Silicone Coatings: An Anti-Aging Elixir for Solar Cells
Sometimes, the success or failure of a technology comes down to a bare handful of cents. As industry observers have noted, as long as solar power is more expensive than conventional fossil fuel energy, it will not be competitive in the free market, regardless of how large—or small—the price difference may be. “Both in Germany and the United States, power generated from solar energy is still dependent on government subsidies”, notes Dr. Christian Hoepfner, Scientific Director of Fraunhofer CSE. “If we want renewable energies to prevail globally in the long run, we need to lower their prices considerably.” There is no “magic bullet” for achieving this goal—the production of solar PV modules is expensive and their efficiency limited. This is why engineers from all over the world are actively seeking new techniques and production methods to decrease cell and module prices while simultaneously increasing their effectiveness, resistance and reliability.
Silicones: stable and resilient
One promising avenue for research is silicone, a hybrid material that is closely related to crystals and plastics without firmly falling into either category. At current, the solar industry uses silicone predominantly for PV module encapsulation. However, to date there have been no major attempts to apply silicone to the lamination process. During lamination, the fragile silicon wafers responsible for actually generating power in the solar module are surrounded with a protective layer; in most cases, manufacturers use a material known as ethylene vinyl acetate (EVA) for this purpose.
Could silicone serve as an EVA substitute in lamination? To address this question, a team of Fraunhofer CSE researchers teamed up with Dow Corning, the world leader in silicone applications in medical engineering, cosmetics, automobiles, paper conversion and electronics. At CSE’s module fabrication facility, CSE experts covered solar PV cells with a layer of liquid silicone. Fraunhofer CSE project manager Dr. Rafal Mickiewicz explains: “As soon as the liquid silicone hardens, it seals the cells, and therefore provides optimal protection for the electronic components.” The CSE team used these silicone-laminated cells to build prototype PV solar modules, then tested them in a climate chamber at low temperatures under cyclic mechanical loading conditions. Finally, they assessed module durability, using electroluminescence to search for micro-fractures caused by the temperature and mechanical stresses. The end result: compared to conventional solar modules, the silicone-covered PV module was much more likely to stand up the damage caused by extreme weather conditions (e.g. wind, cold).
CSE Intern John Lloyd loads a solar module into a mechanical test stand. This device, developed at CSE, allows researchers to measure the impact of mechanical stress and strain during climate tests. Image courtesy of Daniel Downs.
“Dow Corning Corporation has collaborated with Fraunhofer CSE for two years. This interaction has significantly strengthened our understanding of the material requirements in PV modules, especially in areas of overall module durability and performance”, says Andy Goodwin, Global Science & Technology Manager at Dow Corning Solar Solutions.
The results of the tests were finalized and presented at the 26th European Photovoltaic Solar Energy Conference 2011. As Dr. Mickiewicz notes, “our results demonstrate that a lamination process using silicones is suited for many different applications because the silicone protects the fragile components inside the module and is able to stand up to severe temperature fluctuations. One possible application would involve creating more robust thin solar PV modules.”
For more information: http://cse.fraunhofer.org/