December 2013 saw the launch of the online calculator for solar thermal district heating systems. Its basic analysis helps users to determine whether a solar district heating system could be an interesting choice for a given project. The German Heat & Power Association, AGFW, provided information about the target group’s requirements for such a tool. The calculator was developed by Solites, Germany, and financed by the German Federal Environment Ministry under the Intelligent Energy Europe (IEE) project SDHtake-off and a national project for multi-purpose heat storage systems.
“Our target group consists of potential users of solar district heating, such as municipalities or district heating operators, in the concept phase of a new district heating system. They can use the online tool to support their decision-making process with some hard data, for example, by entering the size and orientation of the collector field, as well as the operation temperatures of the heating network, etc,” Thomas Schmidt from the Solites institute says. Schmidt was responsible for developing the tool.
The tool’s calculation results show solar-specific data, such as yield and required storage volume, but also grid losses and needed backup heating capacity. In addition, the tool also calculates the system’s economics. They include the overall investment costs, the solar heat generation costs that take the plant’s and storage unit’s total costs into account, as well as the specific interest rate.
Online calculator based on 250,000 TRNSYS simulations
The online calculator is based on the results of more than 250,000 dynamic TRNSYS simulations carried out by Solites and stored in a database. Extrapolations are performed whenever the database cannot provide an exact match for the entered information. Solites opted for this compromise, because as precise as dynamic TRNSYS simulations may be, they require a lot of computing time and are also complicated to use.
In contrast, the calculator itself is easy to understand and only requires some basic choices from a slide menu. Users can select either a central solar heating system with a buried storage tank or a distributed solar heating system which feeds into a heating network of ideal, unlimited size. They can also pick one of six locations (three of them in Germany), choose the collector type, the area, the azimuth and the slope and enter a combination of feed and return temperatures. In case of a central system with a storage unit, users can additionally type in the storage volume per m2 of collector area and give information about the total heat demand. The tool does not yet include other seasonal heat storage designs, such as borehole heat storage, but these might be added later.
This text was written by Eva Augsten, a German freelance journalist specialised in renewable energies (augsten(@)solrico.com).