Pipeline

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*

Controllers

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.

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