Helmholtz Association

More Light for Tandem Cells

The tow individual cells currently are still stacked mechanically in the lab to form a tandem cell. Photo: HZB/M. Schmid

A solar cell always uses only a portion of the solar spectrum, that is it converts into power only a certain range of colours (frequencies). Therefore, what is more logical than to stack several kinds of solar cells on top of each other, in order to transform a larger portion of light into power? This approach is being pursued to assemble tandem solar cells consisting of a top and a bottom cell. In doing so, certain colours of the light are absorbed by the top cell and converted into electric power, while the bottom cell uses the remaining parts of the colour spectrum.

Yet in practice it appears that the top cell allows too little light to pass through to the bottom cell even at those frequencies, which cannot even be used for power production in the top cell itself. Now, Dr. Martina Schmid from the team of Professor Dr. Martha-Christina Lux-Steiner at the HZB achieved a significant improvement: In her PhD thesis on the optimal construction of chalcopyrite tandem solar cells, she developed an optical model of this layered cell and calculated which losses occur and where. This model enabled optimisation of the stacking structure and layer thicknesses of the tandem cell, so that the transparency of the top cell increased from 60 to 80 percent. As a result, the efficiency of the entire tandem cell could increase to above 10 percent. Before the optimisation only 8.5 percent was achieved. “If one now would optimise the electric properties of the top cell, for example by improving the material characteristics, then efficiencies of above 20 percent were feasible for the tandem”, says Schmid. The physicist is now working on strengthening the absorption of certain frequency ranges and their conversion into electric power by aid of specially applied nano-structures.

Insights into research: Energy

Strong Parts from the Cold Furnace

Many parts of aeroplanes and automobiles are long since not made out of steel but from modern composite materials. They consist of carbon or fibreglass laminates bonded with special resins to form an extremely resilient material withstanding crash tests, elastically absorbing virbrations and which at the same time are as light as a feather.

To 'Strong parts from the cold furnace'

Insights into Research: Energy

Hidden Reserves

A new term is spreading amongst Europe’s energy experts: “Shale gas” could be translated “Schiefergas” in German. This denotes a natural gas located in dense, ancient clay formations yet which cannot be extracted with the usual methods.

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Insights into Research: Energy

Salt, Concrete and Compressed Air: Storage Systems Deliver Energy on Demand

Solar and wind power stations rarely conform to demand from electricity customers. Therefore, low priced and efficient energy storage systems are the key towards a reliable supply of electricity produced from regenerative sources. Researchers from the German Aerospace Centre (DLR) develop thermal and compressed air energy storage for the future supply with energy.

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Insights into Research: Energy

High temperature materials increase efficiency

Fossil power plants probably will remain a basic pillar of the world-wide provision with energy for a long time. Therefore, an important element in the battle against climate change could be the separation and storage of carbon dioxide from the exhaust fumes of coal or gas power stations. In order for this to be achieved with the minimum of energy possible, researchers within the Helmholtz Alliance MEM-BRAIN under leadership of the Forschungszentrum Jülich develop membranes made from polymer and ceramic materials.

To 'Sieves for Carbon Dioxide'

Insights into research: Energy

Wendelstein 7-X progresses

One of the most important industry commissions in building the fusion plant Wendelstein 7-X was completed in May 2010: the production of the fifty superconducting solenoid magnets. The commission for this technologic core part of the experiment currently being developed at the Part-Institute Greifswald of the Max Planck Institute for Plasma Physics (IPP) was the hitherto largest single procurement in the Institute’s history.

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Insights into research: Energy

Fuel Cell on Continuous Duty

It runs and runs and runs. With 25,000 hours, the Jülich hightemperature fuel cell has achieved a new endurance run world record in June 2010. Good preconditions in order to provide not only cars or laptops with power in the future, but also homes and industrial processes. For fuel cells are hot candidates for a future and also more decentralised power supply.

To 'Fuel Cell on continuous Duty'

Insights into Research: Energy

Models for Energy from the Depth

When the GFZ researchers get geothermal energy from several kilometres deep down to the surface in order to produce electric power and supply heat energy, they literally advance into unknown regions. Nobody knows exactly what it looks like deep down, which fissures and cracks there are and how the geothermal power station changes the underground. Yet such questions are of interest not only to researchers but also to enterprises.

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Einblicke in die Forschung: Energie

Bioenergy can turn "Bio"

Energy can be won from maize, rape or other plants, yet the large-scale cultivation of energy plants is not automatically environmentally friendly. “Bioenergy will play a role in many regions of the world, but it will very much depend on how this bioenergy is obtained”, says Dr. Daniela Thrän from the Department Bioenergy of the Helmholtz Centre for Environmental Research - UFZ in Leipzig.

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Insights into Research: Energy

Refuelling with Straw

Residual plant matter such as straw or wood shavings can be processed to make high-quality fuels, as researchers from the KIT have shown on a small scale already some years ago. The ecological balance of such synthesis fuels is much better than that of fuels derived from rapeseed oil or other energy plants, for which separate cultivation ground are reserved, fertilised and watered.

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12.06.2013