Seung Bum Rim

Generation III high efficiency lower cost technology: Transition to full scale manufacturing

This paper reports on the first large scale manufacturing of Gen III solar cells. The Gen III product has been designed to deliver increased performance and lower cost throughout the value chain. Reduced emitter recombination is the key feature to deliver the efficiency improvement. Gen III is now ramping on a production line in SunPowers Philippines manufacturing plant. Production run median efficiency is 23.6%. Total area module efficiency is 21.2 %. The Gen III solar cell architecture has a low breakdown voltage in reverse, which minimizes power loss and wear on module materials under shaded conditions.

Temperature of solder contact in back-contact Si solar cells and its effect on reliability of modules under localized shading environments

Reliability of Si solar modules during thermal cycling and shading conditions strongly depends on the maximum temperature of the solder contact between the solar cells and the cell to cell interconnects [1]. While the maximum temperature of the solder contact is known to be critical for the lifetime of a solder joint, typical reliability tests and simulations are conducted under the assumption that the solder contact is the same temperature as the cells. This test condition and assumption is true for typical front-contact Si cells. However, the actual temperature of solder contacts is cooler for back contact Si cells. The present study investigated the temperature of solder contacts in the SunPower cell with a high resolution IR camera and found a substantially lower temperature for the solder contacts of a hot cell neighboring a normal temperature cell. The pads on the hot cell are 0.34 degrees C cooler for each additional watt dissipated by the hot cell over its neighbor. A finite element analysis was conducted to validate the experimental results and to simulate the temperature of the solder contacts in real-world conditions. The simulation provides important insight on the temperature of the solder contacts under various mismatch conditions induced by localized shading. The good agreement between the simulation and IR experiments indicates that the interconnect design in SunPowers back-contact cells reduces the temperature of the solder contacts under partial/full shading, providing an additional safety margin to the module reliability.

Temperature of solar cells in reverse bias: Theory and applications

Solar cells are reversely biased, consume power generated by neighbor cells and become hot when they are shaded or do not function properly. It is necessary to quickly measure their temperatures and accurately estimate them for screening. This paper presents the theory behind thermal emission measurement under constant current reverse bias and estimation methods of steady state temperatures of cells and modules. A simple physical model describes thermal emission measurement system based on knowledge that heat is transferred by heat convection, conduction and radiation and the power is fed by electrical bias. We confirm the model by short time thermal emission measurement and electrical current voltage characterizations. A quantitative and quick estimation method of steady state temperatures is presented based on the model. This model applies to estimate the temperature of modules by incorporating thermal resistance. The results also suggest that low temperature can be achieved by low reverse voltage or low thermal resistance. This study helps to understand physics behind reversely biased solar cells to develop a quick and convenient method to estimate steady state temperature of cells and modules.