catalytic converters could be fabricated into PEM cells, were the putative conversion from oil-power to H2-power to be made, but this is only sufficient to put around:
150 tonnes x 1000 kg/tonne x 1000 g/kg x 0.4/50 g/cell = 1.2 million new "vehicles" on the road each year, out of a world total of about 700 million. Hence in 15 years we could replace just 3% of the current number. Thus, unless more platinum is recovered on a huge scale (from sources as yet unknown to geology), or some alternative fuel cell technology is brought to a commercial level of development on some similarly immediate timescale, the enterprise looks set to fall at the last fence, in this, the last race that humankind will ever have to place bets on.
Related Reading.
(1) http://www.memagazine.org/backissues/membersonly/june02
(2) NREL National Renewable Energy Technology Laboratory, "Technology Brief: Analysis of Current-Day Commercial Electrolyzers."
(3) Ulf Bossel, Proceedings of the IEEE, Vol. 94, 2006, 1826.
(4) W.Weindorf, U.Buenger and J.Schindler, LBST, "Comments on the paper by Eliasson and Bossel 'The Future of the Hydrogen economy: Bright or Bleak. July 2003. www.efec.com/reports
Tuesday, October 09, 2007
Mass of the Earth.
I had a phone-call from a friend the other morning, who was driving her kids to school, aged 8 and 11. They wanted to know, "if you could weigh the Earth, how heavy would it be?" I recalled the mass to be about 6 x 10^21 tonnes, which when I checked is about right, and so I said, "it's 6 thousand, million, million, million tonnes... No, million, million, million; not million million," and then I said, "that's the trouble, once numbers get bigger than a few thousand, we can't imagine what they mean!" Then the 11 year old asked, "how do you know how heavy it is?" and I said, "you can measure it from its gravity," which seemed to suffice for that moment. It's a good question, though, and the answer provides a sense of perspective regarding the planet.
In the case of the Earth, we can estimate its mass because we know the acceleration due to gravity at some point near the Earth's surface, g = 9.8 m s^-2. This may be equated with the gravitational constant, G = 6.67 x 10^-11 m^3 kg^-1 s^-2 and the (mean) radius of the Earth, r = 6.37 x 10^6 m. Thus:
GmM/r^2 = mg,
where M = Earth's mass and m = some smaller mass close to the Earth's surface. By cancelling the terms, m, and solving for M, we get:
M = gr^2/G
= 9.8 m s^-2 x (6.37 x 10^6)^2 m^2/6.67 x 10-^-11 m^3 kg^-1 s^-2 = 5.96 x 10^24 kg (i.e. about 6 x 10^21 tonnes).
Another approach to the problem is to use the "satellite method", which in the present case refers to the Earth-Moon system, but is used by astronomers to determine the masses of the other planets, the Sun, distant stars in binary systems, the Milky Way galaxy and even entire clusters of galaxies. We can express (according Newton's Law):
F(gravity) = GMm/r^2,
where G is the gravitational constant, M is the Earth's mass and m is the mass of the satellite (Moon), with r being the distance between the centres of the two bodies. We can further express for a simple circular orbit, the centrifugal force (which acts in opposition to the gravitational force):
F(centrifugal) = mv^2/r,
where v is the angular velocity of the satellite. For a stable stationary orbit to exist, the two forces must be equal and opposite, and so we can write that F(gravity = F(centrifugal), and hence:
GMm/r^2 = mv^2/r. By, once more, cancelling the terms, m, and rearranging, we get:
M = v^2 r/G.
Assuming a circular orbit, the mean angular velocity, v is the circumference of the orbit divided by the time (t) taken for the satellite to make that orbit, i.e. v = 2 pi r/t, and so if we substitute for v, we find:
M = 4 pi^2 r^3/G t^2.
Since the mean distance between the Earth-Moon centres is 384,000 km and the orbital period is 27.32 days ( = 2.36 x 10^6 seconds),
M = 4 pi^2 (3.84 x 10^8 m)^3/6.67 x 10^-11 m^3 kg^-1 s^-2 (2.36 x 10^6 s)^2 = 6.02 x 10^24 kg.
Thus the methods agree pretty well. In a posting "Carbon in the Sky" (January 6th 2007), I worked out that the mass of the Earth's atmosphere is about 5.3 x 10^18 kg, and so we can deduce that the relative mass of the atmosphere to the total mass of our blue planet Earth is 1/1,136,000 (i.e. less than one millionth of it), a value that might easily be thought insignificant...
but not from our point of view!
Related Reading.
(1) http://www.astronomycafe.net/qadir/q1223.html
(2) Nelkon and Parker, Advanced Level Physics, 4th Edition, Heinmann Educational Books, London, 1978.
In the case of the Earth, we can estimate its mass because we know the acceleration due to gravity at some point near the Earth's surface, g = 9.8 m s^-2. This may be equated with the gravitational constant, G = 6.67 x 10^-11 m^3 kg^-1 s^-2 and the (mean) radius of the Earth, r = 6.37 x 10^6 m. Thus:
GmM/r^2 = mg,
where M = Earth's mass and m = some smaller mass close to the Earth's surface. By cancelling the terms, m, and solving for M, we get:
M = gr^2/G
= 9.8 m s^-2 x (6.37 x 10^6)^2 m^2/6.67 x 10-^-11 m^3 kg^-1 s^-2 = 5.96 x 10^24 kg (i.e. about 6 x 10^21 tonnes).
Another approach to the problem is to use the "satellite method", which in the present case refers to the Earth-Moon system, but is used by astronomers to determine the masses of the other planets, the Sun, distant stars in binary systems, the Milky Way galaxy and even entire clusters of galaxies. We can express (according Newton's Law):
F(gravity) = GMm/r^2,
where G is the gravitational constant, M is the Earth's mass and m is the mass of the satellite (Moon), with r being the distance between the centres of the two bodies. We can further express for a simple circular orbit, the centrifugal force (which acts in opposition to the gravitational force):
F(centrifugal) = mv^2/r,
where v is the angular velocity of the satellite. For a stable stationary orbit to exist, the two forces must be equal and opposite, and so we can write that F(gravity = F(centrifugal), and hence:
GMm/r^2 = mv^2/r. By, once more, cancelling the terms, m, and rearranging, we get:
M = v^2 r/G.
Assuming a circular orbit, the mean angular velocity, v is the circumference of the orbit divided by the time (t) taken for the satellite to make that orbit, i.e. v = 2 pi r/t, and so if we substitute for v, we find:
M = 4 pi^2 r^3/G t^2.
Since the mean distance between the Earth-Moon centres is 384,000 km and the orbital period is 27.32 days ( = 2.36 x 10^6 seconds),
M = 4 pi^2 (3.84 x 10^8 m)^3/6.67 x 10^-11 m^3 kg^-1 s^-2 (2.36 x 10^6 s)^2 = 6.02 x 10^24 kg.
Thus the methods agree pretty well. In a posting "Carbon in the Sky" (January 6th 2007), I worked out that the mass of the Earth's atmosphere is about 5.3 x 10^18 kg, and so we can deduce that the relative mass of the atmosphere to the total mass of our blue planet Earth is 1/1,136,000 (i.e. less than one millionth of it), a value that might easily be thought insignificant...
but not from our point of view!
Related Reading.
(1) http://www.astronomycafe.net/qadir/q1223.html
(2) Nelkon and Parker, Advanced Level Physics, 4th Edition, Heinmann Educational Books, London, 1978.
Thursday, October 04, 2007
Building-Integrated Photovoltaics (BIPV).
Building-Integrated Photovoltaics (BIPV) is is a version of photovoltaic technology which is being increasingly incorporated into the fabric of both commercial ind domestic buildings as a major or augmenting source of electricity. The essential idea of BIPV is that a cost-reduction is possible for a PV system which is effectively made by fabricating solar-cells within the structure of a building element, e.g. a roof-tile, roof-membrane or a facade-panel. The BIPV modules are thus made component parts of the roof or walls of a building using normal construction techniques, but with the need for additional electrical connections. In Japan the technology has been encouraged in the form of government incentives for PV generally, and this has allowed a significant number of new houses to be fitted with BIPV; however, elsewhere, the relatively high cost of BIPV modules or their limited availability has restricted their use.
In some countries, extra incentives are offered for BIPV over PV but only in France is that differential sufficient to be of significant service. France currently makes around 80% of its electricity from nuclear power, having very little in the way of natural resources, and so as part of a strategy of being as independent as is possible on gas, oil and coal, an investment in solar-power might be expected, and particularly BIPV if it is the most cost-effective version of the latter.
I was reminded of BIPV by a recent e.mail promoting investments in the technology, and which among all the lush information about financial growth expected in the sector, were given some cornucopian figures to the effect that the sunlight hitting the Earth amounts to 174 petawatts of energy per day. In fact that is the amount impinging onto the upper atmosphere, and which is filtered to some extent but in anybody's terms it is an awful lot of energy. This can be broken down into tasty chunks, e.g. 1 petawatt is enough to keep New York City running for 3,846 days. It is claimed that installation of BIPV systems on a mass scale could eventually produce in a single month more energy than Saudi Arabia will in the next 50 years.
It all sounds great, but like is not being compared with like. All resources of energy are not the same in how they are used to release that energy. Most of Saudi's "energy" is oil, and that is used mostly to fuel transportation. More oil is used in the US for space heating and electricity generation than is the case in Europe, but the vast bulk of world oil goes to run cars and planes etc. However, the direct production of electricity from PV (and BIPV since it is cheaper to install as a part of the overall costs of a building) is a special case, and it would be used to power the latter only in the form of a huge (electric) vehicle infrastructure which would need to be installed within probably a couple of decades to keep the cars on the road, even if it could still keep all the lights on.
My final concern is over the resources necessary to collect the sunlight and turn it into electricity by BIPV or indeed any form of solar technology. Conventional silicon solar-cells are presently used in BIPV and this is probably too resource-intensive for widescale exploitation, or at least so on the world-scale that is needed to offset the fall in other energy resources expected. However, "thin-film" technology uses perhaps just 1% of the resources of silicon or cadmium sulphide, gallium arsenide etc. semiconductor materials currently required to make solar-cells, and might provide the lynch-pin of success, although much of it remains to be rendered commercial. As is true of many technologies (including new generations of nuclear reactors) proposed to produce energy into the future, if we are serious about them, we should be going hell-for-leather to install them as soon as possible, otherwise there will be nothing in place to meet our energy needs in the next couple of decades when oil is running short, and demand on gas supplies is relentless.
The fundamental equation seems to include both the actual amounts of resources available and how quickly we can both recover these and fabricate them into practical devices; and also whether we have enough energy remaining from other sources to do all of this by the time such action begins. Either way, time is of the essence.
Related Reading.
http://en.wikipedia.org/wiki/Solar_roof.
In some countries, extra incentives are offered for BIPV over PV but only in France is that differential sufficient to be of significant service. France currently makes around 80% of its electricity from nuclear power, having very little in the way of natural resources, and so as part of a strategy of being as independent as is possible on gas, oil and coal, an investment in solar-power might be expected, and particularly BIPV if it is the most cost-effective version of the latter.
I was reminded of BIPV by a recent e.mail promoting investments in the technology, and which among all the lush information about financial growth expected in the sector, were given some cornucopian figures to the effect that the sunlight hitting the Earth amounts to 174 petawatts of energy per day. In fact that is the amount impinging onto the upper atmosphere, and which is filtered to some extent but in anybody's terms it is an awful lot of energy. This can be broken down into tasty chunks, e.g. 1 petawatt is enough to keep New York City running for 3,846 days. It is claimed that installation of BIPV systems on a mass scale could eventually produce in a single month more energy than Saudi Arabia will in the next 50 years.
It all sounds great, but like is not being compared with like. All resources of energy are not the same in how they are used to release that energy. Most of Saudi's "energy" is oil, and that is used mostly to fuel transportation. More oil is used in the US for space heating and electricity generation than is the case in Europe, but the vast bulk of world oil goes to run cars and planes etc. However, the direct production of electricity from PV (and BIPV since it is cheaper to install as a part of the overall costs of a building) is a special case, and it would be used to power the latter only in the form of a huge (electric) vehicle infrastructure which would need to be installed within probably a couple of decades to keep the cars on the road, even if it could still keep all the lights on.
My final concern is over the resources necessary to collect the sunlight and turn it into electricity by BIPV or indeed any form of solar technology. Conventional silicon solar-cells are presently used in BIPV and this is probably too resource-intensive for widescale exploitation, or at least so on the world-scale that is needed to offset the fall in other energy resources expected. However, "thin-film" technology uses perhaps just 1% of the resources of silicon or cadmium sulphide, gallium arsenide etc. semiconductor materials currently required to make solar-cells, and might provide the lynch-pin of success, although much of it remains to be rendered commercial. As is true of many technologies (including new generations of nuclear reactors) proposed to produce energy into the future, if we are serious about them, we should be going hell-for-leather to install them as soon as possible, otherwise there will be nothing in place to meet our energy needs in the next couple of decades when oil is running short, and demand on gas supplies is relentless.
The fundamental equation seems to include both the actual amounts of resources available and how quickly we can both recover these and fabricate them into practical devices; and also whether we have enough energy remaining from other sources to do all of this by the time such action begins. Either way, time is of the essence.
Related Reading.
http://en.wikipedia.org/wiki/Solar_roof.
Tuesday, October 02, 2007
Peak Oil 10-20 years away, according to WEC.
The debate continues and we will not know the answer to the question of when peak oil will arrive until it does exactly that. Nor will we know it at the time, but only by looking at production some years beyond it, which will show a fall in output from the maximum (peak). It is estimated by the World Energy Council (WEC) that proven recoverable reserves of oil stood at 1.215 trillion barrels (160 billion tonnes), at the end of 2005, which is somewhat higher by 117 billion barrels than were costed at the end of 2002 which amounts to an extra 4 years supply given that we get through 30 billion barrels a year and rising, worldwide.
Most of the world's oil lies under the Middle East to the tune of 61% of the total; 11% lies under Africa; South America and Europe - including the whole of the Former USSR - have 8% each; while North America holds less than 5% of the total. WEC concludes that oil will not run-out as such for many years but that we were likely to see peak oil within 10 - 20 years; a figure to be compared with the Norwegian Statoil's recent prediction that it will come somewhere between 2010 and 2015. To be fair, the peak is imminent. It is debatable just how much oil Saudi has amid concerns that the regime has revised upward its estimates of its oil holdings, and this is true across the Middle East in general.
Cheap oil will run-out first - world light crude production peaked at the end of 2005 - and following the peak the commodity itself, and everything that depends on it, which is everything, will rise inexorably in price. The price of a barrel of oil is now around $84, which is a short throw from the putative $100 barrel that seemed outlandish as a prospect only a few years ago, but now appears an inevitability, and then $150, $200 or who knows how much? Transportation will be hit hard and as I have predicted throughout these postings, I see no alternative but to curb the use of cars, trucks and planes on a massive scale, resulting in the localisation of communities based on local economies, not strawberries and all manner of consumer products flown thousands of miles to us. I sometimes speculate that the economic miracle in China and India may prove a flash in the pan, since it is largely those of us in the West who buy their goods from them, and if we cannot readily ship and fly them over, then where is the incentive to make them in the first place?
Reserves of natural gas are, in contrast, reasonably healthy. The volume of proven gas reserves have doubled since 1980, as a result of new technologies for exploration and more encouraging estimates of the reserves held in existing fields. It is thought there is sufficient gas to last another 56 years. However, it is the Middle East which holds the trump card, and for example, 44% of the world's gas is contained in about 20 mega and supergiant fields, and nearly half of that is the North Field/South Pars which lies under the waters of Qatar and Iran.
WEC acknowledge that gas exploration is a younger technology than oil exploration, and through its further developments, gas might be brought out from deeper and more complex geologies. For example, coal-bed methane is already a significant contribution to the amount of gas used worldwide, and non-conventional sources such as tight gas sands and methane-hydrates could be harvested in the future. Gas can of course be converted into synthetic crude oil, as I have described before, by steam-reforming it into syngas and catalytic transformation of the latter into liquid hydrocarbons using Fischer-Tropsh methods.
Related Reading.
"Peak Oil 10-20 years away, claims world energy council," http://www.thisisnorthscotland.co.uk/displayNode.jsp?nodeId=149212&command=
displayContent&sourceNode=150624&contentPK=18540474&folderPk=85744&pNodeId=150607
Most of the world's oil lies under the Middle East to the tune of 61% of the total; 11% lies under Africa; South America and Europe - including the whole of the Former USSR - have 8% each; while North America holds less than 5% of the total. WEC concludes that oil will not run-out as such for many years but that we were likely to see peak oil within 10 - 20 years; a figure to be compared with the Norwegian Statoil's recent prediction that it will come somewhere between 2010 and 2015. To be fair, the peak is imminent. It is debatable just how much oil Saudi has amid concerns that the regime has revised upward its estimates of its oil holdings, and this is true across the Middle East in general.
Cheap oil will run-out first - world light crude production peaked at the end of 2005 - and following the peak the commodity itself, and everything that depends on it, which is everything, will rise inexorably in price. The price of a barrel of oil is now around $84, which is a short throw from the putative $100 barrel that seemed outlandish as a prospect only a few years ago, but now appears an inevitability, and then $150, $200 or who knows how much? Transportation will be hit hard and as I have predicted throughout these postings, I see no alternative but to curb the use of cars, trucks and planes on a massive scale, resulting in the localisation of communities based on local economies, not strawberries and all manner of consumer products flown thousands of miles to us. I sometimes speculate that the economic miracle in China and India may prove a flash in the pan, since it is largely those of us in the West who buy their goods from them, and if we cannot readily ship and fly them over, then where is the incentive to make them in the first place?
Reserves of natural gas are, in contrast, reasonably healthy. The volume of proven gas reserves have doubled since 1980, as a result of new technologies for exploration and more encouraging estimates of the reserves held in existing fields. It is thought there is sufficient gas to last another 56 years. However, it is the Middle East which holds the trump card, and for example, 44% of the world's gas is contained in about 20 mega and supergiant fields, and nearly half of that is the North Field/South Pars which lies under the waters of Qatar and Iran.
WEC acknowledge that gas exploration is a younger technology than oil exploration, and through its further developments, gas might be brought out from deeper and more complex geologies. For example, coal-bed methane is already a significant contribution to the amount of gas used worldwide, and non-conventional sources such as tight gas sands and methane-hydrates could be harvested in the future. Gas can of course be converted into synthetic crude oil, as I have described before, by steam-reforming it into syngas and catalytic transformation of the latter into liquid hydrocarbons using Fischer-Tropsh methods.
Related Reading.
"Peak Oil 10-20 years away, claims world energy council," http://www.thisisnorthscotland.co.uk/displayNode.jsp?nodeId=149212&command=
displayContent&sourceNode=150624&contentPK=18540474&folderPk=85744&pNodeId=150607
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