Power optimization for a-Si solar modules

Large-area a-Si modules suffer from power losses not present with small-area laboratory cells. Resistive, shunt, active-area, and uniformity losses can be measured on a finished module. Experimental data are presented to illustrate the dependence of resistive, shunt, and absorption losses on the thickness and sheet resistance of the conductive transparent oxide (CTO) front contact. Reflection and absorption losses at the front of the module were estimated using an optical model. It is noted that shunt losses, uniformity losses, and resistive losses in the busbars and interconnects are avoidable and are usually low for good modules. The sum of resistive loss in the CTO, absorption loss in the CTO, and active-area loss at the interconnect can be minimized by optimizing CTO thickness and segment width. A recent 1000 cm² Solarex production prototype module had about 20% loss relative to a comparable small-area cell. Relative losses of about 10% should be achieved in the near future