5th May 2019
Every year Lawrence Livermore National Laboratory in California releases an infographic showing all the energy used by the United States in a given year, where it is used and (crucially) its efficiency.
On the left side there are the sources of energy – petroleum (oil and oil products), gas, coal, nuclear, wind, solar, hydro, geothermal, and biomass. In the middle there are the uses of the energy sources (residential, commercial, industrial, and transportation). Lines of different thickness connect the energy sources with their uses. The thickness of the lines indicates the amount of energy used.
There are many interesting things about this infographic but the most astounding takeaway is in the two boxes on the right hand side. The top box shows the total ‘energy rejected’ (i.e. waste energy) and the bottom box shows the total ‘energy services’ (i.e energy which is used for doing something). The overall proportion of rejected energy to energy services is called the efficiency.
https://www.llnl.gov/news/us-energy-use-rises-highest-level-ever
The entire US energy use is 33% efficient. This means that of the all the energy that could be used in 2018 only 33% is used for something ‘useful’, i.e. transporting people, heating homes, making goods, powering computers etc…
That means that 67% of the energy produced in the USA is not used!
This is certainly not a USA specific phenomenon, rather this is a problem to do with the production of energy via thermal process. At all stages where the energy sources are used there are inefficiencies, primarily caused by the loss of energy as heat. Some industries are more efficient than others – for example, both residential and commercial waste much less than 50% of their energy use, but electricity production wastes 66% of energy, and transportation wastes a phenomenal 79%!
Why? Three main reasons:
- Fossil fuels have to be burnt to extract their energy, which creates heat. That heat must then be converted to another form of useful energy such as motion, and the laws of physics (specifically the second law of thermodynamics) mean that this conversion process can never be 100% efficient.
- Coal: best technology is around 40% [1]
- Gas: best technology is around 60% [2]
- Diesel: peak efficiency is around 50% [3]
- Heat is hard to contain and easily leaks. Therefore, heat can easily dissipate and is wasted to the environment.
- Energy is lost through the conversion and processing of fossil fuels to other types of fossil fuels. Crude oil especially cannot be used straight out of the well. It must go through a series of conversion processes to turn it into useful products such as petrol/gas and diesel. These processes are energy intensive and themselves require the burning of fossil fuels [5,6,7].
Why does this matter?
Much of the wasted heat is generated by burning fossil fuels, and the process of burning fossil fuels releases carbon dioxide. Therefore, in the US (and in many other countries) two thirds of the carbon emissions will be attributed to energy which is not used.
So can this be avoided? No, not really, because to get the one-third of emissions which are useful we need to generate the other two-thirds. We can’t do anything to change the laws of physics when it comes to the burning of fossil fuels.
What about energy efficiency improvements? Yes that is an option, by colocating inefficient energy producers and users waste heat could be utilised. However, if we were to rebuild entire economies it may be possible to reduce (but not eliminate) the inefficiencies. Facilities that produced waste heat could be linked to places where that heat is needed e.g. using waste heat from a factory to heat homes. This is done in many colder countries already, such as Denmark [4]. However, this is hard to achieve quickly as much of our energy infrastructure in other countries is already in place.
Are renewables better in terms of wasted energy?
That depends on your viewpoint, and what you care about.
If you take into account the efficiency of converting nature’s forces to energy then renewables seem to have a similar problem to fossil fuels.
- Current commercial solar maxes out just above 20% [8]
- Wind’s upper limit is around 40% [9]
- Hydroelectricity can do a lot better at 90% [10]
But there are three crucial differences:
- The energy not captured by renewable devices is free in the first place
- The energy not captured does not contribute to carbon emissions (neither does the useful energy).
- Once the energy is turned into electricity the primary mechanism of energy transfer and conversion uses electricity, which is a much more efficient mechanism than using heat.
In a 100% renewable world there will still be inefficiencies. Heat will still leak but these inefficiencies could be said to be less damaging. In addition, much of the renewable energy infrastructure is being built at the moment or is still to come, which gives great opportunity to mitigate these inefficiencies were possible; e.g. through joined up energy projects.
References
- https://www.powermag.com/who-has-the-worlds-most-efficient-coal-power-plant-fleet [accessed 05/05/19]
- http://www.guinnessworldrecords.com/world-records/431420-most-efficient-combined-cycle-power-plant [accessed 05/05/19]
- https://www.nuclear-power.net/nuclear-engineering/thermodynamics/thermodynamic-cycles/diesel-cycle-diesel-engine/thermal-efficiency-for-diesel-cycle/ [accessed 05/05/19]
- https://geospatial.blogs.com/geospatial/2010/01/energy-efficiency-of-fossil-fuel-power-generation.html [accessed 05/05/19]
- https://www.youtube.com/watch?time_continue=245&v=BQpX-9OyEr4 [accessed 05/05/19]
- http://electricmini.blogspot.com/2011/10/it-takes-lot-of-coal-to-make-gasoline.html [accessed 05/05/19]
- https://insideclimatenews.org/news/20130219/oil-sands-mining-tar-sands-alberta-canada-energy-return-on-investment-eroi-natural-gas-in-situ-dilbit-bitumen [accessed 05/05/19]
- https://www.nrel.gov/pv/module-efficiency.html [accessed 05/05/19]
- http://www.reuk.co.uk/wordpress/wind/betz-limit/ [accessed 05/05/19]
- http://www.wvic.com/content/facts_about_hydropower.cfm [accessed 05/05/19]
More Reading – This is not an in depth article. Check out the links below for more info in the topic
https://simple.wikipedia.org/wiki/Thermal_efficiency
https://en.wikipedia.org/wiki/Thermal_efficiency
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.html