Because of the steep, forested terrain, all the conduit trenching was done by hand, with a mattock and 4-inch-wide trenching shovel. We set into the trench 2-inch-diameter PVC conduit, with plastic pull boxes every 200 feet, and a 1.5-inch plastic pipe for bringing domestic water along with the power to the house.
For the turbine base, I found a 24-inch-diameter cast concrete culvert pipe in a local boneyard of surplus and salvage materials. We used a gasoline-powered cut-off saw from the rental shop to shave 2 feet off one end so that it could be set vertically, holding the Harris turbine securely and allowing the water to exit freely out of the bottom. A rotary hammer and a cold chisel were used make a 6-inch-diameter hole in the side of the culvert about 4 inches from the end. The culvert was sunk vertically in a 1-foot-deep hole near the creek. We poured a concrete floor in the pipe level with the exit hole. Then, we dug a short trench across to the creek, caulked a 6-inch-diameter flexible plastic pipe to the tailwater exit hole and ran the other end into the creek below the turbine.
The penstock installation occurred on a rainy day in April 2003. Ian brought 20 workshop students. We rented a polyethylene pipe-welding machine from the pipe supplier and used a small pop-up canopy to keep the rain off the welding crew. The machine has a facer that cuts the pipe ends smooth so they will match and line up perfectly. A heater element softens the pipe ends until a small bead of soft plastic begins to form on the hot metal. At that point, the heater plate is removed and the ends are brought together quickly by pulling the lever on the pipe clamp jig and held under pressure until the joint cools. It is a relatively simple process that makes a strong and leakproof joint with only a minimal bead on the inside of the pipe to minimize water friction in the line.
Our pipe-welding station was at the top of the penstock installation to take advantage of gravity. As each 20-foot section of pipe was added to the penstock, we simply dragged the lengthening pipe 20 feet down the hill. However, as the penstock got longer, it became heavier and wanted to slide down the hill on its own. We used rope to temporarily anchor it to trees and roots during the descent. Once all 300 feet were in place, we attached a bolted flange adapter with a rubber gasket to the PVC manifold at the turbine. Later, I added galvanized cable anchors bolted to the bedrock and boulders to permanently hold the pipe in place on the steep hillside.
The turbine was set on top of the vertical concrete culvert section using a frame of cedar 2 by 4s. This allowed a friction fit for the turbine—the frame held it securely, yet the turbine could still be easily removed from the base without tools for maintenance and nozzle replacement. The 48-volt DC wiring was placed in flexible plastic conduit to allow the turbine to be lifted up and swung to ground level to access the nozzles on the underside without needing to disconnect any wiring.
The turbine is a four-nozzle, vertical-shaft Pelton design. Borrowing ideas from other systems I had seen on the island, I used flexible hose with cam-lock quick-disconnect fittings for connection to both the turbine nozzles and the manifold. The manifold is made from PVC wye fittings that reduce and split the single 4-inch pressure line into five 2-inch pipes, with brass gate valves in each pipe. A fifth valve, at the very end of the penstock, is for supplying water to the building site. A 4-inch-diameter wye on the penstock above the manifold is for future system expansion. By adding a second turbine in parallel, more power can be made during the highest flow times of the year (winter/spring).
From the turbine, 2-gauge wiring runs up the hill 650 feet to the batteries in the power house. A Trace C-40 diversion-load controller keeps the batteries from being overcharged by dumping excess current into a 48 V heater element in a water storage tank.
After the pipeline installation, I built a proper intake dam, with cedar timbers set across the creek. A 16-inch square of stainless steel Hydro-Shear screen placed under the overflow notch captures water but allows debris to be washed easily across the surface of the screen. After seven years of continual operation, the intake screen is still working perfectly, with the only screen-clogging problem being a slow growth of algae that needs to be scrubbed off with a wire brush every few years.