Phoenix summers are extreme dry heat. Cooling equipment and the building envelope do most of the comfort work for much of the year.
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Service types
Site assessment
Shade, roof age, structure, and electrical service, before anyone talks about a system size.
Roof-mounted systems
How an array is attached, flashed, and warranted relative to the roof.
Equipment questions
Modules, inverters, and monitoring. Ask what is specified, not what is typical.
Permits and interconnection
The building permit and the utility's permission to operate.