Category Renewable Energy

Fuel Cells for Road Vehicles

For vehicular applications, the demands on a fuel-cell sys­tem are very rigorous. Decisive factors compared to sta­tionary applications are the desired minimal volume and weight for a given power output. Furthermore, a fuel-cell power plant must be adapted to short operating times (stop – and-go operation), which is the reason that only low-tem­perature fuel cells are suitable, due to their distinctive dy­namics. They must be ready to de­liver power within a few seconds and able to follow rapid changes in power demand during accelera­tion and braking of the vehicle.

Along with the technical hur­dles, the cost factors are most strin­gent in the vehicular applications area...

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How Expensive Would Wave Energy Be?

A rough estimate of the most important cost factors yields the following results: The price per kilowatt hour from in­stallations which are integrated into breakwaters and can therefore be favourably costed, would, according to the es­timate of Voith Hydro, be 15 N-cent/kWh [6]. This is already notably lower than the cost of photovoltaic power in the foreseeable future (see the corresponding chapters in this book).

The energy price for floating systems is in fact strong­ly dependent on the costs of underwater power cables, which are required to transport the current generated. The increasing number of offshore wind-energy parks will cer­tainly lower the production costs of these cables...

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Operating Lifetimes

Precisely with regard to cycling stability and operating life­time, one finds differing results depending on the applica­tion. While the battery is usually very deeply discharged in all-electric or plug-in hybrid vehicles, in hybrids it is more
frequently but less deeply discharged, as mentioned above [8]. Another important factor for the cycling stability of lithium-ion batteries is their operating temperature. Higher operating temperatures reduce the number of cycles that can be performed. Furthermore, the batteries lose some of their storage capacity even on the shelf – the higher the temperature, the greater this loss.

As a third factor, the charging and discharging power during operation limits the operating lifetime of the bat­tery...

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Hydrogen in the Gas Tank

As the lightest element, hydrogen has a high mass-specific energy storage density of 120 MJ/kg. This corresponds to about three times the storage density of diesel fuel, at 43 MJ/kg, referred to the so-called lower heating value. How­ever, this physically favorable property of hydrogen cannot readily be applied in a technological setting. While an automobile tank for gasoline or diesel fuel weighs about 10 kg, a pressurized gas system to store hydrogen for a cruis-

Подпись: Fig. 1 This hydrogen filling station is a demonstration project for the Clean Energy Partnership ( (photo: CEP). ing range of 500 km at today’s best technical level would weigh 125 kg (see also the diagram in the chapter on fuel cells, p. 140). The corresponding storage density of the tank plus fuel is only about 5 MJ/kg.

Even though only about 4 % of the original physical en­ergy density of hydrogen remains, the comparison to stor­age...

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Подпись: HOПодпись: HПодпись: 2image194

Fuel cells are electrochemical energy converters. They convert the energy of a chemical reaction directly, i. e. without a thermo-mechanical intermediate step, into electrical energy. Normally, in an (exothermal) chemical reaction, the electric charges (electrons) are exchanged directly between the reacting atoms or mole­cules. So, for example, hydrogen reacts sponta­neously with oxygen in the detonating gas reaction; the large amount of energy released by the oxidation of hydrogen is completely converted into thermal energy.

The trick in the fuel cell consists of not allowing the “fuel" to react directly with the atmospheric oxygen, but rather making it first give up electrons at the anode...

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Salty vs. Fresh Water

by Klaus-Viktor Peinemann

Подпись: FIG. 1Подпись: A schematic of an osmosis power plant. Salty and fresh water flows through a basin with a semiper-meable membrane. Osmosis has the effect of pushing the fresh river water into the salty seawater compartment, whereby an overpressure results. A portion of the surplus water can flow out of this compartment and drives a turbine.

One possibility of obtaining sustainable ener­gy from seawater is the use of osmosis. The key to this technology is the development of efficient membranes which allow water to pass through, but not salt.


smosis is an omnipresent process, which for example causes sausages to burst in hot water. Osmosis plays an important role in every living cell for materials trans­port, and it allows trees to pump water up to great heights. It can also be used as a source of sustainable energy every­where where fresh water flows into salty seawater at the mouths of rivers.

The Norwegian energy concern Statkraft, which has been working on the development of such osmosis power plants since 1997, estimates the global potential of this tech­nology to be in the range of 16...

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Operating Parameters

Подпись: Lead-Acid Battery NiCd NiMH Li ions Titanate Phosphate Energy density (Wh/kg) 40 45-60 80 120-200 60-80 90-110 Cycles 200-300 1000-1500 300-500 500-1000 8000 2000 Temperature range (°C) -20 - 60 -40 - 60 -20 - 60 -20 - 60 -30 - 80 -20 - 60 Self-discharge (%/month) 5 20 30 5 2 5 C-rate (power density) Very high Very high High Low Very high Very high Nominal voltage (V) 2.0 1.2 1.2 3.6 2.3 3.3 Typical charging time 2.3-2.6 V: 20 h C/10: 11 h C/4: 5 h 4.2 V: 3 h 2.8 V: 1.5 h 4.0 V: 1.5 h Output voltage (V) 1.7-1.8 1.0 1.0 3.0 1.8 2.0 C = nominal capacity of the battery. Source: Leclanche SA

The charging and discharging characteristics of the bat­teries at different temperatures and currents are particu­larly important during operation. They give a measure of the available quantity of energy – that is, how full the “tank” still is. However, only Li-ion batteries with cobalt cathodes have an approximately linear relationship be­tween the charge removed and the battery voltage; this is no longer the case for cells with lithium-iron phosphate or titanate cathodes. Their charge state is registered by the newest battery management systems using an ampere – hour counter: It determines the charge removed from the battery by integrating the current over the time of opera­tion.

Подпись: FIG. 6Подпись:Подпись:The amount of energy that can be extracted from the battery also depends strongly on its...

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The Hydrogen Infrastructure: A Roadblock?

The question arises as to whether setting up a whole new infrastructure for using hydrogen as a motor fuel does not represent a serious obstacle to its widespread use. The an­swer is given by a study which was commissioned by the

German Federal government to evaluate the marketability of fuel-cell powered vehicles, and thus paid particular at­tention to the infrastructure required [6]. A principal as­sumption of this study was that the infrastructure should be set up in several regions of high population density, where a sufficient number of vehicles could be concentrated. The hydrogen supply is to be provided using tank trucks for liq­uid hydrogen or by connecting the filling stations to the ex­isting industrial pipeline network; pipelines transport gaseous hydrogen...

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