  We analyze the problem of partial shading in monolithically integrated thin
film photovoltaic (TFPV) modules, and explore how the shape and size of the
shadows dictate their performance and reliability. We focus on the aspects of
shading problem unique to monolithic TFPV, arising from thin long rectangular
series-connected cells, with partial shadows covering only a fraction of cell
area. We find that due to the cell shape, the unshaded portion of a partially
shaded cell experiences higher heat dissipation due to a redistribution of
voltages and currents in this two dimensional geometry. We also analyze the
effect of shadow size and orientation by considering several possible shading
scenarios. We find that thin edge shadows can cause potentially catastrophic
reverse bias damage, depending on their orientation. Finally, we show that
external bypass diodes cannot protect the individual cells from shadow-induced
reverse stress, but can improve the string output for larger shadows.
