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The image shows the air intake for a solar thermal system in Senftenberg with an output of around 5 megawatts.
© Stadtwerke Senftenberg
Calculation program for large-scale solar thermal systems
08.03.2017

Screenshot of the ScenoCalc Fernwärme 2.0 calculation software: According to the tool, a 1,000 square metre solar thermal system will deliver 405 MWh of heating energy in the assumed period from 1 January to 31 December in Würzburg.
© Solites

Predictable heat yield

The demand for large-scale solar thermal systems in district heating networks is increasing. Thereby the need for more powerful calculation programs is also increasing. Investors require predictions of the expected heat yield of solar thermal systems for their projects. A new calculation program shall now make that possible.

In order to achieve the national and international targets for climate protection and reduce CO2 emissions, the considerable potential provided by solar thermal heat needs to be exhausted. Large collector systems in the megawatt range for supporting district or process heating offer many advantages in this regard. The German Energy Efficiency Association for Heating, Cooling and Cogeneration (AGFW) forecasts a demand for 800,000 square metres of collector area in heating systems by the year 2020.
With these systems, an optimum design and operation determine the amount of energy yields or losses. A tool that predicts the results of such installations based on a generally accepted process increases both the credibility of this technology and its providers. This is a prerequisite in order to gain the confidence of investors.

Precise yield forecasts for individual collectors can be easily and uniformly ascertained using the ScenoCalc Solar Keymark certification tool. However, until now there have been no simulation tools that take into account the conditions and requirements of heating networks and which are also based on ScenoCalc. Although numerous installations for supporting heating networks also already exist abroad, especially in Denmark, and there are constantly new additions, no yield forecasting tools have been available until now that are based on this software and which provide reliable predictions.

Calculation software for large-scale solar thermal systems

Investors expect forecasts that are as accurate as possible for the expected heat yields of solar thermal systems. This is easily and uniformly possible for individual collectors. However, each of the existing simulation programs delivers different results for complete, large-scale solar thermal systems. "This is mainly due to the fact that until now there have been no easy-to-use simulation programs that fully take into account the conditions and requirements of heating networks," explains Solites Institute head Dirk Mangold. This provides the starting point for the ScenoCalc Fernwärme (District Heating) research project, or SCFW for short. The researchers have developed an open, freely available calculation program in Excel, which is based on ScenoCalc. It is used for predicting the yield and for comparing different systems for solar thermal power installations that either feed into district heating systems or are used for providing process heat.

New software utilises proven algorithm

Collector testing institutes use the ScenoCalc Excel program for producing yield forecasts when certifying collectors as part of the Solar Keymark process. The software is limited to considering single collectors and constant collector mean temperatures. In the SCFW project, in a first step the calculations carried out by ScenoCalc were transferred from macros to Excel formulae and furnished with additional functionalities that are mainly aimed at improving the ease of operation. These include the introduction of a collector database and the enhanced ability to limit calculations to a specific time window, enter hourly temperature and load profiles, or archive projects.

The scientists have expanded the tool to make it possible to calculate entire solar thermal power systems in heating networks, including the pipe systems, optional storage units, heat exchangers and with hourly variable load conditions. "In its basic version, the SCFW tool adheres strictly to the algorithms of ScenoCalc and ISO 9806, and in its expanded version it takes into account the yield-relevant effects of the overall system," says Mangold.

The solar thermal power system under consideration can be integrated centrally or decentrally into the heating network. In addition, it is possible to select the collector type, pipe systems, heat exchanger (solar circuit and network), storage unit and network. The main parameters can be defined for each component. Boundary conditions such as weather data and the thermal load of the heating network can also be determined from databases or defined by the users themselves. The results are available as hourly data for an entire year.

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