John,

Thanks for the great map, and the follow-up note! I understand that you can only work with averages in a project like this, but I thought I would highlight a little variability.

The PVWatts "average" retail rate seriously understates Salt Lake City rates for many customers, and rates are projected (by the local utility)to rise about 8% per year between now and the end of the decade. Obviously, each potential PV system purchaser has a different expectation for return-on-investment, another critical "grid parity" calculation input. "Grid parity" is normally defined as unsubsidized cost, but the economic reality for a system owner always includes post-subsidy costs and all available benefits. The good news is that, with currently available incentives and tax effects, solar power is already a viable investment alternative for certain individuals and organizations in the Salt Lake area. For those parties, "grid parity" has arrived, and the public-relations, environmental and energy-independence benefits are free.

Salt Lake City was left out because of its population, not its solar resource. It will reach grid parity around the same time as Tampa, FL, in the year 2020.