Saturday, October 17, 2015

The Big Picture – Energy Supply and Consumption in Botswana

Dumelang.* The best way to approach most country- or statewide energy considerations is to understand the big energy flow picture. To do so, we use Sankey, or flow, diagrams which are often used in the energy industry, an example of which is shown below. In these diagrams the magnitude of the flow of energy is indicated by the width of the arrow. These diagrams were first used in the energy field by an Irish engineer and captain in the British army, Matthew Henry Phineas Riall Sankey, in 1898, to illustrate energy flows in steam engines. The modern version below neatly shows how input energy into a steam engine, in the red flows, is lost to smoke, friction, and heat loss via the steam condensor. Useful energy as forward motion of the steam engine, a small recirculating flow of energy that comes from the recirculated condensed water and a small amount going to the alternators are shown as the blue flows.

The great thing about Sankey diagrams is that they are not restricted to energy flows. They can be applied to quantities of many types. For example, material and cost flows are often depicted. One of the most famous of these flow diagrams is that prepared by the French engineer, George Charles Minard, in 1869, and shown below. This illustrates the fate of Napoleon's army in 1812 – 1813 as they progressed through their disastrous Russian invasion. The width of the lines shows the fate of the invading army. Napoleon crossed into Russian with 422,000 men and, through attrition, minor skirmishes, and some great battles, he entered a largely abandoned Moscow with about 100,000 men under his command. He then turned back to return to France: on the way back, starvation, battles, and incessant harassment by guerilla forces decimated his army to 10,000 survivors. The harsh winter also took its toll on his men - the line graph below the flow diagram shows the decreasing temperatures encountered on the army's return from Moscow. The diminishing width of the flow is a skillful, albeit harrowing, representation of what was happening to the army in the field, the prisoners that were taken, and the lives that were lost. 

But I digress… Let's return to energy flows. I have prepared the following Sankey diagram for energy flows in Botswana, based on 2012 data from the International Energy Agency (IEA). The IEA have prepared Sankey diagrams for most countries in the world (including Botswana), and, although this is a wonderful source of data, their flow diagrams are two-part figures showing a complicated spaghetti of flows. I have taken their data and distilled it down to the more easily understood diagram shown below.

Although I am highly impressed with the data that the IEA has collected for most of the world’s countries, we need to be cautious about some of the numbers. In my previous postI pointed out some discrepancies regarding biofuel usage. I am, as yet, not in a position to verify all the Botswana-related data that the IEA has collected, but I hope to do so over the next year.

There is a lot of data incorporated into this diagram, so let’s work from left to right to get a sense of some of the larger flows. On the left, we have the energy sources for Botswana. There are only four types: local biofuel (wood), imported electricity, locally mined coal, and imported oil products. For 2012, the total energy supply available in Botswana was 109,165 terajoules (TJ), as shown in the pie chart below.

Almost one half of Botswana’s energy supply is in the form of oil products, such as petrol and diesel. The green flows in the Sankey diagram show that these are mainly used in transportation and industry. The small flow to non-energy applications show use largely as lubricants, oils and greases, for industry and transportation.  Biofuel, largely wood, is still very important in Botswana: the brown biofuel flows show that all wood is used in household applications, most likely for cooking and heating in the rural and poorer areas.

As shown by the black Sankey flows, Botswana produces a good amount of coal. Much of this was stockpiled in 2012, but a fair quantity was used by industry and about 11% was used for electricity generation at Botswana’s only coal-fired station, Morupule, which is near the town of Palapye. However, Botswana does not generate sufficient electricity for its own needs. If we refer to the center of the Sankey chart and we follow the red flows, we can see that, in 2012, Botswana only produced a small portion, 7%, of its domestic energy needs. The bulk of its electricity was imported from the Southern African Power Pool grid and came from Mozambique and South Africa. The bulk of this electricity is used by industry, followed by households, and the commercial and public sector.

In my last post I noted that energy consumption for 2012 was 86,206 TJ. The large difference between the 109,165 TJ of supply and the 86,206 TJ of consumptions accounted for by several reasons:
  • More coal was mined than was actually used. The difference ends up in stockpiles to be used in the future.
  • Electricity generation in coal-fired power plants is very inefficient. Only about 23% of the energy in coal ends up as electricity.  
  • Transmission and distribution of electricity to end users results in line losses of the order of 8 to 10%.
  • There are small differences due to statistical variations, own use, and storage of petrol and diesel at various locations.

The overall usages of energy by the main categories, as shown on the right of the Sankey chart and the pie chart below are split as follows: transportation uses just over one-third, followed by households, and then industrial use.

So here you have the overall energy picture for the country of Botswana, at least for 2012.  It will interesting to see over the next year or so, as I collect current data, how much this picture will change.

Until next time, feel free to comment on my post and remember to turn off the lights when you leave the room.

Tsamayang Sentle**

Mike Mooiman

(*Greetings in Setswana)
(**Go well or Goodbye in Setswana)

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