Film-based optical elements for passive solar concentration in a BIPV window application

In this work, film-based optical elements are used as a passive solar concentrator for Building Integrated Photovoltaic (BIPV) window applications. Micro-facets are used to induce total internal reflection allowing window glass to function as a wave guide, thus redirecting light onto the back side of bifacial photovoltaic (BFPV) cells. Seasonal variations in the incident angle at solar noon were considered for Chicago, IL. Three optical models were developed using commercial optical software, validating that the optical elements have a significant impact on the amount of light energy allowed to reach the back side of the bifacial cell. Further, an experimental validation was conducted using two commercially available films. Using a 1:1 film to PV-cell ratio, the first film demonstrated a maximum of 26.3% increase in power on the back side of the bifacial cell. The second film type allowed a maximum of 30.2% increase. Both films allowed solar energy to reach the back side of the cell over the range of incident angles that were evaluated, making it useful as a passive solar concentrator. Finally, both 2:1 and 3:1 film to PV-cell ratios were evaluated for each of the two film types. A maximum power increase of 35.1% was observed. The results indicate that film-based optical elements have potential as a passive solar concentrator for BIPV applications.