In the U.S., the National Renewable Energy Lab (NREL) provides some great resources for examining the potential of solar PV systems, such as PVWatts and the National Solar Radiation Database viewer. Data on real-world pricing ($/watt installed) is available in Berkeley Lab's annual Tracking the Sun report.
One piece of the puzzle that is missing is actual production or capacity factor data. This would account for factors which are either not modeled or not modeled precisely, such as severe weather events, soiling, improper installation, component failure, shading from trees/structures, curtailment, and physical damage, among others. By comparing this data to the solar potential data available from the sources I linked above, you could get a more realistic expectation for production from a proposed PV system.
Is there a database of historical power production from solar PV installations?
I know that some utilities and business publish production data from individual installations (for green-washing purposes), but I'm more interested in a searchable database of this information.