I am busily researching a series of articles on energy, and thought htis article deserved an immediate link…
http://www.environmentmagazine.org/Archives/Back%20Issues/September-October%202008/gardner-stern-full.html
Category Archives: Education
Energy Explained in One Page
Ok, so we all want to be good to the environment. The first step to doing this, as is often the case – is to understand the main characters in the story – and possibly the biggest character in the story in Energy.
However, energy is such a very vague concept, so where do you go to learn more? Do you have to do a physics course?
I don’t think so, and to test my theory, I have tried to explain energy as briefly as I can in this post.
Energy 101
Energy is what makes the world go round. Literally. Every neuron that sparks in your brain, every electron that fires down a wire, every molecule burning in a fire, carries with it a sort of momentum that it passes on like a baton in a complex relay race. The batons are flooding in all directions all around us and across the universe – they are energy and we have learned how to harness them.
The actual word “Energy” is a much abused term nowadays – because energy is used to represent such a disparate range of phenomena from heat to light to speed to weight, and because it seems to be able to change forms so readily, it is cannon fodder for pseudo-scientific and spiritual interpretation. However, you will be pleased to hear that it actually has a very clear (and consistent) nature.
I like to think of energy being a bit like money – it is a sort of currency that can be traded. It takes on various forms (dollars/pounds/swiss francs) and can be eventually cashed in to achieve something. However, just like money, once spent, it does not vanish. It simply moves on a new chapter in its life and may be reused indefinitely.
§Energy currencies:{1}Matter is energy(see footnotes) {2} Radiation {3} Chemical energy {4} Thermal (heat) energy {5} Compression energy {6} Kinetic (movement) energy {7} Electrical energy
To illustrate the point, let’s follow a ‘unit of energy’ through a visit to planet Earth to see what I mean. The [number] shows every time it changes currency (see the key on the right).
The energy starts off tied up in hydrogen atoms in the sun [1]. Suddenly, due to the immense pressure and heat, the nuclei of several atoms react to form a brand new helium atom, and a burst of radiation[2] is released. The radiation smashes into other nearby atoms heating them up so hot [4] that they glow, sending light [2] off into space. Several minutes pass in silence before the light bursts through the atmosphere and plunges down to the rainforest hitting a leaf. In the leaf the burst of power smashes a molecule of carbon dioxide and helps free the carbon to make food for the plant [3]. The plant may be eaten (giving food ‘Calories’), or may fall to the ground and settle and age for millions of years turning perhaps to coal. That coal may be dug up and burned to give heat [4] in a power station, boiling water to supply compressed steam [5] that may drive a turbine [6] which may be used to generate electricity [7] which we may then use in our homes to heat/light/move/cook or perhaps to recharge our mobile phone [3]. That energy will then be used to transmit microwaves when you make a call [2] which will mostly dissipate into the environment heating it (very) slightly [4]. Eventually the warmed earth radiates [2] this excess of heat off into the void where perhaps it will have another life…
This short story is testament to an enormous quantity of learning by our species, but there are some clear exclusions to be read into the story:
- Energy fields (auras) or the energy lines in the body that conduct the “chi” (or life force) of Asian medical tradition
- Energy lines on the Earth (aka Ley lines)
- Negative or positive energy (as in positive or negative “vibes”)
These energy currencies relate to theories and beliefs that science has been unable to verify and thus they have no known “exchange rate”. Asking how many light bulbs can you power with your Chi is thus a nonsensical question, whereas it would not be for any scientifically supported form of energy. And since energy flows account for all actions in the universe, not being exchangeable would be rather limiting.
Where exactly is Energy kept?
This may sound like s strange question, we know Energy is kept in batteries, petrol tanks and chocolate chip cookies. But the question is, where exactly is it stored in those things?
Energy is stored in several ways:
- as movement – any mass moving has energy by virtue of the movement, which is called Kinetic Energy
- as matter – Einstein figured out that matter is just a form of energy, and the exchange rate is amazing – 1g = 90,000,000,000,000,000 joules (from E=mc^2)
- as tension in force fields
That last one sounds a bit cryptic, but actually most of the energy we use is in this form – petrol, food, batteries and even a raised hammer all store energy in what are essentially compressed (or stretched springs).
What is a force field? Why on earth did I have to bring that up?
All of space (even the interstellar vacuum) is permeated by force fields. The one we all know best is gravity – we know that if we lift a weight, we have to exert effort and that effort is then stored in that weight and can be recovered later by dropping it on your foot.
Gravity is only one of several force fields known to science. Magnetic fields are very similar – it takes energy to pull a magnet off the fridge , and so it is actually an energy store when kept away from the fridge.
The next force field is that created by electric charge (the electric field). For many years this was though to be a field all on its own, but a chap called Maxwell realised that electric fields and magnetic fields are in some senses two sides of the same coin, so physicists now talk of ‘electromagnetic’ fields. It turns out that electric energy (such as that stored in a capacitor) consists of tensions in this field, much like a raised weight is a tension in a gravity field. Perhaps surprisingly, light (as well as radio waves, microwaves and x-rays) are also energy stored in fluctuations of an energy field.
Much chemical energy is also stored in electric fields – for example, most atoms consist of positively charged nuclei and negatively charged electrons, and the further apart they are kept, the more energy they hold, just liked raised weights. As an electron is allowed to get closer to the nucleus, energy is released (generally as radiation, such as light – thus hot things glow).
The least well known force field is the strong ‘nuclear’ force. This is the forces that holds the subatomic particles (protons) together in the nucleus of atoms. Since the protons are all positively charged, they should want to repel each other, but something is keeping them at bay, and so physicists have inferred this force field must exist. It turns out their theory holds water, because if you can drag these protons a little bit apart, they will suddenly fly off with gusto. The strong nuclear force turns out to be bloody strong, but only works over a tiny distance. It rarely affects us as we rarely store energy with this energy field.
Now we understand force fields we can look at how molecules (petrol, oxygen, chocolate) store energy. All molecules are made of atoms connected to one other via various ‘bonds’ and these bonds are like springs. Different types of molecules have different amount of tension in these bonds – it turns out coal molecules, created millions of years ago with energy from the sun, are crammed full of tense bonds that are dying to re-arrnage to more relaxed configurations, which is exactly what happens when we apply oxygen and the little heat to start the reaction.
The complexity of the tensions in molecules are perhaps the most amazing in nature, as it is their re-arrangements that fuel life as we know it.
What exactly is Heat then?
You may have noticed that I did not include heat as a form of energy store above. But surely hot things are an energy store?
Yes, they are, but heat is actually just a sort of illusion. We use heat as a catch all term to describe the kinetic energy of the molecules and atoms. If you have a bottle of air, the temperature of the air is a direct consequence of the average speed of the molecules of gas jetting around bashing into one another.
As you heat the air, you are actually just increasing the speed of particles. If you compress the air, you may not increase their speed, but you will have more particles in the same volume, which also ‘feels’ hotter.
Solids are a little different – the atoms and molecules in solids do not have the freedom to fly around, so instead, they vibrate. It is like each molecule is constrained by elastic bands pulling in all directions. If the molecule is still, it is cold, but if it is bouncing around like a pinball, then it has kinetic energy, and feels hotter.
You can see from this viewpoint, that to talk of the temperature of an atom, or of a vacuum, is meaningless, because temperature is a macroscopic property of matter. On the other hand, you could technically argue that a flying bullet is red hot because it has so much kinetic energy…
Is Energy Reusable?
We as a species, have learned how to tap into flows of energy to get them to do our bidding. So big question: Will we use it all up?
Scientists have found that energy is pretty much indestructable – it is never “used-up”, it merely flows from one form into another. The problem is thus not that we will run out, but that we might foolishly convert it all into some unusable form.
Electricity is an example of really useful energy – we have machines that convert electricity into almost anything, whereas heat is only useful if you are cold, and light is only useful if you are in the dark.
Engineers also talk about the quality (or grade) of energy. An engineer would always prefer 1 litre of water 70 degrees warmer than room temperature, than 70 litres of water 1 degree warmer, even though these contain roughly the same embodied energy. You can use the hot water to boil an egg, or make tea, or you could mix it with 69 litres of room temperature water to heat it all by 1 degree. It is more flexible.
Unfortunately, most of the machines we use, turn good energy (electricity, petrol, light) into bad energy (usually “low grade heat”).
Why is low grade heat so bad? It turns out we have no decent machine to convert low grade heat into other forms of energy. In fact we cannot technically convert any forms of heat into energy unless we have something cold to hand which we are also willing to warm up; our machines can thus only extract energy by using hot an cold things together. A steam engine relies just as much on the environment that cools and condenses water vapour as it does on the coal its belly. Power stations rely on their cooling towers as much as their furnaces. It turns out that all our heat machines are stuck in this trap.
So, in summary, heat itself is not useful – it is temperature differences that we know how to harness, and the bigger the better.
This picture of energy lets us think differently about how we interact with energy. We have learned a few key facts:
- Energy is not destroyed, and cannot be totally used up – this should give us hope
- Energy is harnessed to do our dirty work, but tends to end up stuck in some ‘hard to use’ form
So all we need to do to save ourselves is:
- Re-use the same energy over and over
- by finding some way to extract energy from low grade heat
Alas, this is a harder nut to crack than fission power, so I am not holding my breath. It turns out that there is another annoying universal law that says that every time energy flows, it will somehow become less useful, like water running downhill. This is because energy can only flow one way: from something hot to something cold – thus once something hot and something cold meet and the temperature evens out, you have forever lost the useful energy you had.
It is as if we had a mountain range and were using avalanches to drive our engines. Not only will our mountains get shorter over time but our valleys will fill up too, and soon we will live on a flat plane and our engines will be silent.
The Big Picture
So the useful energy in the universe is being used up. Should we worry?
Yes and no.
Yes, you should worry because locally we are running out of easy sources of energy and will now have to start using sustainable ones. If we do not ramp up fast enough we will have catastrophic shortages.
No, should should no worry that we will run out, because there are sustainable sources – the sun pumps out so much more than we use, it is virtually limitless.
Oh, and yes again – because burning everything is messing up the chemistry of the atmosphere, which is also likely to cause catastrophe. Good news is that the solution to this is the same – most renewable energy sources do not have this unhappy side effect.
Oh, and in the really long term, yes we should worry again. All the energy in the universe will eventually convert to heat, and the heat will probably spread evenly throughout the universe, and even though all the energy will still be present and accounted for, it would be impossible to use and the universe would basically stop. Pretty dismal, but this is what many physicists believe: we all exist in the eddy currents of heat flows as the universe gradually heads for a luke-warm, and dead, equilibrium.
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Ok, so it was longer than a page, so sue me. If you liked this article, my first in a series on energy conservation, you might like my series on efficient motoring.
Please leave a comment, I seem to have very clued-up readers and always love know what you think!
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§ Footnotes:
[1] Matter is energy according the Einstein and the quantity relates to mass according to E=mc^2 (c is a constant equal to the speed of light).
[2] Radiation (like sunlight) is a flow of energy, and energy content relates the frequency according to E=hf (h is the Planck constant).
[3] Chemical energy – the most complex energy, a mixture of different tensions in nuclear and electromagnetic force fields.
[4] Thermal (heat) energy- this is really just a sneaky form of kinetic energy [6 below] – small particles moving and vibrating fast are sensed by us as heat.
[5] Compression (or tension) energy – while compressed air is again a sneaky form of kinetic energy [6], a compressed spring is different – it’s energy is more like chemical energy and is stored by creating tension in the force fields present in nature (gravity, electromagnetism and nuclear forces).
[7] Electrical energy – this energy, like a compressed spring, is stored as stress in force fields, in this case electromagnetic force-fields.
What exactly is ‘science’?
I used to think science was the practice of the scientific method; i.e. you propose a hypothesis, you develop a test of the hypothesis, execute it and prove the hypothesis.
That worked for me until the end of high school.
At university, I was a true nerd. I read all my textbooks cover to cover (mainly because as I was too shy for girls and too poor for booze). During this time, the definition above started to fail. So much of the science was maths, statistics, observation, pattern recognition, logic and quite a bit of rote learning. Not all of it fitted into my definition of science. I became a fan of a new definition: science is the study of the nature of reality .
But then I did post-grad, and I realised that not much in science is ‘proven’ (I guess this is the point of post grad study). Evolution, for example, is not proven. That the sun revolves around the earth is not ‘proven’. I discovered that the only things that could be proven were ‘ideas’ about ‘other ideas’. Bear with me on this one.
Let us say we define the number system – this is an ‘idea’ or conceptual construction. Within this construction we can ‘prove’ that one and one is two. Because we ‘made’ the system, with rules, then we can make factual and true statements about it. We can’t do this about the real world – we cannot say anything with absolute certainly because we rely on flaky inputs like our own highly fallible perception.
It’s like that old chestnut: how can you be sure you are not living in a giant simulation? Of course you can argue that it is pretty unlikely and I would agree, and right there we have a clue to a better definition of science.
It turns out that much of modern science deals in ‘likelihood’ and ‘probability’ rather than proof and certainty. For example, we can say that the theory of evolution is very likely to be more-or-less right, as there is a lot of corroborating evidence. Science cannot be run like a law court – where the prosecution only need to reach a threshold of reasonable doubt to ‘prove’ someone guilty.
Anyway, good science cannot just give up and say once there is consensus something passes from theory to fact. This is sloppy. We have to keep our options open – forever.
Think for example of Newton’s Laws of Motion. They are called ‘Laws’ because the scientific community had so much faith in them they passed from theory (or a proposed model) to accepted fact. But they were then found wrong. Strange that we persist in calling them laws!
It took Einstein’s courage (and open mindedness) to try out theories that dispensed with a key plank of the laws – that time was utterly inflexible and completely constant and reliable.
So it is that the canon of scientific knowledge has become a complex web of evidence and theories that attempt to ‘best fit’ the evidence.
Alas, there are still many propositions that many so-called scientists would claim are fact or at least ‘above reproach’. Evolution is attacked (rather pathetically), but the defenders would do well to take care before they call it ‘fact’. It is not fact, it is a superbly good explanation for the evidence, which has yet to fail a test of its predictions. So it is very very likely to be right, but it cannot be said to be fact.
This is not just a point of pedantry (though I am a bit of a pedant) – it is critical to keep this in mind as it is the key to improving our model.
Two great examples of models people forget are still in flux…
1) The big bang theory
2) Quantum theory
I will not go into global warming here though it is tempting. That is one where it doesn’t even matter if it is fact, because game theory tells you that either way, we better stop making CO2 urgently.
Back to the big bang.
I heard on the Skeptic’s Guide podcast today about an NSF questionnaire that quizzed people about whether they believed the universe was started with a massive explosion, and they tried to paint the picture that if you didn’t believe that, then you were ignorant of science. This annoyed me, because the big bang theory is now too often spoken of as if it were fact. Yes, the theory contributes viable explanations for red-shifted pulsars, background radiation, etc, etc, but people are quick to forget that it is an extrapolation relying on a fairly tall pile of suppositions.
I am not saying it is wrong, all I am saying is that it would be crazy to stop exploring other possibilities at this point.
You get a feeling for the sort of doubts you should have from the following thought experiment:
Imagine you are a photon born in the big bang. You have no mass, so you cannot help but travel at ‘light speed’. But being an obedient photon, you obey the contractions in the Lorentz equations to the letter, and time thus cannot pass for you. However, you are minding your own business one day when suddenly you zoom down toward planet earth and head straight into a big radiotelescope. Scientists analyse you and declare that you are background radiation dating from the big bang and that you have been travelling for over 13 billion years (they know this because they can backtrack the expansion of the universe). Only trouble is, that for you, no time has passed, so for you, the universe is still new. Who is right? What about a particle that was travelling at 0.999 x the speed of light since the big bang? For it, the universe is some other intermediate age. So how old is the universe, really?
This reminds us of the fundamental proposition of relatively – time is like a gooey compressible stretchable mess, and so is space, so the distance across the universe may be 13.5 billion light years, or it might be a micron (how it felt to the photon). It all depends on your perspective. It is much like the statement that the sun does not revolve around the earth and that it is the other way around. No! The sun does revolve a round the earth. You can see it clearly does. From our perspective at least.
Now, quantum theory.
Where do I start? String theory? Entanglement? Please.
The study of forces, particles, EM radiation and the like is the most exciting part of science. But being so complex, so mysterious, so weird and counter intuitive, it is super vulnerable to abuse.
Most people have no idea how to judge the merits of quantum theories. Physicists are so deep in there, they have little time (or desire or capability) to explain themselves. They also love the mystique.
I do not want to ingratiate myself with physicists, so I will add that the vast majority have complete integrity. They do want to understand and then share. However, I have been working in the field for long enough to know that there are weaknesses, holes and downright contradictions in the modern theory that are often underplayed. In fact these weaknesses are what make the field so attractive to people like me, but is also a dirty little secret.
The fact is that the three forces (weak nuclear, strong nuclear and magnetic) have not been explained anything like as well as gravity has (by relativity). And don’t get me started on quantum gravity.
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Anyway, thinking about all these issues, I concluded that science was (definition #3) the grand (platonic) model we are building of reality, ever evolving to best fit our observations.
My man, Plato
That works well for me. However, I recently came across a totally different definition for science:
# 4) “Science is a tool to help make the subjective objective.”
OK I paraphrased it to make it more snappy. It was really a discussion about how science was developed to overcome the fallibility of the human mind. Examples of weaknesses it needs to overcome are:
- The way our perception is filtered by preconceptions
- How we see pattern where there is none
- How we select evidence to match our opinion (confirmation bias)
- How we read too much into anecdotal evidence
- etc etc.
I could go on. So ‘science’ is the collection of tricks we use to overcome our weaknesses.
I like this definition. We are all going about, and in our heads we are building our model of the world… and its time for an audit!
Through doubt comes certainty
This occurred to me this morning while driving to work, listening to Dr Karl’s Science Phone In on BBC Radio 5 Live’s Up All Night show.
Maybe it should be:
“Only through doubt comes true certainty” which sounds more sage but is less snappy. What do you think?
How to drive more efficiently
In this article I hope to describe some efficient driving ‘tactics’ and hopefully also explain why they work.
To do this I start with a question… what, exactly, is energy?
Many people think scientists know this, but alas, they don’t. It is one of science’s great mysteries.
On the other hand, they do know an awful lot about how it flows (they call it thermodynamics which is science-jargon for “heat-flows”). And when energy flows, we also know how to harness it.
If we consider the car, we can think of a fuel tank as bottled energy. The engine then turns that bottled energy into motion. But the laws of physics say energy is never destroyed – in only flows. So where does it go after that?
Understanding the answer to this simple question will help us all to drive more efficiently.
Here are some of the outlets for the energy from your petrol tank:
1. Accelerating your car – energy is transferred into the mass of the car. They call this ‘kinetic’ energy – kinetic is just latin for ‘movement’.
Aside for nerds: It’s the kinetic energy in a car that makes it so dangerous – when a car crashes into a tree this energy flows at a speed comparable to a bomb-blast, bending the metal and hurting the people.
2. Going uphill – the energy is also put into the mass of the car. They call this ‘potential’ energy – we’ll see why in a minute.
3. Friction – the friction inside the engine, of the wind on the car – and last but not least the rubbing of your brake shoes on your brake disks – all turn your energy into heat
Too much energy ends up in the brakes...
4. Noise – some goes into people’s ears, but eventually it all just heats the environment.
And that’s it.
So the first thing to notice is that friction and noise are bad. It is not our aim to heat the world up.
So how do we avoid heat and noise? Firstly, keep your car in good nick. Keep your tyres properly inflated too.
Secondly, drive slowly. Air friction is much more significant the faster you go. Doubling your speed quadruples the frictional loss per km and multiplies the energy loss per second (power) by 8! Thus there is about 21% more energy loss to friction at 77mph than at 70mph, despite being only 10% faster. (and it requires 33% more engine power!)
My third tip is a little controversial. Try not to brake.
If you are approaching a stop, try to coast to a halt by taking your foot off the gas far in advance. If you do this, you will avoid heating your brakes and rather spend your energy on air friction, which was inevitable anyway. We will come back to braking in a minute.
Now can we do anything about the energy required to accelerate and go uphill?
Yes, we still ‘have’ this energy- so it can be recovered!
The mass in your car (including you yourself) become a store of energy when you are a) going fast, and are b) at the top of a hill.
Using potential energy...
The hill energy is called ‘potential’ energy because its got the ‘potential’ to be recovered. We generally recover it without even thinking – when we go back down the other side – gravity does much of the work.
However, we only get it all back if we don’t brake (or use engine compression) to slow ourselves. If failing to brake would lead you to exceed the speed limit, then that’s a pity, as I can’t condone breaking the speed limit, especially if my children are about.
What about the kinetic (going fast) energy? We usually also recover this – but only if we allow ourselves to coast to a stop. Again, if we use the brakes, we turn all that precious energy directly into heat, which is literally burning it.
We also tend to brake when we approach corners, again, it is more frugal to take your foot off the pedal far in advance of the corner such that you are already going slow enough to take it safely when you (eventually!) reach it.
All that might sound complicated, but it all translates to a simple rule of thumb: don’t use your brakes unless you have to. Of course this logic can be taken to its extreme (and occasionally unsafe) conclusion – take a look at the practices of the hypermiler community.
Anyway, that’s all you need to know to get a good 10-20% more miles from each tank.
That concludes this series of articles on greener motoring, I hope it has been of use. Please don’t hesitate to add your own tips in the comments section. Thanks!
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Could the internal combustion engine be greener?
For most people, fully electric cars are some way off. Most people still prefer to have a range of 300+ miles, and to fill up in a few minutes at one of several thousand filling stations.
So how bad is the car we know and love? Can it be made any better? In this article I look the most popular technologies and developments in this area.
The Internal Combustion Engine…
Until all-electric / fuel-cell / nuclear cars are fully realised – we will be stuck with the internal combustion engine. It is therefore well worth looking at how we can make the most of them.
The basics are simple – you heat up some gas, it expands and pushes a piston. In theory you should be able to get all of that heat and turn it into force.
The Internal Combustion Engine
Alas, there are details. We can’t extract all the energy because of the laws of thermodynamics – in fact the limit is about 37% given the temperature range in a typical petrol engine. Then you also have to spend some energy on sucking the gases in. You have to spend energy pumping the gases out. There is friction. There is the heat. The list goes on. Eventually we extract a pathetic 20-25%.
It is therefore not surprising that the piston-driven engine is still being improved despite nigh-on 300 years passing since the earliest versions. There are still redesigns of the inlet manifold, of the valves, of the crankshaft – all designed to lessen the waste.
To pick one example, we can look at the Atkinson Cycle. One of the many great minds to apply itself to engine efficiency was James Atkinson. He realised that if the power and exhaust strokes were designed to be longer than the intake and compression strokes (see a good animation here), you could let the hot gases expand to a greater volume then they previously occupied – and thus be cooler – so your exhaust gases carry away less embodied energy.
It really works – but is not used. Why? Well mainly because we are too committed to the current design and too much money has been spent in its evolution (which was driven by the need for power, not efficiency); to go back the drawing board has simply been too much hassle. Of course, times they are a-changing…
Another technology waiting for its time in the sun is the “VCR” engine, which stands for Variable Compression Ratio. This is a system in which the volume of the combustion chamber may be adjusted depending on whether you are accelerating, coasting or pulling a caravan up the Col du Tourmalet. It promises to constantly optimise the energy extraction. If its developers can convince major car manufacturers to trust the rather complex crank arrangement it may well be a viable alternative in as soon as 5 years from now. Watch this space.
The Transmission
Enough about the engine – what about the clutch and gearbox? That’s the “tranny” to my American friends, which means something totally different here in the UK.
The transmission’s job is to allow the car to vary speed from 0 to over 100 mph whilst the engine only varies only from around 800 – 6000 rpm, which is a much smaller range. With only 4 or 5 gears you need to use a fair range of engine revs to drive, however, the engine is not equally efficient at all speeds.
Principle of the pulley-based CVT, with thanks to the brilliant HowStuffWorks.com
The idea has therefore been brewing for a device that can allow complete freedom for the engine to run at its most efficient speed, regardless of the car’s speed.
Its called the ‘continuously variable transmission’ or CVT. The most practical design is the pulley-type (see image), though others are also being developed.
In addition to allowing the engine to run at its most efficient speed, there is also no disruption of power flow due to gear changes. All of this will add a few vital % to your overall efficiency.
Aside: The CVT is also a vital part of an electric car using regenerative braking, as the gearing can be used to control the braking effect created by the motor/generator.
The fuel…
While hydrogen produced from renewable electricity (say hydroelectric) is one route to reduced carbon emissions, another is the idea of renewable versions of liquid fuels, the so-called bio-fuels.
While bio-fuels do not have as many issues to overcome as hydrogen, they are still far from a clear-cut solution.
Bio-fuels are simply flammable liquids made from plants (nature’s solar panels) – not only is it a renewable energy source (i.e will not run out), but the growing plants also suck CO2 from the air, so could indeed evolve less net CO2 than sources like coal-derived electricity (or hydrogen made from coal-derived electricity). On the other hand, the balance only works well if the bio-fuel is farmed in an energy (and carbon) efficient way.
The idea is fundamentally good, but as with almost all of the other ideas I have discussed, there is a flip-side.
For the first time, there is a risk of direct competition between poor farmers in remote tropical zones, and the big, fat westerner in his or her gas-guzzler. The latter wants something in their fuel tank and the former wants something in their stomach.
There was much speculation last year that the trend towards bio-fuels was responsible for the crisis in commodity food prices. This may or may not have been the cause – it may well have been the result of irresponsible speculation by commodity traders because few bio-fuel crops have directly displaced food crops. However, the question remains: will the drive for bio-fuels interfere with food supply in the future?
There is also the question of whether rain-forests may be razed to make way for the required crops (there are many choices depending on the rainfall and sunshine levels – cane, corn, beet, sorghum, rapeseed, sunflowers or palms to name a few). If an existing forest is razed it not only destroys biodiversity, but usually also results is a massive belch of CO2 into the atmosphere that will takes many years to offset.
However, bio-fuels are still too promising to let alone.
In Europe most diesel already contains a certain percentage of bio-fuel and the EU has targets for bio-fuel use in transport (5.75% by 2010). Even though the target is unlikely to be met, the trends are strong.
The technical barriers are not too serious – most diesel cars can take bio-diesel blends and can usually be made to take pure bio-diesel with minor adjustments. Bio-ethanol can equally be blended with petrol, and at 10%, many modern cars would in fact run better. However, higher levels are still the reserve of so-called “flex-fuel vehicles’ (FFV’s). These are very popular in Brazil, the world’s leading producer or sugar-based bio-ethanol. The US (especially California) is also leading in this initiative. Although to be fair, this too is not a new idea: the Model-T Ford was a FFV!
In the next article I will looking at the driving techniques that can get 20% more miles out of each tank.
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Green Car Technologies Explained
Let’s say you are a big-shot. You need to get around. And public transport is just not going to cut it.
You do a lot of miles and want to go the extra mile to minimise your impact – what should you do?
The answer any good car salesman would give you is: get a Prius (in case you missed it, this is Toyota’s flagship ‘hybrid’ high efficiency offering).
Sounds good, but what is a a hybrid? Is that electric? Do I need to plug it in at night? And what are the alternatives? Are there any?
In this section, I hope explain this and some of the other things coming down the turnpike.
Electric, Hydrogen and Hybrid Cars
Time to plug in?
Time to plug in?
Electric cars are not new. The idea has been around since cars were first made. The problem has always been with the batteries – you need big ones to go far, but the bigger they are, the heavier the car, and so the more batteries you need.
Add to this that batteries take hours to “fill up”, whereas you can can fill the petrol tank in about a minute, and you start to see the issues.
Once you point out that electrical energy is not exactly cheap, and that you are probably not saving the planet unless you get your power from a hydro-electric dam, and you can see why they have not taken off.
So why don’t they just make smaller batteries that charge-up quicker?
Well they are trying. The cell phone industry has driven up the ‘energy density’, but batteries are still rather pathetic compared with petrol. While 60 litres of petrol contains about 2GJ of energy, a pretty good (NiMH) battery of similar weight will muster a paltry 0.02GJ (less than 100th as much). The very highest-tech batteries – still impractical – such as Lithium Thionyl Chloride (LiSOCl2), still contain less than a 10th the energy of simple gasoline.
As a result electric cars cannot go very far on a single charge, and makes them impractical for most road users.
The smart money has not been holding its breath. The next beacon in the night was hydrogen. It packs in three times more energy in per kilogram than petrol. It makes water when it burns. How lovely.
The first problem with hydrogen is the overall efficiency – first you need to make electricity (with some inefficiency losses) – then you need to ‘make’ the hydrogen (with further losses), then you need to compress the hydrogen (yet more losses) and then you need to either burn it or convert it back into electricity in a fuel cell – both of which have more losses still. They all add up. However, these efficiencies are perhaps temporary problems…
A more permanent problem with hydrogen is its low density and thus large volume. Even when compressed to a liquid it still only contains a third the energy of an equivalent tank of petrol. Oh, and because its under very high pressure, the tank needs to be made from thick steel.
This means hydrogen cars also have poor range – and as hydrogen filling stations are rather rare, again this technology is still far from practical for Joe Public.
Due to these problems, the smart money has been looking elsewhere: a compromise solution, that tries to improve efficiency and also reduce emissions but without the short range: the so-called “hybrid”.
The Next Prius - the Toyota Prius is the top selling Hybrid
This is not rocket science. It is basically a car with a fairly normal engine, but also with an electric motor and battery pack.
The logic is that regular internal combustion engines waste energy when the car is running slowly or stopped at the lights. So why not switch over to an electric motor in these situations? And the electric motor runs off batteries which charge from the regular engine when it is running, though in some models the batteries can get a supplementary charge via a power socket at home .
But there is of course something extra that electric (and hybrid) cars can do: they can recover energy during braking – they call it regenerative braking.
The electrical boffins among you will know that a motor, which turns electric current into rotary motion, can work the other way too – turning rotary motion into electric current – when run this way, a motor becomes a generator.
So a car that uses an electric motor to drive the wheels can be used as a motor as you speed up, and a generator as you slow down.
The ability to recover energy from the brakes is where the big savings can be made, especially in town driving, and especially for heavier vehicles. A 2000kg car going at 40 mph has the kinetic energy equal to about 10ml (2 teaspoonfulls) of petrol, and since internal combustion engines are only about 20% efficient, that’s really about 50ml worth – which you burn every time you brake.
And that ‘s why someone came up with regenerative braking.
Aside on electric cars: Electric motors are generally quieter than standard engines. A very real challenge, believe it or not, for electric and hybrid cars, is pedestrian safety. They’re having to test simulated engine noise generators! Strange but true.
Coming soon?
Coming soon?
Why not Solar Power?
Many people have suggested that solar panels, aka photovoltaic (PV) cells, may have utility for electric and hybrid cars. Surely it would help to add some panels on the roof and bonnet?
It sounds good, but alas, solar power is fairly dilute – about 1kW per square meter is an estimate used in the industry. And while a few kW may drive your household’s minor appliances, it doesn’t do much for a car. Even small car engines pack over 50kW. There is simply not enough return, even if solar panels were 100% efficient.
When you add the fact that the real “insolation” (power of sunlight) is about 1/10th of the industry claimed 1kW/sqm, and that solar panels are typically only 20% efficient you can see where this is going.
Energy storage
We have already noted that energy storage is key to the challenge. Petrol and diesel pack a punch, but are not renewable and belch carbon dioxide, while batteries would need to be enormous and take ages to recharge.
Nickel Metal Hydride Battery
Hydrogen is not dense enough so you need a colossal reinforced tank if you want to go any distance, and pocket-sized cold fusion reactors are still firmly in the SF domain.
There are however a profusion of ways to store energy, so what other options do we have?
Motorsport fans may have heard about the new F1 regenerative braking systems, called KERS (Kinetic Energy Recovery System), will also know that they are looking at flywheels and capacitors as alternatives to batteries.
A flywheel
The flywheel is simply a spinning disc which stores the kinetic energy in rotational form. This sounds simple, and can be very efficient but requires a fantastically strong flywheel, and will disintegrate if over-charged. Flywheels also have an annoying habit of resisting turns – that is to say their axis of rotation likes to stay pointing the same way, and so would probably need to be mounted within gimbals to allow a car to go around corners…
Flywheels can however achieve pretty good energy densities (comparable to batteries) and are very efficient. They can charge up and down faster and more often than batteries, but are, on the downside, far more expensive.
Ultracapacitors from Maxwell
Capacitors are much cheaper – and can also charge and discharge quickly and many times. The capacitor is the electrical equivalent of a spring. You apply the electric equivalent of pressure (voltage) to the capacitor and it creates an electric field which stores energy. It is fundamentally different to a battery in which an applied voltage supplies electrons which drive reversible chemical reactions; it can charge and discharge much quicker too.
So what’s the catch? Rubbish energy density. Significantly worse than batteries or flywheels (which are of course already pretty poor compared with hydrocarbon fuels).
There are many other clever ways to store energy – in springs, elastic bands, compressed gases, raised weights – plenty for inventors to think about, but, alas, too many to cover here.
Despite this profusion, neither batteries or any of the alternatives pack the punch of petrol, so it’s going to figure in our future.
In my next article I ask: what we can do to make the most of our friend, the internal combustion engine? I look at their efficiency and also take a detour of perhaps a ‘green’ way to keep using them: with biofuels.
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What makes an efficient car?
Q: why are some cars so much more efficient than others?
Many people will say small=good, big=bad.
That’s a pretty good start, because big cars are probably heavier and also have more wind resistance.
But the rule does not work universally. Sports cars may be small – and look aerodynamic, but may still use lots of fuel so what’s going on there?
The sad reason for that is that the cars and trucks we drive have most often been optimised for speed, power and appearance and not necessarily for efficiency. This may be due to the circumstances in the 20th century – in which the vehicles we use today evolved – where the supply of oil appeared more-or-less infinite and where there were apparently no consequences for burning it.
So what factors determine how efficient a car or truck will be?
#1 Engine type
Petrol or diesel?
There are two major competing technologies – petrol and diesel.
Diesel engines were not promoted for many years (for cars) as they tend to be sluggish and noisy. However they are the more efficient technology in terms of miles per gallon and carbon dioxide emissions (CO2 is the main ‘greenhouse gas‘).
However they have become steadily smoother and more refined and really took off in the 80’s – helped somewhat by government incentives (mainly in mainland Europe). However, they soon became implicated in city smog problems, so many incentives were dropped.
The engines continue to improve with efficiencies now perhaps 20% better than the equivalent petrol version – and as concern over CO2 grows diesel engines are again increasing popularity.
So why are diesel engines more efficient?
This is for two reasons: firstly, the engine internal losses are lower; petrol engines control their speed by ‘throttling’ the air supply to the engine – that is to say they hold back the air and make the engine suck it in through a small gap – a tactic which takes a lot of energy. Diesel engines just let the air in with arms wide open.
Secondly, diesel engines have a higher compression ratio which allows them to extract more energy (according to the laws of thermodynamics). Petrol engines cannot compress their fuel any more than they already do because petrol will spontaneously explode if compressed too much, and push the compressing piston backwards. It was this very problem that led Rudolf Diesel to invent the Diesel engine in the first place. In his design the fuel is only added after the air is compressed, totally side-stepping the issue.
#2 Car Dimensions
The most important measurement is the frontal projected area; this is unfortunate because a big cross section is what makes a nice roomy car. Tall cars are bad, wide cars are bad. It’s best to use the length if you need volume – which is the trick trains use.
It also turns out that nice fat tyres are also bad. Sorry. Biscuit wheels have less rolling resistance.
Sports cars do not slip through the air, they push it upwards...
What about aerodynamics though? Surely a Ferrari slips through the air? Yes, to a degree, but not as much as you might hope – for one thing, Ferraris are surprisingly wide, but more interestingly, they are not actually designed to slip through the air – they are in fact designed to push the air upward in order to get downforce. Those big wings at the back are not there to cut through the air – they’re there to give the tyres more grip…
#3 Car Mass
It is hard work to lug a heavy suitcase around. It is obviously hard work to lug a heavy car around. That said, the laws of physics say that heavy items also have more momentum and so will roll further once moving – so you can in fact recover much of the energy if you take advantage of that momentum. The energy is really only ‘lost’ when you use the brakes and turn it to heat.
This energy recovery trick, combined with ‘regenerative braking’ can reduce the impact of car weight, however generally speaking all additional weight is bad.
PS. I will cover efficient driving tactics and also ways to recover energy from the brakes in forthcoming articles in this series.
#4 Transmission
I know automatic gearboxes are nice. They free up the brain to worry about other things. But they are still bad for fuel efficiency – and for some interesting reasons.
Firstly, fuel efficiency depends on always being in the right gear to get the most out of the engine. However even the best and newest models still don’t change gear at the ideal time – whereas a skilled driver could. Why not? Surely the brainy chaps at Toyota have perfected it all by now? Alas, no. The reason is this: the gearbox doesn’t have all the information the driver has. The driver may know he or she is about to crest a hill or hit some traffic. The gearbox can’t know this – it simply has to make a judgement based on the angle of your foot on the pedal and the current applied torque.
Secondly, some automatic gearboxes are less good at ‘coasting’ (i.e disconnecting the wheels from any internal machinery to reduce friction and engine resistance).
Aside for health and safety officials from the government: Some might say coasting is unwise; it is suggested that having the power to both slow down or speed up a short notice may improve safety; it is also suggested that engine braking is safer than foot braking because it is less inclined to the lock the wheels. These arguments do actually hold some water. While it is in fact possible to use engine braking to put the car into a skid, it is, in general, wise to take corners in gear as you will have more precise control over speed, and in the (rare) case of brake failure (or the more likely case of a foot slipping off the brake pedal), control is more likely to be maintained. I suggest therefore that coasting should only be done in safe conditions and at low speeds.
The last problem with automatic gearboxes is all the fluid. While manual gearboxes do have some oil to churn, the average automatic gearbox is a veritable fountain. The engine connects to the gearbox through a torque converter, which is a cunning clutch-like device based on discs spinning in fluids.
In the gearbox itself, the rotating shafts are used to pump fluids at high pressures through various tight channels and orifices in order to drive actuators that engage and disengage the absurdly clever planetary gearing. All this fluid-flow has inherent frictional loss, and thus reduces efficiency.
#5 Efficiency of Utilisation
What do I mean by ‘utilisation’? Well answer me this: what is more efficient, a Toyota Prius or a Grand Voyager?
The answer is clear: it depends – on how many people you are carrying.
Much can be said for using the vehicle right for the job. If you need a big van once every six months, look at renting or borrowing one, and drive something smaller.
#6 Age and Embodied carbon
This time I am asking: what is more efficient, a nice new Prius or your 3 year old one? You might think a new one would have the edge, but what you need to remember is that it takes an awful lot of carbon to make a new car, and it may take years to work that off. Rather keep your three-year-old in tip-top shape and hold onto it until its efficiency starts to dip – until the new model really is significantly better.
Classic Cortina
If however you don’t have a Prius but have an old guzzler, the carbon may balance out rather more quickly – it really won’t do to keep driving your 3-litre Cortina for ever.
#7 On-board computer
If you get a car with an instantaneous fuel consumption display, you may find yourself trying to set a record – and learning a lot on the way.
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In my next article I discuss some of the innovative green car technology that is on the horizon.
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The Beginner’s Guide to Green Motoring
The 20th century has the seen the rise of the car in the western world. It has impacted the evolution of our cities, our roads and our houses – and we have therefore become rather dependent on them. We co-exist!
However, the effects of carbon emissions are emerging now and we find ourselves on the horns of a dilemma – to drive, or not to drive?
For those of us who can’t give it up, I have written a series of articles looking at the environmental impact of the motor car and looking at what we should be doing to minimize our impact.
Gas guzzler.
1. What makes an efficient car?
2. Green car technologies explained…
3. Making the internal combustion engine greener
4. How to drive more efficiently
That’s it for now, but I will hopefully add more in time.
©Jarrod R. Hart 2009
Gravity explained in 761 words
People seem to be harbouring the impression that there is no good theory of Gravity yet. I asked a few friends – most thought Newton had explained it, but couldn’t explain it themselves. This is rather sad, 80-odd years after a darn good theory was proposed.
Of course there is still some controvery and the odd contradiction with other beloved theories, but the heart of the General Theory of Relativity really does a great job of explaining gravity and it is really wonderfully beautiful, and can be roughly explained without recourse to jargon and equations.
This is a theory that’s just so darn elegant, it looks, smells and tastes right – once you get it. Of course, the ‘taste’ of a theory doesn’t hold much water; for a theory to survive it needs to make testable predictions (this one does) and needs to survive all manner of logical challenges (so-far-so-good for this one too).
This is not a theory that needs to remain the exclusive domain of physicists, so for my own personal development as a scientist and writer, I thought I might try an exercise in explaining what gravity is – according to the general theory of relativity.
For some reason, my wife thinks this is strange behaviour!
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The story really got started when Einstien realised that someone in an accelerating spaceship would experience forces indistinguishable from the gravity felt back on Earth.
He or she could drop things and they would fall to the floor (assuming the spaceship is accellerating upwards) just as they would fall on earth.
So perhaps that’s all gravity is… some sort of accelleration? Let’s see.
In the spaceship, it’s clear to us that the objects would appear to fall to the floor, but in reality, it is the floor of the spaceship that is rushing up towards the objects – this explains why things fall at the same speed whether heavy or light, matching Galileo’s own test results when he dropped various things, supposedly from the leaning tower of Pisa. It further implies that things will ‘fall’ even if they have no mass at all… such as light beams.
The thought experiment goes thus: Consider if you had a laser-beam shining across the spaceship control room; it would curve slightly downwards, because the light hitting the opposite wall would have been emitted a little time ago, when the spaceship was a little way back, and going a bit slower (remember, its accellerating).
We know the light is not bending, it is just that the source is accellerating, resulting in a curved beam. Imagine a machine-gun spraying bullets across a field – as you swing the gun back and forth the bullets may form curved streams of bullets, but each individual bullet still goes straight.
So Einstein suggested that perhaps light beams will bend in this same way here on earth under a gravitational field. Now Newton’s theory of gravity says light beams may also bend if they have ‘mass’, but the mass of light is a dodgy concept at best (it has inertia but no rest mass, but that’s a whole different blog posting). Anyway, even it it does have mass, it would bend differently from what Einstien predicted. So the race was on to see how much gravity could bend light…
This bending of light prediction was proven by a fellow called Eddington who showed that during a solar eclipse, light from distant stars was indeed bent as it passed near the sun, and by exactly the predicted angle.
Einstein went further though, suggested that light beams on Earth are, just like on the spaceship, really travelling straight, and only appear to bend, and that this can be so if space-time itself is curved. They are going straight, but in curved space.
We know that the shortest distance between two points is a straight line, but if that line is on a curved surface, supposedly straight lines can do strange things – like looping back on themselves. Think of the equator. This model therefore allows things like planets to travel in straight lines around the sun (yes, you read right).
The model has been tested and shown to work, and gives good predictions for planetary motion.
So what can we take home from all this?
Well mainly, if this model is right, we need to let it sink in that gravity may not be a force at all, but an illusion, like the centrifugal ‘force’ you experience when you drive around a corner.
Secondly, it is an open invitation to think about curved space and its marvellous implications!