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Virtual Solar Field (VSF)



VSF - Logo

Line focus systems, like parabolic troughs and linear Fresnel systems, are widely installed and commercially used for thermal and electrical energy production world-wide. Their economic feasibility can be further improved through, for example, improvements in solar field control and operation strategies. A possibility for achieving such improvements is by increasing the amount of the collected solar energy through the reduction of defocusing events during plant operation. Furthermore, temperature drops and pressure fluctuations in the pipe network and in the actuators play a critical role.

 

VSF - Feldschema
Schema eines Parabolrinnenfeldes wie es im Virtual Solar Field abgelegt werden kann.

 

Collector fields of existing solar power plants offer only very limited benefit for the development of new control and operation strategies. The operators of commercial power plants are often reluctant to test new strategies during the normal operation in order to not affect the planned power output and energy yield of the plant. In these cases, the Virtual Solar Field (VSF) offers unique possibilities to test new procedures to improve the plant yield before their implementation in commercial power plants.

The control strategy developed for the VSF is characterized by its robustness. It can be adapted easily for individual purposes through simple adjustments of the input parameters.

During the past years, DLR’s institute of solar research created a detailed solar field model using VSF. This model is used as a virtual test platform with the following most important features:

  • Scope
    • Representation of a whole solar field with and arbitrary number of collector loops.
    • Flexible arrangement of the loops for mapping of asymmetric collector fields
    • Detailed modelling of the distributor and collector systems
    • Applicable to single-phase heat transfer fluids
    • Collector performance data may vary temporally and spatially
  • Physical modelling
    • Transient mass and energy balance for fluid volumes in all piping sections (one-dimensional axial discretization)
    • Energy balance for the absorber tube walls
    • Calculation of the pressure losses in all piping sections and fixtures
    • Calculation of the mass flow distribution in the hydraulic network depending on the actual thermal condition of the collector loops and headers
    • Optical and thermal balancing on the receivers and isolated header pipes
    • Spatially discretized direct irradiance over the whole field according to user-defined resolution of the input data.
  • Control signals
    • Individual sun tracking signals with user-defined characteristics for each collector assembly
    • Valve travel/flap position for flow control in the subfields
    • Valve travel at the loop entrance (either static or controlled)
    • Pressure gain across solar field pumps

The presented specifications allow the simulation of a realistic representation of a whole parabolic trough field. As a result of a computationally efficient implementation, computational times of 1/100 of real-time are reached. The tool is conceived as a computation core where interfaces with many other programs are possible to establish. The department of line-focus systems uses the program for its research activities in the field of control and operation of oil- and salt-based trough systems.


Contact
Dr.-Ing. Tobias Hirsch
Team Leader System Modeling

German Aerospace Center

Institute of Solar Research
, Solar High Temperature Technologies
Stuttgart

Tel.: +49 711 6862-428

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