Category Renewable Energy

BY KAI-UWE GRAW

An old dream of humanity is to make use of the almost im­measurable energy of ocean waves. Their destructive power has however up to now not permitted any economically rea­sonable design to survive for long, although there have been many promising attempts and approaches.

he reduction in carbon dioxide emissions, which is in­creasingly urgent and is a major goal of governments and societies, has conferred a new significance on wave en­ergy – as on all renewable energy sources. Interest in wave energy power plants, which could make appreciable con­tributions to the world’s energy supply, is steadily growing. The use of wave energy for generating electric power has been under investigation for many decades...

The MCFC takes its name from its electrolyte of alkali car­bonates, which is used in molten form at the operating tem­perature of 650° C. The electric current is carried in the electrolyte by carbonate (CO32-) ions. Maintaining the charge transport within the electrolyte thus requires CO2 circulation between the fuel gas used and the air, which is usually achieved by using the CO2-containing anode ex­haust gas. The peripheral system components such as con­necting tubes and heat exchangers require only a limited high-temperature serviceability; however, the extremely ag-

TYPES OF FUEL CELLS

Fuel cells can be classified as low – temperature and high-temperature cells...

At present, the power consumers in the EU-MENA countries have no other choice but to pay the steadily-increasing price of power from fossil and nuclear fuels. This situation is ex­acerbated by the fact that fossil and nuclear fuels tech­nologies today still receive ca. 75 % of all public subsidies for the energy sector. This figure would increase to over 90 % if external costs were also counted as hidden subsidies.

On the other hand, a number of sustainable-energy tech­nologies are available (see the downloadable table at www. phiuz. de special features/Zusatzmaterial zu den Heften). Some of them produce energy on a fluctuating ba­sis, for example wind energy and photovoltaic installations, while others could provide both peak-load and base-load power as needed...

by Roland Wengenmayr

Large buildings full of people and machines that are sources of heat are a challenge to air-conditioning engineers. This is especially true of alternative designs, which dispense with energy-consuming air conditioning and make the most of natural resources such as winds and the chimney effect.

arge buildings often present a challenge for providing a comfortable climate to the inhabitants. Their extensive glass facades turn them into greenhouses on sunny days. The heat output of human beings is also a factor which is not to be underestimated when many people occupy a building; furthermore, one must not forget the energy out­put from technical equipment such as computers...

The technology of aquifers as energy storage systems is in many respects closely related to hydrothermal-geothermal energy. The storage medium is the natural substratum, i. e. the rock layers and the deep water they contain; the latter also serves as heat-transport medium. Aquifer storage sys­tems are as a rule accessed via two boreholes or groups of boreholes. These are placed at a certain distance from each other, in order to avoid mutual thermal influences. The sys­tems are open below ground and closed above ground. Above ground is a heat exchange apparatus, so that only en­ergy transport – and no matter transport – occurs.

Both boreholes are fitted out with pumps and injection piping, which allows the flow of the heat-transport medi­um in the above-ground part of the plant to pass t...

Beginning in 1986, a simply-constructed wave power plant was built in Norway, where it was operated for about twelve years. The plant was on the island of Toftestallen near Bergen, and it was intended as a demonstration project for interested groups. The TAPCHAN (TAPered CHANnel) di­rects the water from the incoming waves into a channel which rises and narrows, then empties into a raised basin. The water then flows steadily from this reservoir back to the ocean. In the process, it can power a conventional low – pressure turbine. The channel of the prototype plant had a 60 m wide opening on the incoming wave side and was be­tween 6 und 7 m deep. The reservoir was at a height of 3 m above sea level...

In the SOFC, a thin ceramic layer of yttrium-oxide-doped zir­conium oxide (YSZ) serves as electrolyte, allowing the pas­sage of oxygen anions at its operating temperature of 900 to 1000° C.

The power output of the systems currently being test­ed ranges from one kilowatt for household energy provision using natural gas up to a pressure-driven 200 kW unit. The latter can be hybridized with a gas turbine. The expected electrical efficiency is in the range of 70 % – thus far, 53 % has been measured.

Marketing of the SOFC technology is to be expected only in the longer term, in spite of the performance already achieved and the attractive perspectives for the future...

Steam and gas turbines powered by coal, uranium, oil and natural gas are today’s guarantees of power-grid stability. They provide base-load and peak-load power. However, tur­bines can also be operated with high-temperature heat from concentrating solar collector fields (Figure 5). Solar thermal power plants of this type with 30 to 80 MW output power have already been operating successfully in California for over 20 years, and new plants are being constructed right now in the USA, Spain and other countries, with up to 1000 MW of output power. By 2015, as much as 10 GW of solar-thermal power capacity could be installed worldwide, and by 2025, even 60 to 100 GW At present, nearly 1 GW is online. According to a current study, today’s solar energy price of 27 €-ct...