Virtual Solar Field (VSF)
Virtual Solar Field (VSF) is a software tool developed by the German Aerospace Center for the simulation of parabolic trough solar fields. Improvements in solar field control and operating strategies can further increase the economic efficiency of such systems.
In parabolic trough power plants, hundreds of rows of parabolic mirrors (known as collectors) bundle sunlight and concentrate it on a heat transfer medium, generating temperatures of up to 550 degrees Celsius. Improvements in solar field control and operating strategies can further increase the economic efficiency of such systems. This is possible, for example, by reducing defocusing events (when solar radiation is not precisely aligned), thereby increasing the proportion of solar energy collected. In addition, temperature drops and pressure fluctuations in the pipe network and in the drives play a decisive role.
Optimising solar fields to increase yields
To develop and evaluate the benefits of such improvements, a precise representation of the solar field under realistic conditions is required. This can be achieved either through tests on existing power plants or through detailed modelling and simulation. Operators of commercial power plants are often reluctant to test new strategies during regular operation so as not to compromise the planned power output and energy yield of the plant. In such cases, the Virtual Solar Field (VSF) offers an effective way to test new methods for improving plant yield before implementing them in commercial systems.
The VSF simulation software can simulate large solar field systems with more than 1,000 collectors. It models the multiple lines and collectors separately. The software calculates time-dependent mass and energy balances for each flow element, while a hydraulic system solver calculates the individual mass flow distribution across the parallel circuits.
Virtual solar field for realistic solar conditions
The virtual solar field can take into account both spatial and temporal variations in solar radiation data. It provides accurate representations of solar field behaviour, for example the outlet temperatures of the heat transfer fluid from individual collectors under dynamic conditions. Researchers use the software to test control and operating strategies and virtually observe the system under realistic solar conditions. It is also possible to link the VSF model with field control software to test control strategies via a TCP/IP connection.
Key features of the virtual test platform
Scope of the model:
- Simulation of entire solar fields with any number of collector loops
- Flexible loop arrangement for modelling asymmetrical collector fields
- Detailed modelling of distributor and collector systems
- Applicable to single-phase heat transfer fluids
- Collector performance can vary spatially and temporally
Physical modelling principles:
- Transient mass and energy balance for fluid volumes in all pipe sections (one-dimensional axial discretisation)
- Energy balance for absorber pipe walls
- Calculation of pressure losses in all pipe sections and internals
- Calculation of mass flow distribution in the hydraulic network based on the actual thermal state of collector circuits and collectors as well as valve positions
- Optical and thermal balancing at collectors and insulated manifolds
- Spatially discretised direct radiation across the entire field based on user-defined input resolution
Control options:
- Individual sun tracking signals with customised properties for each collector assembly
- Valve lift/flap position for flow control in the subfields
- Valve lift at input for each circuit (either static or controlled)
- Pressure boosting via solar field pumps
- TCP/IP interfaces with external simulation management tools
Facts about the software:
- Simulation software written in C++
- Depicts several hundred solar collectors in individually modelled sections
- Coupled hydraulic and thermal equation solver
- Multiple spatially discretised elements per collector
- Simulation speeds of up to 100 times faster than real time
- Can be linked to various other programmes
Possible applications:
- Investigation of the behaviour of larger collector fields over time
- Analysis of the effects of cloud movement on system performance
- Development of control and operational strategies
- Testing of solar field control systems
- Configuration of control parameters and components before commissioning
- Simulation for plant monitoring
The partner RenoGreen Energy distributes the Virtual Solar Field software. The Institute of Solar Research uses the software in its own research projects in collaboration with industrial partners.