This is something I've wanted to do for some time now.
Note that the judgements on this list, I've tried to base on scientific principles more than anything else.
So, to the list.
A summary for those who are lazy:
Of the fuels for transport, the short term solution should be based on natural gas in my opinion, and maybe grid-electricity. Ethanol is a bad idea IMO. Longer-term, we should take a serious look at methane clathrates but ultimately we should be going for hydrogen - although it faces huge technological problems. As for energies: basically it comes down to wind, solar and nuclear.
SECTION I. FUELS
1. Natural Gas (LPG/LNG)
Liquefied Natural Gas as suggested - mostly ethane, propane and butane (please tell me I got it in the right order) and bits and pieces of other gases.
This is probably the most feasible, most economic way of reducing oil usage in the short term. The reason is simple. The chemical formula for ethane is C2H6 - that means 3 hydrogens to one carbon. The general rule for hydrocarbon fuels is that the higher the hydrogen-to-carbon ratio, the better the fuel - i.e. the more efficient, the more energy you get per gram - AND the less carbon dioxide you emit (this is why petrol is 'bad' and coal very, very, very bad, and hydrogen very very 'good'). Win-win on both fronts. Obviously we already have the technology and the resources to convert a large section of the 'oil economy' to LPG/LNG (Australia in the last year or two introduced quite a large subsidy for converting cars to LPG/LNG) - although technological problems still remain (transportation requires liquefication, and that's a difficult and energy-intensive process in bulk. Only recently has this problem been overcome to an adequate level).
In the medium-term onwards, though, this probably won't do as a solution. You still are putting out carbon, although at a markedly reduced rate, and eventually you'll run into the same problem as we currently (or very soon) have with oil: you'll use it faster than you can find it. Plus, these light hydrocarbons are way, way, way more powerful greenhouse gases than carbon dioxide. Any major leakage and you quickly nullify the carbon advantage you get from this fuel.
2. Ethanol (and other biofuels)
This one has had a lot of hype: a lot of people think that this is the centrepiece of the short-to-medium term solution.
But I don't. I personally think that this is a fuel that is just as bad - if not worse - than petroleum. For a range of reasons.
Firstly, it's rather inefficient as a fuel. Ordinary petroleum has a heat of combustion of roughly 50 J/g (that means for every gram you burn you get 50 joules), varies a bit with regional differences in the composition of the fuel but basically about that. Natural gas is about the same (hence its utility). But ethanol has a heat of combusion of about 30 J/g, so you get about 60% of the energy per gram of ethanol compared to petrol. This negates a good deal of the carbon advantage you gain by using a lighter fuel - you have to burn more fuel to get the same distance (about a third more - and this is something that has been noticed and documented when it has been used as a fuel). While this in turn is compensated for by the fact that ethanol-burning engines are more efficient in themselves, it does not leave me particularly impressed. Needless to say it also places it at a big disadvantage in comparison to natural gas.
The second reason is that producing corn-based ethanol is more than just "Corn + Magic = Fuel". It is a hugely complex and energy-intensive process. The operation of the plants in themselves - the fuel alone - is a huge task, expensive and carbon-intensive. This is just one part of a very, very expensive and carbon-intensive process which nullifies a lot of the advantages - carbon and fuelwise - there are from ethanol (advantages which in themselves are slender in comparison to other fuels). Some have even argued that this outweighs the advantages, but it any cases, it weakens the case for this fuel.
Final reason. With food prices going upwards and probably continuing to do so, is it really that wise to be using lots of land - which, by the way, will be increasingly valuable in terms of agricultural output vs. need - and LOTS of water (corn is very water-intensive), which could be scarce in future years - to grow fuel when you have a fair few other ways to produce energy?
I'm sure others will have other opinions and many will still feel that ethanol is a strong short-to-medium term solution. But sorry, I'm not sold on the whole idea of biofuels.
3. Hydrogen
This would be the best fuel by a long, long margin, because of its hydrogen-to-carbon "ratio". Burning a gram of hydrogen gives you zero carbon, and gives you 142 joules of energy - almost three times that of petroleum or natural gas. So, if we can use this fuel it is by far the best option - we're certainly not going to run out of it.
But that's an if - and it's a big if. There are very serious technological challenges to using hydrogen as a fuel.
First is extraction. The most obvious way of getting hydrogen is through the electrolysis of water to give you hydrogen gas and a harmless byproduct, oxygen. Completely clean and you get your hydrogen. But the problem is - the bonds holding the water atom together are very strong. You need a very, very big amount of energy to break it up. At current this means a lot of carbon emissions (no good replacing petrol with coal). Even in the future, if we have, say, a nuclear power plant dedicated to electrolysis, you still lose well over half - and some say three-quarters - of the energy you gain from hydrogen in the inefficiencies of the process itself and the power generation. There's a lot of research being done at current to get around this through other means of extracting hydrogen from water or other forms of electrolysis, but this is some way down the track.
So if we get around the problem of extraction, we then have to transport it. This is the major hurdle in my opinion - because like natural gas, hydrogen has to be in liquid form for it to be transportable and storable - in gaseous form you just can't store it in bulk, plus you have a very real risk of a very, very big explosion. But hydrogen can only be liquefied through cooling (pressure is out of the question), a enourmously energy-intensive task because hydrogen has the second-lowest boiling point of any known substance - one of the few substances to boil below -200 degrees Celsius. The amount of energy required to cool something goes exponentially up as you go down to lower and lower temperatures, so cooling hydrogen to liquid form is no easy task, and will require a lot of energy from non-carbon sources which we currently don't produce at the moment.
There would be one way to partially solve this problem but this would only apply to power generation, not for fuel purposes.
4. Methane Clathrates/Hydrates
A possibility. Methane clathrates are basically ice with lots of methane locked in. It can be burnt, producing energy through burning of methane and has the benefits that natural gas (and then some) has in comparison to petrol. More useful is extracting the methane and using it as a fuel, like natural gas. They exist in enourmous quantities - probably more, much more, than both oil and gas.
A few issues, though, first is that most (really, all save some in Russia) of these are found offshore - making extraction a little tough, and all over the place, making it somewhat uneconomic. Secondly is that the technology to extract the methane from the clathrate isn't exactly great at the moment. Most importantly, though, is that these clathrates are somewhat unstable - they retain their crystalline structure at low temperatures, but warm them up but a little bit and they break down, releasing their methane. This could be really, really bad - if, as some doomsayers say, temperatures rise enough and methane clathrate reserves across the world boil off: well, that's basically the worst-case scenario. Not that I think that will happen any time soon, but it shows how delicate these are - and how catastrophic the results could be if they are mishandled.
Plus in the long-term you still have a carbon problem - albeit smaller.
5. Electricity as a fuel.
Probably the most feasible of all the supposedly "carbon-neutral" alternatives - much better than hydrogen in terms of practicality. The main issue with this though, is that you are plugging your car, before running on petrol, into the grid, running mostly on coal. Until this changes this is not an option for decarbonization - though it could be an excellent way to reduce oil use.
SECTION II. POWER SOURCES
1. Natural Gas
I've already explained the advantages - and some of the issues - regarding this, they apply to natural gas used as a power source as they do a transport fuel.
2. Solar
There are several different types of solar power, although all rely on the same premise - energy from sunlight, whether directly or through heat. This takes advantage of the biggest and most reliable power source - the sun. The energy from all the sunlight falling on earth in one hour is more than humans use in a whole year, so it makes sense to tap into it as a alternative power source.
The most common and well-known type is the photovoltaic, the 'panels'. These directly convert sunlight into electricity. Quite simply, they work by getting sunlight to knock electrons about, thus making electricity. Excellent for domestic purposes, and a lot cheaper than people think, this is the probably the most obvious (read: visible) way to reduce personal carbon emissions. Not so good for larger-scale production, though, due to cost - this applies to most solar technologies currently available.
Solar thermal, using the sun's energy to heat water (either for use or electricity production) is another type of solar power - either through the use of special evacuated tubes, or the use of a parabolic dish (think radar) to concentrate the sun's energy to a single point like so:
One more solar energy technique: Thin-Film Photovoltaic. It works on the same principle as PV, but is a thin-film, really a dye. You can almost paint this stuff on the side of a building and it will start producing power.
The main criticism of solar energy, cost aside, is that solar cannot provide base-load power, i.e. it cannot power a large number of users (say, a town) reliably 24/7 - no sun at night. One way to get around this is through 'ammonia splitting' - excess power is used to split ammonia (NH3), the constituents stored. Then when the sun isn't out, the ammonia can be recombined to give you electricity again - although as with everything a fair bit of energy is wasted. For domestic use, though, the best way to make it economic is a feed-in-tariff.
Another problem with solar is that it is probably the most material-intensive of all the renewables, in that it needs special materials to make it work. Most obvious is the use of Cadmium - which makes for good PV cells, but cadmium is one of the nastiest substances around. However, lifecycle emissions of cadmium from a cadmium-based PV would be very minor compared to similar emissions from coal (coal doesn't just emit carbon dioxide, but a whole range of dangerous chemicals and pollutants) - about 0.3% of coal's, less if good procedures are implemented, and almost nothing is coal isn't used to generate the electricity needed to build the thing. There's also the problem of emissions from the power as well as the extraction of the materials to create such a specialized object, but mostly this relates to power generation, and if renewables become more commonplace this will roughly halve. In terms of total lifecycle CO2 emissions only wind and nuclear are better.
3. Wind
Wind is probably the power source that is being the most actively pursued at the moment, for a whole number of reasons. It has its advantages - the main one being that the materials are easy to procure and the actual construction isn't too hard - it's pieces of metal stuck to some gears and a generator, essentially. It is the most carbon-neutral power source over the entire lifecycle (although in some cases nuclear can be twice as good... or twice as bad) And I wonder at those who say it's an eyesore - would you rather a coal/nuclear power plant?, but the standard, Horizontal Axis Wind Turbine (HAWT - see above) are huge - they really are massive! This poses some problems. Firstly, it means that in order to get maximum efficiency the turbines must be facing into the wind, but with such a massive structure turning it around can take a while - wasted power. Plus, they are incredibly noisy (not machine-noisy, just the noise from the air rushing around) and amazing as it may seem, a danger to birds.
Many of these problems could be solved with a wind generator that spins on a horizontal axis like this:
Not only does it solve the problems of having to turn into the wind, noise and birstrike, it's much easier to build and maintain. The downside is efficiency: you get less power and you can't really take advantage of stronger winds at higher elevations.
4. Nuclear
Nuclear power is probably the leading and most viable current contender to replace coal as the carbon-neutral alternative to widescale base-load power generation. Like most power stations, it runs by heating water so it becomes steam and using that to drive turbines which generate electricity. With nuclear, that energy comes from *controlled* nuclear reactions - at the moment, mostly fission (atom-spitting). In terms of carbon emissions, this makes it relatively 'clean' in the energy-production stage.
Fuel mostly comes in the form of enriched uranium ore - i.e. uranium with a high proportion of the U235 isotope. Notably resources of uranium ore are currently quite large, and should last well into the next century at a minimum, and probably longer as more efficient reactor types become more common. Moreover, nuclear fission is renewable to a large degree - at least, 95% of it is, if you send the leftovers to a reprocessing plant. They are somewhat water hungry though... this may be a problem in future, though all large power plants suffer from this to some degree.
Nuclear power remains highly controversial - especially in Australia and the US - for several reasons. The first and most unavoidable is the risk of nuclear proliferation (read: Iran). There is not much one can do about this except make sure that you know where your ore is going and ensure that everyone with a nuclear plant of any kind, or doing any enrichment, has to do it with glass-like transparency. But this is, by and large, a political question.
Waste is another problem. High level waste and spent nuclear fuel - i.e. the left over, intensely radioactive material from the reactor core itself. Even after 40 years it's still dangerous despite being only 0.01% as radioactive as it was when you first took it out. No one really knows what do with the stuff at the moment. Reprocessing can remove a lot, but not all of it. Mostly they're stored in specially made pools, or in big steel cans. There are quite novel ideas for storage and disposal coming up though - such as storing it in a special glass-like crystal, before burying it deep, deep underground in the middle of nowhere. (Have a look at something called 'Synroc')
Low level waste - like, cups and spoons and knobs and monitors from inside the reactor itself are usually just disposed of normally, though seperate from everywhere else. Really isn't much different from normal toxic industrial waste, and is waay less than the waste from a coal power plant.
Radiation emission from nuclear power plants is very low. Despite what people think you are not going to get a lethal dose of radiation if there is a nuclear power plant within a few hundred km's. A coal power plant releases 100 times the radioactive material of a nuclear power plant, so this is a non-issue (and probably a plus on the nuclear side).
The risk of an accident is there but probably a bit blown-up. Chernobyl was more a result of poor reactor design and very poor safety standards/practices in the USSR more than anything else. Western Europe hasn't had a major reactor accident yet, and they get a huge amount of their power from nuclear. Good reactor design, well trained crews and good practices can basically nullify this. Again, coal stations do worse in this regard, much worse.
Even so, these problems combined with the political aspect make nuclear a very tentative option in many parts of the world. Fusion may overcome this, as it eliminates many of these problems as the fuel is hydrogen and the waste is either hydrogen are helium - harmless. But that is well, well down the track.
5. Hydro - Dams
Currently the other method of large-scale production of renewable energy. Used in very, very large - no, more accurately, very high dams. Relies on the kinetic energy of falling water from gravity (as the dam holds the water way, way, way higher than the natural river, giving the water a very respectable amount of energy when it falls and spins the turbines.
The problem:
Only applicable in a small number of circumstances - only a fraction of the dams in the world are the right type for hydroelectricity, and I've never heard of an existing dam being 'converted' to hydro - and very very expensive, especially the dam itself - Three Gorges Dam is a perfect example of the mammoth task of constructing a really good hydro-dam, so probably not an appropriate choice for many countries. Plus you kinda completely flood the area, killing or dislodging any animals in the area - as well as people, again, Three Gorges Dam. So where it can be taken advantage of, it should, but it really is a limited resource.
6. Hydro - Waves and Tides
This is a fascinating technology. Mainly involves getting power from the waves and tides in the open ocean. Yes, I know they're seperate technologies, but I don't really have the detailed background knowledge to differentiate between the two, but what I do know is: Wave power relies on the circular oscillations that create waves, while tidal power relies on the large-scale movement of water due to the tides. From what I can see, this is a largely unproven technology on a commercial scale. Once again, efficiency and cost are the main issues here.
7. Geothermal
My personal favourite. How I forgot this the first time round... anyway. The premise is incredibly simple. Below ground, the temperature is very constant, and if you go deep enough, very hot. Geothermal power sources mainly center on driving water down to those depths (so it gets very hot) and then bringing it back up and using the steam to drive turbines. Or, on a smaller scale, just use the water as a hot water source - or even use the earth itself as a 'central heater'.
Geothermal power plants, or 'hot dry rock geothermal', involves driving water in deep wells down to a depth of a few kilometres where the temperature is at a constant 200 degrees Celsius. Once enough water is injected, it comes up a second borehole - the difference now that it is very hot - produces power, and is injected back in. The loop is completely closed (and even then the only possible pollutant is steam), the power generator runs baseload (so 24/7, barring an earthquake). Moreover, this is a power source that works on every scale - it will work with 1 well just as well as ten. And, if you later decide that you want ten wells rather than just the one, you can drill more. And it's cheap, too, as we will see - after the initial investment, it's a closed loop.
The best statement to the benefits of geothermal is Iceland - a country that runs entirely on hydroelectricity and geothermal (mainly because it has to, and why not use the most obvious feature of the landscape, namely, volcanism, to produce power?). Moreover, the power is so cheap that sometimes they 'heat the pavements' in winter, which is quite incredible.
The main issue in Iceland is sometimes, due to the geology of the area - namely, the orientation of the 'cracks' in the rock, which are crucial to allowing the water to heat up but in Iceland they mean some water leaks out, reducing the system's efficiency. However, there is a truly enormous geothermal source in Australia. The red bits on this map are areas where the rocks are hot enough:
A fairly sizable area. Moreover, the geology of these areas differs from Iceland: the cracks here don't allow the water to escape so easily, and the whole thing is much more efficient. I can't stress enough how useful this resource can be - and how underused it is at the moment (only 1% of the world's power is geothermal, despite its clear advantages)
The main disadvantages are that it is limited, as the map shows, to certain areas where the rocks are hot enough (but these areas are huge, so this isn't that important - especially given how geothermal is scalable), geothermal areas have a useful service life of about 10-20 years if the rocks are at 200C (after that you have to wait about a century for it to heat up again) before it becomes uneconomic (at today's electricity prices anyway - this may change) and you have to be very careful not to damage the geology of the area when you inject the water, or cause an earthquake.
8. Carbon Capture - Geosequestration
***COMING***
Summary
Clearly, there is no shortage of alternative fuels and power sources - but this number will only increase in coming years, probably dramatically. There's plenty to choose from to fix the current problems, but each solution has its plus's and it's minus's.
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I'll add to this list if I remember something later, or get better data. ~Spark
Need to do a cost/benefit and environmental analysis of extraction/manufacturing. Will do soon.
For a variety of reasons and justifications, pretty much everyone is in agreement now that alternative energies are needed urgently. Whether they be economic or environmental, there is a lot of attention being focussed on sources of power other than coal and petroleum."We didn't leave the Stone Age because we ran out of stones."
--- Amory Lovins
Note that the judgements on this list, I've tried to base on scientific principles more than anything else.
So, to the list.
A summary for those who are lazy:
Of the fuels for transport, the short term solution should be based on natural gas in my opinion, and maybe grid-electricity. Ethanol is a bad idea IMO. Longer-term, we should take a serious look at methane clathrates but ultimately we should be going for hydrogen - although it faces huge technological problems. As for energies: basically it comes down to wind, solar and nuclear.
SECTION I. FUELS
1. Natural Gas (LPG/LNG)
Liquefied Natural Gas as suggested - mostly ethane, propane and butane (please tell me I got it in the right order) and bits and pieces of other gases.
This is probably the most feasible, most economic way of reducing oil usage in the short term. The reason is simple. The chemical formula for ethane is C2H6 - that means 3 hydrogens to one carbon. The general rule for hydrocarbon fuels is that the higher the hydrogen-to-carbon ratio, the better the fuel - i.e. the more efficient, the more energy you get per gram - AND the less carbon dioxide you emit (this is why petrol is 'bad' and coal very, very, very bad, and hydrogen very very 'good'). Win-win on both fronts. Obviously we already have the technology and the resources to convert a large section of the 'oil economy' to LPG/LNG (Australia in the last year or two introduced quite a large subsidy for converting cars to LPG/LNG) - although technological problems still remain (transportation requires liquefication, and that's a difficult and energy-intensive process in bulk. Only recently has this problem been overcome to an adequate level).
In the medium-term onwards, though, this probably won't do as a solution. You still are putting out carbon, although at a markedly reduced rate, and eventually you'll run into the same problem as we currently (or very soon) have with oil: you'll use it faster than you can find it. Plus, these light hydrocarbons are way, way, way more powerful greenhouse gases than carbon dioxide. Any major leakage and you quickly nullify the carbon advantage you get from this fuel.
2. Ethanol (and other biofuels)
This one has had a lot of hype: a lot of people think that this is the centrepiece of the short-to-medium term solution.
But I don't. I personally think that this is a fuel that is just as bad - if not worse - than petroleum. For a range of reasons.
Firstly, it's rather inefficient as a fuel. Ordinary petroleum has a heat of combustion of roughly 50 J/g (that means for every gram you burn you get 50 joules), varies a bit with regional differences in the composition of the fuel but basically about that. Natural gas is about the same (hence its utility). But ethanol has a heat of combusion of about 30 J/g, so you get about 60% of the energy per gram of ethanol compared to petrol. This negates a good deal of the carbon advantage you gain by using a lighter fuel - you have to burn more fuel to get the same distance (about a third more - and this is something that has been noticed and documented when it has been used as a fuel). While this in turn is compensated for by the fact that ethanol-burning engines are more efficient in themselves, it does not leave me particularly impressed. Needless to say it also places it at a big disadvantage in comparison to natural gas.
The second reason is that producing corn-based ethanol is more than just "Corn + Magic = Fuel". It is a hugely complex and energy-intensive process. The operation of the plants in themselves - the fuel alone - is a huge task, expensive and carbon-intensive. This is just one part of a very, very expensive and carbon-intensive process which nullifies a lot of the advantages - carbon and fuelwise - there are from ethanol (advantages which in themselves are slender in comparison to other fuels). Some have even argued that this outweighs the advantages, but it any cases, it weakens the case for this fuel.
Final reason. With food prices going upwards and probably continuing to do so, is it really that wise to be using lots of land - which, by the way, will be increasingly valuable in terms of agricultural output vs. need - and LOTS of water (corn is very water-intensive), which could be scarce in future years - to grow fuel when you have a fair few other ways to produce energy?
I'm sure others will have other opinions and many will still feel that ethanol is a strong short-to-medium term solution. But sorry, I'm not sold on the whole idea of biofuels.
3. Hydrogen
This would be the best fuel by a long, long margin, because of its hydrogen-to-carbon "ratio". Burning a gram of hydrogen gives you zero carbon, and gives you 142 joules of energy - almost three times that of petroleum or natural gas. So, if we can use this fuel it is by far the best option - we're certainly not going to run out of it.
But that's an if - and it's a big if. There are very serious technological challenges to using hydrogen as a fuel.
First is extraction. The most obvious way of getting hydrogen is through the electrolysis of water to give you hydrogen gas and a harmless byproduct, oxygen. Completely clean and you get your hydrogen. But the problem is - the bonds holding the water atom together are very strong. You need a very, very big amount of energy to break it up. At current this means a lot of carbon emissions (no good replacing petrol with coal). Even in the future, if we have, say, a nuclear power plant dedicated to electrolysis, you still lose well over half - and some say three-quarters - of the energy you gain from hydrogen in the inefficiencies of the process itself and the power generation. There's a lot of research being done at current to get around this through other means of extracting hydrogen from water or other forms of electrolysis, but this is some way down the track.
So if we get around the problem of extraction, we then have to transport it. This is the major hurdle in my opinion - because like natural gas, hydrogen has to be in liquid form for it to be transportable and storable - in gaseous form you just can't store it in bulk, plus you have a very real risk of a very, very big explosion. But hydrogen can only be liquefied through cooling (pressure is out of the question), a enourmously energy-intensive task because hydrogen has the second-lowest boiling point of any known substance - one of the few substances to boil below -200 degrees Celsius. The amount of energy required to cool something goes exponentially up as you go down to lower and lower temperatures, so cooling hydrogen to liquid form is no easy task, and will require a lot of energy from non-carbon sources which we currently don't produce at the moment.
There would be one way to partially solve this problem but this would only apply to power generation, not for fuel purposes.
4. Methane Clathrates/Hydrates
A possibility. Methane clathrates are basically ice with lots of methane locked in. It can be burnt, producing energy through burning of methane and has the benefits that natural gas (and then some) has in comparison to petrol. More useful is extracting the methane and using it as a fuel, like natural gas. They exist in enourmous quantities - probably more, much more, than both oil and gas.
A few issues, though, first is that most (really, all save some in Russia) of these are found offshore - making extraction a little tough, and all over the place, making it somewhat uneconomic. Secondly is that the technology to extract the methane from the clathrate isn't exactly great at the moment. Most importantly, though, is that these clathrates are somewhat unstable - they retain their crystalline structure at low temperatures, but warm them up but a little bit and they break down, releasing their methane. This could be really, really bad - if, as some doomsayers say, temperatures rise enough and methane clathrate reserves across the world boil off: well, that's basically the worst-case scenario. Not that I think that will happen any time soon, but it shows how delicate these are - and how catastrophic the results could be if they are mishandled.
Plus in the long-term you still have a carbon problem - albeit smaller.
5. Electricity as a fuel.
Probably the most feasible of all the supposedly "carbon-neutral" alternatives - much better than hydrogen in terms of practicality. The main issue with this though, is that you are plugging your car, before running on petrol, into the grid, running mostly on coal. Until this changes this is not an option for decarbonization - though it could be an excellent way to reduce oil use.
SECTION II. POWER SOURCES
1. Natural Gas
I've already explained the advantages - and some of the issues - regarding this, they apply to natural gas used as a power source as they do a transport fuel.
2. Solar
There are several different types of solar power, although all rely on the same premise - energy from sunlight, whether directly or through heat. This takes advantage of the biggest and most reliable power source - the sun. The energy from all the sunlight falling on earth in one hour is more than humans use in a whole year, so it makes sense to tap into it as a alternative power source.
The most common and well-known type is the photovoltaic, the 'panels'. These directly convert sunlight into electricity. Quite simply, they work by getting sunlight to knock electrons about, thus making electricity. Excellent for domestic purposes, and a lot cheaper than people think, this is the probably the most obvious (read: visible) way to reduce personal carbon emissions. Not so good for larger-scale production, though, due to cost - this applies to most solar technologies currently available.
Solar thermal, using the sun's energy to heat water (either for use or electricity production) is another type of solar power - either through the use of special evacuated tubes, or the use of a parabolic dish (think radar) to concentrate the sun's energy to a single point like so:
One more solar energy technique: Thin-Film Photovoltaic. It works on the same principle as PV, but is a thin-film, really a dye. You can almost paint this stuff on the side of a building and it will start producing power.
The main criticism of solar energy, cost aside, is that solar cannot provide base-load power, i.e. it cannot power a large number of users (say, a town) reliably 24/7 - no sun at night. One way to get around this is through 'ammonia splitting' - excess power is used to split ammonia (NH3), the constituents stored. Then when the sun isn't out, the ammonia can be recombined to give you electricity again - although as with everything a fair bit of energy is wasted. For domestic use, though, the best way to make it economic is a feed-in-tariff.
Another problem with solar is that it is probably the most material-intensive of all the renewables, in that it needs special materials to make it work. Most obvious is the use of Cadmium - which makes for good PV cells, but cadmium is one of the nastiest substances around. However, lifecycle emissions of cadmium from a cadmium-based PV would be very minor compared to similar emissions from coal (coal doesn't just emit carbon dioxide, but a whole range of dangerous chemicals and pollutants) - about 0.3% of coal's, less if good procedures are implemented, and almost nothing is coal isn't used to generate the electricity needed to build the thing. There's also the problem of emissions from the power as well as the extraction of the materials to create such a specialized object, but mostly this relates to power generation, and if renewables become more commonplace this will roughly halve. In terms of total lifecycle CO2 emissions only wind and nuclear are better.
3. Wind
Wind is probably the power source that is being the most actively pursued at the moment, for a whole number of reasons. It has its advantages - the main one being that the materials are easy to procure and the actual construction isn't too hard - it's pieces of metal stuck to some gears and a generator, essentially. It is the most carbon-neutral power source over the entire lifecycle (although in some cases nuclear can be twice as good... or twice as bad) And I wonder at those who say it's an eyesore - would you rather a coal/nuclear power plant?, but the standard, Horizontal Axis Wind Turbine (HAWT - see above) are huge - they really are massive! This poses some problems. Firstly, it means that in order to get maximum efficiency the turbines must be facing into the wind, but with such a massive structure turning it around can take a while - wasted power. Plus, they are incredibly noisy (not machine-noisy, just the noise from the air rushing around) and amazing as it may seem, a danger to birds.
Many of these problems could be solved with a wind generator that spins on a horizontal axis like this:
Not only does it solve the problems of having to turn into the wind, noise and birstrike, it's much easier to build and maintain. The downside is efficiency: you get less power and you can't really take advantage of stronger winds at higher elevations.
4. Nuclear
Nuclear power is probably the leading and most viable current contender to replace coal as the carbon-neutral alternative to widescale base-load power generation. Like most power stations, it runs by heating water so it becomes steam and using that to drive turbines which generate electricity. With nuclear, that energy comes from *controlled* nuclear reactions - at the moment, mostly fission (atom-spitting). In terms of carbon emissions, this makes it relatively 'clean' in the energy-production stage.
Fuel mostly comes in the form of enriched uranium ore - i.e. uranium with a high proportion of the U235 isotope. Notably resources of uranium ore are currently quite large, and should last well into the next century at a minimum, and probably longer as more efficient reactor types become more common. Moreover, nuclear fission is renewable to a large degree - at least, 95% of it is, if you send the leftovers to a reprocessing plant. They are somewhat water hungry though... this may be a problem in future, though all large power plants suffer from this to some degree.
Nuclear power remains highly controversial - especially in Australia and the US - for several reasons. The first and most unavoidable is the risk of nuclear proliferation (read: Iran). There is not much one can do about this except make sure that you know where your ore is going and ensure that everyone with a nuclear plant of any kind, or doing any enrichment, has to do it with glass-like transparency. But this is, by and large, a political question.
Waste is another problem. High level waste and spent nuclear fuel - i.e. the left over, intensely radioactive material from the reactor core itself. Even after 40 years it's still dangerous despite being only 0.01% as radioactive as it was when you first took it out. No one really knows what do with the stuff at the moment. Reprocessing can remove a lot, but not all of it. Mostly they're stored in specially made pools, or in big steel cans. There are quite novel ideas for storage and disposal coming up though - such as storing it in a special glass-like crystal, before burying it deep, deep underground in the middle of nowhere. (Have a look at something called 'Synroc')
Low level waste - like, cups and spoons and knobs and monitors from inside the reactor itself are usually just disposed of normally, though seperate from everywhere else. Really isn't much different from normal toxic industrial waste, and is waay less than the waste from a coal power plant.
Radiation emission from nuclear power plants is very low. Despite what people think you are not going to get a lethal dose of radiation if there is a nuclear power plant within a few hundred km's. A coal power plant releases 100 times the radioactive material of a nuclear power plant, so this is a non-issue (and probably a plus on the nuclear side).
The risk of an accident is there but probably a bit blown-up. Chernobyl was more a result of poor reactor design and very poor safety standards/practices in the USSR more than anything else. Western Europe hasn't had a major reactor accident yet, and they get a huge amount of their power from nuclear. Good reactor design, well trained crews and good practices can basically nullify this. Again, coal stations do worse in this regard, much worse.
Even so, these problems combined with the political aspect make nuclear a very tentative option in many parts of the world. Fusion may overcome this, as it eliminates many of these problems as the fuel is hydrogen and the waste is either hydrogen are helium - harmless. But that is well, well down the track.
5. Hydro - Dams
Currently the other method of large-scale production of renewable energy. Used in very, very large - no, more accurately, very high dams. Relies on the kinetic energy of falling water from gravity (as the dam holds the water way, way, way higher than the natural river, giving the water a very respectable amount of energy when it falls and spins the turbines.
The problem:
Only applicable in a small number of circumstances - only a fraction of the dams in the world are the right type for hydroelectricity, and I've never heard of an existing dam being 'converted' to hydro - and very very expensive, especially the dam itself - Three Gorges Dam is a perfect example of the mammoth task of constructing a really good hydro-dam, so probably not an appropriate choice for many countries. Plus you kinda completely flood the area, killing or dislodging any animals in the area - as well as people, again, Three Gorges Dam. So where it can be taken advantage of, it should, but it really is a limited resource.
6. Hydro - Waves and Tides
This is a fascinating technology. Mainly involves getting power from the waves and tides in the open ocean. Yes, I know they're seperate technologies, but I don't really have the detailed background knowledge to differentiate between the two, but what I do know is: Wave power relies on the circular oscillations that create waves, while tidal power relies on the large-scale movement of water due to the tides. From what I can see, this is a largely unproven technology on a commercial scale. Once again, efficiency and cost are the main issues here.
7. Geothermal
My personal favourite. How I forgot this the first time round... anyway. The premise is incredibly simple. Below ground, the temperature is very constant, and if you go deep enough, very hot. Geothermal power sources mainly center on driving water down to those depths (so it gets very hot) and then bringing it back up and using the steam to drive turbines. Or, on a smaller scale, just use the water as a hot water source - or even use the earth itself as a 'central heater'.
Geothermal power plants, or 'hot dry rock geothermal', involves driving water in deep wells down to a depth of a few kilometres where the temperature is at a constant 200 degrees Celsius. Once enough water is injected, it comes up a second borehole - the difference now that it is very hot - produces power, and is injected back in. The loop is completely closed (and even then the only possible pollutant is steam), the power generator runs baseload (so 24/7, barring an earthquake). Moreover, this is a power source that works on every scale - it will work with 1 well just as well as ten. And, if you later decide that you want ten wells rather than just the one, you can drill more. And it's cheap, too, as we will see - after the initial investment, it's a closed loop.
The best statement to the benefits of geothermal is Iceland - a country that runs entirely on hydroelectricity and geothermal (mainly because it has to, and why not use the most obvious feature of the landscape, namely, volcanism, to produce power?). Moreover, the power is so cheap that sometimes they 'heat the pavements' in winter, which is quite incredible.
The main issue in Iceland is sometimes, due to the geology of the area - namely, the orientation of the 'cracks' in the rock, which are crucial to allowing the water to heat up but in Iceland they mean some water leaks out, reducing the system's efficiency. However, there is a truly enormous geothermal source in Australia. The red bits on this map are areas where the rocks are hot enough:
A fairly sizable area. Moreover, the geology of these areas differs from Iceland: the cracks here don't allow the water to escape so easily, and the whole thing is much more efficient. I can't stress enough how useful this resource can be - and how underused it is at the moment (only 1% of the world's power is geothermal, despite its clear advantages)
The main disadvantages are that it is limited, as the map shows, to certain areas where the rocks are hot enough (but these areas are huge, so this isn't that important - especially given how geothermal is scalable), geothermal areas have a useful service life of about 10-20 years if the rocks are at 200C (after that you have to wait about a century for it to heat up again) before it becomes uneconomic (at today's electricity prices anyway - this may change) and you have to be very careful not to damage the geology of the area when you inject the water, or cause an earthquake.
8. Carbon Capture - Geosequestration
***COMING***
Summary
Clearly, there is no shortage of alternative fuels and power sources - but this number will only increase in coming years, probably dramatically. There's plenty to choose from to fix the current problems, but each solution has its plus's and it's minus's.
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I'll add to this list if I remember something later, or get better data. ~Spark
Need to do a cost/benefit and environmental analysis of extraction/manufacturing. Will do soon.
Last edited by Spark (2008-10-09 21:44:36)
The paradox is only a conflict between reality and your feeling what reality ought to be.
~ Richard Feynman
~ Richard Feynman
