Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Measurement results

The measurements are taken every 10 seconds by a data collecting device (type: Schuehle, MAC 19). Normally, they are saved as 5-minute average values. Other saving intervals are possible. 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 faulty sensors. Incorrect average values can thus be singled out easily. Figure 5.1. and the Tables 5.1. and 5.2. provide an overview of the recorded data. The data logger records power (kW), volume flow (m³/h) and temperatures (°C) every 10 seconds, as well as the total operating hours every 2 seconds. All the values are saved every 5 minutes.

Intensive Measurement

In the course of the program Solarthemie-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 two years of the solar thermal system of the apartment complex on Wilmersdorferstraβe 3 and 5. These include the useable solar energy, the solar fraction, the system’s overall efficiency and the collector efficiency.

Specific daily sums of the radiation and useable solar energy (averaged over weekly sums) and weekly averages of the system’s efficiency (1st year of intensive measurement)
Specific daily sums of the radiation and useable solar energy (averaged over weekly sums) and weekly averages of the system’s efficiency (2nd year of intensive measurement)

System’s Efficiency

In the first year of measurement, a total of 127207 kWh was transferred via the heat exchanger of the collector circuit to the buffer storage (QSP) (secondary circuit). This corresponds to an irradiation on the surface of the collector field (EITK) of 311206 kWh or 1634 kWh/m² respectively.

In the second year of measurement, the irradiation on the surface of the collector field amounted to 317698 kWh respectively 1392 kWh/m² (+ 2,1 %). Out of these, 128121 kWh were fed into the buffer storage (QSP). 

The energy difference between EITK and QSP was either reflected at the collectors or emitted as thermal loss to the environment. In percentage terms, this amounts to a transfer of 40.9  % of the total irradiation to the loading of the solar storage in the first year and of 40.3 % (collector circuit efficiency) in the second. 

The usable solar energy from the solar thermal system (QSV), i.e. the energy transferred from the solar reservoir to the potable water via heat exchanger, was 122 472 kWh (537 kWh/m² or 1.47 kWh(m²d))  in the first year and 123 945 kWh (543 kWh/m² or 1.49 kWh/(m²d)) in the second. 

The system’s efficiency thus lay at 39.4 % in the first year and 39.0 % in the second.

The pictures on the side show the exact daily sums of irradiation and the usable solar energy as well as the system efficiency (averaged over the weekly sums and weekly averages).

Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used (1st year of intensive measurement)
Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used(2nd year of intensive measurement)
Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used and circulation (1st year of intensive measurement)
Weekly sums of the useable solar energy, energy for warm water heating and the weekly averages of solar fraction in relation to the energy of the water used and circulation (2nd year of intensive measurement)

Heat Consumption and Solar Fraction

With the usable solar energy, supplied by the solar thermal system, 41.7 % of the required energy for the warm water could be covered in the first year of measurement, and 42.9 % in the second (solar fraction of the amount of warm water used)

The two diagrams on the side (top) show the solar fraction as related to the energy requirement for warm water consumption. The bars show the weekly sums of usable solar energy of the solar thermal system and the corresponding energy demand for warm water consumption only, i.e. without taking circulation losses into account. 

When taking the circulation loss of 297824 kWh (1st year) 306567 kWh (2nd year) into account, the solar fraction amounts to 20.7 % and 20.8 % respectively (solar fraction of the energy required for warm water consumption and the energy covering the circulation loss).

The two diagrams on the bottom show the solar fraction in relation to the energy of the water used and the energy covering the circulation loss.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

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