A new DSS furnace for energy saving in the production of multi-crystalline Silicon

Due to the feedstock amount over the solar cells final cost, the production of low-cost and high quality Si in photovoltaic application is a main topic in PV industrial research. The large grained columnar poly crystalline Silicon obtained via Directional Solidification Systems (DSS) was found to be a convenient alternative to the expensive mono crystal obtained via Czochralski: production costs are much lower and the solar cells efficiency is significantly increased in comparison with the ones obtained via traditional growth. Among the main manufacturers of DSS systems the traditional resistance heating is used both in the phase of melting the raw Silicon and in the phase of re-crystallization in order to maintain the proper temperature gradient between the top and the bottom of the crucible. The induction heating technology could be a valid option, but only few manufacturers use it. In the paper a comparison between the two different technologies used in DSS for the production of columnar poly Si ingots will be presented and discussed: electric resistors and induction furnaces. The former is a well known and widely used technology. The latter is increasing in the last years. Pros and cons are considered for both systems: energy consumption during the whole process, heating up time, melting time, controlled cooling strategies, process regulation and global efficiencies are evaluated using electromagnetic and thermal simulations. The models used are based on real crucibles capacity in order to simulate processes and to compare the two different approaches. In collaboration with an Italian induction heating company a real iDSS prototype has been built and the process is going to be tested.