Building Above the Flood
By SETH MASIA
Elk Grove, Calif., lies 15 miles south of downtown Sacramento, and right on the edge of what California calls The Delta, a warren of rivers and ponds and dyke-protected farmland copiously watered by Sierra snowmelt as it makes its way to San Francisco Bay. Almost the entire area is considered floodplain.
S-Energy, the Korean module manufacturer (formerly a subsidiary of Samsung) wanted to put up a 4.8-megawatt (MW) array to sell power to the Sacramento Municipal Utility District. The company found 29 acres of land alongside Interstate 5, mere yards from the nearest groundwater. While the lot is in a 100-year flood zone, it slopes from 3 feet to 9 feet above sea level. Realistically any large storm can flood it, but it drains naturally. Happily, the soil is firm: It’s mostly clay underlain with sand, and the geoengineering report called it suitable for vibratory-driven piles.
According to S-Energy General Manager David Yoo, piles 12 to 22 feet in length were driven 5 to 11 feet into the ground, depending on ground height.
The modules bolt to single-axis trackers, 9 feet above grade. Inverter pads are elevated 12 feet, and the substation 15 feet.
The system uses three SMA 1.6-MW MV Power Platforms, with UL-certified Sunny Central HE-US inverters. DC and AC collectors are direct-buried copper.
The project was started, and completed, over the summer of 2012.