Modular solar systems comprise one or more module units that are connectable into a system/assembly for convenient installation on a roof or other surface that receives solar insolation. The modules are adapted for electrical, and preferably also mechanical, connection into a module assembly, with the number of modules and types of modules selected to handle the required loads. Each module is adapted and designed to handle the entire power of the assembly and to provide or receive control signals for cooperative performance between all the modules and for monitoring and communication regarding the assembly performance and condition.