Category Renewable Energy

Taming the Flame

by Joachim Hoffmann

Подпись:Подпись:image190"Подпись: Comparison of the masses and volumes of various fuels, in each case for a cruising range of500 km. The transparent figures represent the weight (above) and the volume (below) of the complete energy-storage system. Gaseous hydrogen (center) is under 700 bar pressure; the data are for electric-drive vehicles using fuel cells. The 6 kg of H2 required contain 200 kWh of energy and thus twice as much as the lithium-ion batteries (right). The efficiency of the batteries for charging and discharging is considerably higher than the energy conversion in the fuel cells (see also the following chapter on electricvehicles) - but at the price of a much greater weight (graphics: Adam Opel AG) [7].Подпись: Renewable Energy. Edited by R.Wengenmayr, Th. Buhrke. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The German chemist Christian Friedrich Schonbein dis­covered the basics of fuel cells as early as 1838. Since then, this technology has developed only very slowly, al­though Jules Verne recognized over a hundred years ago that, “Water is the coal of the future. The energy of tomor­row is water which has been decomposed by electrical cur­rent. The elements resulting from this decomposition, hy­drogen and oxygen, will secure the energy supply of the earth in the foreseeable future” [1].

Nevertheless, it was only the much publicized interest of the automobile industry which awakened the fuel cell

from its long sleep. Several well-known automobile manu­facturers have demonstrated the technical feasibility of fu­el-cell powered vehicles in the past decade...

Read More

Other Technologies for the Exploitation of Wave Energy

As mentioned at the beginning, there are numerous differ­ent ideas for extracting energy from ocean waves. Two of them are distinguished by their special designs. Their de­velopers are trying to take the bull by the horns and solve the main economic problem of wave energy plants: the re­quirement that the plant be able to survive “monster waves’. Both systems have been built as prototypes.

Figure 8 shows the Archimedes Waveswing. It consists of submerged cylinders which are anchored to the ocean floor; they are 21 m high and 10 m in diameter. A wave which passes above this structure gives rise to a “dynamic" variation in its buoyancy; the oscillating water flow moves the closed cylinders up and down...

Read More

Lithium-ion Batteries

Storage batteries based on lithium-ion technology have many advantages. They for example have neither a memo­ry effect like nickel-cadmium batteries, i. e. a loss of storage capacity after frequent partial discharge, nor an inertia ef­fect as in nickel-metal hydride batteries. This lazy effect’ causes the operating voltage to drop after recharging a bat­tery which was previously not fully discharged.

In particular, the high energy-storage density of the lithi­um-ion batteries, already better than all their competitors, has been doubled within less than ten years, so that they dominate the market for portable devices such as laptops or mobile telephones. For hand-held tools, such as battery-op­erated screwdrivers, a similar development is rapidly taking place...

Read More

Hydrogen: An Alternative to Fossil Fuels?

BY Detlef Stolten

In times when nuclear power in some countries is being phased out and CO2 emissions must be reduced, the path towards renewable energy sources is clearly marked out. However, due to their strong fluctuations, renewable sources can not be very readily integrated into existing energy infra­structures. Can hydrogen serve as an energy-storage medium and provide a breakthrough here?

H

ydrogen as an energy carrier was intensively discussed and investigated as early as the 1970’s, due to the two oil price crises then. However, it soon became apparent that the technology was not mature enough for widespread applications and that it would not be cost competitive. The last hydrogen projects were discontinued in the early 1990’s.

In the meantime, the situation has again c...

Read More

Applications of Fuel Cells

Fuel cells have proven their reliability for decades in space applications, which provided the stimulus for their contin­uing technical development. They became sadly notorious during the flight of Apollo 13, when a leak in an oxygen tank not only endangered the supply of breathing air for the crew, but also shut down the electrical system [4]. Anoth­er field of application, which is now well established, is as power sources for submarines. Both applications are based on very stringent requirements on the reliability of the fu­el cell systems. They are thus niches which have a negligi­ble effect on the overall energy economy, in comparison to the widespread applications of fuel cells for stationary, mo­bile, and portable power which are currently being planned.

For stationary operatio...

Read More

Can Wave Energy Soon Be Commercially Exploited?

The energy crisis in the 1970’s aroused strong interest in renewable energy sources. Thus, the use of wave energy for electric power generation, like many other renewable en­ergy sources, became the subject of intense research. After the end of the crisis, the technology was however deemed too expensive and was put aside. Only a few, for the most part Asian research institutions continued working on the topic. In Europe, this situation changed only in the 1990’s. At that time, the European Union included wave-energy conversion in the research program JOULE. A major part of the European prototypes described here are based upon this research effort. In Germany, there is no official program of research support for wave energy...

Read More

Battery Types and Characteristics

For the usual lithium storage batteries, the active material of the negative electrode (the anode for the inner-cell cir­cuit) is graphite. The positive electrode (cathode) usually contains lithium-metal oxides such as LiCoO2, LiNiO2, or

Cathode Material

Average Voltage (V)

Energy Density (Wh/kg)

LiCoO2

3.7

110-190

LiMnO2

4.0

110-120

LiFePO4

3.3

95-1 40

Li2FePO4F

3.6

70-105

LiNi1/3Co1/3Mn1/3O2

3.7

95-130

Li4Ti5O12

2.3

70- 80

Source: Leclanche SA.

TAB. 1

CATHODE MATERIALS

Подпись:the spinel LiMn2O4, with a layered structure. Depending on the material, different energy densities and cell properites (high-power or high-energy battery) result. A summary of the typical cathode materials is given in Table 1.

For further consid...

Read More

The New Scenario for Hydrogen

With regard to energy technology, hydrogen has become rel­evant again today due to environmental problems. The ex­tensive combustion of fossil fuels such as coal, petroleum and natural gas is a large-scale intervention by mankind in­to the natural balance of the earth. The global warming pro­voked by the increasing concentration of CO2 in our at­mosphere will have threatening effects if a further rise in the average temperature cannot be kept within narrow lim­its. The EU has set an ambitious goal of 2° C above the preindustrial level for this rise [4]. Today, 0.8° of this EU goal has already occurred [4], so that many countries have es­tablished climate-protection programs. They support tech­nical alternatives to an energy supply which releases large quantities of CO2...

Read More