Island Power x2: Page 3 of 4

System 2: AC Grid-Tied

In Sync with the Grid

After the success of the system at the top of the creek, we decided to move ahead with an even larger system, using the remaining 650 feet of elevation that the creek drops after it passes my turbine and before it reaches the salmon ponds, stream channels, and incubator boxes in the hatchery building at the bottom of the hill. The hillside is steep, rocky and very porous—so much that the entire creek goes subterranean for most of the way down the mountain. At the base of the hill, the water resurfaces through the lower springs, which sit just above the highest hatchery ponds. 

Our plan was to capture the water just below the Harris turbine system, run it down the hill in the shortest route possible to a power house just above the highest hatchery ponds. An existing road would enable us to minimize the impact to the land, and the tailrace would reintroduce the water into the watershed just above the lower springs, keeping the water flow to the hatchery unchanged.

This grid-tied system couples a 60 W AC induction motor/generator to the utility grid through a grid-protection control panel. Our local utility, Orcas Power and Light Co-op, gave us permission to interconnect a system up to 100 kW. During the peak winter to spring season, the creek flow regularly exceeds 1,000 gallons per minute (gpm) and we wanted to maximize power production during those peak months. Dan New from Canyon Hydro flew over from Deming and we hiked the watershed. After some assessment, we decided to use 800 gpm as our design flow rate. Canyon’s engineers designed a system using a two-nozzle, 10.5-inch Pelton turbine.

A 6-inch penstock was chosen to keep head loss within reason. I located used 6-inch, thin-wall steel pipe with ends for use with Victaulic couplings—two cast-iron jaws bolted around a rubber gasket to make a watertight and high-pressure-worthy joint. That steel pipe was the least expensive pipe available for the higher-pressure sections of the run. The pressure at the top of the pipe was lower, so we started with 700 feet of 100 PSI-rated HDPE plastic pipe for the top section, reserving the steel pipe for the bottom 1,000 feet.

What I did not anticipate was how much labor it would take to install the heavy steel pipe on the steep rocky mountainside. If I were to do it again, I’d use two parallel runs of 4-inch-diameter, heavy wall HDPE. The material would have cost more than the 6-inch steel pipe, but the installation would have taken a few weeks, rather than a few months! A single run of 6-inch, heavy wall HDPE would have reduced the internal dimension significantly and introduced too much head loss. Two runs of 4-inch, heavy wall HDPE would have had enough internal dimension to keep head loss in the allowable range.  

We installed the system during the spring and summer of 2006, preparing the route using “hydro excavation.” A long stretch of 11/2-inch HDPE pipe connected to my hydro penstock and a high-pressure fire hose with a long brass nozzle was used to shoot a jet of water to clear the route for the penstock. Some of the sections needed substantial amounts of earth cleared to make a straight path. It’s really quite impressive how much dirt and rock high-pressure water can move!

The 20-foot sections of 6-inch pipe each weighed about 250 pounds and required about four people to move. We devised pipe-lifting and positioning techniques using ropes, straps, “come-along” hand winches, and a rope capstan winch mounted on a chain-saw body, combined with tree-mounted anchor points, blocks of timber, or “cribbing,” and hydraulic jacks.

Parts of the route passed over exposed bedrock, so we used a 1-inch-diameter rotary-hammer to drill anchor holes for securing eye bolts and pipe anchor attachments with two-part epoxy. In places without exposed bedrock, the hillside is loose shale rock that provided little solid ground to attach to. In those locations, we dug holes for gabions—large wire cages filled with rocks and concrete—into the loose rocky hillside to form a solid anchor point and prevent the heavy, water-filled pipe from sliding downhill.

The Canyon turbine arrived with a steel frame designed to be cast into the concrete of the power house floor. The middle of the frame is left open so the water can exit the turbine. We built a concrete basement under a third of the power house floor, with a pedestal to hold the turbine. The floor above the tailrace section is 4-inch-thick, red cedar planks. A 2-foot gap in the wall at the lowest level is connected to a short concrete-sided channel to the streambed. 

We had to address long-distance electrical transmission issues to get the power to the grid. We relocated the utility’s transformer closer to the power house and switched from 120/240 single-phase to 480 V three-phase power. By switching to 480 VAC, the energy from the turbine can travel on smaller-gauge wire. The 480 V power also powers an electric sawmill and several large wood-processing machines in the shop.

Production Payoffs

These two systems have given me quite an education in hydro-electricity, and energy economics in general. The contrasts between the systems are insightful. My small off-grid system was built for about $7,000 and paid for itself almost immediately, since the cost of bringing in grid power to the remote home site would have been at least $10,000. Now, we’ll never need to pay a utility bill. The 23+ kWh that it produces each day is more than enough for my off-grid home. Because electricity consumption is moderate, the investment in generation was scaled to match it.