Energy | 09. August 2010 | posted by Jan Oliver Löfken

Energy question of the week: Which type of electricity generation has the least impact on climate?

Coal-fired power stations burn lignite or, for the most part, coal imported from overseas. Solar cells need crystalline silicon that first needs to be extracted from quartz, an energy-intensive process. Therefore, when examining the climate compatibility of power generating plants, it makes sense to not restrict the analysis just to the operation of the plant. Instead, the total energy required should be considered across the entire service life of the plant, typically in excess of 30 years. Viewed against this benchmark, which type of power plant has the best environmental credentials?

Answering this question requires the most comprehensive details on the energy consumption of a power plant: from the manufacture of its constituent parts, through its operational lifetime, to its decommissioning and disposal. This challenge was taken up by energy experts from the DLR Institute of Technical Thermodynamics in Stuttgart and from the Institute for Energy and Environmental Research in Heidelberg. Their results were published in June 2009 by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, on whose behalf the sustainability of different types of power plants was investigated.

Wind power and solar-thermal power offer high levels of energy efficiency

Montage von 80 Windenergieanlagen des Typs Vestas V 80 vor der dänschen Nordseeküste. Bild: Vestas Central Europe, Bild oben: Solarturmkraftwerk, Bild: DLR/
Installation of 80 Vestas V80 wind turbines off the Danish North Sea coast. Credit: Vestas Central Europe, Image at top and lower right: Solar tower power plant. Credit: DLR/

Wind farms are the most efficient when it comes to matching the total energy required for their manufacture, operation, decommissioning and disposal. Their ‘energy-related amortisation period’ fluctuates between three and seven months, depending on the choice of location and the efficiency rating of the equipment. Comparable figures were otherwise only achieved by solar-thermal power stations in sunny locations such as Morocco. Hydroelectric power stations need up to 13 months. Solar (photovoltaic) power stations in central Europe need to generate electricity for up to five years before they deliver an equivalent energy balance. However, modern thin-layer solar cells are able to produce energy more efficiently, cutting this timescale to just three years.

By virtue of their operating principles, all power stations generating electricity from fossil fuels or uranium are incapable of achieving this type of energy balance. This is because they consume fuels with higher energy content than the electricity they generate. A perpetual motion machine offering efficiency ratings in excess of 100 percent simply does not exist.

The best solution lies in an intelligent mix

Although wind turbines, both on the coast of the North Sea and offshore, and solar-thermal plants in southern regions deliver the best energy balance, it would be unwise to dispense with other forms of electricity generation. "There is simply no such thing as one single 'best' technology for reliable electricity supply," says DLR researcher Franz Trieb, who also contributed to the BMU report on sustainable energy provision. In order to feed affordable electricity into the power grid with security of supply, a diverse mix of renewably-fuelled power stations would need to be employed.

The DLR Energy question of the week in 'The future of energy' Year of Science

The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog.


About the author

Energy journalist Jan Oliver Löfken writes among other things, for the Technologie Review, Wissenschaft aktuell, Tagesspiegel, Berliner Zeitung and P.M. Magazin on issues involving energy research and industry. For DLR, he answered the Energy question of the week during the Year of Energy 2010. to authorpage