Computational colour matching of laminated photovoltaic modules for building envelopes

Abstract

The widespread adoption of photovoltaics (PV) in architecture as a source of renewable energy is often limited due to poor visual acceptance. We propose the use of coloured frontglass manufactured by digital ceramic printing to cover the PV cells, thus concealing the latter while admitting sufficient light to produce electricity. The apparent colour of the PV laminate is a combination of the transparent colour on glass and the colour of the PV cells, which is difficult to predict. In this paper we compare 1400 unknown PV laminate colours with 320 known façade colours from the NCS Exterior Set to find potential matches. We use an image-based approach in which photographs are compared computationally by CIE ∆E colour difference. For a barely discernible ∆E < 3.5, this yielded 20 unique matches between the candidate and target sample sets, increasing to 74 matches for an obvious difference of ∆E ≤ 10. A subset of these computed matches was then visually confirmed by untrained volunteer observers, with average deviations of ∆E ≈ 5 between computed and visual matches, and a similar tolerance for the visual matches based on standard deviation. We conclude that our image-based computational approach enables a rapid and comprehensive matching of large sets of printed glass colours, which would be impractical with human subjects, yet delivers matches consistent with the latter's observations.