Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar cooling at Telekom in Rottweil

The solar thermal system consists of 124 vacuum-tube collectors with a surface of 503.13 m². 62 collectors have an aperture surface of 2.034 m² each (S-POWER DF 20/2000 TPS insideS) and the other 62 have an aperture surface of 3.051 m² each (S-POWER DF 30/3000 TPS insideS). The total aperture surface thus amounts to 315.27 m². The collectors are installed on the flat roof of a production building. Their azimuth is 54° East with an inclination of 20°. The rather small angle of inclination of the collectors was chosen to avoid putting the second row in the shadow of the first. This has a positive effect, which is not least due to the azimuth of the entire collector field, as energy can still be harvested late in the day when the angle of the sun is no longer ideal. Once collector module combines one DF 20/2000 and one DF 30/3000 collector. Once collector thus consists of 60 vacuum tubes that are connected parallel. The resulting 62 collectors with an aperture surface of 5.085 m2 are also connected parallel and joined to a Tichelmann pipe network. The collector field is subdivided into two fields of the same size, one behind the other. The water glycol mixture in the collector circuit is heated by solar irradiation. It is then pumped into the basement via a heat exchanger to heat the water that is fed into the buffer storage. The storage tank has a capacity of 20 000 liters and is erected out of doors next to the building. 

In summer, solar heat is pumped from the tank to the chillers via a distributor. In winter, the heat is fed into the heating network of the building via the same distributor. Both chillers, manufactured by York International/Mitsubishi Type ES-IA 2 MW, have a cooling capacity of 340 kW each. Before the solar thermal system was set up, those two chillers were operated by the waste heat of the independent thermal power station as well as the two gas boilers. With the solar thermal power station a third heat source has become available to the absorption chillers; it not only reduced the primary consumption of energy considerably but also the costs.

A special feature of this system is the emergency chiller. It is integrated into the emergency circuit. If the system is starting to stagnate due to low heat consumption, solar heat is discharged via this emergency chiller thus avoiding excessive thermal use of the collector fluid.

An absorption chiller works as follows: similar to a compression chiller, a liquid (in this case water) is evaporated in order to generate cold. The evaporation enthalpy needed for this process is drawn from the coldwater circuit – which is to say it is cooling it down.

In order to makes sure that enough water enters the gas phase at a low temperature, the absorption chiller generates a vacuum. The evaporated chilling agent is absorbed by the lithium bromide solution. The condensation heat thus released must then be discharged via a cooling tower. 

The diluted lithium bromide solution is pumped into the extractor, where the solution is saturated again through water evaporation that is fuelled by solar heat. The solution is heated up to 99°C. Then, the water steam is cooled down in the condenser of the chiller and the condensed water is again transferred to the evaporator.

Simplified diagram of the solar thermal system in Rottweil


This table shows the most important specifications of the solar thermal system at Telekom in Rottweil

Project data
Collector/Aperture surface503 m² / 315 m²
Collector typeVacuum tubes
Buffer storage20 000 ltrs
Heat exchangerPlate heat exchanger
Azimuth/ InclinationSouth -54° / 20°

Click on the pdf-file to receive detailed information on the specifications of the solar thermal system at Telekom, Rottweil. The file also includes details of the collectors, the pipes, the carrier medium in the collector circuit and the heat exchanger between the different circuits.

Measurement Technique

The following diagram shows the system’s measurement and monitoring sensors. The monitoring sensors are essential for the functioning of the whole system; the measurement sensors are used for the extended functionality control of the solar thermal system.

Diagram of the measurement and monitoring points of the solar thermal system at Telekom, Rottweil

DATAPOOL provides access to our data server

Via DATAPOOL you can access selected data of this solar thermal system. You can choose from various illustrations like line charts, carpet plots, or scatter plots.

The solar thermal system at Telekom in Rottweil can be found on the Datapool pages under Solar Thermal Systems as far as measurement data are available for this system.

The individual measurement points of the data pool can be found in the diagram above or here.

For a list of the measurement points, click here.