How to assess the electrical quality of solar cell interconnection in shingle solar modules

This work deals with the resistance induced by interconnecting shingle solar cells by means of an electrically conductive adhesive (ECA), which is labeled Rint throughout the work. A new approach to measure Rint directly from shingle joints of actual strings is presented and evaluated. For non-laminated strings and two different ECAs that are applied as a continuous line on shingles with an edge length of 158.75 mm, similar interconnection resistance Rint ≈ 2.5 mΩ is found. In a full-size shingle module, such an interconnection resistance would result in a cell-to-module loss of around ΔPMPP = -0.8%. Another aspect of the present work is to increase the awareness that in case Rint is unknown, it is not trivial to assess the electrical interconnection quality (of different ECAs, different amounts of the same ECA, etc.). It is demonstrated experimentally that the string/module fill factor can be highly sensitive to current mismatch and is thus not an ideal representative of Rint. The power at maximum power point PMPP tends to indicate Rint differences even less clearly. By simulating virtual strings from a pool of slightly varying shingle I-V curves, it is shown that a more suitable representative of Rint is a quantity that can be derived from the string's/module's dark I-V curve.