Rabbits and Energy Return on Investment

Introduction

Energy Return on Investment (EROI) is a ratio of the amount of energy you need to expend versus the amount of energy you get in return.

If we use Winnie the Pooh, to get to the honey Pooh will need to climb a tree. So Pooh will need to expend energy.

However if Pooh gets lots of honey then this is well worth the effort.

If the amount of honey Pooh get allows him to climb 40 more trees, then the Energy Return on Investment (EROI) is 40.

The same applies to humans and all the energy sources we use, both non-renewable and renewable.

Learning Objectives

• Understand the concept of Energy Return on Investment
• Understand the EROI for different energy sources.
• Understand what happens if we need to shift to low EROI sources of energy.

Rabbits understand Energy Return on Investment or Energy Surplus

• Rabbits spend between 6-8 hours a day eating [1]
• The rest of the time they stay in their burrows sleeping and digesting their food to gain energy.
• All the energy in the food that rabbits eat comes from the sun. It is a real form of renewable energy and produces no toxic waste products (just rabbit poop and wee which soil bugs love)
• Rabbits don't use up much energy looking for food. It is mostly locally grown.
• In simple terms, because a rabbit spends 6 hours eating out of 24 hours in a day, the Energy Return on Investment is approximately 24/6 or 4. This is normal for herbivores in the natural world.
• If rabbits spent only 1 hour eating and the rest of the time doing other rabbit activities then the EROI would be 24/1 = 24

Energy Return on Investment for Early Humans

• When humans were hunters and gatherers the Energy Return on Investment would have been similar to rabbits.
• Like the Aboriginal Australians, the women would gather, cultivate and hunt [2].
• The men would also hunt and help gather plants for food.
• It is estimated that they spent between 4 and 6 hours each day gathering food. The rest of the time was for leisure and other cultural activities.
• The indicative Energy Return on Investment was 24/4 = 6.

Energy Return on Investment and the Industrial Revolution

• Once humans discovered how to use coal to produce steam to make machines do work (1780) the overall EROI for human society increased significantly.
• Coal is created from the remains of dead plant material. The energy in the plant material originally came from the sun. This energy has been stored in the Earth for millions of years.
• Early coal was easy to dig up. Steam machines gradually became more efficient.
• The work output from burning coal was so large that Engineers had to use horses to explain work output and so the concept of horse power was invented.
• Human work is the equivalent to 75 Watts
• One horse power unit is the equivalent to 746 Watts (about 10 times more than humans)

World per Capital Annual Energy Consumption

• This graph shows how the amount and type of fuel consumption has changed from 1950 to 2015.
• it shows that the total amount of primary energy consumption by humanity has increased significantly.
• And that we are still produce most energy from non-renewable energy sources [3]

Energy Scale Progression

• In this graph we can see how surplus energy has been used over time.
• Early humans only used the equivalent of 100 Watts of energy and this was mainly for their food provisions.
• During the time of the Egyptians primitive agriculture increased our energy consumption to 600 Watts per person.
• During the industrial revolution coal and steam engines allowed humans to increase energy consumption to 3,850 Watts
• In modern times the energy consumption in countries such as the USA and Australia is 11,500 Watts [4]
• The hidden cost associated with the large increase in energy consumption has been the concomitant increase in GHG emissions and the warming of the planet.

Energy Equity

• The amount of energy used by the average person in the USA and Australia in 2016 is equivalent to 100 x 100 Watt light globes.
• By comparison, the energy consumption averaged for all humans on planet Earth is 26 x 100 Watt light globes*
• In the short term rich countries could easily reduce energy consumption and allow poorer countries to increase their share of energy consumption, while still reducing overall energy consumption for humanity.

Energy Impacts

• CO2 levels for the past 10,000 years have been stable [5].
• However, since the start of the industrial revolution the levels of CO2 in the atmosphere have increased significantly.
• Annual atmospheric CO2 levels are shown in the adjacent graph showing increases from 1960 to 2015.
• Annual atmospheric CO2 levels are currently increasing by 2-2.5% per year.
• As our energy consumption has increased so too have our CO2 emissions and the concentration of CO2 in the atmosphere.

The Switch to Renewables

• There is the expectation that society will replace fossil fuel energy with renewable energy.
• However renewable energy has the following drawbacks:
  • Raw materials need to be mined and processed (e.g. copper, cobalt, lithium, nickel).
  • Renewable energy assets are mostly produced with fossil fuels
  • The Energy Return on Investment for solar PV and wind renewables is relatively low in comparison to coal and oil.
  • Storage solutions such as batteries are resource intensive and also use fossil fuels in their production.
  • 54% of renewable energy raw materials are on indigenous land [6]
  • Renewable technology does not last forever and will need to be recycled and rebuilt.
• The reality is that while increasing the amount of renewable energy we will also need to reduce energy and material consumption, especially in developed countries.
• A decrease in energy and material consumption (degrowth) will have recessionary impacts for the economy but significant benefits for the Earth.

References

• Energy Return on Investment for Beginners [7]
• Nate Hagens Reality 101 Course [8]

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