After designing an intake structure and selecting a turbine, you’ll need to design a pipeline* Pipelines are typically made from either 4-inch PVC or smaller polyethylene pipe* PVC is used almost exclusively when the pipe needs to be over 2 inches in diameter, although 1*5- to 2-inch PVC can be and is used* Four-inch PVC pipe comes in 10- and 20-foot sections that are glued together* Assembly is quick and painless and can be mastered by anyone* PVC pipe not only goes together easily, it is relatively inexpensive* In addition, PVC pipe is very light, so it is easy to install, which is especially helpful in steep terrain* Two-inch polyethylene pipe is used for smaller flows* It comes in very long rolls that are laid out from intake to turbine* Because there’s no gluing (unless two rolls must be connected), polyethylene pipe goes in much faster than PVC*
Although plastic pipe is fairly inexpensive, the pipeline can be a costly and time-consuming aspect of a microhydro system* “It’s not unusual to use several thousand feet of pipe to collect a hundred feet of head," notes Schaeffer. Additionally, in cold climates, pipe may need to be buried below the frost line to prevent it from freezing* This can add significantly to the cost and labor required to install a system, especially if the soils are rocky and difficult to work in, which is often the case in mountainous terrain* However, Scott Davis points out that “even if the pipe is not quite below the frost line, water running through the pipe may keep it from freezing*"
Burying the pipeline not only protects the pipe from freezing, it helps protect it from damage, for instance, from falling trees or tree limbs* And it helps keep the pipe from shifting around as high-pressure water flows through it. PVC pipe deteriorates in sunlight, too, necessitating burial*
Microhydro systems require special controllers to prevent batteries from overcharging, and hence from being permanently damaged* Unlike the charge
controllers on PV systems that termin’ ate the flow of electricity to the batteries, microhydro system controllers shunt excess electricity to a secondary load, typically an electric resistor or two (Figure 10-11). These resistors are typically water – or space-heating elements that put excess electricity to good use heating domestic hot water or the house. They are referred to as dump loads* (Note: PV charge controllers should not be used in a microhydro system, as they could damage the generator.)
Excess power is shunted to secondary loads in off-grid systems when the systems batteries, if any, are full and when the household demands are being met by the system. In grid-connected systems, excess power is diverted onto the grid.
Load controllers and water heater and air heater diversion devices can be purchased from Gaiam Real Goods and other suppliers that cater to folks interested in microhydro.