Electricity powers almost every aspect in our life; but do we know where it comes from?
Photo by: Manel Torralba
There’s a bit of the comedian Dara Ó Briain that narrates what would happen if a simpleton from our time would try to describe how any machine we use in our everyday life is powered: “well.. it’s connected to the wall by a cable…”. Absolutely clueless.
Since we all know that time travel is about to be invented, here is an explanation of where some of our electricity comes from, so you will not be caught unprepared.
How does it work?
Figure 1: Rudimentary scheme of a power plant. By James Albasi
Most of the electricity used in the world comes from thermal power plants. If we want to summarize how a thermal power plant works, we could say that the fuel is burnt to boil water, turning it into high pressure steam. The steam is then passing trough tubes in which it moves the turbines in a generator and violà! We have electricity! But let’s go step by step, shall we?
Heat engines and wasted energy
An interesting way of thinking what happens from the boiler (heating of the water and formation of high pressure steam) to the turbines (movement transmitted from the steam to the turbines) is that we transform heat in some kind of energy that moves objects, energy called Kinetic energy.
Knowing that, we can schematize this part of the power plant using the model of a Heat engine (the same type that powers all non-electric vehicles)
Figure 2: scheme of the Heat engine. By James Albasi
Looking at the figure, we can see that not all the incoming heat is converted in kinetic energy. How come some heat gets wasted?
Scientist and engineers have observed that every time energy is converted from one form to another, some of it get wasted.
In order to exemplify this loss, we could imagine cutting a circle from a square piece of paper: we can see that there is no way to cut a circle from a square without wasting some of the paper, the same we can say for cutting an hexagon out of a circle piece of paper.
Figure 3: Every time we try to cut out a new shape we lose something.
Every time we try to cut out a different figure we lose some piece of paper. In an analogous way, every time we convert from one type of energy to another we lose some of it, and no matter how far our technology will advance, there will always be some energy wasted during the conversion.
Now, in Figure 1 we can observe the conversion between different types of energy: first between energy stored in the fuel is converted in heat, then the heat is converted in the movement of the high pressure steam, then the steam rotates the turbines and finally the rotation of the turbines generates electricity. Once we know this it is evident that a power plant will not convert 100% of the energy stored in the fuel into usable electricity.
Magnets and coils
We have all seen water boiling, steam coming from it and we know that its movement (specially under pressure) can move other objects, so the first steps in the engine should be straightforward, but we still have to discover how can the rotation of the turbine produce electricity.
In order to figure it out we have to step back and imagine what happens when we move a magnet trough a circuit that powers a light bulb, coiled around a tube. We will see that when we move the magnet towards the coil, the light bulb will start to glow, from which we can conclude that some electricity is flowing in the circuit. But then when the magnet stops moving, even inside the circuit, the current stops. The same effect is obtained if the magnet stands still and the coil moves towards or away from the magnet. This interesting experiment shows that whenever there’s motion between the magnet and the coil electricity will flow.
Now, if we apply this experience to our case of a power plant, it is easy to understand how the rotation of the turbines can create electricity: the turbines pass the movement to a coiled circuit, which creates a motion between the spires and a magnet, generating electrical current.
Smart(er) than in the past
The explanation above is based on the work of a thermal engine, which is one of the simplest and first known ways to create electricity than humans invented. And even though it is still how much of the electricity is produced in the world, we all know that burning fuel is very harmful for the environment. Luckily, this system can be easily modified to generate electricity from very many sources, which are renewable and environmentally friendly. I invite you to think of a few, and which parts of the system can be avoided or replaced if, for example, we want to take advantage of the natural movement of water, wind, or even the wheels in a gym spinning class! Let’s use the knowledge from the past, and find smart(er) solutions in the present!