First Solar is the Engineering, Procurement and Construction (EPC) contractor for the Topaz Solar Farm, a 550 MW nameplate photovoltaic (PV) renewable energy project located in San Luis Obispo County, California. Because of the large size of the solar farm, solar panels are located on the north and south side of California State Highway 58 (Hwy 58). A crossing under Hwy 58 was needed to connect the collection system. First Solar retained TRC as the EPC contractor for the underground crossing. The underground crossing, by jack and bore methods so as not to disturb the highway, needed to be completed prior to energization of the solar panels located on the south side of Hwy 58.
TRC’s EPC scope of services involved using jack and bore methods to install three large steel encasement pipes under Hwy 58 to house conduits in which First Solar installed the collection system power conductors and fiber optic cables. To accomplish this, TRC’s scope included the following services:
- Performing a site specific geotechnical investigation, including assessing the thermal resistivity characteristics of native soils.
- Performing a value engineering assessment of which power conductor to use. Based on this assessment, the conductor chosen increased the reliability of the collection system, while reducing overall project costs.
- Preparing civil and electrical designs, including plans and specifications, a thermal analysis assessment and report, a Method of Construction document, Health and Safety Plan, and Quality Control Plan.
- Preparing permit applications and obtaining permits needed to construct the project, which included the California Department of Transportation (CalTrans), San Luis Obispo County Building Department, and California Department of Occupation Safety and Health (CalOSHA). Due to the size of the encasement pipes, CalOSHA considered this a tunneling project, which triggered additional requirements.
- Procuring materials needed to construct the project.
- Constructing the project, including the installation of three 48 inch O.D. steel en-casement pipes by jack and bore methods under Hwy 58. Each pipe was 80 feet long. Conduits were installed inside the pipes, and the annular space was filled with grout/concrete slurry for thermal considerations.