There is an interesting, but non-technical, article in the Arizona Republic about batteries in PV systems.
Most of the major Phoenix area cities have documents that detail the requirements for new solar systems and it is likely that the cities will be updating their documents soon with battery requirements.
SEPTEMBER 20, 2019
Citing the wild success of its Series 6 module, First Solar has announced that it is closing its engineering, procurement and construction business in the United States in order to concentrate on scaling, developing, and selling modules.
There is no further news on the First Solar website, but this seems to be unwelcome news for Tempe.
See the pv magazine USA article for more detail: First Solar exits the EPC business
A look at some of the more significant changes under consideration for the 2020 National Electrical Code (NEC) that will affect future distributed generation systems (solar electric wind, etc.). Article 690, Solar Photovoltaic (PV) Systems and Article 705, being renamed Interconnected Electric Power Production Sources, are specific to distributed generation.
The referenced article below by IAEI, a membership driven, non-profit association promoting electrical safety, has a good summary of upcoming changes.