Thermodynamics and EROEI (Part 1)

If you are new to the peak oil debate you may not have seen the acronym EROEI. If you have any financial background you may however have seen ROI (return on investment). EROEI is a similar concept used to evaluate energy systems (e g. corn ethanol production, oil production and refining, electricity generated from wind turbines). EROEI stands for Energy Returned on Energy Invested.

Oil production and refining have a very wide range of reported EROEI's. Crude oil from Saudi Arabia is (or was) sometimes quoted as having an EROEI of 100:1 while Syncrude produced in the tar sands of Alberta has been quoted as having an EROEI of 1.5:1. Overall the EROEI of the Oil and Gas industry has been steadily dropping. The crude oil with the highest EROEI is extracted first while oil with the a lesser EROEI balance is left for later. It is accepted wisdom that a process with a negative EROEI cannot be sustained indefinitely. However that hasn't always stopped people from trying.

The 1st law of thermodynamics states that, "energy cannot be created or destroyed; rather, the amount of energy lost in a steady state process cannot be greater than the amount of energy gained". The 2nd law of thermodynamics states that, "energy systems have a tendency to increase their entropy over time". So for example, when gasoline is burned in an engine, some energy is converted to mechanical energy while some is converted into heat and some is left as unburnt vapors that get released into the atmosphere. Energy will tend to dissipate from a more concentrated form to a less concentrated form if left alone.

So how does EROEI and the laws of thermodynamics apply to one another? The laws of thermodynamics cannot be used to validate or contradict the use of EROEI calculations. However both concepts are talking about the same stuff, namely energy. The laws of thermodynamics applied to an energy production system mean that the energy put into a process must ultimately equal the energy out. A positive EROEI means the energy returned in a particular process is in excess of the energy put in. The key difference is that EROEI calculations are only accounting for energy invested. So this energy investment has to come from a stored source of usable energy and the energy returned includes energy you can pull free from the environment. While some of the returned energy is added free to a given process and some of the energy invested in the process in lost to various inefficiencies in a given conversion, if all inputs and outputs could all be accounted for then (applying the 1st law) the resulting ratio must be 1:1.

If the natural tendency of the universe is to take concentrated energy and dissipate it then wouldn't it make sense that long term the challenge to sustained energy production is finding ways to concentrate energy versus dissipating it?

If we can accept this idea as fact, can we look at how we currently produce (harness) energy to see if we are concentrating or dissipating energy? I'll conduct that exercise in a subsequent blog.

velomobility