Month: April 2009

What goes up, must come down!

For most Sankey diagrams I find when browsing the web, a ‘left-to-right’ or ‘bottom-to-top’ orientation prevails. ‘Top-to-bottom’ is less common, but there are also examples like this one.

A rather untypical shape for a Sankey diagram has been up on the German page of the e!Sankey webpage.

It shows the energy balance for a pumped storage power plant as a curved shape, with the energy input at the left leg, and the energy that can be recovered (77.3%) at the right one.

Energy is stored “in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high electrical demand, the stored water is released through turbines. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. Pumped storage is the largest-capacity form of grid energy storage now available.” (Wikipedia)

I searched for the original Sankey diagram in the source given (Quaschning 2007) and found this text with the diagram in chapter 6.1.2. That diagram already featured the curvy shape, and has just been reproduced similarly.

The use of the curve layout seems justified here. The author chose it to point out the difference in altitude. The upper basin is at the apex of the curve. Water pumped up from the lower basin requires energy, which can partly be recovered when the water runs down again.

What goes up…

World and US GHG diagrams from WRI

Last August I reported about a Sankey diagram showing World GHG emissions, published on the website of the World Ressource Institute (WRI). I couldn’t show the diagram due to copyright concerns in that post, but to my delight, Tim Herzog, co-author of the WRI publication and Director of Online Communciations at WRI in a comment to my post granted permission. Thanks, Tim!

So here it is:

The diagram shows the activity sectors from which of greenhouse gases (GHGs) originate. The largest portion is from energy generation (including transport), followed by land use change and agriculture. Direct emissions from other industrial processes (other than combustion processes) and waste is comparatively small. The arrows on the right side give a breakdown into the individual gases with carbon dioxide as the main greenhouse gas (77%) followed by methane and N2O.

All data is for 2000 and given in CO2 equivalents with the GWP 100a weighting factors for methane, nitrous oxides, HFCs and PFCs from the IPCC 1996 report. The total quantity is an estimate of 41755 MtCO2 equivalent. Land use change shows negative numbers too, because credits can be given for reforestation (newly planted trees absorbing CO2).

Here is the Sankey diagram from the same report just for the 2003 GHGs in the United States.

The overall CO2 equivalents are 6978 Mt in the US in that year, but the portion of GHGs from fuel combustion is higher. CO2 is 85% of the GHGs. For more details on the US GHG Sankey diagram, go to the WRI web page.

Kudos to the makers of these Sankey diagrams. Apart from the rich content they convey, they are also beautiful examples of how elegant Sankey diagrams can be.

Data Center Electrical Efficiency Sankey

The 2007/2008 White Paper #154 Rev 1 published by APC explains “Electrical Efficiency Measurements for Data Centers”. The author points out that DCIE (Data Center Infrastructure Efficiency), defined as ‘IT Load Power’ divided by ‘Total Data Center Input Power’ is a good metric to analyse data center efficiency.

In fact, as can be seen from the Sankey diagram shown in the paper, the majority of electrical energy consumed in a data center is for cooling, UPS and other supporting infrastructure equipment.

No typical DCIE is given, but the samples shown suggest that it ranges between 30 and 50 %. Several constraints have an impact on the actual DCIE, such as the IT load itself and the outside temperature, and thus should be reported along with the measurement.

A nice idea to present the breakdown on electricity consumption as a Sankey diagram, rather than as a (boring?) pie chart, especially when speaking of “power flows”.

Download the WP #154 from APC’s website.

Teaching kids energy efficiency

Mr. Palmer, a UK physics tutor, has many of his physics lectures for General Certificate of Secondary Education (GCSE) online, with notes and illustrations. You can find topics such as “motion”, “heat”, “nuclear radiation”, and even “the origins of the universe”. Very infomative, and well illustrated, even if you are not a high school student.

To attract student’s interest and make them understand efficiency in the “electricity” topic, he asks them to draw a Sankey diagram for their iPod.

The three Sankey diagram examples Mr. Palmer shows in his notes use the simple but effective grid paper approach that I have shown in this post.

I have tried to get to the numbers behind the diagram, but even in the tech specs, in the product environmental report for the iPod and on Apples environment website, they don’t give details on how much of the power is used for screen lighting and sound, and how much is lost as heat. So I guess that Mr. Palmer might have made these up, and that the energy efficiency of 31% for the iPod is just an arbitrary number…

Even though I didn’t find the hard facts, I came across some ideas and fancy gadgets for the iPod, that make its use “greener”, even though they do not increase the energy efficiency of the appliance itself:

And of course there are several hints, that help to really reduce energy consumption and make your iPod more energy efficient, such as dimming the display and avoiding to do a skip search on titles.