Category Renewable Energy

Heat-Engine Processes

A thermal power process can unfortunately not convert all the heat energy provided to it into mechanical work. It fol­lows from the Second Law of Thermodynamics that part of the heat energy must be extracted from the process at a lower temperature than the input heat (so called “waste heat”). The higher the input temperature and the lower the output temperature, the greater the fraction of heat which can be converted into mechanical work (and thus into elec­tric power in a power plant). It therefore follows from ther­modynamics that a high “temperature head” between the hot and the cold heat reservoirs is more favorable for the thermal efficiency than a lower one.

In conventional thermal power processes to which so­lar energy can be applied, steam thermal engines (Clausius – Ran...

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Ethanol from Cellulose

In the long term, the production of biofuels could be rev­olutionized by technologies which open up new methods for using resources or make use of completely new re­sources. One of these possibilities is cellulose. The forests of the earth produce 1012 tons of cellulose annually from CO2 and water during their growth phases [4]. Cellulose could become one of the major energy sources in the fu­ture.

Chemically, cellulose is a polysaccharide, a polymer sug­ar molecule containing many monomer units. It can in prin­ciple be split up into its simpler monomer sugars, e. g. glu­cose. The latter can then be fermented to yield alcohol as a fuel component (pulp alcohol). However, cellulose is chemically very stable. Current technologies for splitting it must overcome its stability...

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The utilization of energy from the biomass is often under­estimated. At present, biogenic heating fuels are being re­discovered in Germany. Wood, biowastes, liquid manure and other materials originating from plants and animals can be used for heating and also for electric power generation. The combination of the two uses is particularly efficient. In Ger­many, currently 90 % of the renewable heat energy origi­nates from biofuels, mainly from wood burning – but in­creasingly also from wood waste, wood-chip and pellet heat­ing and biogas plants, as well as the biogenic component of waste. Its contribution to electric power generation is al­so increasing: in 2011, it was 6 % of the overall German de­mand, corresponding to 37 TWh.

Biofuels are available around the clock and can be uti­...

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Solar Cells from Ribbon Silicon

by Giso Hahn

Подпись: The solar-cell market is booming. But photovoltaic cells are still too expensive to be able to compete effectively with con-ventional power generation. A notable cost reduction can be achieved if ribbon silicon is used instead of the usual silicon wafers, which are sawed from massive blocks of silicon.image52Подпись: A bank of furnaces from which silicon ribbons are being pulled from the melt in the form of hollow, octagonal columns up to 5 meters high, using the EFG process (photo: Schott Solar GmbH).

The term photovoltaic energy, derived from the Greek, can be translated descriptively as “electrical energy from light”. In the year 2003, the solar cell, which is at the heart of every photovoltaic module, celebrated its 50th birth­day. There are many reasons for the increasing success of solar power. Although in the beginning, satellites were the main users of solar modules as an independent source of electric power, photovoltaic energy soon came down to earth. In terrestrial applications, a number of advantages play a role: For one thing, photovoltaic (PV) power permits a sustainable energy supply within closed systems, and thus provides freedom from the limited supplies of fossil fuels and their negative effects on the environment...

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Obstacles to the Use of the Biomass

In comparison to the use of fossil energy carriers, the pro­duction of synthesis gas from the biomass is more complex and more expensive. Therre are several hurdles to the tech­nical application of biomass fuels on a large scale.

For one thing, the biomass accumulates over wide­spread geographical areas and therefore has to be collect­ed and transported, often over long distances. In particular, less valuable biomass such as straw or forest wood residues have a low volumetric energy density (baled straw ca. 2 GJ/m3, as compared to 36 GJ/m3 for diesel fuel). Here, the question arises as to the distances over which it is eco­nomically and energetically reasonable to transport these materials. In addition, there is a great variety of potentially usable biomass materials...

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Grid Integration in Spite of Varying Power Outputs

In general, it is expected that a proportion of up to 20 % of renewable energy sources such as wind power and solar power can be integrated into the power grid without ma­jor problems. Following the decision of the German Federal government to shut down successively all the nuclear pow­er plants by 2022, the integration of new plants into the grid represents a technical and economic challenge. The fraction of power from sustainable sources is expected to increase from 20 % in 2011 to 35 % by 2020, in order to decrease the emissions of greenhouse gases relative to 1990 by 40 %.

The particular challenge for wind energy is due to the re­gional concentration of wind plants in the Northern and Eastern coastal areas, and to the daily and seasonal variations of the wind...

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A simple Coating Procedure

One of the reasons for the favorable fabrication costs of CdTe solar cells is an important property of CdTe: it sub­limes congruently. Sublimation’ refers to the vaporization of a solid material, without its previously having melted. Due to sublimation, snow vanishes’ in dry winters; the water molecules go directly from the solid ice into the air, as wa­ter vapor. CdTe exhibits a similar behavior: When it is heat­ed to a temperature above about 500° C, CdTe vapor is formed directly. If a sheet of glass at a lower temperature is held in this vapor, the latter condenses as a thin film on the glass.

Now the property congruent’ enters the picture: It means that the CdTe vapor maintains precisely the same chemical composition as in the solid CdTe from which it



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Case Study: The Technology of Voith Hydro

At Voith Hydro in Heidenheim, Germany, one of the world s leading hydroelectric equipment manufacturers, the Ocean Energies division is developing, testing and marketing tidal – stream installations. A prototype on a 1:3 scale with an out­put power of 110 kW and a rotor diameter of 5.3 m (see photo on p. 95) was installed in the winter of 2010/11 off the coast of South Korea’s Jeollanam-do Province, near the Island of Jindo. Following this test run, beginning in 2015, a large tidal-stream park with an overall output of several hundred megawatts is to be constructed.

A tidal-stream plant can be subdivided into three main functional groups: foundation, turbine, and the installation and maintenance equipment...

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