Microhydro Upgrade

Intermediate

Inside this Article

The Farm in the New River watershed of North Carolina.
The main farmhouse also has a grid-tied PV array. The new hydro system is battery-based and uses the grid only as backup, when electrical demand exceeds hydro energy production.
The hydro power shed, cleverly disguised as a log cabin.
The original hydro intake screen system was prone to clogging with debris and sediment.
The Harris Hydro turbine on its treated and caulked plywood tailrace.
Four Deka AGM batteries provide 200 Ah of energy storage at 48 VDC for dedicated loads.
A Xantrex 4048 inverter powers the loads, while a C40 acts as a diversion controller, dumping excess energy to a 3 kW resistor.
A dedicated AC subpanel is served by the inverter.
Appalachian State University students further reinforced the intake to slow water velocity at the screen, and added wood blocks to prevent leaves from catching on the Hydroscreen side walls.
The first step in the system upgrade was extending the penstock to a better location upstream, which gained a few feet of head, and installing a Hydroscreen intake. Note the cable-tie anchoring on the slippery HDPE pipe.
Without a HDPE welder, the new penstock was joined with rubber couplers, which required bracing and anchoring against the forces of gravity.
The sand-blasted brass Pelton runner (right) was worn completely through in spots. The new runner (left) is ready for another 10 billion revolutions.
The finished intake—with tapered weir timbers and solid anchoring—is ready to weather the extremes of seasonal flow.
A new manifold was constructed, switching from rigid to braided PVC, which allows smoother transitions to the turbine nozzles.
A new pressure gauge with HOBO data logger provides monitoring of intake, penstock, and turbine performance.

The Farm at Mollie’s Branch in Todd, North Carolina, is a small, on-grid farm that always finds itself on the local farm tour. This family farm features llamas, free-range chickens, stands of nettles, a shiitake mushroom nursery, and a rustic creekside cabin for visitors and interns. With aspirations of greater energy sustainability, the owners wanted to pursue an on-site, clean energy project, reducing the consumption of utility-supplied energy and directly powering critical farm loads, such as lighting and refrigeration.

The Farm has a creek running through the property that eventually flows into Pine Orchard Creek and then Elk Creek, a tributary to the South Fork of the New River. In 2006, the farm’s owners, Diane Price and Rob Griffith, expressed interest in tapping the creek’s energy and reached out to the local agricultural extension agent, who contacted Appalachian State University for assistance. A student club, the Appalachian State University Sustainable Energy Society (aka the Solar Club), visited the farm to assess the resource.

An estimated 100 feet of head and a typical flow of about 300 gallons per minute (GPM) was good news, and the farm worked with the local agricultural extension office in Watauga County, North Carolina, to receive a $15,000 Small Farm Innovation grant from North Carolina Agricultural and Technical University.

The system was designed to run part of the house on hydro energy while leaving some less critical loads on-grid. Critical loads were identified as refrigerators; barn loads (lights and chicken brooders); bedroom receptacles; a furnace fan; living room lights; kitchen receptacles; garage (lights and freezer); utility room lights; study lights; and kitchen lights. These loads were pulled from the main electrical panel and placed in a new subpanel. The battery-based hydro-electric system would run these loads, with the grid serving as backup if the hydro system was down or unable to keep up. Any excess energy from the microhydro turbine would be diverted to a resistance heater diversion load that warms the garage. Since no turbine-generated energy would be exported to the grid, there was no need to deal with the local utility.

The system was designed and installed by Appropriate Technology students at Appstate, and served as my class project when I was a grad student, using a good amount of student labor from the Wind and Hydro Power Technology class. This service-learning relationship served all parties well, enabling hands-on work in the creek for students, and greatly improving our experience and knowledge of what does and does not work in microhydro design.

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