Table 2 gives a summary of the investment cost for the heat supply system. For the ATES a specific cost of 39 Euro/m3 water equivalent can be calculated (without VAT, including design). This is very favourable compared to other types of seasonal heat stores that have been built in Germany /3/.

Based on the given cost, with operational cost and maintenance included, and the solar heat delivery from the year 2003 the solar heat cost turns out to 26 Ct./kWh (calculation according to VDI-Guideline 2067, interest rate 6 %, life time for solar collectors 20 years, life time for the ATES 40 years).

Conclusions

The demonstration plant in Rostock is the first central solar heating plant with a seasonal aquifer thermal energy store in Germany. The results of the first four years of operation prove the technical feasibility and reliability of all components of the heat supply system. With a solar fraction of 49 % in the year 2003 the design target was reached after some improvements in the hydraulic adjustments and the control system.

Acknowledgements

This work was financially supported by the Federal Ministry of Economics and Labour and the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Project No. 0329606S and 0329607F. The authors gratefully acknowledge this support. The authors themselves carry the responsibility for the content of this paper.

References

/1/ M. Benner, M. Bodmann, D. Mangold, J. Nuftbicker, S. Raab, T. Schmidt, H. Seiwald: Solar unterstutzte Nahwarmeversorgung mit und ohne Langzeit-Warmespeicher (Nov. 1998 bis Jan. 2003); Report to the Research Project 0329606S (solar assisted district heating with and without seasonal heat storage, in German), ISBN 3-9805274-2-5, University of Stuttgart, 2004

/2/ J. Bartels, F. Kabus, T. Schmidt: Seasonal Aquifer Solar Heat Storage at Rostock — Brinckmanshohe — First Operational Experience and Aquifer Simulation; Futurestock 2003 9th International Conference on Thermal Energy Storage, Warsaw, Poland /3/ T. Schmidt, D. Mangold, H. Muller-Steinhagen: Seasonal Thermal Energy Storage in Germany, ISES Solar World Congress 2003, Gothenburg, Sweden