Welcome to the first in a series of blogs explaining the science that supports the goals of Exeter City Futures. We will break down the different aspects of energy independence and zero congestion into their simplest terms, in preparation for Exeter’s energy report which we will be releasing in early 2017.

These are not highly scientific guides, but easily digestible explanations on key concepts intended to help anyone who’s interested understand what it is we’re trying to change, and how we’re going to change it.


We are all familiar with the term “watt”, we choose our lightbulbs depending on how many watts it has – the higher the number of watts the brighter the bulb. But what does it really mean?

A watt is one unit of power, and a measure of how much energy is used during one second.

To really understand what a watt is, we must first understand the difference between energy and power.


Understanding Energy

Energy is the “stuff” that makes things happen, if we didn’t have that “stuff” nothing would happen. Our lights wouldn’t come on, our phones wouldn’t charge, and our cars wouldn’t start.

Power measures how fast that “stuff” is used.

When we talk about electrical energy one unit of the “stuff” that makes things happen is called a joule. When one joule runs through an electric circuit, we call the speed (or rate) at which the energy is being used “one joule per second”, or one watt.

If there were 60 joules running through a circuit (like a lightbulb) we could call this rate “60 joules per second” or 60 watts.

The rate at which energy is used is what we call power and we measure it in watts.

Confused? Let me introduce Joulie.


Girl Power

Joulie is a single joule of energy. She’s also a runner of electric circuits. She runs any circuit in one second.


What is a watt? Joulie the Joule


When the circuit is turned off Joulie is stood still and no energy is running through it. None of Joulie’s energy is being transferred to the circuit, and no watts are generated.

When the circuit is turned on Joulie starts running. When she runs she generates one watt of power, because she’s transferring all her energy to the circuit in one second.


What is a watt? Circuit diagram


On her own Joulie could power a one watt light for as long as she can keep running. Luckily she has a friend that hands her energy drinks at the finish line – this keeps her recharged!

If she wanted to power something that required more energy each second she’d have to call some of her girlfriends.

It would take Joulie and 59 of her friends to power a 60w light bulb.

If they wanted to keep it on for 60 seconds they’d have to run around the circuit 60 times. 60w of power is generated for 60 seconds.

If they wanted to keep the lightbulb on for an hour, they’d all have to run around the circuit 3,600 times. Although more energy is used during the hour, the rate is still 60w. So 60w of power is generated, for 60 minutes.

If Exeter was powered by Joulies she’d need one billion friends, about one seventh of the world’s population, to run around the city’s circuits every second.

Now that’s a lot of girl power!


So What is a Watt?

A watt is a unit of electrical power that measures how much energy is used to make something happen each second a circuit is turned on.

It’s the rate at which energy is transferred or the power.