Implement validated dynamic PVT collector model (based on EN12975 + electrical coupling)

[LoneMeertens]

Summary:
This issue tracks the implementation of a new dynamic Photovoltaic-Thermal (PVT) collector model in the IDEAS library. The model builds upon the existing EN12975 formulation for solar thermal collectors and adds a discretized, physically-coupled electrical model. This results in a fully dynamic PVT collector model that is fully compliant with ISO 9806 standards and requires only manufacturer datasheet values (no empirical fitting) for calibration and simulation.

Background and Motivation:
Current PVT implementations in Modelica typically rely on steady-state simplifications. While these may suffice for conventional (glazed) STC simulations, they fail to capture the dynamic behavior crucial to accurate PVT performance modeling, particularly in unglazed systems and varying boundary conditions.

This new model:

• Extends the existing EN12975 thermal model to include a thermal–electrical coupling via a datasheet-derived internal heat transfer coefficient (UAbsFluid),
• Uses a two-node, one-capacitance thermal model that is ISO 9806-compliant (see Figure 1),
• Calculates electrical output dynamically using the PVWatts V5 formulation,
• Requires only manufacturer datasheet parameters—no empirical parameter fitting needed,
• Has been validated against experimental data (Meertens et al., 2025).

Figure 1. Two-node, one-capacitance thermal network for PVT collectors (ISO 9806: dashed lines; extension: solid lines).

Model description:
The model includes:

• A thermal part based on a quasi-dynamic EN12975 formulation extended with wind and sky temperature terms, as described in ISO 9806.
• An electrical part using PVWatts V5, with segment-based cell temperature estimation and coupling to the thermal side through a derived UAbsFluid value.
• Automated calibration based on typical datasheet values

References:
Meertens, L., Jansen, J., Helsen, L. (2025). Development and Experimental Validation of an Unglazed Photovoltaic-Thermal Collector Modelica Model that only needs Datasheet Parameters, submitted to the 16th International Modelica & FMI Conference, Lucerne, Switzerland, Sep 8–10, 2025.