Monday, December 21, 2015

The Potential for Solar Energy in Botswana

Dumelang*. In my past few posts, I have focused on Botswana’s main energy resource: coal. However, Botswana has another very important energy resource that is presently poorly utilized: that of sunlight. Anyone who spends even just a little time in Botswana always marvels at the sunshine and the long days of clear skies that roll one into the next for weeks at a time. Combine this with vast expanses of low-population-density, semi-arid, flat countryside and the potential for tapping the solar resource of Botswana becomes obvious. In many countries, there is a remarkable roll-out of solar energy generation operations underway, both large and small scale, driven by improvements in technology and the falling prices of solar panels.  In some respects, Botswana is arriving late to the game, but, as I will highlight in future posts, there are positive steps being taken. In next series of posts, I will discuss various aspects of solar energy, how Botswana is benefitting from its ~3200 hours of sunshine per year, and how the country could further tap into this solar energy potential. 

There are several ways to harness the energy of the sun:
  • Solar thermal uses the heat of the sun to warm up water so that it can be used for showers and other hot-water applications like washing.
  • Concentrating solar power concentrates the energy of sunlight by mirrors onto a focal point. The focused sunlight heats a fluid, which is used to generate steam, which then turns a turbine to generate electricity.
  • Photovoltaic generation of electricity through the use of solar panels is the most widely used and most promising approach to tap into the sun’s energy. Its application is growing exponentially in many countries and it represents one of the most significant resources of renewable energy.

Each of these applications requires sunny days and the direct radiation of the sun, so let’s start with some measures of solar radiation. Botswana has about 300 clear days annually and, as noted above, about 3200 hours of sunshine. In comparison, the state of New Hampshire in the US, where my home university of Franklin Pierce University is located, has ~2500 hours of sunshine and only 90 clear days per year. For a more exact determination of the power available from the sun, we use the concept of irradiance, which is a measure of sunlight intensity on one square meter of horizontal surface at a point in time. This, of course, changes during the day: it is low in the early morning; at a maximum at noon when the sun is directly overhead; and then it tapers off towards evening. It also changes depending on the location, time of year, and the amount of cloud cover. The typical average peak irradiance at noontime is 1000 watts per square meter (W/m2) for the planet. This value is referred to as the peak sun value. Measurements of irradiance taken over one summer day at the University of Botswana in Gaborone 20 years ago appear in the figure below. It is notable that there are times when the peak irradiation is greater than 1000 W/m2, which is indicative of the solar potential available for harnessing.

Irradiance is a measure of the intensity or power of sunlight at a point in time, but what we are really interested in is the energy that we can harvest over a period of time. In an earlier post, I explained the difference between power and energy. Energy is the amount of power expended over a period of time (an hour or a day). The mathematical relationship between Energy and Power is given by the simple formula:

Energy = Power x Time

In the solar field, we determine the energy that can be potentially harvested over a day by calculating the area under the irradiance curve, such as the yellow area in the figure above. This measure of energy over a day is termed insolation; it is measured in kilowatt hours per square meter (kWh/m2). Another measure of insolation is to calculate how many hours of peak sun (with a fixed irradiance of 1000 W/m2) will deliver the same energy as the sum of the varying (irradiation x time) values over the day. The hours of peak sun per day is a particularly useful measure and is extensively used in the solar energy field to determine the daily output of electricity from solar panels. Insolation data are often available in tables of peak sun hours for different times of the year and different locations around the world. For example, the figure below shows peak sun hours for Gaborone at different times of the year and compares it with Manchester, New Hampshire, in the US (the location of Franklin Pierce University’s graduate campus). The differences are stark: the lows in the winter months in Gaborone are not that much lower than the highest value for Manchester in the summer! On average, the annual peak sun value for Gaborone s is 5.64 hours, while for Manchester, it is only 3.48 hours. This is to be expected, because the latitude of Manchester, NH, is further north (43o) than Gaborone is south (25o) and the former also has far more cloudy days.

Now these insolation measures are for a panel lying flat on the ground, but that is not the normal orientation for most solar projects. In the southern hemisphere, solar panels are angled towards the north, so as to capture as much sunlight as possible as the sun rises and sets in the northern skies. In the northern hemisphere, panels are angled towards the south. Typically, the mounting angle of the panels is equivalent to the latitude of the location: panels in Gaborone are often oriented at an angle of 25o from the horizontal. With the correct mounting angle, the average annual insolation value increases to 6.07 peak sun hours, an 8% improvement over a horizontally mounted panel. This is the average improvement for a fixed-angle array, but further improvements can be achieved by adjusting the orientation of the panels during the year. In winter, panels should have a higher mounting angle to capture the sunlight from the sun sitting low in the northern skies and, in summertime, the panels should lie flatter to catch the rays of the sun that sits high in the skies during the day. Some solar arrays are designed to allow for manual adjustment of the angle of the array during the year. If optimized monthly, a further 5% increase in the average annual insolation value over the fixed-angle array can be achieved.

Some solar arrays are very sophisticated, with intricate motor drives and control systems that can follow the sun from east to west during the day and also make small daily adjustments in mounting angle to follow the sun’s seasonal orientation.  Dual-axis systems, such as these, can boost the insolation by about 30% or more over a fixed-angle array. These dual-axis systems are expensive and maintenance issues with the drives and controllers often occur. Solar panels are pretty cheap these days, so a 30% gain in efficiency can rather be captured by simply adding more panels and avoiding the maintenance headaches. For this reason, most solar systems are simple fixed-angle systems.

Let’s return for a moment to measures of solar insolation. We have been using units of peak hours, which are particularly useful when calculating the energy that a photovoltaic (PV) panel will generate. Another useful unit is the direct measure of energy per square meter, i.e., kilowatt hours per square meter, kWh/m2. We determined above that the average peak hours for a horizontal array for Gaborone was 5.6. So, at a peak sun value of 1000 W/ m2, we can calculate the average annual insolation value as:

                5.6 hours/day x 1 kW/m2 x 365 day/year = 2044 kWh/year.

Of course, higher irradiation values created by improved mounting angles lead to higher annual insolation values. To gauge the amount of solar energy that can be harvested, maps of annual solar insolation have been prepared for the whole planet. Those below show the average annual insolation, in kWh/m2, for Africa and Botswana. An examination of the African map shows areas of very high annual insolations, >2200 kWh, particularly in the desert areas of North Africa, but also in areas covering a good part of Namibia and Botswana. The Botswana map shows that the best areas for high solar insolation lie in the western and northern parts of the country, particularly the Ghanzi and Maun areas.

It is clear that Botswana has large areas that are subject to high-intensity solar irradiation that can be used to generate electricity. In an earlier post, I noted that annual electricity consumption for Botswana in 2014 was ~ 4000 gigawatt hours/year (GWh/y) (one GWh is equal to one million kWh). Using a value of 2200 kW/m2 (such as that seen in the western and northern parts of the country), we can calculate roughly how much land area would be needed to generate Botswana’s annual electricity demand using the following assumptions:

PV panel efficiency: 15% (a typical value for modern panels)
Electrical and storage system losses: 50%
Panel coverage of land area: 50%

Based on these assumptions, we can determine that an area of approximately 50 square kilometers would be needed to generate sufficient energy to meet Botswana’s annual electricity needs. This hardly seems much in a country with a footprint of 566 730 km2. This suggests that it would not require much land area to generate all of Botswana’s electricity needs. However, it is important to put these fun-to-do order-of-magnitude calculations into perspective and to consider technical feasibility of these ideas.  

Let’s start with the size of the plant. Very large solar plants are being built today. There are several in the 550 MW range in the US and some larger ones are being planned. As of the date of this post, the largest solar power plant in the world is the BHE Renewables Solar Star operation in Antelope Valley, California. This is a 579 MW AC output plant, capable of generating ~1785 GWh of electricity per year or about 45% of Botswana’s needs. It uses 1.7 million solar panels and is located on 13 km2 of land. Technically, large-scale solar plants are feasible, but the costs are high. The cost for a 550 MW plant in California was reported to be $2.4 billion, which yields an installed cost of $ 4400/kW. Coal-fired power plants have lower installed costs (especially if pollution control equipment is not included)—of the order of $ 1300 to $ 2300/kW. However, one should not just consider capital costs, but operating costs as well. Taking into account all costs for a power plant is a complicated topic and it is a subject I will tackle in a future post.

Cost is an issue, but the bigger problem associated with solar power is that it is an intermittent and variable resource. Unlike a traditional power plant that can vary its output day or night (within a certain range), a solar resource can only produce energy during the daylight hours and is subject to the whims of cloud cover and passing storms – during which output can drop considerably. To fully utilize solar energy, we need electricity storage in batteries to provide power for the nighttime and when it is cloudy. Unlike grid-scale electricity generation from large PV plants, grid-scale battery storage is still in its infancy. It is complicated and very expensive. To date, the largest grid-scale battery-based storage operation is in Japan – a 40 MW unit with storage of 20 MWh. To store just three days’ worth of electricity for Botswana, would require some 40 GWh of storage. This is 2000 times the largest plant storage plant at the moment and is simply not feasible at this time. In many respects, generation of the electricity from sunlight these days is fairly straightforward; the storage aspect is the bigger challenge that we face this century.

This is the first in a series of posts about solar power and its potential for Botswana. I trust that I have given you a sense of the tremendous resource available and the scale that is needed to harness it, but also a sense of the technical challenges, complexities, and costs involved in developing this resource.

Until next time, remember to turn off the lights when you leave the room. 

Tsamayang Sentle**
Mike Mooiman

(*Greetings in Setswana)

(**Go well or Goodbye in Setswana)

Tuesday, December 8, 2015

Coal Based Energy in Botswana: Coal-to-Liquids, Coal-Bed Methane, and Underground Coal Gasification

Dumelang.* There is more to coal utilization than just burning it to make steam to generate electricity. In my previous post, I carried out a general overview of coal projects in Botswana, but it was heavily weighted towards coal mining and coal-fired electricity projects. In this post, I take a close look non-coal-fired electricity projects, such as coal-to-liquids, coal-bed methane, and underground coal gasification, to get a better understanding of the benefits and challenges associated with these other ways of drawing out the energy stored in coal. Even though some appear to offer advantages over traditional coal mining and coal-fired electricity, it is always important to understand the shortcomings associated with these alternatives. Various proposals for implementing these technologies in Botswana have been made, there has been a lot of information about these projects in the Botswana press over the past few years and some exploratory work has been carried out but, as yet, no commercial operations have been implemented. 

Coal to Liquids (CTL)

Let’s start with coal-to-liquids technology. A large CTL operation producing 20 000 barrels per day of petroleum liquids has been proposed for Botswana. The proposal incorporates a 300 MW coal-fired power plant, a fertilizer plant that will produce 300 600 tonnes/year of ammonium nitrate, and 15 200 tons of sulfur as a byproduct. The budget for this project is $4.6 billion and construction is supposed to start in 2016. When I read about this project, its size and scope surprised me because it is beyond the price and scale of anything that has ever been built in Botswana.

Let’s look first at the technology. The CTL process, also known as coal liquefaction, involves taking the carbon in coal and converting it into hydrocarbon molecules that can be used for a variety of purposes, including liquid fuels, such as diesel or petrol.

This is carried out in three ways:
  • Coal is heated in an oxygen-free atmosphere to distill off coal tars and oils (also known as pyrolysis).
  • Coal is treated at high temperature and high pressure in the presence of solvents, hydrogen gas, and catalysts to hydrogenate the coal and form hydrocarbons. 
  • Coal is treated in a three-stage process, which first involves its high-pressure reaction with steam to form syngas – a mixture of carbon monoxide (CO) and hydrogen (H2). Syngas is treated at high temperatures in the presence of a catalyst to form hydrocarbons, which then need to be refined and separated to produce individual hydrocarbon products.

This series of steps will usually convert one tonne of coal into one to two barrels of hydrocarbon fuel. If we consider that the heat content of one tonne of coal is ~24 000 megajoules (MJ) and that of one barrel of hydrocarbon fuel is 6120 MJ, you can see that the process is not very energy efficient: only ~26% of the energy in coal is converted and distilled into one barrel of fuel. That being said, the convenience of liquid fuels cannot be overstated – our transportation system is now dependent on liquid fuels like petrol and diesel and not, as at the start of the industrial age, on solid fuels like coal.

All these CTL options are technically complicated, capital-intensive, highly polluting operations with high operating costs. They involve sophisticated and large-scale high-pressure, high-temperature chemical processing equipment. Depending on their size, location, and coal supply, these operations only tend to be profitable in a world where crude oil costs more than $50 - $110 a barrel. The price of crude oil is presently around $40/barrel. As a result, there are a limited number of these operations in the world. The largest is the Sasol complex in Secunda, South Africa. There are some operations in China and several smaller operations scattered around the world. To give some sense of the polluting nature of these operations, Sasol’s Secunda operation, which produces ~150 000 barrels per day of synfuels, is the largest point source for CO2 emissions on the planet!

Implementing the technology successfully involves requires large numbers of skilled, well-trained, and experienced personnel, and—in the case of Sasol—years and years of government subsidies. In a country like Botswana, there are insufficient trained personnel for such an operation and there will be a heavy reliance on expatriate personnel at the start. The water demand for these operations is also substantial; in Botswana, reliable, high-volume water supply is presently a difficult resource to come by. Moreover, these operations are very energy-intensive and require a reliable high-voltage electric grid. Reliable power supply can be difficult to achieve in Botswana at this time, so the incorporation of a 300 MW coal-fired power plant into the operation appears to be a wise, albeit expensive, way to guarantee reliable power.

Although the promises of local infrastructure, industrial development and employment opportunities are alluring, the scale of this project, as well as the demand for energy, water, and personnel resources required for a project of this size, suggests that caution and extensive scrutiny is warranted.

One of the axioms of the energy business is: It takes energy to get energy. We have to expend energy drilling into oil deposits, pumping, refining, and transporting the oil before we can use it as petrol to power our cars; we have to expend energy mining, processing, and transporting coal before we can burn it; even in the renewable energy field, where we have free fuel sources, such as sunlight, we have to expend energy creating the components of solar panels, transporting, and installing them. Every energy source requires an investment of a certain amount of energy to recover energy that we can use somewhere else. The trick is to be sure that the energy invested is less than the energy produced. This concept called EROI – energy return on investment (also referred to as EROEI – energy recovered on energy invested). The formula for EROI is straightforward:

EROI = Energy recovered/Energy Invested = Energy output/Energy input

One always wants the EROI to be greater than 1, i.e., one wants to recover more output energy than input energy. There are many ways to calculate the inputs and outputs, but the most rigorous way is to undertake a life-cycle analysis and compare all the inputs and outputs over the whole life of the project. The range of EROI values in the energy field is wide: for hydropower, it is of the order of 80; for ethanol from biomass, it is of the order of 5. The figure below provides ranges of EROI for some important energy sources. It is interesting to observe the wide range. The reason I have raised this concept is that questions have been raised regarding the EROI of coal to liquids technology. As I noted above, this is an energy- (and water-) intensive technology and there are concerns that the input energy might be greater than the output energy. There may well be other compelling reasons to consider CTL processes, such as job creation, access to and the convenience of liquid fuels – it is difficult to fill up a car with coal – but, nevertheless, the EROI is important factor to consider, particularly in a country like Botswana that is already energy-challenged.

Coal-Bed Methane (CBM)

A number of CBM methane projects have been proposed for Botswana. Methane is the simplest hydrocarbon. It is a gas that contains one carbon and four hydrogen atoms and it is a very useful chemical. It can be used as a starting block to build longer chain hydrocarbons, such as the molecules that are found in fuels like petrol and diesel, and it can be burned directly to generate electricity. One of the great advantages of methane, also called natural gas, is that natural gas-fired power plants have higher conversion efficiencies than coal plants and are far less polluting. Coal-fired plants typically have conversion efficiencies of 30% to 35%, whereas modern natural gas-fired plants have efficiencies of 50% or higher. On a per kilowatt hour of electricity basis, coal plants tend to generate 40 to 50% more carbon dioxide emissions than natural gas operations. As a result, methane is a highly desirable fuel: the large volumes of natural gas that have been released from shale deposits in the USA via fracking technology have had a profound impact on US energy markets and a depressing effect on their coal mines and coal-generated electricity industries.

Methane is found in underground deposits, such as underground reservoirs and gas-rich shales. It is also often a byproduct of crude oil production as well. Methane is recovered by drilling down into these deposits and pumping out the gas. In shale deposits, horizontal drilling is utilized, followed by fracturing the deposit with high-pressure water in a process known as “fracking” to create a web of small channels that release the natural gas locked up in the shale.

Methane is also found associated with coal deposits, where it is a byproduct of the process that led to the formation of coal. In fact, methane is often the cause for the terrible explosions that occur in coal mines that can lead to the deaths of many miners.

Coal-bed methane technology involves drilling holes into coal deposits and then pumping out water to lower the pressure. This creates the conditions that lead to release of methane which can then be pumped out of the coal bed. However, the methane produced by this process often needs to cleaned up to remove water, carbon dioxide, and nitrogen, which reduce the heating value of natural gas. Once methane is treated, it then needs to be transported to its point of utilization. This requires a pipeline network with compressor stations every 80 to 100 km. Pipelines are expensive, they need to run parallel to an electric grid to power the compressor stations, they run across peoples’ property, they require maintenance to run, and are vulnerable to damage. That is why it might be best to build a generating plant close to the source of the coal-bed methane, provided the source of methane is large enough to support such an investment.

The figure above shows the basic operation of a CBM operation. One of its drawbacks is the water issue. Water has to be pumped out from the coal bed to create the low-pressure conditions that lead to the release of methane. The removal of large amounts of water from a coal deposit can result in the lowering of water tables in local underground reservoirs if there is a linkage. At first one might think that water is not necessary a problematic byproduct, especially in an arid country like Botswana, but the snag is that the water is often saline, which leads to disposal challenges.

CBM is an interesting technology and might have applicability in Botswana, however the transportation of gas across hundreds of kilometers of non-electrified areas and the water disposal issue need to be carefully considered.

Underground Coal Gasification (UCG)

Another way to exploit coal resources without direct mining involves a combination of the CBM and CTL approaches, known as underground coal gasification and there has been some interest in applying this technology in Botswana. UCG involves the direct controlled burning of coal in an underground deposit and then using the generated heat and injected air, oxygen, and steam to generate syngas (that mixture of carbon monoxide and hydrogen gas referred to in CTL technology). The syngas is then drawn to the surface where it is dried, cleaned, and then can be combusted to turn a gas turbine to generate electricity or it can be transported in pipelines elsewhere where it can be used to produce liquid hydrocarbon fuels.

An underground gasification operation usually involves the drilling of two wells into an underground coal deposit. One is the injection well where air, oxygen, and or steam are injected into the burning coal bed and the other is the production well where the produced syngas is drawn out from underground. The key is obtaining a linkage between the two wells so that heat, steam, and the syngas produced in-situ can move from one well to another. Once the coal bed is ignited, the extent of combustion is controlled by air or oxygen injection. In the process, the combustion zone grows and moves towards the production well.

One of the attractive features of the UG process is that the coal ash is left underground and this removes a disposal problem associated with aboveground coal gasification. The process also allows exploitation of low-value and difficult-to-mine coal deposits and, because no direct mining is involved, it is far more energy efficient than aboveground gasification. Compared with traditional coal mining and CTL technology, the capital and operating costs are lower and the water consumption is relatively low. Because no mining is undertaken, the surface disturbances are much less and there are no open shafts or depleted mine works to deal with once the coal has been mined. The emissions from UCG, such as carbon dioxide, metals, particulates, sulfur, etc., are reported to be less as well.

However, and this is a big however, it needs to be understood that UCG involves setting fire to underground coal deposits. There is a possibility of runaway or poorly controlled combustion that could result in disastrous consequences, such as uncontrolled emissions of carbon dioxide, carbon monoxide, methane, and other hydrocarbon gases, contamination of local water tables, and uncontrolled subsidence into the burnt-out chambers. The very high temperatures of combustion could also affect the local geology, with the formation of cracks and fissures that result in uncontrolled flow of water and emissions into areas where control is not possible. There are thousands of uncontrolled coal seam fires presently burning in countries across the planet: just across the border in South Africa in the coal mining area of eMalahleni, abandoned coal mines have been burning for years. In the US, the town of Centralia in Pennsylvania had to be abandoned in 1984 due to an uncontrolled underground coal fire that made living and safety conditions unbearable. Once they start, these fires are difficult to reach and almost impossible to extinguish.

Another disadvantage associated with UCG is that produced syngas has to be transported to its point of use so a surface pipeline network has to be built to transport it. Additional complications are introduced by the nature of the syngas produced from UCG: it contains a great deal of nitrogen from the air used in burning and therefore has lower heating value than syngas produced above ground. Depending on the final application of the syngas, i.e., direct burning or hydrocarbon production, the nitrogen might have to be removed.

UCG is an intriguing and attractive concept and numerous pilot-scale tests have been carried out around the planet with mixed success: despite the promise of UCG, it still has to take off. Problems of uncontrolled gas emissions, pollution of farmland, and acidification of water supplies have occurred. The longest running underground gasification plant is the Linc Energy Yerostigaz plant in Uzbekistan. This has been running since 1961 and produces 1 million cubic meters per day of syngas that is used to power a nearby power station. There have been recent reports of commercial-scale UCG operations in China.

This post has covered a lot of ground from coal-to-liquids technology, to coal-bed methane, to underground coal gasification. In all cases, these operations appear to provide some advantages over traditional coal mining, but their complexity, costs, and potential environmental impacts create challenges that could be difficult for a resource-constrained country like Botswana to deal with. Some of these approaches have promise, but, in every case, require caution and extensive scrutiny so that we clearly understand and appreciate the tradeoffs between energy production and energy input, water, expertise required, and long-term environmental impact. These tradeoffs can be difficult and, at times, unpopular to consider in the face of demands for natural resource utilization, industrial development, and job creation, but prudent, unbiased, and in-depth evaluation of these interesting approaches is warranted.

Until next time, remember to turn the lights out when you leave the room so that less coal has to be burnt.

Tsamayang Sentle**
Mike Mooiman

(*Greetings in Setswana)

(**Go well or Goodbye in Setswana)

Wednesday, November 18, 2015

Under Pressure – Botswana’s Coal Energy Resources

Dumelang*. As I have been reading the local press, internet articles and other literature, I was surprised at the number of coal-based projects that have been proposed for Botswana over the years. I was having trouble keeping them all straight so I decided to collect, summarize, and tabulate these coal projects. At the same time, I wanted to take a hard look at coal as an energy resource.

It is generally believed that Botswana has significant coal resources and it is clear, based on the existing, planned, and proposed projects listed in the table in the Coal Projects in Botswana tab on this blog, that coal will continue to be an important resource for Botswana well into the future. These projects range from the new coal-fired generators at Morupule, the refurbishment of the Morupule A operation, new coal-fired operations, coal-bed methane, coal-to-liquid projects, and new mining operations.

A number of years ago there was a flurry of project proposals to start up new coal mines and to build new power plants on-site or close to these collieries to feed electricity into the Southern African Power Pool. However, since the construction and partial commissioning of the large Kusile (4800 MW) and Medupi (4800 MW) coal-fired projects in South Africa, in combination with load shedding, efficiency drives, and renewable energy projects, there appears to be less call for smaller independent coal-fired power plants. Few, if any, of these smaller projects have gained traction.

The list of coal projects proposed for Botswana is long. (See the Coal Projects in Botswana tab on this blog.) Most of the projects are at varying stages of preliminary assessment—some are still under review, some have completed detailed feasibility studies, and some are just proposals—but most are currently on hold because of the large capital investments required and low coal prices. Moreover, many of the projects have been suspended because they are export-market driven and require the establishment of railroad infrastructure to Namibia or Mozambique to deliver coal to the international markets.

Coal is a troublesome energy resource. It is cheap and readily available. One tonne of coal, which costs about $50 on the world market, contains 24 000 MJ of energy—or approximately four times that of a $50 barrel of oil. Despite its high energy content, coal needs to be converted into another energy form to be useful: this could be as electricity or, in the case of the Sasol operations in South Africa, into liquid hydrocarbon fuels.

The ready availability and high energy content of coal is offset by the high levels of pollution associated with its use. Coal consists largely of carbon, as well as varying amounts of hydrogen, oxygen, nitrogen, and sulfur. Coal used for electricity generation normally has a carbon content greater than 75% and also contains compounds of aluminum, calcium, and silicon that form ash when the coal is combusted. Coal is also contaminated with deleterious metals, such as cadmium, mercury, selenium, lead, and others. The key problem associated with coal is that, on burning, it releases these nasty elements, as well as fine particulate matter, sulfur dioxide, nitrogen oxides, and carbon dioxide: these all end up in the off-gases and are released into the environment. Some coal plants incorporate expensive particulate-capture and gas-scrubbing units to reduce the emissions, but considerable quantities of these pollutants are still released into the atmosphere. In terms of greenhouse gases and increasing levels of carbon dioxide in the atmosphere, coal is particularly bad and coal-fired electricity is the largest contributor to man-made carbon dioxide emissions.

Coal or fly ash is another problematic byproduct of coal combustion. This consists largely of a fine, non-combustible silica and calcium oxide residue and can contain appreciable amounts of deleterious elements like cadmium, chromium, and others. The ash is stored on-site at power plants or is disposed of in landfills. In some cases, it can be used as a component of Portland cement.

It is all these nasty byproducts (deleterious metals, coal ash, carbon dioxide, fine particulates, and sulfur dioxide) that are behind the widely accepted assertion that coal is a dirty fuel…And this does not even begin to consider the issues associated with coal mining—which is a dangerous, difficult, and complex operation that has significant environmental impacts. Mined coal cannot just be used as is: it needs to be treated through various mineral-processing operations to upgrade its quality and reduce the portion of non-coal components. This beneficiation requires water and also produces a significant quantity of byproducts – known as middlings and discards. These byproducts can represent up to 50% of the mined ore and are typically accumulated on site at the colliery and stored indefinitely. Moreover, the sulfur in this mining waste reacts with air and water to form sulfuric acid which leads to acidic runoff, known as acid mine drainage, which, if not controlled, can contaminate local water supplies.

In a future post, I will take a look at “clean coal” and the many options available to mitigate the harmful effects of coal combustion. Each of these approaches has pros and cons, but in every case there is a significant economic penalty to be paid. As a result, promoting coal projects with state-of-the-art clean coal and pollution control installations requires enormous political will, stringent regulations, and the willingness to take on increased capital and operating costs—which will ultimately result in higher electricity costs. This is a price that many less developed countries are simply not in a position to pay.

When I cover coal as an energy source with my MBA students in the Energy and Sustainability track at Franklin Pierce University, I have them consider the entire value and utilization chain associated with coal, along with its inputs and outputs, so that they can appreciate the complexity and implications of the coal-fired electricity business. A summary of this value chain is reproduced below. As can be seen, the coal-fired electricity business is complicated, with several energy, water, and labor inputs and numerous outputs that have significant impacts on the environment. All of these energy and water inputs and the polluting and harmful outputs need to weighed against the benefits of useful electricity generation—without which our modern lives would not be possible.
Coal Value Chain

Despite these drawbacks, coal will continue to be a very important fuel for a very long time all around the world. Some countries are moving away from coal and closing down aging coal plants, but these countries possess alternative sources of energy, such as those of natural gas and nuclear reactors, and, in some cases, renewable energy from solar and wind. These alternatives are not options for less developed countries like India, China, and much of Africa at present: coal will continue to be a very important part of the energy supply in these countries, regardless of the long-term environmental impacts. Ideally, one would like all coal-related projects to carefully evaluate the long-term environmental impacts of coal mining and coal burning against the immediate benefits of electricity production, but, unfortunately, this is (for various reasons) not always done.

Exploiting the coal resources in Botswana is a challenging endeavor. Mining is straightforward, but, once mined, the coal becomes a stranded resource. It is difficult to export due to the lack of direct rail links to the port of Walvis Bay in Namibia or to Mozambique via Zimbabwe, and there is limited rail traffic to Richards Bay in South Africa. Moreover, exporters of Botswana coal have to compete against large established coal mines in South Africa that have better access to transportation and export networks. There have been several proposals to build rail links to Namibia or Mozambique, but, owing to the cost of these rail links and low prices for coal, there has been little progress of these beyond the discussion stage.

The world is presently awash in coal: demand in countries such as the US and China is down; there is an excess of supply from coal-exporting countries like the United States, Australia, and Indonesia; so coal prices are depressed. The figure below shows spikes in coal prices in 2008 and 2011, which drove a lot of the interest in coal mining and coal-based projects. Since then, however, prices have fallen off considerably and are currently the lowest they have been in the last 10 years.
Source: InfoMine**
The exploitation of coal resources in Botswana is further complicated by the present water crisis in the country. As shown in the value chain above, coal mining and electricity generation require a great deal of water: any coal-related projects need to ensure a steady supply of water in the face of challenging shortages in the country.

Overall, coal exploitation in Botswana can be viewed as being under pressure from five directions, as shown in the figure below: 1) capital investment, 2) coal prices, 3) water resources, 4) environmental impact and increasingly stringent legislation, and 5) lack of transport infrastructure. Pressure can be relieved, to a degree, by exploiting these resources internally, such as by building more in-country power plants and perhaps even coal-to-liquid operations. Even so, such projects need large capital investments, large water requirements, and will still have significant environmental impacts. The successful exploitation of coal in Botswana will require dealing with all of these factors.
Coal Pressure

In my next blog, I will take a closer look at coal projects that do not involve the generation of electricity, particularly those involving coal-bed methane and coal-to-liquid production. Until next time, remember to turn the lights out when you leave the room so that less coal has to be burnt.

Tsamayang Sentle***
Mike Mooiman

(*Greetings in Setswana)

(**Coal pricing is complicated: it depends on source and destination locations, quality, ransportation, and a host of other factors, so I have just used the North American Central Appalachian price (CAPP) as a proxy for international coal prices.)

(***Go well or Goodbye in Setswana)

Wednesday, November 4, 2015

History of Electrical Energy Generation in Botswana

Dumelang*. In this post, I take a look at historical trends to see how electricity generation in Botswana has changed over time. I noted in an earlier post about Sankey diagrams that Botswana generated only 7% of its electricity needs in 2012. This seemed an extraordinarily low number, so, in my research for this post, I also took a close look at the source data and uncovered some interesting discrepancies.

Utility-scale electricity generation in Botswana began in 1970 with the commissioning of a small oil-fired station in Gaborone. This provided for the needs of the capital and surrounding areas until its decommissioning in 1989. In 1974 a 65 MW coal-fired operation was built in Selebi-Pikwe to service the mining industry. 1985 saw the start-up of a large coal-fired plant at Morupule near Palapye and the shutdown of the Selebi-Pikwe plant a few years later in 1989.  The Morupule operation consisted of four 33 MW air-cooled units, providing a total generation capacity of 132 MW. This operation, known as the Morupule A plant, served Botswana’s needs well for a time. However, with increasing population, electrification of the country, and industrialization, demand rose and increasing quantities of electricity had to be imported from neighboring countries. The construction of the Morupule B coal-fired plant, consisting of four 150 MW air-cooled units, commenced in 2009. The deadline for completion was 2012, but many startup and operational problems have been encountered and today—three years past the scheduled completion date—the new plant has not lived up to its promise. There have been frequent breakdowns and, as a result, a great deal of Botswana’s electricity is still sourced from the Southern African Power Pool (SAPP).

Location of Morupule power plant near Palapye

In the figure below, I have plotted two sets of data for the past 18 years. The orange line shows the percent of electricity generated in-country by the Botswana Power Corporation (BPC), largely from their Morupule operations. The blue bars show the total annual amount of electricity (generated locally and imported) supplied in gigawatt hours (GWh). Data for 2015 are for the first three quarters only.

Data Source: 1997 to 2004; Adjusted BPC annual report results. 2004-2015; Statistics Botswana

An examination of the data shows that, from 1997 to 2008, the amount of electricity supplied steadily increased, with a compounded annual growth rate of 5.7%. During this same period, the proportion of local generation, which was as high as 60% in the late 1990s, decreased. This is to be expected from a fixed source of local generation in the face of increasing demand. However, the decline in local generation accelerated because of operational problems at the aging Morupule A power station. In 2011, an extreme situation was reached, when only 9% of the electricity supply was locally generated.

The difference in supply was made up of imports from the SAPP. However, since late 2008, supply shortages in the entire SAPP region have become acute and electricity imports to Botswana were reduced. As a result, rolling blackouts, also known locally as load shedding, were introduced across the country to curtail demand. Since then, the annual electricity supply has been up and down and there have been some years (specifically 2009, 2011, and 2013) in which energy supply was actually lower than the previous year. Load shedding, combined with the introduction of demand reduction initiatives, prepaid electricity, smart metering, and hot water load control, has slowed the rate of electricity supply growth since 2008 to a compounded rate of ~3% per year.

Since 2012, with the startup of the Morupule B operation, the local supply situation has improved and there have been year-on-year increases in electricity output from this operation. In 2014, Botswana again generated 60% of its electricity demand, significantly reducing the amount of electricity that it needed to import. However, the first quarter numbers for 2015 are disappointing because they indicate a similar level to that of 2014. It was anticipated that this value would be higher, but the performance of the Morupule B plant has been problematic, with only 300 MW of the specified 600 MW generation capacity currently available. We are hopeful for an improvement by the end of the year.

(In my post, The Big Picture, I noted that Botswana only generated 7% of its electricity needs in 2012. However, the historical data in the figure above indicate that this low actually occurred in 2011. My earlier statement was based on data from the International Energy Agency, IEA. A careful analysis of the IEA data led me to conclude that they were using information from the BPC annual reports. Because the BPC financial year ends in March, use of their data requires adjustments to take into account that their annual numbers actually incorporate the last three quarters of the previous year’s data. As a result, IEA reports of low levels of energy generation in 2012 actually correspond largely to the previous year, 2011.)

In my last post, I noted that energy students sometimes confuse capacity factor with conversion efficiency. The concepts are quite different: capacity factor is a measure of how much of the theoretical capacity of an energy-generating device was utilized over a time period (typically one year), whereas conversion efficiency is a measure of the effectiveness of the conversion of one form of energy to another, such as the conversion of energy in coal to electricity. To get a sense of conversion efficiencies, let’s take a closer look at the Morupule coal-fired plant.

According to the data provided by the IEA, the Morupule operation burnt 169 kilotons (kt) of coal and generated 250 GWh of electricity in 2012. To calculate conversion efficiency, we need to compare the input energy in coal and output energy as electricity in the same energy units by converting the energy in coal to GWh equivalents. If we assume that the Morupule plant burns coal with a heat content of 24 MJ/kg (a typical value for Botswana coal), we can calculate that 169 kt of coal contains 7.1 billion MJ of energy. Considering that there are 3.6 MJ in a kWh, we can calculate that the energy input was equivalent to 1126 GWh, which generated 250 GWh of electricity.

With this common set of units, we can now calculate that the conversion efficiency is Input/Output x100 = 250/1126 x 100 = 22%.

In fossil fuel plants, a different measure of conversion efficiency is often applied. This is heat rate, which is the amount of input energy (usually measured in kilojoules (kJ)) that is needed to produce one kilowatt hour (kWh) of electricity. One kWh of energy is equivalent to 3600 kJ, so if a fossil fuel plant is 100% efficient, it would have a heat rate of 3600 kJ/kWh, i.e., the plant would take 3600 KJ or 1 kWh of coal-based energy and convert it into 1 kWh of electricity. A plant operating with 50% efficiency would have double this heat rate or 7200 kJ/kWh (= 3200/0.5). At 22% conversion efficiency, the heat rate would be 16,363 kJ/kWh (= 3200/0.22).

Compared with other coal-fired plants around the world, which have conversion efficiencies of 30 to 40%, this value of 22% seemed extraordinarily low. To understand this discrepancy, I undertook a careful review of the IEA data and determined that they used a standard conversion efficiency of 22% every year to back calculate the amount of coal burnt in producing electricity in Botswana, i.e., their coal consumption numbers are not based on actual coal consumption data! The correct way to do this calculation would be to use the actual coal consumption numbers for the Morupule coal-fired operations. Unfortunately, I have not yet been able to source this data.

Further research led to some old 2006 data from SAPP which indicates that conversion efficiencies for the old Morupule A plant were actually more of the order of 30%. Additional evidence for higher conversion efficiencies was provided by data from the World Bank, which indicate that the heat rates at the Morupule plant were 11,621 kJ/kWh. This is equivalent to an efficiency of 31% (= 3600/11,621 x 100). As a result of this analysis, I am forced to conclude the IEA numbers for coal consumption in Botswana have a high bias.

A conversion efficiency of 30% (although significantly better than a value of 22%) still means that only 30% of the energy in coal ends up as useful electricity. The remaining 70% is lost due to process inefficiencies and heat losses.

To understand why this occurs, we need a better understanding of how the Moropule coal plant works. Coal is burned and the heat produced is used to boil water to generate steam. The steam is used to drive a turbine which then drives an electrical generator. In the process, we have the conversion of the chemical energy in coal, to thermal energy in the steam, to the kinetic energy of the turbine, to the electrical energy leaving the generator. In this process, there are heat losses in the hot off-gases that leave the combustion chamber and then exit those tall stacks at the Morupule operation. Another problem with a steam plant is that steam can only be used once to turn the turbine: it then needs to be condensed into water so that the water can be again be boiled to generate steam. The Morupule plants are air-cooled so the energy that was in the hot steam is lost to the atmosphere during the cooling process. The challenge with air cooling is that this is an energy-intensive operation itself, because large air fans need to be powered to drive air past heat exchangers. A significant portion of the energy generated by an air-cooled plant, typically 10%, is used to run the cooling units, which reduces the amount available for distribution. 

There are certainly coal-fired steam plants that have higher conversion efficiencies. Many modern coal-fired power plants have conversion efficiencies greater than 35% and water-cooled plants, such as those located near rivers or oceans, have even higher efficiencies. The world’s most efficient coal plants have conversion efficiencies as high as 47%. One hopes that, as the operational problems are solved at the Morupule plant, attention will be focused on improving its conversion efficiency to above 30%.

Until next time, remember to turn off those lights when you leave the room

Tsamayang Sentle**

Mike Mooiman

Click here to be notified of new Energy in Botswana blogposts.

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

Friday, October 23, 2015

Electricity Production in Botswana

Dumelang*. My post this week is part informative and part instructional. When we discuss energy issues, a couple of key concepts come up time after time and, to be a contributor to an energy discussion, we have to know, or familiarize ourselves with, some technology and terminology. In this post, I want to explain two fundamental energy concepts. The first is the difference between energy and power, and the second is capacity factor. I will then show how they can be applied to electricity production in Botswana. 

Let's start with the difference between energy and power. These terms are often used interchangeably. This is okay in a general conversation, but in an energy-related discussion, it can lead to confusion, misunderstanding, errors and bad decisions. It is essential to be specific about which term you are discussing, so let’s take a look at distinguishing between the two.

The standard scientific definition is that Energy is the ability of a system to do work. It is the quantity which we need to get something to move, heat up, light up, burn, explode, etc. Energy is not just one thing, however – it comes in different forms, for example, electrical energy, chemical energy, nuclear energy, kinetic energy, etc.: much of energy technology deals with converting one form of energy to another in the most efficient manner. For example, converting the chemical energy in petrol into the kinetic energy of a moving car.  Some of the more common units of measurement for energy are kilowatt hours (kWh), megawatt hours (MWh), megajoules (MJ), and terajoules (TJ).

Power, on the other hand, is the ratio of energy per unit of time or the rate at which energy is produced from a fuel source or is converted from one energy type into another. Units of measure for power include kilowatts (kW), megawatts (MW), joules/second or horsepower (HP).

The confusion between these two often stems from the similarity of the units like kilowatt hours (which is an energy unit), and kilowatts (which is a power unit). However, it is necessary to understand that, even though the units seem similar, there is a world of difference between them. This difference stems from the simple mathematical relationship between energy and power:

Energy = Power x time.

One my students in the Energy and Sustainability program at Franklin Pierce University  noted that energy and power are analogous to distance and speed. Energy, like distance, is a quantity, whereas power is a rate like speed. Like the relationship between energy and power, the relation between distance and speed is written as:

Distance = Speed x time.

Let's consider a simple backup generator that I have been looking at in the Game Store in Gaborone. 

This unit is rated at 5500 Watts or 5.5 kilowatts (kW) under long-term running conditions, so the power of the unit is 5.5 kW. If I were to run this unit for 1 hour, I would produce:

5.5 kilowatts (kW) x 1 hour = 5.5 kilowatt hours (kWh)

of electrical energy that I could use to run my home. Running it for 24 hours would produce 5.5 kW x 24 h = 132 kWh of electrical energy. The power rating of 5.5 kW is a measure of the rate at which the backup generator can take the chemical energy in the diesel fuel and convert it to electrical energy that I can use to keep my home running during load shedding. The larger the motor on the generator, i.e., the greater the power, the faster is the rate of energy conversion.

Let’s take a look at another example. In a car, we convert the chemical energy in petrol into forward kinetic motion to get us from point A to B. Again, the greater the power of the engine, the faster will be the rate of energy conversion. The pictures below illustrate this point.

The Mercedes S500 sedan has a high-powered 5 liter, 302 HP motor that can more rapidly convert the energy in the petrol tank into forward kinetic motion than my rental Toyota with its  1.5 liter, 89 HP motor. These two automobile engines, under specific circumstances, can produce the same amount of energy, however, the Mercedes can do so in substantially less time. It is likely that the Mercedes will do so a lot less efficiently than the Toyota—but with a whole lot more fun.
Let's go back to the Ryobi generator unit so that we can discuss the second fundamental concept for this post – capacity factor. If I could run the generator solidly for 24 hours a day for an entire year, I theoretically could produce:

5.5 kW x 24 h/day x 365 day/year = 48 180 kW of electrical energy.

However, if I were to use the generator only for 1 day per month during the year, say during a load shedding, I would produce:

5.5 kW x 24 h/day x 12 days = 924 kWh of electrical energy.

Dividing actual produced energy by the maximum that theoretically could have been generated in a 24/365 scenario produces a ratio called the capacity factor. In my example above, we would divide 924 by 48 180 to produce a figure of 0.019, which converts to a percentage of 1.9%: this would be the capacity factor of my generator for that year. In other words, my generator only ran at 1.9% of its maximum potential output. Students in the energy field often confuse capacity factor with conversion efficiency and it is important to appreciate that they are very different concepts. The capacity factor is a measure of how much of the theoretical capacity of an energy-generating device was utilized over a time period, typically one year. On the other hand, conversion efficiency is a measure of the effectiveness of the conversion of one form of energy, say that in coal, to another form of energy, for example, electricity. We will be taking a look at conversion efficiencies in a future post.

With these basic terms—energy, power and capacity factor—under our belts, let's turn back Botswana energy issues and particularly electricity generation.

I have examined the 2013 electricity generation figures for Botswana that were published in the Botswana Power Corporation (BPC) 2013 Annual Report and have combined, in one table, the  generating units, their combined power, the energy produced from these units, the  calculated capacity factors, and the overall capacity factor for the combined generators in Botswana.

In 2013, there were five energy-generating operations, including the new (and trouble-prone) generators at Moropule B, the aging and largely shutdown Moropule A operations, two large-scale diesel generating operations, one near Orapa and the other near Francistown, and the 1.3 MW solar plant in Phakalane. The combined nameplate capacity of the generating units was 743 MW and they generated just over 877 000 MWh of electrical energy for an overall capacity factor of 13%. (Note that there are 1000 kilowatts in a megawatt, similarly there are 1000 kilowatt hours in a megawatt hour.)

On examining the capacity factors, it is interesting to note how far they are from 100%. The only way a generating device can run at a capacity factor of 100% is by running 24 hours 365 days a year—which is simply not practical or realistic. Equipment breaks down and has to be repaired or has to be shut down for maintenance. Moreover, operators of power plants make operating choices, based on the cost of coal and diesel compared with that of imported electricity, as well as demand to throttle back their units from their rated or name plate capability. This reduces the amount of electricity produced which, in turn, reduces the capacity factor. However, the low capacities of the coal-fired units are of concern. Typically, coal-fired plants have capacity factors that range from 50 to 80%, depending on location and demand. Low capacity factors for coal-fired plants result from either low demand or operational issues. In the case or Moropule B, the problems that have plagued the startup of new generators have been extensively reported on in the media.

Generating electricity using diesel is an expensive proposition and therefore the low capacity factors of diesel plants are not surprising. These units are seldom used and they function as back-up generators and are only used in an emergency. In many respects, they are just like the Ryobi generator I presently have my eye on.

Even though the Botswana-based generating units are operated separately with different technical and economic considerations, it is useful to consider their aggregated capacity. As noted above, the combined nameplate capacity of the generating units is 743 MW. This combined capacity in a single unit would be one mammoth-sized generator – we could call it the "Botswana Megarac 743" – which is almost a 140,000 times larger than the Ryobi unit I am eyeing at the Game Store in Gaborone. Looking at this another way, if Botswana bought 140 000 of these units, it would match the country’s present generating capacity.

Based on 2013 financial year data, this Botswana Megarac 743 was operated at a capacity factor 0.13 which means the combined Botswana facilities only generated 13% of the electricity that was theoretically possible. Over time, it is hoped that the start-up problems at Moropule B will be solved and the overall capacity factor for Botswana’s generating facilities will increase. However, we need to keep in mind that practical considerations, such as cost and availability of imported electricity, will also have to be factored in and that Botswana electricity generation is not an island unto itself. Botswana draws electricity from the Southern African Power Pool (SAPP) power generation and transmission system which coordinates electricity supply and demand throughout Southern Africa.  The SAPP system has a combined capacity of about 55 000 MW of electrical generating capacity.

Hopefully, this has been an informative and instructional post and you now know the difference between energy and power and you have an appreciation for capacity factors. As you can see, capacity utilization of generating facilities is low in Botswana: hopefully this will improve in the future, but it is crucial to appreciate that not all of this capacity can be tapped at any one time. Running these generators depends on complex issues, which include demand, cost and availability of fuel, maintenance shutdowns and financial considerations.

In the meantime, if you see me in the parking lot at the Game Store in Gaborone trying to load up that Ryobi generator into my rental Toyota, stop and give me a hand. Until next time, remember to turn off those lights when you leave the room.

Tsamayang Sentle**
Mike Mooiman

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