Commercial rooftops are often large and flat, which makes them good candidates for solar. They also carry rooftop units, skylights and access paths that the design has to work around.

Start with the roof

• Roof type, age and remaining life, since the array will outlast a worn roof
• Structural capacity for the added weight and wind uplift, especially on ballasted systems
• Rooftop equipment, drainage and required access paths

Match the system to the load

The best commercial systems are sized around the building's daytime consumption and demand profile, not simply around the largest array that fits. Utility interconnection rules and net-metering terms affect the right size.

Electrical and permitting

Commercial interconnections are usually three-phase and often need an engineer's stamp. Starting the utility application early keeps the schedule predictable.