A Small Creek Provides Plenty of Power For This Off-Grid Home
For eight years, Tracey and I lived in a solar powered home and for eight cloudy winters, we ran a small Honda generator every week to recharge our batteries. We understood that the original owner of our home had operated a small hydro system from the property's year round creek but we never investigated this option because the creek ran through dense forest. Besides, we could just tell there wasn't sufficient drop over its course.
We finally decided to use Backwoods Solar's Site Level just to confirm hydro didn't make sense.Much to our surprise, our traverse through the woods from a potential turbine site to a convenient intake location revealed about 80' of drop. Not possible, we declared, assuming our technique must have failed. To double-check our method, we used the same Site Level to measure the drop from our water cistern to kitchen sink. We knew this drop equaled 56 feet because we had used a transit to measure it when this gravity fed system was installed. The review with the Site Level gave us about 60 feet and confirmed we knew how to use the level.
Voila, hydro potential. At the driest time of year, our creek measures about 3 feet wide by 3-4 inches deep and a five-gallon bucket and stopwatch suggested we had over 300 gpm flowing past our intake site. Wow, lots of potential. With 80 feet of drop, a nozzle flow chart indicated we could theoretically pass 134 gpm through a Harris 4-nozzle turbine equipped with 7/16" nozzles. Next, we turned to Don Harris' Motorcraft alternator watts output chart. With 134 gpm and 80 feet of drop, we extrapolated that we could generate 725+/- watts. However we would have an 1100 foot penstock to install. More charts. To reduce friction loss and maintain close to maximum output potential, we determined 4" pipe would only sacrifice about 9 feet of gross head if all four nozzles were in use.
A quick assessment of the benefits of this quantity of energy convinced us to proceed with an installation. However, the year was 1999 and Backwoods Solar was incredibly busy catering to allot of Y2K hype leaving Tracey and I with little time for an install. And at that time, my hydro expertise wasn't exactly expertise. So we called on Lee Tavenner of Solar Plexus of Missoula, MT to develop a turnkey system which would include his installation labor. Lee graciously pieced the components list together even though he understood we would provide the majority of the components; we agreed on a price; and he found time in his busy schedule for an install over one weekend in September.
Prior to that weekend, Tracey and I had to develop the route for the penstock through the woods through which the creek meandered. The path of least resistance followed old and overgrown logging skid roads as well as dense forest. We used survey ribbon to mark a path and hired a neighbor with a bulldozer to cut and clear the path. Another neighbor with a backhoe was hired to dig the intake pond, 4' deep trench, turbine site, and discharge channel to the creek.
Lee recommended we use high-density polyethylene pipe given its resistance to crushing and the fact that it doesn't crack when frozen. His Missoula distributor delivered thirty 40 foot pieces of the 4" pipe to our remote homesite but could only get to within 1000 feet of our trench line. A Honda three wheeler could drag three pieces at a time to within 300 feet and Tracey and I carried each piece the balance of the distance. Not unbearable labor but a 40' pipe can develop some great bouncing waves in it if your mutual pace isn't synchronized properly!
Next, we gathered and installed the various power system components. Given the distance from the turbine to our battery bank measured 350 feet, we chose to install a 24 volt system. (Even though the PV system powering our home was 12 volts and many of our loads were 12 volt DC, we knew an EQ12/24-20 would enable us to maintain our 12v DC circuits and insure our 24v battery bank remained balanced.) The 350 foot distance from turbine to batteries and our 700 watt generating potential led us to select 1/0 direct burial copper cable in order to minimize transmission losses.These lengths of pipe must be fused together rather than glued as with PVC. Lee would rent the small machinery for this procedure and bring it with him when the installation weekend arrived. Our Honda 3500 watt generator would power the fusion machine.