Welcome to our 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.

In our previous blog, What is a Watt-hour, we looked at how we measure domestic energy use in kilowatt-hours.

When a whole city gets its energy bill, the quantities are measured in terawatt-hours (TWh).

We know that a kilowatt-hour is one thousand watt-hours. A terawatt-hour is a much larger quantity of energy, and is equal to one billion kilowatt-hours.

For the Exeter region the total on its energy bill is 10TWh each year.

Quadrillions of Joules

If we were to write 10TWh down in the number of individual units of energy, joules, that were used it would be 36000000000000000 joules, or 36 quadrillion joules.

This is the total of over one billion joules used each second, or energy used at a rate of one billion watts, for every second in a year.

It’s much simpler to just say 10TWh.

10TWh in context

To give a sense of the magnitude of 10TWh here are a few things it is equal to:

  • Boiling the water for 250 billion cups of tea
  • Keeping your iPhone charged for 3.7bn years
  • Cooking 75bn 10minute meals in an 800w microwave
  • Cooling your beers for 29m years in an average fridge
  • Watching 50bn football matches on an average TV
  • Making 368 trips to the moon
  • Powering 120m 60w (equivalent) LED lightbulbs for a year
  • Doing 15.9bn washes on a standard 2kg cycle at 40 degrees
  • Driving 67bn km in a Nissan Leaf

Now that’s a lot of energy. It’s hard to imagine this amount of energy, but the above comparisons give a sense of scale. If the earliest form of life on Earth (way before the dinosaurs!) had discovered electricity and invented a smartphone, that smartphone could still be being charged today.


What is 10TWh


Despite this enormous energy use only 1.5% of what we consume is generated by renewable energy sources. If we want to ensure the future well-being of the city and the region then we need to become energy independent by adopting renewable energy sources. We’ll be looking in detail at how renewable energy is generated in our next series of Energy Explainers blogs.