Deep-Tech Software Defining Utility Scale Solar Systems of Tomorrow

Publication highlight: A. C. J. Russell et al, “DUET: A novel energy yield model with 3-D shading for bifacial photovoltaic systems”

Our core software DUET has been under development and validation in the SUNLAB research group for the past seven years. SUNLAB is a leading solar research lab at the University of Ottawa, ON, Canada. This publication by PhD candidate and DUET developer Annie Russell is a comprehensive description of how this software works, and the value of our modeling capabilities for all stakeholders from solar asset owners to designers & engineers. All quotations and figures contained within this post are directly from this citation, which can be found below. 

DUET is a numerical PV performance software that integrates optical and electrical models to represent bifacial solar systems from a cell to system level. The optical model takes a 3D view-factor approach, supplemented by deterministic ray-object intersections to produce 2D front and rear panel nonuniform irradiance profiles. This enables our model to capture the effects of environmental objects, racking structure, and ground reflectivity on front and rear face illumination. The shading algorithm approximates objects as combinations of three primitive shapes: polygons, rectangular prisms, and cylinders.

The optical model takes into account direct, anisotropic diffuse, and reflection radiation. The deterministic ray characteristics include both static rays, where all sources and objects are stationary, and dynamic rays, where at least one of the components moves at every time step. Ground albedo inputs can be modified at each time step to represent changes in ground reflectivity depending on material, through concentric rings on a flat surface below the module under test. We are currently in the process of integrating ground terrain into this model to account for changes in illumination as a function of ground level. 

The electrical model produces current mismatch losses based on the nonuniform irradiance profiles generated by the optical model, to provide module-, string-, and array-level energy yields. IV curves are generated for each time step based on the single-diode model. Compared to 2D VF models like PVsyst, users don’t rely on loss factors to represent changes in performance across the system. Instead, DUET users “obtain array results in a computationally efficient manner by weighting M module IV curves with coefficients w from 1 to M based on the number of modules in a string”. 

One of the core crucial capabilities of DUET is its temporal specificity. Our model is able to simulate systems at any time interval, from minutes to hours, depending on available input data timesteps. This captures the temporal specificity of outputs that is lost when using annualized loss factors, providing invaluable information about site operation based on input conditions. 

“DUET provides computationally efficient bifacial performance modeling with geographic, temporal, and structural specificity—without reliance on estimated shading and electrical mismatch loss factors. The software can also be used to acquire, and better understand, such loss factors for use in other performance models or in system design optimization.”

To read more about DUET in detail, check out the full version of this open-access publication here. 

DUET Spotlight #1

System modeling is important throughout the lifetime of a solar system. From site conception, design, and operation, the model is the baseline by which stakeholders evaluate system performance. However, not all models are created equal: this introduction to DUET will teach you the differences between various optical models and explain where our software model lies in this landscape. DUET’s unique algorithm makes simulating complex bifacial designs simple and worry-free for a clear line of sight towards optimal site performance. With optimal performance comes maximum profit with minimum maintenance costs! 

Let’s start with the basics: DUET’s shining star is our bifacial modeling capability. So what exactly are bifacial solar panels?

Traditional solar panels - like the ones you see on the top of houses or buildings, are known as monofacial: light incident on only the front face of the panel produces energy. If light incident on both sides of the panel produces energy, they are known as bifacial solar panels. Bifacial solar panels are becoming increasingly prevalent in the utility-scale market segment, as their costs of production are reducing and they can increase energy yield by up to 30%. 

With these dual-sided panels comes increased modeling complexity. To effectively capture how these panels - especially the rear faces - perform in a system, models must take into account shading, racking configuration, the surrounding environment, and more. With this in mind, let’s look at some of the types of models used in the industry today. 

Ray-tracing models, exactly like they sound, break down light into rays from the light source to the objects under investigation. This method allows for multiple reflections and absorptions of a single ray [1]. Ray-tracing simulations are highly computationally expensive, although the reward of this time and power is the ability to represent complex features of the solar system including shading, and edge effects [1]. 

The primary limitations of ray-tracing models are the duration of simulations and the computational power of simulating complex systems with the specificity that is required to capture the nuance of bifacial systems. 

In contrast, view factor (V-F) models are computationally inexpensive, meaning that the system can be modeled fairly quickly and without large amounts of computational power. V-F models calculate the irradiance on solar panels through integration - they assume isotropic scattering of reflected rays [1]. However, the price of this speed is oversimplification: these models can only represent the basic geometry of solar systems, in either 2D or 3D. 

DUET is the best of both worlds: it is a numerical photovoltaic performance software that combines the computational efficiency of 3D V-F modeling with geographic and temporal specificity [2]. Our algorithm can capture the nuance of rear-side illumination through deterministic ray-object intersections [2]. DUET can model from the individual cell-level, all the way out to the full system. These capabilities are critical for an accurate assessment of the plant, including shading, time-varying albedo, and edge effects - factors that are exceptionally important for bifacial systems. 

[1] S Ayala Pelaez et al., Understanding Bifacial PV Modeling: Raytracing and View Factor Models, 2020.

[2] A. C. J. Russell et al, DUET: A Novel Energy Yield Model With 3-D Shading for Bifacial Photovoltaic Systems, 2022. 

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DUET Spotlight #1

Ray-Tracing, View-Factor, and DUET: Oh My!