  Partial shading in photovoltaic modules is an important reliability and
performance concern for all photovoltaic technologies. In this paper, we show
how cell geometry can be used as a design variable for improved performance and
resilience towards partial shading in monolithic thin film photovoltaic (TFPV)
modules. We use circuit simulations to illustrate the geometrical aspects of
partial shading in typical TFPV modules with rectangular cells, and formulate
rules for shade tolerant design. We show that the problem of partial shading
can be overcome by modifying the cell shape and orientation, while preserving
the module shape and output characteristics. We discuss two geometrical designs
with cells arranged in radial and spiral patterns, which (a) prevent the
reverse breakdown of partially shaded cells, (b) improve the overall power
output under partial shading, and (c) in case of spiral design, improve the
module efficiency by reducing sheet resistance losses. We compare these designs
quantitatively using realistic parameters, and discuss the practical approaches
to their implementation.
