San Francisco, CA

Mosaica Housing San Francisco


Citizens Housing Corporation always planned on installing a large solar PV system at Mosaica, a 117 unit affordable housing, mixed-use, green-point rated project located in San Francisco, California. However, the original solar subcontractor pulled out at the beginning of construction. Consequently, after discussion with a few subcontractors, Borrego Solar was selected to take over.


Mosaica Housing complex was a new construction project taking up a full city block in San Francisco’s Mission District. Three-quarters of the installation is ULA tilted racking on flat roof surfaces with the remaining quarter Unirac solar flush mounted on curved TPO roofs. Utilizing prefabrication techniques, Borrego Solar’s installation team loaded 748 PV modules on to the roof in one day with a crane. This was achievable because we pioneered the “component pre-fabrication process” in which we pre-wired and pre-racked the PV modules on to 1 x 4’s in a warehouse, which enabled us to control the quality of the product and save production time. In the field, pre-fabrication allowed us to quickly drop and bolt the module racks on to the mounting frames in a systematic and efficient manner. From start to finish, it took less than six weeks to complete the 131kW installation.

Once on the roof, there were a variety of obstructions like air vents, HVACs, and physical structures making it slightly difficult to maneuver around. Some of the panels had to be moved up slightly to adjust for railings and structures that didn’t appear in the initial design plans of the building, but the installation team was able to think quickly and found solutions that worked.

On a new construction project, we prefer working directly with the rest of the contractor team. So we arranged to install the mounts almost six months prior to installing the racking and panels to work around the roofer’s schedule. Through discussion we also suggested the painters finish the upper exterior floors of the building first, to avoid overspray and paint debris covering the solar panels and potentially reducing their efficiency. Currently the Mosaica Housing solar PV installation is over producing what was projected.


Mosaica was financed by combining the generous rebate from the San Francisco Public Utilities Commission rebate program as well as a significant subsidy from the CA New Solar Homes Partnership (NSHP).

The New Solar Homes Partnership is administered by the California Energy Commission and is part of the comprehensive statewide solar programs, known as the California Solar Initiative. The NSHP provides financial incentives and other support to home builders, encouraging the construction of new, energy efficient, solar homes that save homeowners money on their electric bills while simultaneously protecting the environment.

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