Solar Farm Uses Underground HDPE Conduit For Longevity, Quick Install

October 2012, Vol. 67 No. 10

The largest solar farm of its kind in North America elected to locate power and control cables in underground conduit made from high-density polyethylene (HDPE) as a way to increase the life of the facility. The 2.2 MW solar farm covers 25 acres and includes 382 solar trackers.

Cables convey power from the solar trackers to the electric grid. AllEarth Renewables Inc. (Williston, VT), designed the solar farm and manufactured the AllSun Trackers Series 24 solar trackers.

"From a sustainability standpoint, HDPE pipe and solar power are a unique partnership," stated Tony Radoszewski, executive director of the Plastics Pipe Institute, Inc. (PPI), the major trade association representing all segments of the plastic pipe industry.

"Like solar, a plastic pipe system is a sustainable and environmentally responsible choice that will serve generations to come. The HDPE conduit is ecologically efficient during manufacturing. The conduit is also strong, durable, light-weight and flexible while providing excellent protection for the power and fiber cables inside, and requires significantly less energy to fabricate, transport and install than other pipe products. And here in Vermont, HDPE conduit is the perfect choice to stand up to the extreme cold weather and frozen earth, plus it was the key to a successful trenchless run in one section."

Installation of the HDPE conduit was done using cut and cover, and horizontal directional drilling (HDD) under a forested area. All low voltage wiring used UL 1990 certified Cable In Conduit (CIC) provided by Blue Diamond Industries.

Major pipe order

The AllSunTracker conduit included nearly 70,000 feet of 3/4 inch CIC pipe with three 6AWG and 5,000 feet of 2.5-inch diameter CIC with 4/0 wiring for the panel feeder lines. Blue Diamond supplied Cable In Conduit on reels ranging from 2,000 to 10,000 feet. The company is listed by UL for specification UL 1990, Nonmetallic Underground Conduit with Conductors and its CIC is manufactured under ASTM D 3485.

"Most solar farms use underground PVC pipe," stated Doug MacDonald, engineering technician for AllEarth. "Wire is pulled onsite after conduit installation. For this project, the HDPE conduit came preloaded with the wire, so it was really just a one step process after digging the trench. It also enabled us to use a smaller conduit size, reducing the cost of materials."

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