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Tuesday, 5 June 2007

Understanding Energy - Part 2 of 2

Yesterday's bottom line was this: all the Earth's energy comes from the Sun, it provides life with the ability to grow and to modify the materials of the Earth, and the majority of it eventually heads back out into space as waste heat.

The ancient civilisations of places like Egypt and South America seemed to understand this much better than we do today. Modern man knows clever words like "photosynthesis" but has lost the deep understanding that the Sun is ultimately what puts leaves on the trees and life in our bones.

My best guess at why this is comes down to the discovery of fire, and of "non-living" things which could be burned. Of course I'm referring to coal, oil and natural gas.

Fire is a chemical reaction in which energy that was previously holding atoms together to form molecules is released as heat. Because there's a high concentration of heat energy in one place it's possible for us to channel some of it into causing desirable changes (such as pushing a piston in an engine, melting metal in a furnace or cooking food on a BBQ) before it dissipates and becomes "lost".

For many thousands of years the primary source of chemical energy which humans could harness by setting it alight was wood. Trees spend years soaking up solar energy and converting it to chemical energy that holds together the atoms which form the molecules that comprise its living tissues. At this level the connection between the Sun and the energy available to us in a wood fire is still somewhat intuitive. It's fairly obvious that the trees have to grow before they can be burned.

But coal, oil and gas don't have that same obvious relationship to the Sun. Instead of waiting for a tree to grow you can just dig them up and burn them. And what's more, the amount of chemical energy they contain is far greater than in their equivalent weight of wood. The industrial revolution was unleashed upon the world when people started to figure out more sophisticated ways of using that stored chemical energy to cause changes in materials and motion. That revolution never stopped - we are still living it at full throttle today.

There's just one little problem. Do you remember the two rules of the energy game from yesterday's post?

1. Energy cannot be created or destroyed.
2. Whenever energy is used, some of it gets "lost" and can't be used again.

All that energy in oil didn't just magically appear. Scientists are pretty darn sure that coal and oil and natural gas were formed from the accumulation, over hundreds of millions of years, of solar energy converted by plants into chemical energy and then trapped underground in landslides, floods or similar events. That's why they're called "fossil fuels".

It's like the Earth has an internal rechargeable battery. It's capable of storing an unimaginable amount of energy, and it's in a form which is wonderfully convenient for us to use. It took hundreds of millions of years to charge it up, but in the span of a couple of hundred years we've managed to run the battery down to about 50% charge remaining and at this rate it'll be fully exhausted by about the end of this century.

Let me say that again. We've consumed hundreds of millions of years worth of stored solar energy in just a few centuries, and now we're starting to run out.

The discussion about how much fossil fuel energy remains to be dug up and burned is a complicated one and is made worse by the unfortunate side-effect that we call climate change. I'm going to side-step the whole question of exactly when fossil fuels will cease to be able to meet our energy needs for transport and electricity production - but it will inevitably happen. In many parts of the world energy supply is already struggling to keep pace with demand.

But what else is there?

Governments and corporations the world over are turning to "biofuels" to try and compensate for falling oil production. But the math just doesn't add up: the rate of conversion from sunlight to chemical energy is far too slow to allow it to meet the current demand for oil. Besides which, studies seem to show that in many cases you use about as much oil producing the crop (for powering farm machinery etc) as you get back from the crop in the final product, making the whole enterprise a waste of oil and food at this point in time. Technological advances may make the process more efficient in the future, though, so continued research is worthwhile.

Solar photovoltaic technology - which uses tricks of physics to convert sunlight falling on a substance directly into electricity - has a similar problem. The technology keeps getting better but there's a limited amount of the raw materials needed to make the panels and producing them consumes significant amounts of energy. We probably can't produce enough of them and they don't give back enough energy to make them a silver bullet solution to our electricity dependency, but again more research is needed.

Heating water with solar collectors is a no-brainer and I applaud moves from the Queensland government to phase out the old electric-powered type. Wish it would happen sooner.

Using wind to generate electricty (converting kinetic energy from the moving air into electrical energy in the turbine) is also a pretty smart idea. The wind moves because the Sun heats the air, so tapping into that energy flow is sustainable in the true sense of the word. There are some concerns about the amount of energy used in construction vs the amount of energy the turbine can harness over its lifetime, but those issues can probably be solved through engineering.

Hydro-electric systems are also driven by the Sun. It's the Sun which heats the water and causes it to evaporate. It's the Sun which drives the wind that carries the vapour up over the higher land, imbuing it with gravitational potential energy. As the water flows down again towards sea level we can extract some of that energy to turn a turbine and convert it to electricity.

Wave and/or tidal energy. Waves are caused by the wind, which in turn is powered by the Sun, and there's a colossal amount of kinetic energy in the movement of the water. Harnessing that's a great idea. The tides are due to the gravitational pull of the Moon on the water. Taking energy from that system will actually cause the Moon to orbit more slowly and crash into Earth... but that's going to happen eventually anyway and it's unlikely we'll make any significant impact. (No pun intended.)

Geothermal (hot rocks). Not, strictly speaking, a renewable resource but definitely a clean one. Worth looking at where the geology is appropriate.

Nuclear. Ah, had to get to this eventually. Ultimately, nuclear energy is a form of stored energy that was locked into atoms by long-dead stars. It's completely natural but - like molten lava or the Sydney funnelweb spider - not something you want to get too close to. It's interesting to note that some of the geothermal heat which people want to harness was actually released during the radioactive decay of unstable nuclei. There is a lot of nuclear energy available to us here on Earth but like fossil fuels there are undesirable side-effects and it's not a renewable resource.

And that, pretty much, is it. We need to stop using fossil fuels now due to global warming but we will simply run out of oil soon anyway. Nuclear technology will continue to play a role in the global energy mix for a very long time, and it's possible that new developments could greatly reduce the risks associated with radioactive waste and other concerns. The rest of them are all important because none of them can supply so much energy in such a convenient form as fossil fuels have done for the past couple of centuries.

There's a lot of work needed to secure energy supplies and maintain a habitable planet, even just for the rest of this century. I've started doing my bit and you can too.

Thanks so much for reading this far. Questions, comments, corrections all are welcome.

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