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Energy Technology

Efficient energy generation with steel

The German government has initiated the energy transition. This would be impossible to achieve without steel. Because only this material makes the technology for generating non-renewable and renewable energies efficient.

Energy from atomic fission was yesterday, energy from atomic fusion is tomorrow. Until it can be used, however, we remain dependent on non-renewable and renewable energies. Demand for reliable, reasonably priced and environmentally friendly electrical energy is rising worldwide. The most important aim in the further development of power station technologies is to increase energy efficiency to reduce fuel consumption and emissions. Strong and temperature-resistant steels in thermal power plants improve efficiency and reduce the consumption of primary energy carriers. The modernisation of fossil-fuel power stations saves 400 times as much CO2 as was used for their construction.

Energy efficiency is determined by the efficiency of power station processes. This is about 34 per cent in the case of conventional combustion power plants. Tubes made of highly heat-resistant steel withstand extremely high pressures and temperatures in the boilers and steam pipes of power stations. The generation of electricity from lignite achieves efficiency levels of up to 43 per cent, while coal power stations offer efficiencies of up to 45 per cent. The performance of a 1,000 MW lignite power station with optimised plant technology and with a 43 per cent level of efficiency replaces ten old power station units of 100 KW each with an efficiency of just 31 per cent. This corresponds to a climate-friendly lowering of the burden on the atmosphere of about 1.8 m. tonnes of CO2 per year.

The gas turbine developed by Siemens and used as a power plant in the Bavarian power station Irsching 4 can do better: it has an efficiency of over 60% in combined gas and steam mode. 2.8 m. tonnes of CO2 less per year are emitted compared to a conventional coal-driven power station with the same performance.

With the increasing proportion of renewable energies, e.g. from wind, photovoltaics and other solar technologies, modern power stations must be able to react increasingly rapidly to power and load fluctuations. With a start-up time of just a few minutes, the gas turbine beats a conventional power station that requires several hours to reach its nominal capacity.

Solid oxide fuel cells have an even higher efficiency: they deliver clean energy in the form of heat and electricity – with an efficiency of up to 80 per cent. Specially developed steels withstand temperatures of up to 900°C.

Electricity from wind

Steel is the material of choice for wind turbines.

The use of renewable energies from sun, wind and water would be unthinkable without steel. Wind turbines, for example, save 32 times more CO2 than is emitted during their production. The generation of electrical energy from wind conserves resources and eases the burden on the environment. The yield is particularly large at sea, where more constant and stronger winds blow than inland. The demands made of the plant at sea, however, are greater than on land. Steel is thus the material of choice for constructors of offshore wind turbines. They use it in the foundation, tower, nacelle and rotor.

Water on the march

Humans have been exploiting water power for about 5,000 years, e.g. with bucket wheels for irrigating fields. Grain mills, saws and hammer mills have been directly driven by water wheels. More than one hundred different trades were using water power as a drive at the end of the 18th century. Werner von Siemens invented the electro-dynamic generator in 1866. The world’s first large hydroelectric power station started operation at Niagara Falls in America 30 years later. 7,500 plants are now installed in Germany.

Wasserkraftwerk Isar (Quelle: SWM)

Hydroelectric power plant on the River Isar
(Source: SWM)

Conversion of the energy in flowing water into rotational energy takes place in turbines. Kaplan, Francis or Pelton turbines are used, depending on the drop height and throughflow. They achieve efficiencies of well over 90 per cent. The power of the tides can also be exploited by damming narrow estuaries. They then generate electricity during the ebb and flow, as at St. Malo in France. Free-standing underwater turbines – for use in river mouths such as the Thames in England – are still in the experimental stage.

Everything turns on steel

The rotational energy of the turbine drives the generators in which the kinetic energy is converted to electrical energy. Within the generator itself, grooved and laminated sheet metal cores in the rotor and stator accept the windings in which the electricity is generated. To prevent eddy currents, the stator is constructed of many individually insulated sheet metal lamellae. The non-grain-oriented electrical sheets used here, so-called dynamo or motor sheets, permit efficiencies of over 95 per cent.

What works in one direction also functions well in the other: the generator becomes a motor that serves as an electrical drive in many technological fields.

The electricity generated must be transformed in order to minimise line losses during the transmission of electrical energy from the generator to the user. Transformers are employed for this, with grain-oriented transformer sheets that achieve over 99 per cent efficiency. The core of the transformer also consists of thin sheets in order to prevent eddy currents.