Bader S. Aldalali

The efficiency of PV cells is greatly affected by their operating temperatures. Depending on the locale, this change in efficiency can be significant. However, most energy yield frameworks only consider cooling by natural convection due to ambient conditions. What many of these frameworks neglect is the effect of forced convection on the temperature of the cells. In this study, PV modules are modeled numerically to quantify the effect of forced convection on the temperature and thus efficiency. The initial results show that for a typical summer day, the reduction in temperature due to forced convection-as opposed to natural convection alone-can exceed 12°C. The module efficiency increases from 15.25% to 16.53%. This 1.3% increase in efficiency is significant, and warrants reconsideration of forced convection in energy yield modeling.

We report on polydimethlysiloxane (PDMS) microlenses and microlens arrays on flat and curved substrates fabricated via a relatively simple process combining liquid-phase photopolymerization and a single molding step. The mold for the formation of the PDMS lenses is fabricated by photopolymerizing a polyacrylamide (PAAm) pre-hydrogel. The shrinkage of PAAm after its polymerization forms concave lenses. The lenses are then transferred to PDMS by a single step molding to form PDMS microlens array on a flat substrate. The PAAm concave lenses are also transferred to PDMS and another flexible polymer, Solaris, to realize artificial compound eyes. The resultant microlenses and microlens arrays possess good uniformity and optical properties. The focal length of the lenses is inversely proportional to the shrinkage time. The microlens mold can also be rehydrated to change the focal length of the ultimate PDMS microlenses. The spherical aberration is 2.85 μm and the surface roughness is on the order of 204 nm. The microlenses can resolve 10.10 line pairs per mm (lp/mm) and have an f-number range between f/2.9 and f/56.5. For the compound eye, the field of view is 113°.