A window transmissivity control assembly having a power source with scalable size and power capacity is provided. The assembly includes an insulated glazing unit including a variably transmissive glazing, a photovoltaic module attached to the insulated glazing unit and electrically coupled to the variably transmissive glazing, and a control module having a control circuit for controlling transmissivity of the glazing and a battery for providing power to the glazing. The photovoltaic assembly is attached to an exterior face portion of the insulated glazing unit, and a control module is attached to an interior face portion of the insulated glazing unit. Each module may extend from a first end of the insulated glazing unit to an opposing second end of the insulated glazing unit, wherein the length of the module being substantially the same as the distance between the first and second ends of the insulated glazing unit.