Development and optimization of a parabolic trough solar collector for generation of process heat for industrial processes
In 1998, industrial process heat accounted for 21% of the Austrian final energy consumption. Only 12% of this is currently supplied from renewable energy sources. Process heat up to a temperature level of approx. 100°C can be supplied by solar collectors currently on the mar¬ket such as flat plate or evacuated tube collectors. A large share of the process heat is needed at a temperature level between 100°C and 200°C, for example in the food, textile and chemical industry. However, these temperature levels can only be reached with concen¬trating solar collectors as heat losses of conventional collectors increase dramatically at these temperatures. This leads to very low collector efficiencies.
In the present project, a small-scale and low-cost concentrating parabolic trough collector will be developed. A small-scale collector that can be installed without the need of heavy equip¬ment and that can also be installed on factory roofs due to its small size and low weight, is a novelty in solar engineering.
The operating characteristics of the first prototype, manufactured by the company Knopf Design, Vienna (Austria), were measured at the test facility of AEE INTEC in Gleisdorf (Austria). The main goal of these tests was to determine the optical and thermal efficiency of the prototype. The optical efficiency of the first prototype (at just below 50%) was still too low to compete with conventional collectors. Measurements of the radiation intensity in the focal line of the collector led to the conclusion that one of the main reasons for the relatively low optical efficiency was the poor positioning of the receiver tube. This and other improvements were incorporated in the second prototype by Knopf Design and, consequently, tested at the test facility in Gleisdorf. The optical efficiency has been improved from about 50% to about 60%.
Based on the measurement results of the prototypes, possible system concepts (including collector, heat transfer to the consumer, connection to the existing heat supply system and storage, if necessary) have been drawn up. 6 basic system concepts were identified. Depending on the application (load profile, desired solar fraction etc.) one of these concepts has to be chosen.
One application has been set up at a laboratory scale at the test facility. The setup will include a realistic heat consumption pattern. During the operation of this test facility, experience with the operation and, especially, possible control strategies of a parabolic trough collector system were gained.
These experiences were used to work out a case study for supplying process heat with the parabolic trough system to a selected industry. In the case study, a parabolic trough collector system was compared to a ‘conventional' evacuated tube collector system. This allowed to get an idea from which temperature level a parabolic trough collector system is energetically better than evacuated tube collectors that are currently on the market. The results show that at operating temperature of 100°C parabolic trough collectors and evacuated tube collectors have a similar annual solar gain. Because of the fairly complex tracking system of parabolic trough collectors, evacuated tube collectors will be used in most applications. But already at temperatures as low as 120°C parabolic trough collectors have significant advantages.
In parallel to the collector development, a study has been carried out that identifies storage concepts that are suitable to store heat at a temperature level up to 300°C. A survey of these storage technologies has already been completed. In the second part of the study the technologies that are appropriate for use in industrial applications were identified.
Dipl.-Ing. Dagmar Jähnig
Arbeitsgemeinschaft ERNEUERBARE ENERGIE - Institut für Nachhaltige Technologien
Project or cooperation partner
- IMG - Innovation Management Group GmbH
DI Dr. Manfred Peritsch
Technologiepark, Parkring 2, A-8074 Graz - Grambach
Tel.: +43 (0)676 84846464-6
Fax: +43 (0)1 959591064-6
- Knopf Design
Ing. Richard Matthias Knopf
Gurkgasse 16, A-1140 Wien
Tel.: +43 (0)1 9833046
Fax: +43 (0)1 9831202
Feldgasse 19, A-8200 Gleisdorf
Tel.: +43 (0)3112 5886 28
Fax: +43 (0)3112 5886 18