In the current paper parabolic trough collectors with direct solar steam generation are employed to supply steam to the preheating section of a conventional power plant. Although other solar thermal concepts feature higher concentration factors and higher system efficiencies the parabolic trough technology has been chosen because it is a proven technology which has demonstated its reliability in large scale applica­tions (80-100MW) [1].

Tracking the sun from sunrise to sunset the cylindrical parabolic mirrors concentrate the sun’s radiation on the black absorber tubes along their focal line transforming ra­
diation into heat. In these absorber tubes water gets vaporized and superheated to temperatures of more than 400°C.

Figure 2 shows a typical parabolic trough collector. The aperture area is about 545 m2 with a length of 99 m and the reflectivity is more than 97%. [7].

Favourable locations within Europe to operate solar power plants are southern coun­tries like Spain, Italy or Greece. Because of the italian legislation having a special interest in promoting renewable energy sources the location Greater Bari in south Italy was chosen. The yearly global irradiance is about 1600-1750 kWh/m2a and the yearly direct normal irradiance, that is used by the parabolic trough collectors, is up to 2200 kWh/m2a.

In order to design and simulate a parabolic trough collector the monthly average val­ues of irradiation were chosen at first. In figure 3 the average direct normal irradiance of the last ten years in greater Bari can be seen exemplarily for the months January, July and October. The highest maximum irradiance occurs in July at noon (884 W/m2) and the lowest is observed in January (349 W/m2).

The parabolic trough collector plant which is the basis for the current study is not an existing one but is an approach to similar existing plants and investigations in the field of direct solar steam generation [1].

Figure 3: Average direct normal irradiance in Greater Bari