Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Measurement Results

The measurements described below are taken every 1-2 seconds by a data collecting device (type: HWH DL32). Normally, they are saved as 5-minute average values. Shorter saving intervals (< 5 mins) are possible; they are usually carried out to monitor the dynamic behavior of the system, e.g. during trial runs. For most of the measurement values, the system also records the minima and maxima over a 30-minute interval. These provide further information of the system’s operation. Regular controls of the minima and maxima can detect measurement errors, which might be caused by a faulty sensor. Incorrect average values can thus be singled out easily.

Intensive Measurement

In the course of the program Solarthermie-2000, an intensive measurement phase of two years is a requirement. Thereby, system values are intensively monitored and evaluated. The objective of this detailed monitoring is twofold: on the one hand, it serves to optimize the plant operation and increase the system’s efficiency, on the other, it helps to test the manufacturer’s specifications in relation to the energy yield.

The pdf documents below show the most important measurement results of the first three years of the solar thermal system for the supply of solar heat for the district heating network Holzgerlingen. These include the useable energy, the solar fraction, the system’s overall efficiency and the collector efficiency.

Specific daily averages (of weekly sums) of the radiation and useable solar energy and weekly averages of the system’s efficiency

System’s Efficiency

In the first year of measurement, a total of 84033 kWh was transferred via the heat exchanger of the collector circuit to the buffer storage (QSP). This corresponds to an irradiation on the surface of the collector field (EITK) of 352 997 kWh (1 419 kWh/m²). The energy difference between EITK and QSOL was either reflected at the collectors or emitted as thermal loss to the environment. In percentage terms, this amounts to a transfer of 23.8 % (system’s efficiency) of the total irradiation from the charging circuit to the solar storage tanks.

The diagram on the right shows the daily averages calculated by the weekly sums of irradiation and usable energy as well as the system’s efficiency. It is noticeable that the solar yield reduces with decreasing radiation and rises with increasing radiation. Towards the end of November/ beginning of December, the yield is almost 0 since the solar thermal system was not in operation at that time. 

Weekly sums of the useable solar energy, the energy for the local heating network and weekly averages of solar fraction in relation to the energy used in total.

Heat Consumption and Solar Fraction

The picture on the side shows the course of the solar fraction as related to the energy needed for feeding into the dictrict heating network. The bars show the weekly sums of useable solar energy of the solar thermal system and the corresponding energy demand of the heating network. On average, the solar fraction was 9.5 of the total heat consumption.





Further Information

Click on the pdf documents below for an overview of the results as well as more information on the energy guaranteed for the individual years.