This component computes the electrical power output of a photovoltaic-thermal (PVT) collector using the PVWatts v5 methodology (Dobos, 2014), adapted for PVT systems. It is part of a validated, open-source Modelica implementation that relies solely on manufacturer datasheet parameters, as described in Meertens et al. (2025).
The model calculates the electrical output for each segment i ∈ {1, ..., nseg} as:
Pel,i = (Ac / nseg) · (Pnom / A) · (Gtilt / Gnom) · (1 + γ · ΔTi) · (1 - eleLosFac)
where:
The PV cell temperature is estimated from the fluid temperature and thermal power density using:
Tcell,i = Tm,i + qth,i / UAbsFluid
The internal heat transfer coefficient UAbsFluid is approximately calculated from datasheet parameters. For the mathematical description and visualisation, see IDEAS.Fluid.PVTCollectors.UsersGuide.
The electrical submodel includes an overall system loss factor
eleLosFac. PVWatts reports a total electrical power
loss of 14%, resulting from the following mechanisms:
| Electrical power loss mechanism | Default value |
|---|---|
| Soiling | 2 % |
| Shading | 3 % |
| Mismatch | 2 % |
| Wiring | 2 % |
| Connections | 0.5 % |
| Light‑induced degradation | 1.5 % |
| Nameplate rating | 1 % |
| Availability | 3 % |
| Total | 14 % |
For well-maintained, unshaded modules, experimental validation
(Meertens et al., 2025) found that using eleLosFac =
9% gives excellent agreement with measured electrical
output. For PVT collectors with a high positive tolerance on the
electrical output, this system loss factor can even be lower. Users
may adjust eleLosFac to account for site-specific
soiling or shading effects.
This model is designed for (unglazed) PVT collectors and supports discretization into multiple segments to capture temperature gradients along the flow path. It is compatible with the thermal model based on ISO 9806:2013 and is suitable for dynamic simulations where irradiance and fluid temperatures vary over time.