Sankey Diagrams

To compensate for the rather awkward Sankey diagram from NZ in my last post, here is a more colorful, and more recent one from Aotearoa. It shows the energy flows of New Zealand in 2007. The Ministry of Economy published a report “Energy in Brief”, which also contains this Sankey diagram:

The diagram shows the main flows in gross PJ (1 petajoule = 10¹⁵ J) and is “to approximate scale”. Flows below 2.5 PJ are neglected.

Energy produced domestically from various sources comes from the left, imports of coal and oil enter in the leftmost column from the bottom and the top. The energy flows pass through transformation and conveyance phases, to be finally shown in the different use sectors. Losses in transformation and conveyance are visualized with downward arrows, while losses in the end use are not considered.

There are some design flaws, especially when you look at the arrow curves. Also the fact that flows are only “to approximate scale” is in my opinion not acceptable [an arrow representing a flow of 3 PJ has the same width as one for 6 PJ, and both are only half the width of the 30 PJ flow]. But the overall impression is much better than in the version 10 years before.

Click here for a larger version of the diagram (PDF).

From the deepest and darkest parts of my bookmark list, here is a Sankey diagram for energy flows in New Zealand in 1997. I found it in a PDF document on this website of the Ministry of Economic Development (maori: Manatû Ôhanga).

The text under the diagram reads: “This energy flow diagram summarises New Zealand’s energy use. Primary energy sources are at the left. The flow of these through conversion processes to consumers is pictured, with final end-use classified by consumer type. The width of the bands is approximately to scale.”

Well, almost everything that can go wrong in information visualization goes wrong in this diagram… No quantities or units are given. Flows that are “approximately to scale” narrow down along the way. [The only explanation I have for this, is that this a novel way to account for transmission losses.] Streams meet, but don’t seem to merge. No idea what the spaghetti flows are good for…
In defense of the authors of this diagram I can say that in 1997 there probably weren’t any Sankey diagram software tools around.

I have a nicer one for NZ, which I will present in of my next blog posts. Better energy flow Sankey diagrams from other countries can be seen here, here or here.

GWP guy at Green World Pictures blog posted an article on average spendings on energy in an U.S. household.

Data is from an Energy Star flyer, that presents the data in a pie chart. The average yearly 1900 US$ for energy are spent as follows:

Heating and cooling is almost half of the spendings on energy, followed by water heating and lighting.

Found Sankey diagrams with the energy balances of France for several years, thanks to this Planète Bleue blog post.

These energy balances are apparently produced annually by French DGEC (Direction Général de Énergie et Climat) and are different from the energy flow Sankey diagrams for various countries I have shown here in other posts.

In these French energy balances the left side shows the primary energy (expressed in mégatonne équivalent pétrole Mtep, mega tonnes of oil equivalent Mtoe in English) broken down into the different sources, the right side shows the final consumption of energy with the same breakdown. The differences are the energy losses and internal consumption in energy generation.

The large losses for nuclear energy are explained in a footnote for the 2007 diagram, where it says that these can be attributed to the fact that ‘Observatoire de l’Énergie’ (OE) accounting standard is based on heat value:

L’importance des pertes dans le domaine de l’électricité tient largement au mode de calcul adopté depuis 2002 par l’OE: l’électricité d’origine nucléaire est comptabilisée, au niveau de la production, en termes de chaleur, dont les deux tiers sont perdus lors de la conversion en énergie
électrique

Nevertheless the Sankey diagram gives a good idea about the efficiency of energy generation for each of the different fuels and the energy mix for France.

For those of you who wish to compare the developments over the last years, here is what I have dug up so far:
2003 is shown on Planete Bleue in this post.
2004 is shown above
2006 can be found here on page 25 (PDF)
2007 can be found here on pages 6/7 (PDF)

A followup to my last post: This thread on ‘The Oil Drum: Europe’ features similar national energy flow diagrams for UK (2007), The Netherlands (2006) and Switzerland (2007).

For the UK these Sankey diagrams are published by BERR (Department for Business, Enterprise and Regulation). Historic charts back to 1974 can be found on their website.

A commentor to Chris Vernon’s original post added the Swiss version of this Sankey energy flow diagram:

These Sankey diagrams have some nice details, which a worth a mentioning: The UK diagram shows stock increases and decreases with circles. The size of the circle has no significance, but the magnitude of the in and out flows seem to be to scale, thus allowing to see if the stock has increased or decreased in that year. Losses at transformation steps are shown with “hanging arrows” (the flows branching off to the bottom line of the diagram). The Swiss version also shows exports this way, but visualizes losses with a pin with a big round head.

Even though your run the risk of being overwhelmed by a gloomy feeling when your read through the comments to Chris Vernon’ post, I would like to draw your attention to a comment by “realist” on Sept 5. He writes: “Deceptive graph! Why show losses for electric power generation and not transportation? The heat losses from the internal combustion engine in most transport is 70-80%”. This is true, but I have always understood that losses explicitly shown in these energy flow Sankey diagrams are the losses occuring in the energy generation, conversion and grid, while losses in the energy consumption (such as use for transport) are not shown. This let alone that they are worthwile to discuss.

One type of Sankey diagram layout seems to get popular recently. A representation of national energy flows of a country with the energy carriers on the left side (source), and the consumption sectors on the right side (sink). The Sankey flows in between show how energy from these sources are consumed and in which sector. Wasted energy is shown, and the overall energy (in)efficient use of primary energy is made clear with such a Sankey diagram.

I just discovered the energy flow diagram for Spain for 2006 on Joan Vila’s blog.

Unfortunately I don’t speak Catalán (well, I learned that “blog” is “bloc” in Catalán!), and the image quality isn’t very good. You can see nuclear, natural gas, coal (“carbó”) and crude oil (“petroll”), as well as hydro an wind (the two green lines) on the left side. The top box on the right side that takes the big red Sankey arrow for losses from electricity generation (“pérdues”). The others are the use sectors transport, industry, and domestic / services / agriculture. Vila calculates an efficiency of 38,2% for the electric power generation.

Joan advocates Sankey diagrams for visualizing and being able to better understand the issue. He says, that you won’t understand many things about what’s going on, if you don’t study this [kind of] diagram (“No entendrem moltes coses sobre el que passa si no estudiem aquest diagrama.”).

Check out simiular diagrams for Japan, Scotland, Ireland, Canada, United States.

A presentation titled ‘La eficiencia energética: una opción estratégica para la empresa y para el país’ (‘Energy Efficiency – a strategic option for companies and for the country’) by Pedro Maldonado of the Energy Research Program (Programa de Estudos e Investigación de Energía) at Universidad de Chile features a Sankey diagram as an important tool in energy auditing.

The diagram shows exemplary losses (pérdidas) in heat generation, heat transmission and the use of heat. Use of heat is broken down into drying, pasteurization, evaporation, etc. The main message of the author: “The energy we purchase is not what we ultimately use as energy for our productive processes”.

A reminiscence to the days when Sankey diagrams were drawn in black&white by hand and labeled with a typewriter. The three Sankey diagrams below from a 1990 article on “Energy conservation in the mechanical forest industries” by FAO (Food and Agriculture Organization of the United Nations, FAO Forestry Paper No. 93, Rome 1990) illustrates energy use in sawn timber, plywood and particleboard production.

The article explains that

“Although the diagrams are of an approximate nature they do serve to identify the relationship that each major energy consuming centre has with each other and also readily identifies the prime energy users to which particular attention should be paid in any conservation effort.

In all three product manufacturing processes heating is by far the largest user of energy, representing some 82-87 percent of the total energy requirement in the manufacture of sawntimber, plywood and particleboard, with drying accounting for approximately 87 percent, 61 percent and 62 percent respectively.”

Use of Sankey diagrams with kind permission of FAO