OTSun, a python package for the optical analysis of solar-thermal collectors and photovoltaic cells with arbitrary geometry

Abstract

Ray tracing software systems are commonly used to analyze the optics of solar energy devices, since they allow to predict the energy gains of devices in real conditions, and also to compare them with other systems constantly emerging in the market. However, the available open-source packages apply excessive simplifications to the model of light-matter interaction, making that the optical behaviour of the systems can not be properly characterized, which in turn implies disagreements between physical experiments and computer simulations. We present here the open source python package OTSun, which applies the Fresnel equations in their most general form, without further simplifications, and is suitable for the simulation of both solar-thermal and photovoltaic systems. The geometrical objects used in this package are created using the parametric 3D modeler FreeCAD, which is also a free and open source program and allows for the construction of arbitrary geometries that can be analyzed with OTSun. These, and other software capabilities, make OTSun extremely flexible and accurate for the optical analysis of solar devices with arbitrary geometry. Additionally, OTSun has a companion webtool, OTSunWebApp, that allows for the usage of certain features of the package without the need to install anything locally. We also show here two numerical experiments that we performed in order to validate the model and implementation: The analysis of the optical efficiency of a Linear Fresnel Reflector (with moving objects), and of a second surface mirror (with variable wavelengths). In each case, the numerical computations had deviations of less than 0.25% from reference models (either computed with another program or with exact formulas).

In-Situ Solar Tower Power Plant Optimization by Differentiable Ray Tracing

“…For each ray, the intersection with the target surface x is evaluated. Up to this point, the presented ray tracing scheme is common in the domain [12][13][14][15][16][17][18][19]. A modified last step, however, is crucial to ensure differentiability of the approach.…”

“…We here present a novel machine learning solution that allows for inferring all faulty heliostat characteristics within the existing heliostat calibration infrastructure. Our technique ties in with common ray tracing approaches, but extends them by a differentiable formulation [12][13][14][15][16][17][18][19]. This allows us to define a comprehensive heliostat model which can be inferred using gradient-based optimization procedures.…”

A review of linear Fresnel primary optical design methodologies

“…The majority of optical performance studies are completed with Monte Carlo Ray Tracing (MCRT) simulations, using either commercial software such as SPRAY (Osório et al, 2016) and HFLCAL (Bode and Gauché, 2012); or publicly available software such as SolTrace (Wendelin et al, 2013), Tonatiuh (Blanco et al, 2011), OTSun (Cardona and Pujol-Nadal, 2020) and Tracer (Y. Wang et al, 2020).…”

“…Optical properties can vary angularly, thermally and based on the wavelength of the light hitting the surface. While MCRT models typically do not incorporate thermal and wavelength based variations of optical properties directly, provision is made within a number of programs to incorporate angular variations in optical properties (Cardona and Pujol-Nadal, 2020;Cardoso et al, 2018;Wendelin et al, 2013). In addition, surface errors (slope, specularity, tracking and alignment errors) affect the optical interactions within the domain.…”

“…In addition to an array of ray tracing programs, supplementary programs have been developed to assist with postprocessing (Blanco et al, 2019) and geometry visualisation within a Computer Aided Design (CAD) environment (Cardona and Pujol-Nadal, 2020;Cardoso et al, 2018). The maturity, accuracy and adaptability of the Monte Carlo Ray Tracing methodology have therefore made it the most widely used modelling tool in optical design and performance assessment for CSP applications.…”