The parabolic-trough collector field, which is installed in the outdoor laboratory area of SESL/NCSR-D in Agia Paraskevi, Attica.
1. General Information
For the concentrating-solar “Archimedes’ infrastructure, parabolic-trough collectors (PTC) were selected, equipped with a receiver tube carrying a selective absorbing surface and located at the linear focus of the parabolic mirrors.
The array comprises two units, with a total length of 20 m each and with a mirror aperture of 2.4 m, connected in series and the collectors are compatible with thermal oil used as the working, heat-carrying fluid.
The reflecting surface of the parabolic mirrors is made of low-iron, hardened glass, with high durability in adverse weather conditions.
The total thermal output of the collectors under reference conditions (e.g., direct normal irradiation of 900 W/m2, average working fluid (thermal oil) temperature of 150°C and ambient temperature of 30°C) amounts to 46 kWthermal.
The maximum allowable temperature of the working fluid is 250 °C, whereas the maximum allowable pressure is 9 bar.
2. The Overall Installation
The thermal energy produced feeds a suitable storage tank of 2 m3 volume, using a solid storage medium (magnetite), as described in the Thermal Energy Storage section of this site.
In the picture below, a schematic depiction of the PTC array is shown, along with the primary hydraulic loop connecting it to the
other subsystems as well as the secondary loop of the storage tank.
3. The different stages of construction
In the pictures below, two characteristic phases during the construction of the parabolic-collector field are illustrated. In the first one, the position of the footings and the metallic supports of the collectors are depicted,
while in the second one the metal frame on which the reflecting surface mirrors are mounted is shown.
4. Theoretical Investigation – Estimation of efficiency and characteristic equation of a parabolic-trough system
Parallel to experimental measurements conducted on the installation described above, at SESL simulations models are also developed, aiming at parametrically investigating the effect of operating conditions on the collector efficiency.
As a typical example, the results of
a relevant recent study may be mentioned, within which a considerable number of numerical experiments were carried out, based on optical and thermal analysis models. This aimed at deriving a suitable form for the characteristic equation, which could be used for estimating the efficiency of parabolic-trough collectors.
The major results of this investigation have been included in the following paper published in an international journal :
Vouros A., Mathioulakis E., Papanikolaou E., Belessiotis V., “Modelling the overall efficiency of parabolic trough collectors”, Sustainable Energy Technologies and Assessments, vol. 40, art. no. 100756, 2020,
https://doi.org/10.1016/j.seta.2020.100756 .
