The present invention provides solar concentrators incorporating photovoltaic receiver assemblies with improved thermal dissipation, dielectric, encapsulation, and cell/wiring protection characteristics. The concentrators are particularly useful for photovoltaic power systems such as rooftop mounted systems. The present invention teaches that the geometry of the substrate used to support receiver assemblies can have a dramatic impact upon thermal/dielectric performance. In particular, the present invention teaches how contours incorporated into such substrates can improve thermal performance (i.e., dissipation of thermal energy from photovoltaic cells through the substrate) while still maintaining dielectric and encapsulation objectives. In the past, dielectric and encapsulation objectives have been obtained at the expense of such thermal dissipation. Also, material choice and form also impacts thermal, dielectric, and encapsulation performance. In preferred embodiments, components of receiver assemblies are provided in sheet form and laminated together in the course of making the receiver assemblies.