Hierarchically Textured Glass: A Solution for Improved Efficiency, Low Glare and Self-Cleaning for Solar PV Modules

Abstract

The solar PV industry has grown enormously over the course of the last decade, owing largely to the reduction of the cost of solar modules. As solar panels have become cheaper, they have been deployed more on rooftops, often at suboptimal tilt and orientation. This leads to sunlight often striking the solar panels at glancing angles which can produce significant glare as well as loss of electrical output. Glare is unpleasant and is a cause for the rejection of solar PV installations in the planning system. The electrical losses due to reflection can reach 15% for solar panels in high latitude regions which are not oriented optimally. Soiling is another issue which typically leads to 3-5% losses to output in temperate climates (more without regular cleaning) and as much as 50% losses in arid regions with fine sand and dust. The problems of glare, reflection losses and soiling can all be addressed by modifying the top glass surface of a solar panel. I used COMSOL ray tracing simulations to predict good geometries for an anti-reflective textured surface. I then made range of bio-inspired hierarchically textured glass surface with microscale pits and nanoscale pillars. These modified glass surfaces showed a 3% improvement in light transmission at normal angle of incidence (out of a maximum of 4%) as well as an incidence angle modifier (IAM) that extends out to higher angles. The surfaces were also demonstrated to reduce glare, both by reducing the total amount of reflected light and increasing the reflective haze of that light. The surfaces with glass nanopillars were also super-hydrophilic (contact angle < 5 degrees) and I was able to show that the textured glass samples facilitate the removal of fine sand when a water droplet lands on the surface. A large range of glass patterning techniques were considered, and I ultimately used hydrofluoric acid wet etching to produce the microscale pitted patterns and reactive ion dry etching to form the nanopillars. I decided to pattern glass directly instead of patterning a polymer film that could be retrofitted on a solar module. This was more challenging as there are limited patterning techniques suitable for glass. The superhydrophilic properties were achieved by texturing rather than chemically modifying the glass surface. By achieving anti-reflection and self-cleaning by texturing the glass surface my coating should be more robust than many alternative technologies.