Category Renewable Energy

Dish-Stirling Systems

Dish-Stirling systems are at present the least technological­ly mature. Companies in the USA and in Germany are cur­rently working on four different sys­tems worldwide (Figure 1c). The sys­tem which is furthest along in its development originated in Germany and has accumulated several tens of thousands of hours of operation.

Such systems aim at independent power generation, not coupled to a power grid, for example for providing isolated villages with electric power. Their principal advantage is a very high efficiency of up to 30 %: This is provided by the combination of a near­ly ideal paraboloid concentrator with an excellent heat engine. If the sun is not shining, then dish-Stirling systems can in principle be operated with fu­el combustion, in order to meet the de­mand for power...

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Twists and Turns around Biofuels

by Gerhard Kreysa

  Twists and Turns around Biofuels

… with its linked long-term reservoirs. The figure shows the carbon content of the reservoirs, reversible flows and uni-directional flows (italics), and the derived residence times for CO2 in each compartment and in the whole cycle (a: year).

 

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Twists and Turns around Biofuels

If we leave the superficially-correct economic delibera­tions out of consideration for the moment, then it would ac­tually be preferable if we were facing immediate exhaustion of our fossil raw materials...

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Geothermal Energy

The renewable energy resource which at present is the least developed is geothermal heat. Deep-well geothermal ener­gy makes use either of hot water from the depths of the earth, or it utilizes hydraulic stimulation to inject water in­to hot, dry rock strata (hot-dry rock process), with wells of up to 5 km deep (see the chapter “Energy from the Depths”). At temperatures over 100 °C, electric power can also be produced – in Germany for example at the Neustadt – Glewe site in Mecklenburg-Vorpommern. Favorable regions with high thermal gradients are in particular the North Ger­man Plain, the North Alpine Molasse Basin, and the Upper Rhine Graben.

Geothermal heat has the advantage that it is available around the clock...

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Ribbon Silicon

A major portion of the costs of the current c-Si photovoltaic technology are due to the wasteful usage of expensive high – purity silicon. One possibility for reducing wafer costs con­sists of simply using thinner and therefore more readily breakable wafers. In principle, it is already possible to re­duce the wafer thickness to 150 pm and thus to obtain more wafers from a cast ingot and reduce the cost per wafer, if the efficiency and the production yield (breakage) remain constant. This is however currently not the case. Furthermore, more sawdust’ would be produced, so that the percentage of wasted silicon would increase.

Another, more elegant method is offered by the use of ribbon silicon...

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Costs and Development Potential

The Karlsruhe Biomass-to-Liquid process is particularly suit­ed to the requirements of the widely distributed biomass production from agriculture: The rapid pyrolysis and pro­duction of the bioslurry are carried out at a large number of decentrally located plants. They provide the decisive en­hancement in energy density needed for further economi­cal transport of the raw materials. The gasification and the following steps of gas conditioning and synthesis can then be performed at a large central installation of a size which makes it commercially cost-effective, and which is supplied with the bioslurry raw material by road or rail transport.

In this way, using the bioliq process, a ton of synthetic fuel can be produced from about seven tons of air-dried straw...

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