Biogas: Energy supply - today and in the future

1

Energy supply - today and in the future

Today, globally most energy is provided by burning oil. Only a very small per­centage is generated by nuclear power plants. The contribution of energy from renewable resources is almost negligible. But this will change in the future with increasing prices of oil.

In the future, countries may use different technologies, depending on their cli­matic and geographical location. Germany refrains from using nuclear power plants as a source of energy. This makes Germany one of the leading countries in the development of technologies for alternative and renewable energy sources.

1.1

Primary energy sources

In general, primary energy sources are classified as follows:

Fossil energy sources

• Hard coal
• Brown coal
• Petroleum
• Natural gas
• Oil shale
• Tar sand
• Gas hydrate

Renewable energy sources

• Water
• Sun

Wind

• Geothermal heat
• Tides
• Biomass

Nuclear fuels

 

Until the late 19th century, wood, the traditional biomass, was the only primary energy source used for cooking and heating. This ended when wood was replaced by hard coal, an epoch which lasted ca. 75 years. This was followed in the late 1950s by a continuously increasing use of petroleum and natural gas. Around 1950, nuclear power technology was first time industrialised, but it never became truly accepted. For some years now, this technology has remained stagnant and has not expanded because of still unresolved issues such as the storage of the radioactive waste and the risk of explosion of a reactor. This leaves "renewable energies", showing the biggest potential for securing the availability of energy in the future.

As an example: the total consumption of primary energy in Germany is ca. 4100 TWh a^-1, which has been provided by the use of different primary energy sources, shown in Figure 1.1. The primary energy source used during the past few years in Germany was mainly mineral oil (Figure 1.2). In the early 1990s, quite a significant part of energy in the Eastern part of Germany was also generated by processing brown coal. After the German reunification, however, the mining of brown coal was stopped because of the great environmental damage it was causing.

After this, the consumption of energy provided by hard coal remained almost static, while the energy from natural gas, mine gas, or sewage gas strongly increased to make up for that previously provided by brown coal. The use of renewable energy has been almost static during recent years, with a very slight though con­sistent upward trend.

Consumers using primary energy are shown in Figure 1.3. This chart shows that the traffic sector consumes 21% of the primary energy, which is even more than industry (19%). In fact the amount of energy supplied to industry is decreas­ing, and increasing amounts go to traffic. This is explained by the current trend toward a society with a high number of cars per family leading to a high demand of petrol, a secondary energy source of petroleum.

1.2

Secondary energy sources

Secondary energy sources are defined as products that have been produced by transforming primary energy carriers into higher quality products by applying processes such as refining, fermentation, mechanical treatnrent, or burning in power stations:

Products derived from coal

• Coke
• Briquettes

Products derived from petroleum

• Petrol
• Fuel oil
• Town gas
• Refinery gas

Products derived from renewable resources

• Biogas
• Landfill gas
• Pyrolysis gas

The secondary energy sources are converted to end-point energy.

1.3

End-point energy sources

The end-point energy is the energy used by the final consumers and provided in form of, e.g. district heating, wood pellets and electricity. In Germany, for example, the consumption of end-point energy is about 2600Twha^-1. It is important to emphasize that only electricity and not gas is defined as end-point energy since gas is the energy source that electricity is derived from.

Usually the amount of end-point energy consumed is used for calculation pur­poses and is taken as a base to reflect energy balances.

1.4

Effective energy

Only about 1/3 of the primary energy is effective energy which is actually used by customers in form of heating, light, processing, motion, and communication. The other 2/3 is lost when transforming the primary energy sources into effective energy. As an example, in Germany only 1400 TWha^-1 of energy is effectively used. About 570TWa^-1 of this energy is actually electricity. To cover these quantities, the electricity is produced mainly by using fossil energy sources (60%) like hard coal, petroleum, or natural gas (Figure 1.4); 30% is derived from nuclear power stations, while the amount of electricity from renewable energy sources is only about 7.25% to date.

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