Researchers at Spain's Technical University of Madrid (UPM) developed a model framework to simulate the performance of vehicle integrated photovoltaic (VIPV) modules under realistic dynamic shading and seasonal conditions. The demonstrator model, based on Madrid urban conditions, is able to calculate yields but can also be used to evaluate alternative maximum power point tracking (MPPT) algorithms.
The team combined simulation with high-resolution video recordings of pre-defined and characterized routes captured at different times of the year to include seasonal variability and daily variability. These were supplemented with meteorological data, vehicle positions and orientation, to estimate irradiance distribution affecting simulated PV modules.
“The novelty of the vehicle-integrated photovoltaic (VIPV) study is its focus on using the same routes across seasons to understand the variation in irradiance patterns to be able to calculate the energy yield of VIPV modules in the same landscape,” Ricardo Moruno Lobato, corresponding author of the research, told pv magazine. “Given the high speed of light fluctuations, we used a high frames per second (fps) camera to record a video of the shading profiles and then simulated a PV module under those same shading profiles to evaluate its behavior.”
The recording had a frame rate of 240 fps. The simulated PV module was small-sized to represent one submodule of a larger system that could follow a distributed MPPT layout in which “every submodule is linked to its own DC/DC converter with independent MPPT algorithms,” according to the research team.
Images were captured, transformed, segmented and converted into a temporal sequence of matrixes of the shadows cast on each of the module's cells, according to the research. The framework integrated dynamic shading, irradiance and thermal modelling, estimation of I-V curves, and electrical simulation of two common interconnection schemes, series and total-cross-tied (TCT).
The researchers evaluated the yield over five different routes near the UPM campus. Three routes in winter: morning (W-M), midday (W-Mid), and afternoon (W-A), and two in summer: morning (S-M) and afternoon (S-A). The routes followed similar sequences and distances to ensure comparability, according to the study. In addition, four pre-defined zones were included: dense trees, scattered trees, open low-rise, and open midrise to reflect the roadside foliage and height of the buildings.
“Regarding the electrical model, we used a two-diode model, although similar results can be achieved with single diode,” said Moruno Lobato. He also said that the team's use of a “simplified flat plank thermal model” to cover general trends, but noted that reality an improved model is necessary to be validated with experimental data.
Once the complete sequence of I-V curves was available, an ideal or lossless DC-DC converter with an integrated MPPT algorithm was simulated. Three MPPT algorithms were assessed: fixed-voltage control; Perturb & Observe (P&O) and artificial neural network (ANN).
“Results indicated that, if properly tuned, the P&O algorithm can achieve efficiency levels comparable to those of conventional PV applications for a substantial portion of the total energy harvested during vehicle motion,” explained Moruno Lobato. “Scenarios where dynamic conditions significantly hinder its performance, and where an ANN-based method might offer an advantage, represent only a minor share of the total potential energy along a route in most cases (11-38%), with the exception of W-Mid route (57%).”
They also said that “significant zonal and seasonal variations” affect the module's performance, and that the main factor “hindering the performance ratio is the shading factor, relegating other factors to a secondary role.”
The researchers concluded that their framework supports the simulation of different cell-interconnection schemes and MPPT algorithms under identical irradiance and temperature conditions. “Moreover, it provides access to the spatiotemporal evolution of shadow shapes and their distribution across categorized urban environments, representing a significant advancement for the analysis of realistic dynamic shading in VIPV applications,” they said.
Additional results and details of the study are provided in “Comprehensive VIPV energy yield and MPPT evaluation under realistic dynamic shading in urban environments,” in Solar Energy Materials and Solar Cells. Also participating in the study was a team from Solar Added Value, a UPM spinoff company.
Noting that the outcome of the study may “provide key data for forthcoming VIPV studies,” Moruno Lobato said that the research group is working on the evaluation of VIPV for buses based on irradiance sensor data from several bus lines in Madrid.
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