h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

On a large scale I mean, as in power stations that supply electricity for a country.

Why are they all mechanical? With all the knowledge we have of particle and atomic physics, with the progress made on non mechanical electricity generation such as fuel cells, do we not have industrial scale generation that doesn't involve large bits of metal whirling about?

Not that I know what other methods there are (outside of the fuel cell stuff) but surely there are other chemical and nuclear/atomic reactions that free up electrons that could be used?

I think the problem is capturing the power produced. Generally in fossil and nuclear fuel plants, I believe water is heated, producing steam to drive a turbine.

I've wondered this too - surely there must be a method to turn heat directly into electricity...

There was something on Bang Goes the Theory last series which was a Solar panel that worked on InfraRed - and was clothlike in texture... Theoretically you could wear it and generate electricity from your own body heat.... So why not in a furnace, etc...

"water is heated, producing steam to drive a turbine"
Exactly! All so very 19th/20th century!

The question was, in fact, sparked off by a convo with someone where we discovered we'd both been disappointed to find out that the nuclear bit of a nuclear power station was basically just used as a big water heater.

I guess nothing else is as efficient. Though you'd think when we've got floppy solar panels that can be incorporated in a rucksack the technology could be adapted.

The type of solar panel that converts sunlight directly into electricity is very expensive to make. Last time I looked, the cost of making the panel was the equivalent of the price of 20 years' worth of electricity made in the normal turbine way. I'm sure they've come down in price, but they've a long way to go.

Similarly, you can make electricity using the Peltier effect which generates electricity directly from a temperature difference, without moving parts, but again it is ferociously expensive.

I suspect a fusion reactor would also still just be a glorified kettle.

Ultimately you always fight a battle in transducing any form of energy to another against waste in the form of heat.

Hence it's likely to be always more efficient to harness the heat than fight against it.

there are a few things about electricity generation: efficiency, cost, reliability (and indeed, these are not unrelated).

your normal generator has steam generation (oil, coal, gas, nuclear), a steam turbine and a generator.

steam turbines, and generators, are more efficient, more reliable, and cheaper than "other" methods. steam turbines can have up to 50% efficiency, and can easily be controlled

direct conversion has low efficiency, is expensive (life cycle cost), and is not reliable on the long run. thermogenerators can have up to 5% efficiency. that's not enough, your energy bills would be five to ten times higher.
Ah yes, thermogenerators also deliver relatively low voltages, and direct current: almost useless unless you'd like to use bicycle lamps for lighting.

DC almost useless?

Most Laptops run on DC, LED lights only work with a transformer (not the right word...) to convert to DC. It seems most electronic devices have to convert AC to DC in order to work at all...

AC is (IIRC) safer and "easier" to transmit long distances, for some reason that escapes me ATM.

I can't remember why it is safer, but it is easier to transport because you can transform it to very high voltage, transmit it, then transform it back down again. This reduces losses in the transmission lines. Low voltage / high current transmission would lose most of it by heating the wires, or would require enormously thick conductors.

It is very difficult to transform direct current, so you basically transmit at the voltage you're going to use it at, which means huge losses in transmission.

That's what I thought...

It's not *that* hard making AC from DC.

However, no-one would bother doing it if the DC came from a conversion method less efficient than an AC one running from the same original power source.

The only efficient way to make AC from DC in large quantities is to get the DC to run a motor and to get the motor to run an AC generator.

In small quantities you can do it using a simple electronic circuit called an inverter, but you couldn't run a city with the power from one of those, as it would melt down.

They manage to electronically convert back and forth between DC and AC at pretty high power levels for HVDC transmission lines.

Certainly, it takes some serious kit to do the conversion, but it's certainly possible - it's just a matter of whether it makes economic sense to do it, balancing the cost of the necessary kit against the advantages of DC transmission.

that AC-DC conversion is only done if there are serious reasons not to couple two adjacent AC transport networks.

What are the advantages of DC transmission?

You can send it long distances inside a sealed insulated cable. This is used for sending electricity under the sea for long distances, such as for connecting the UK National Grid to the French National Grid.

There are various problems associated with sending alternating current along this sort of cable, so they use direct current.

I guess direct current gets there faster as well as it doesn't have to go round all those corners.

It's good for electrocutions as well.

Westinghouse invented the electric chair, which runs on direct current, so that people would get the idea that direct current is dangerous, so that they would prefer alternating current, which his company was promoting.

I thought it was Edison who promoted the electric chair as a way of showing that AC was more dangerous?

For point-to-point transmission, HVDC has an advantage over very long distances due to better utilisation of power lines.