Development of high emissivity coating for flexible CIGS modules for space applications
Udayan Banik, India (EUREC 2015/16), DLR Institute of Network Energy Systems, Oldenburg
Engineering photovoltaic devices for space environment comes with totally different set of challenges compared to terrestrial applications. Materials have to be tested stringently for degradation due to charged particles, micrometeoroids, UV radiation, extreme temperature cycling, arcing, atomic oxygen etc. Irrespective of the fairly long development history of CIGS, it still hasn’t found application in space industry yet. To this date no satellites had CIGS modules as a primary power source on-board.
The temperature on solar panels in lower earth orbit varies from -120°C to +120°C due to sun’s irradiation, whereas in geostationary earth orbit it could be -150°C to +150°C. This temperature cycling can cause extreme and undesired power fluctuations in CIGS modules. Appropriate thermal management systems using high emissive thin film coatings can keep system power fluctuations at check. Having a high ε coating on the module would allow dissipation of excess heat by radiative heat transfer but it should also demonstrate properties that are suitable for solar cell operation like transparency in the visible range.
My main motivation of this PhD is to find a comprehensive coating for CIGS and demonstrate that thin film PV can be used as a dependable power generator for space applications. The coating can be easily applied by a dip coating process using a silicon-based polymer precursor solution. The optical and mechanical properties can be altered to an extent using various post-processing and curing steps. Following the development, a series of test will be carried out on such coated cells on ground to analyze beginning of life and estimate the end of life properties of the material in space. The coating will also be tested for flexibility limits, UV radiation resistance, cosmic radiation and atmospheric oxygen resistance.
My PhD work is a part of the GoSolAr mission which is a collaboration project between DLR Bremen, DLR Braunschweig and DLR Oldenburg. GoSolAr intends to demonstrate a 5m x 5m highly flexible sail or membrane structure in stowed configuration during launch, which will be deployed in space using carbon-fiber reinforced plastic booms. Photovoltaic arrays of flexible and lightweight CIGS coated modules of approx. 200 mm x 200 mm each will be fixed on the deployed sails to have a large available area for energy generation. Additionally the PV temperatures, cosmic radiation and irradiance will be observed during mission time using various sensors and telemetered back to earth for PV characterization.