The underground conduit carrying the power and control cables for South Burlington’s 2.2MW solar farm is made of high density polyethylene (HDPE) and is intended to last as long as the sun itself.
The solar farm at South Burlington, Vermont, is the largest of its kind in the USA. It covers 25 acres and uses 382 solar trackers. (photos: PPI)
The solar farm at South Burlington, Vermont, is the largest of its kind in the USA. It covers 25 acres and uses 382 solar trackers, which are quite common in Europe but not widespread in the US. The farm has been supplying electricity to the grid since July 2011. AllEarth Renewables of Williston, Vermont, designed the solar farm. It made the AllSun Series 24 solar trackers and specified the HDPE conduit that carries the power and control cables.
Total power produced by the South Burlington Solar Farm is estimated to be approximately 3,000,000kw/h a year, which is 45% more than the amount of electricity that could be produced by a fixed roof-top PV system of the same size and is estimated to be worth € 714,000/year. (photos: PPI)
“A plastic pipe system is a sustainable and environmentally responsible choice that will serve generations to come,” Tony Radoszewski claimed. He is Executive Director of the Plastics Pipe Institute (PPI), the major trade association of the plastic pipe industry. “The HDPE conduit is ecologically efficient during manufacturing. The conduit is also strong, durable, lightweight and flexible, while providing excellent protection for the power and fibre cables inside, and requires significantly less energy to fabricate, transport and install than other pipe products.”
Most solar farms use PVC pipe but Vermont experiences extreme cold weather and frozen earth during winter, and HDPE’s ability to withstand these conditions added to its attractiveness. It was the key factor in achieving a trenchless run in one section, and it offered commercial advantages as well. The norm for PVC pipes is for wire cables to be pulled through after installation; the HDPE conduit had wire preinstalled during the extrusion process, which saved labour, handling and material costs. The AllSunTracker conduit used nearly 21,000m (70,000ft) of 3/4 in Cable-In-Conduit (CIC)with three 6AWG cables – black, green and white – and 1,524m (5,000ft) of 2.5-inch diameter CIC with 4/0 wiring for the panel feeder lines.
“Installing the cable in the conduit at the factory ensures that a clean and damage-free cable is delivered to the field,” said Aaryn French, Project Manager for Engineers Construction, “CIC also eliminates the added expense of pulling the cable onsite under muddy and dusty field conditions.”
The 382 dual-axis GPS guided AllSun Tracker units move from east to west and up and down, tracking the sun in order to maximize efficiency. Total power produced by the South Burlington Solar Farm is estimated to be approximately 3,000,000kw/h a year, which is 45% more than the amount of electricity that could be produced by a fixed roof-top photovoltaic system of the same size and is estimated to be worth € 714,000 per year (US $924,000/a). The project is owned and operated by Chittenden County Solar Partners, and produces enough power for more than 400 homes. French said that a four-person crew took just a month to install all the low and medium voltage conduit at an average depth of 0.9m (3ft).
“The trenching, which was the majority of the work, went very smoothly,” he said. “This was more efficient than using sticks of PVC – probably five to ten times faster.”
Cable-In-Conduit can be used for commercial installations to run the line from panels located on a roof to the inverter in the basement, for example. Built Well Solar’s Dan Sabia examines one of his company’s large-scale solar panel systems located on a school’s roof.
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