Work is reportedly nearing completion on Tesla's largest Supercharger site to date.

This site has 20 Supercharger stalls and it's located in south Fremont, California just to the south of Tesla's factory.

In the map below, the 901 Page Avenue marker denotes the approximate location of these new Superchargers.  Update: actual address is nearby at 47400 Kato Rd Fremont CA (thanks to Tyl)

Note: Tesla has another set of Superchargers at the factory nearby - upper left of map:

901 Page Avenue Is Location Of 20-Stall Tesla Supercharger

901 Page Avenue Is Location Of 20-Stall Tesla Supercharger

Seagate Technology bought most of the old Solyndra plant when the solar company folded. Tesla leased one of the remaining Solyndra sites located at 901 Page Avenue. This is approximately where Tesla is constructing its 20-stall Supercharger.