SolarThermal
Symbol |  |
|---|
Use
This model represents a scalable solar thermal collector. Solar thermal collectors use solar radiation as an environmental energy source to produce thermal energy (heat).
Parameters and Connectors
The solar thermal has to be connected with the Environment model via the ▶EnvironmentConditions to get the information about radiation and ambient temperature. The collected heat energy can be transferred and used via the ▶FlowST and ▶ReturnST connectors. The solar thermal system to be modeled should be configured using the parameter dialog. Here, the system inclination (alphaModule - 90° vertical, 0° lying flat) and orientation angle (betaModule - 0° North, 90° East, 180° South, 270° West) must be defined. It must also be set whether it is an CPC collector or flat plate collector.
The number of connected collectors (nSeries and nParallel) and the collector surface area (AModule) and liquid volume (VAbsorber) per module must also be parameterized. Note that an increased number of collectors connected in series increases collector flow temperature. Several collectors connected in parallel increase the volume flow output.
Further details must be transferred from the data sheet of the collector to the parameter dialogue, such as etaOptical, a1 and a2. The parameters alpha, tau and eps must also be overwritten. Parameters CCollector and gThermal are different. They can be used to calibrate the model to measurement data. The initial collector temperature (TCollectorInit) must also be set.
The heating medium is needed whose solidification temperature is below the minimum ambient temperature of simulated location. A mixture of water and glycol (38% glycol-water mixture is pre-defined in parameter dialog - cpMed, rhoMed) is most commonly used.
Influences of additional shading by surrounding objects (epsShading - e.g. buildings, trees etc.), dirt (epsDirt) and snow (epsCover), can be considered statistically. These factors thus stay constant over the whole simulation time period. For annual simulations, special conditions like snow lying on the collector should be defined with an appropriate correction factor. As an example, if there is snow present for 1 day a year on the collector, the corresponding correction factor should be set to 1/365.
Model Background
Heat Capacity of the Collector
The model itself calculates system states related to 1m2 collector surface area and scales these results to the defined system configuration. That is why the specific heat capacity of the collector must be parameterized with surface-area-specific heat capacity ([CCollector=J/(m2*K)). Note that in the parameter dialog, no unit is given as this unit size is not available in Modelica. This combined SI-unit parameter is normally, available in collector data sheets.
Temperature Calculation
Incidence Angle Modifier
Besides constant module parameters which can easily be extracted from collector module data sheets, the Incidence Angle Modifier (IAM) is a very important influencing value, which describes the system influences of non-vertical angles of incidence onto the collector plane. This factor is dependent on the angle of incidence in transversal and longitudinal direction and the collector design.
For flat plate collectors (left picture above) a reduction of the angle of incidence, related to the vertical, causes a decreased system efficiency (longitudinal and transversal). This is different for CPC collectors (Compound Parabolic Concentrator - right picture above). Due to their design, these types of collectors concentrate direct solar radiation. As a result, the overall system efficiency can even be increased for inclined solar radiation. If a CPC collector is to be modeled, the parameter 'CPC' should be set to 'true.' Internally, different efficiency characteristics are used for simulation.