Global Energy Inputs

In thermodynamic terms the Earth is an isolated system. The energy it receives from the Sun each year is balanced by the heat energy radiated back to space. As we're not about to get a delivery of energy from Alpha Centauri any time soon we have to live with what we can harvest from the Earth's renewable energy system, or extract from the energy reserves stored in the rocks near the surface.

The Earth receives 5.4 million exa-Joules (EJ) of energy from the Sun each year. An 'exa' is '1' with eighteen noughts after it. A Joule is the international standard unit of energy, equivalent to lifting a hundred grams (something like a Bramley apple) 1 meter up against gravity.

About 30% of this energy is reflected back to space. We could trap this on the Earth, but it would affect the thermal equilibrium of the planet in space and make the surface hotter. About a quarter of the energy evaporates water in the oceans to drive the hydrological cycle. We can extract energy from the equatorial oceans using something called 'ocean thermal energy conversion', but if we extracted too much we'd diminish the hydrological cycle and affect the weather. Just less than half of the energy goes into heating air and water to make the world's wind and ocean currents. This is probably our best source of renewable energy, but again, taking too much would adversely affect the environment.

At the moment the human species uses between 470EJ and 500EJ per year. Compared to the 5,400,000EJ the Earth receives from the Sun that's next to nothing, but if the world economy keeps on growing demand at the average rate of the last few decades then in about 600 to 800 years that's how much energy we'd require (and in 1,200 years it's about the output of the Sun itself!).

There is a fallacy promoted by some in the environment movement that the human species "uses less than 1% of the energy the Earth receives from the Sun". That's true, but it assumes that it's all ours for the taking. We must share that energy with the Earth's natural climate system and all the other animal and plant species on the planet. In reality, only a few percent of that energy is there for us to take without causing damage to the world's environment – and in any case solving the energy problem doesn't solve the greater resource problem (e.g, phosphorus for intensive agriculture or rare earth metals for our hi-tech electronics) that are at the heart of our modern society.

Background Information

Books:

• Energy Systems and Sustainability, Boyle, Everett & Ramage, OUP (2003), ISBN 978-0199261796.
• Renewable Energy, Godfrey Boyle, OUP (2nd ed., 2004), ISBN 9780 1992 6178 9.

Wikipedia:

• Sun – http://en.wikipedia.org/wiki/Sun
• Earth – http://en.wikipedia.org/wiki/Earth
  

The Annotated 2-hour EBO Presentation Slides (3.7 megabyte!!) – a PDF file containing explanatory text and web links relating to each of the slides in the 2-hour Energy Beyond Oil presentation. http://www.fraw.org.uk/download/ebo/
ebo_annotated-2008.pdf

Large format EBO presentation slides (1.7 megabyte!!) – a PDF file with a larger copy of the slide images in the presentation. http://www.fraw.org.uk/download/ebo/
ebo_presentation-2008.pdf