We all know that some kinds of energy are a lot more eco-friendly than others – and when it comes to generating electricity, that often has us thinking about power generation from low, or even no, carbon renewable options instead of getting it from high-carbon fossil fuels.
As far as it goes, it’s not a bad way of looking at things, but it gets a little more complicated when people start to talk about the idea of ‘green electricity’, because in a sense, there is no such thing.
There are, if you want to think of it like this, ‘good’ and ‘bad’ sources of electricity – but the actual electricity itself is the same, no matter where it comes from in the first place. In the end, all electricity is just a flow of electrons – huge numbers of mind-bogglingly tiny particles stripped off atoms, and then delivered down the wires to our homes.
What’s more, with the exception of solar photovoltaic systems, whether it comes from a nuclear plant, a conventional gas or coal burning power station, a wind turbine or wave generator, all electricity is made in the same way – and perhaps a little surprisingly, it’s all done with magnets!
Thank you, Mr Faraday in 1831
Almost all of the electricity we use today – except, you will remember any from PV cells – comes to us thanks to a scientist by the name of Michael Faraday, and an experiment he did way back in 1831, using a length of wire, a piece of paper and a (yes, you guessed it) a magnet.
To cut a very long story short, he rolled up the paper, wrapped the wire around it to make a coil, and then moved his magnet quickly in and out – and when he did so, he found that he had generated electricity within the wire. It might seem a strange thing to do – but he did have his reasons, and we did say we were going to keep things brief and in any case, the ‘why’ part isn’t actually that important; the point is, it worked.
It took many, many more experiments, of course, but from that simple start, what became known as “electromagnetic induction” was to enable the huge generators to be built that supply us with power today. Huge and impressive pieces of engineering though they are, while some of the workings of their massive coils of copper wire and equally enormous magnets have changed, they are still basically doing the same thing.
To get them to work, however, we need to supply some other kind of energy to make them move. For some sources, such as wind or hydro power, seeing how that happens is pretty straightforward. The ‘movement energy’ (called “kinetic energy” by scientists) is supplied direct; the moving wind or water drives the blades of the generator’s turbine, the turbine turns the coil, and electricity results. In the case of gas-turbine generators, the turbines are turned by the fast-moving exhaust of the burning gases, while for other kinds of generation, such as coal-fired or nuclear for example, there has to be another step, and that involves steam.
Steam power was pretty hi-tech back when Faraday himself first started playing around with magnets and wires, so in some ways it’s a bit odd to find that 200 years later, it’s still to be found at the heart of today’s electrical generation. Even stranger to think that the basic idea is almost unchanged from the old steam trains that your great-great-great-great-grandparents would have ridden in!
Heat produced by burning coal, or from the controlled atom-splitting that takes place in the core of a nuclear reactor, turns water to steam, the steam drives the turbine, the turbine spins the coil and, once again, electricity is generated. As that nice Mr Meerkat says, ‘simples!’
The Photo-Electric Effect
OK, so magnets and coils generate most of our electricity, but what about those photovoltaic cells? How do they work?
Surprisingly, the answer to that also takes us back to the 1800s – to 1839, in fact, when the French scientist Edmund Bequerel noticed that some kinds of materials could produce small electric currents when light shone on them – the ‘photo-electric effect’. The world had to wait for another 66 years, however, for the science mega-genius, Albert Einstein, to come along and explain how it happened – and then it wasn’t until the 1960s and the start of the Space Age that anyone paid PV much attention.
PV cells are made up of what are called semi-conductor materials – the likes of silicon which is used throughout a whole range of micro-electronics, including, of course, computers. To make them, a very thin wafer of this material is precisely engineered to have one side that is electrically positive and one electrically negative; when light falls on the cell, electrons are knocked off from the individual atoms of the semiconductor material, and then flow as electricity.
That’s probably a good place to leave PV – and electricity too, for that matter; after all even Faraday, Bequerel and Einstein didn’t get their heads around all the science behind things a single day!