Solar thermal tower plant (solar one)
Solar one, which operated from 1992 to 2000, was the world’s largest power tower plant. In that plant water was converted to steam in the receiver and used directly to power a conventional steam turbine. The project met most of its technical objectives by demonstrating (1) the feasibility of generating power with a power tower, (2) the ability to generate 10MWe for eight hours at summer solstice and four hours a day at winter solstice. During its final year of operation, Solar One’s availability during hours of sunshine was 96% and its annual efficiency was about 7%. (Annual efficiency was relatively low because of the plant’s small size.) The Solar One thermal storage system stored heat from solar-produced steam in a tank filled with rocks and sand using oil as a heat transfer fluid. The system extended the plant’s power capability at night and provided heat for keeping parts of the plant warm during off-hours and for morning start up.
Unfortunately, the storage system was complex and thermodynamically inefficient. While Solar One successfully demonstrated power tower technology, it also revealed the disadvantages of a water/steam system, such as the intermittent operation of the turbine due to clouds and lack of effective thermal storage.
To encourage the development of molten-salt towers, a consortium of utilities redesigned the Solar One plant to include a molten-salt heat transfer system. The goals of the redesigned plant, called Solar Two, are to validate nitrate salt technology, to reduce the technical and economic risk of power towers, and to stimulate commercialization of power tower technology. Solar Tower has produced 10 MW of electricity with enough thermal storage to continue to operate the turbine at full capacity for three hours after the sun has set. Long-term reliability is next to be proven. Solar Two was the first to be attached to a grid in early 2001.
solar thermal power plant – тепловая электростанция, работающая на солнечной энергии/солнечная тепловая электростанция
conventional – обычный, традиционный
feasibility – осуществимость, возможность выполнения, выполнимость
to generate power – производство энергии
off-hours – нерабочее время, простой
start up – разгонять, запускать
disadvantages – недостатки
intermittent operation – прерывистая работа, перемежающийся режим работы
consortium of utilities – коммунальное хозяйство, комплекс
molten-salt – расплавленная соль
a grid – энергетическая система, сеть
TEXT IV
PROPERTIES OF MATERIALS
Densityis the amount of mass per unit volume. It is measured in kilograms per cubic meter. The density of water is 1000 kg/m3, but most material have higher density and sink in water. Aluminium alloys, with typical densities around 2800 kg/m3, are considerably less dense than steel, which has typical density around 7800 kg/m3. Density is important in any application where the material must not be heavy.
Stiffness(rigidity) is a measure of resistance to deformation such as stretching or bending. The Young modulus is a measure of resistance to simple stretching or compression. It is the ratio of the applied force per unit area (stress) to the fractional elastic deformation (strain). Stiffness is important when a rigid structure is to be made.
Strengthis the force per unit area (stress) that a material can support without failing. The units are the same as those of stiffness, MN/m2, but in this case deformation is irreversible. The yield strength is the stress at which a material deforms plastically. For a metal the yield strength may be less than the fracture strength, which is the stress at which it breaks. Many materials have a higher strength in compression than tension.
Ductilityis the ability of the material to deform without breaking. One of the great advantages of metals is their property to be formed into the shape that is needed, such as car body parts. Materials that are not ductile are brittle.
Toughnessis the resistance of the material to breaking when there is a crack in it. For a material of given toughness, the stress at which it will fail is inversely proportional to the square root of the size of the largest defect. Brittle materials have low toughness: glass can be broken along a chosen line by first scratching it with diamond. Composites have considerably greater toughness than their constituent materials. The example of a very tough composite is a fiberglass that is very flexible and strong.
density – плотность
amount – количество
resistance to – устойчивость к
stiffness (rigidity) – жесткость
irreversible – необратимый
yield strength – предел текучести
stress – напряжение, давление
fracture strength – сопротивление излому/разрушению
ductility – ковкость
brittle – ломкий, хрупкий
toughness – прочность, стойкость
constituent – компонент, составляющая часть, элемент
TEXT V