| Work Detail |
Danish scientists have examined three facades installed on a mobile office container to conduct experiments on building-integrated photovoltaics.
Researchers at the Technical University of Denmark (DTU) built a building-integrated photovoltaics (BIPV) test facility and monitored it for a year to analyse the performance of different types of panels. They focused on BIPVs of different colours and rear-vent configurations. The test facility also included a section with differently structured front glass and a module with rear-contact cells (IBC), the results of which will be published later.
“The base structure consists of a mobile office container with a footprint of about 3 × 9 m. Prefabricated curtain wall elements consisting of an aluminium frame with 200 mm of mineral wool insulation were subsequently mounted as the outer wall,” the researchers explained. “In the elements on which rear-ventilated PV modules are mounted, a thin fibre cement board provides wind and weather protection for the insulation material. Unventilated PV modules are mounted directly touching the insulation as a rain screen, fixed with aluminium frames integrated into the curtain wall structure.”
Sixteen non-ventilated modules were mounted on the south side of the container to test the effect of ventilation. In the modules without rear ventilation, the distance to the insulation varied between 0, 10, 20 and 30 mm. The modules with rear ventilation were mounted on horizontal supports, with air gaps of 50, 100, 150 and 200 mm for natural rear ventilation.
Five different coloured modules and one reference module without an air gap were installed on the west façade. For these, coloured interlayers based on pigments were laminated with an additional encapsulating layer between the cellular matrix and the front glass. The colours used were red, grey, green, beige and terracotta. The panels were monitored between 1 September 2022 and 30 August 2023.
“On the west façade, the reference and green modules have the lowest annual CC performance ratios (PR) of 0.86, grey, beige and terracotta have slightly higher annual CC PRs of 0.88 to 0.89, while the red module has a considerably higher annual CC PR of 0.95,” the academics said. “The higher PR of the red module can be partly attributed to spectral mismatch gains in the afternoon, which can amount to up to 10% at night.”
An analysis of the operating temperatures of the south façade showed that the temperature difference with the ambient was 40% to 50% lower in the rear-ventilated externally mounted modules than in the insulated modules. The annual coefficient of efficiency of the better ventilated modules was found to be 6% higher on average.
After obtaining results from both the ventilated and non-ventilated sides of the container, the same façade was simulated in the National Renewable Energy Laboratory’s (NREL) System Advisor Model (SAM) in an attempt to identify errors in the models that this software contracts. “Four scenarios were simulated using data from modules S2 (top insulated), S6 (bottom insulated), S9 (top with 200 mm air gap), and S13 (bottom with 200 mm air gap), as these represent the most extreme mounting configurations for both the top and bottom rows,” they explained.
The results showed acceptable agreement between modeled and measured data for irradiance, except for some morning and afternoon periods.
“Regarding operating temperatures, SAM is able to predict the temperature of ventilated modules fairly well on clear days; however, for isolated modules, the modelled temperature can be about 10 K lower than the measured one,” they conclude. “On intermittently cloudy days, the model performs significantly worse, although the transient thermal model correction in SAM reduces the error. Finally, for DC performance, a general overestimation by SAM was observed, which is significantly higher in winter than in summer months.”
Their findings were presented in “ Yield analysis of a BIPV façade prototype installation,” published in Energy & Buildings . The underlying dataset is being published for researchers to use in model validation. |
