A fossil fuel that is burnt in order to produce electricity, coal is a non renewable resource that is fast depleting. The combustion of fossil fuels releases various gases that are hazardous to the environment and the atmosphere. During combustion it gives off carbon dioxide (CO2), which is the main greenhouse gas that is linked with global warming. It produces emissions such as sulfur, nitrogen oxide (NOx), and mercury, which can pollute the air and water. Sulfur mixes with oxygen to form sulfur dioxide (SO2), a chemical that can affect trees and water when it combines with moisture to produce acid rain. Emissions of nitrogen oxide help create smog, and also contribute to acid rain. Mercury that is released into the air eventually settles in water. This mercury in the water can build up in fish and shellfish, and can be harmful to animals and people who eat them. Read more about coal power on Eskom’s website.

Pros – A Coal power plant is one of the cheapest means of electricity production and thus seems like a viable option in many developing countries. Coal power plants are considered to be reliable and many countries already have the necessary infrastructure for such plants. A country like South Africa has abundant coal reserves.

Cons - Although governments of the world are establishing various environmental laws and policies that are targeting the prevention of the impacts of burning fossil fuels, their use is still detrimental to the extent that it is contributing to global climate change.

In recent years natural gas has gained increasing significance in South Africa and Namibia. Extensive offshore deposits have been found in existing mining operations off the coast of the Northern Cape and Southern Namibia, including the Kudu gas field developments by Nampower. Natural gas consists primarily of methane and is essentially the remains of the decomposition of plants, animals and micro organisms that existed millions of years ago. It is organic matter transformed into fossil fuels as a result of compression under the earth’s surface. A more detailed explanation of this process can be found at the educational website Naturalgas.org.

Pros - Natural gas is considered a very clean and safe fossil fuel. The by products of its combustion such as carbon dioxide, carbon monoxide and nitrogen oxides are said to be almost half that of coal use. Thus by using natural gas we can reduce the emissions of greenhouse gases that contribute to climate change, smog over cities, poor air quality and acid rain. It is also economical as costs and time periods required in order to build a gas plant are considerably less than for coal plants.

Cons – numerous environmental impacts arise from gas exploration. Dangers include explosions and oil spills. In addition, ocean habitats can be disturbed. Natural gas is still a non renewable resource.

In the early seventies oil represented approximately 40% of all global fossil fuel use. Oil consumption has decreased during the nineties due to improved energy efficiency, as well as a shift to other fuels such as natural gas and nuclear energy and stricter environmental restrictions. Oil is extracted through large drilling platforms from oil reserves, where the remains of marine micro-organisms accumulate over millions of years and gradually infiltrate the sea floor sediment and rock as they decay. Visit the chapter on fossil fuels of The Energy Story for more information on crude oil.

Pros – It is considered easy to handle, store and transport. It is easier to extract from the ground than coal and more cost effective to transport.

Cons - The burning of oil for energy production purposes, like coal, results in the emission of carbon gases into the atmosphere. In addition there are numerous safety hazards involved in the exploration of oil in onshore and offshore sites. Drilling may affect ocean and terrestrial habitats. The threat of oil spills exists.

Nuclear power is generated using uranium or plutonium. Uranium is a highly radioactive material that needs to be dug up and processed generating a huge amount of waste in the process. Before uranium can be used in nuclear reactors it needs to be enriched. Nuclear reactors generate heat through a process of nuclear fission. The steam generated from this heat drives turbines and generators. Most nuclear plants are situated along the coast so that the sea can be used as a cooling mechanism instead of cooling towers.

Pros – with nuclear energy, countries can rely less on fossil fuels and thus limit hazardous atmospheric pollutants. Nuclear plants are considered to be one of the more cost effective alternatives to fossil fuels. The energy output is great.

Cons – the excavation of uranium and plutonium causes devastation to the surrounding environment. The waste from these excavations is also radioactive. If these are stored in a poor condition they lead to the contamination of surface and groundwater. Vast resources have be spent on safety mechanisms and precautions at nuclear plants. If harmful radioactive materials are released, this could cause tremendous negative impacts on the health of people, plants and animals. The meltdown of the nuclear reactor in Chernobyl, Ukraine in 1986 is listed as the world’s worst nuclear accident, which killed 30 people and affected thousands across Europe with regard to health (populations becoming prone to cancers), socio-economically and politically as well as environmentally.

Nuclear energy is a hot topic that has always generated intense debate. Find out more on the websites of the World Information Service on Energy , World Nuclear Association, the Chernobyl Legacy and Greenpeace.

Wind energy is one of the fastest growing sources of renewable energy sources around the world. Wind machines use blades to collect the wind’s kinetic energy. Windmills work because they slow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift and making them turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity. There are two types of wind machines: horizontal–axis (the majority) and vertical-axis wind machines. One wind machine can produce 1.5 to 4.0 million kilowatthours (kWh) of electricity a year. That is enough electricity to power 150-400 homes. Wind turbines start operating at wind speeds of 4 to 5 metres per second. Wind speed increases with altitude and over open areas with no windbreaks. Therefore good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling.

Pros – wind turbines have a low impact on the environment, they produce only low frequency noise. It is safe and produces no by products. The turbines do not disturb livestock on farms and the land can continue to be used for grazing and crop production. There are no interferences as in the past with television or radio frequencies.

Cons - At times when the wind is not blowing, other types of power plants must be used to generate electricity. Wind turbines may have a negative effect on wild bird populations as well as a visual impact on the landscape. There is also the impact on the land during construction. Capital costs are high.

Read more about the topic on the websites of the Global Wind Energy Council, the British Wind Energy Association.

‘Everyday the sun gives us 20,000 times more energy than the entire planet needs’. This statement alone illustrates that the sun is not only the primary energy source for most living things but also a major potential for energy production. Yet up until now the sun’s energy has not been harnessed to its full potential.

thermal (hot water) - Electricity can be produced from sunlight through direct heating of fluids to generate steam for large scale centralized electrical generation. Solar hot water heaters use the sun to heat either water or a heat-transfer fluid in collectors. A typical system will reduce the need for conventional water heating by about two-thirds. High-temperature solar water heaters can provide energy-efficient hot water and hot water heat for large commercial and industrial facilities.

electric (photovoltaic) - Electricity can also be produced from sunlight through a process called photovoltaics. "Photo" refers to light and "voltaic" to voltage. Thus the term describes a solid-state electronic cell that produces direct current electrical energy from the radiant energy of the sun. Solar cells are used to generate electricity for household power, street lighting, highway telephones, calculators and watches, water pumping, and other applications.

passive solar energy – passive solar heating, cooling and daylighting are techniques that make use of the steady supply of solar energy by means of careful building design. These techniques use building elements such as walls, windows, floors and roofs, in addition to exterior building elements and landscaping, to control heat generated by solar radiation. Passive heating collects and stores thermal energy from direct sunlight; passive cooling uses shading and generation of air flows with convection ventilation to minimise the effects of solar radiation; and daylighting design optimises the use of natural daylight, contributing greatly to energy efficiency. Buildings can incorporate design features such as large north-facing windows and building materials that absorb and slowly release the sun’s heat. Incorporating passive solar designs can reduce heating bills as much as 50 percent.

Pros – solar energy production is safe, renewable, clean (pollution, waste and noise free). It can be used on a small scale for domestic and household use, as well as for larger operations. The area needed to build a solar plant is less than half the area needed to build a coal plant. Passive systems require no additional mechanical equipment, and are thus simple and require minimal maintenance.

Cons – only slight environmental impacts are experienced with the construction of more large scale solar panels. The cost of generating solar energy is much higher than that of fossil fuels, although costs are decreasing. Reduction of costs and increase in efficiency becomes progressively more important as the world’s developing nations are situated in regions that receive vast amounts of solar radiation.

For more information on how the suns energy is harvested see the chapter on solar energy of The Energy Story or explore the Green Building.

Geothermal energy originates from natural processes beneath the earth’s surface, and is recovered as steam and hot water. Underground hot rocks heat water to produce steam. This steam is accessed through drilling and exploration which is then purified and used to drive turbines and electric generators.

Pros – Geothermal energy does not produce any pollution, and does not contribute to the greenhouse effect. Power stations do not have much impact on the environment. No fuel is needed. Energy may be needed to run pumps but this can be taken from the energy being generated.

Cons – One of the negative aspects of geothermal energy concerns geography and geology. There are not many regions where a geothermal plant can be built as hot rocks of a suitable type, at a suitable depth need to be found. Sometimes a geothermal site may run out of steam perhaps for decades, which has to do with geological processes. Hazardous gases and minerals may come up from underground, and can be difficult to safely dispose of.

Visit the International Geothermal Association for information on the use of geothermal energy around the globe.

According to the British Wind Energy Association, some studies suggest that the marine environment stores enough energy in the form of heat, currents, waves and tides to meet total world wide demand for power many times over. But although the energy supply is dependable and abundant, converting it into useful electrical power is not easy and there are few technologies that have gone as far as full construction and testing. One of the methods used is a tidal barrage in which a dam or "barrage" is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. Offshore turbines are also utilized, and they are structured much like an underwater wind farm. This method is much more cost effective to build, and does not have the environmental problems that a tidal barrage would bring.

Pros – it produces no atmospheric waste. It needs no fuel. It is not expensive to maintain. Tides are predictable. Offshore turbines and vertical-axis turbines do not have a large environmental impact and are less costly to maintain, but can be expensive to build.

Cons – A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. There are few suitable sites for tidal barrages. And it only provides power for around 10 hours each day, when the tide is actually moving in or out. Turbidity, salinity and sediment movements become affected.

The British Wind Energy Association has useful information on wave and tidal energy.

Biomass energy relates to the energy created by organic matter. Biomass is formed when the sun shines on plants and trees. Previously wood used to be the main source of biomass, but today other sources are also used such as the waste from industries and cities. Biogas or methane is produced from the decomposition of biomass and sewage. The capturing of this gas is useful because of its effect within the greenhouse effect.

Pros – utilising waste materials to produce energy reduces the impact that their treatment or disposal of would otherwise have on the environment. The fuel tends to be cheap. Places less demand on the Earth’s resources.

Cons – Collecting the waste in sufficient quantities can be difficult. Fuel is still being burnt so this is still generating greenhouse gases.

See the chapter on biomass of The Energy Story for more information.