Micro Hydro Systems: What Are They?
Today’s micro-hydro Run-of-River system designs are dependable, economical, efficient, and environmentally friendly. Harnessing the power
of water to generate electricity allows us to gain some sense of responsibility for meeting our own needs and for reducing our impact on the environment.
Micro-hydro systems are typically 4-5 times better cost to energy output
and corresponding reduction in total emissions, including manufacturing and installation, than other renewable technologies.
Modern micro-hydro turbines have come a long way from the clunky
metal turbines seen in the past. Advancements in turbine wheel (turgo or
pelton) construction and generator design allow today’s turbines to operate
reliably in a wide variety of water conditions.
If you are lucky enough to have a stream running down your hillside,
micro-hydro is the resource to visit frst! Before deciding on a micro-hydro
system, it is important to know the potential of your site. Ample,
year-round water is a prerequisite for successfully siting a micro-hydro
turbine, and generally speaking, the more the better. The power that can
be generated is directly related to the “head” or height of the water in feet
and the Now of the stream in gallons per minute. Typical “high-head”
micro-hydro installations involve the placement of sufficient water pipe
(PVC or polyethylene) to move water stored (pond) or harvested from a
high point adjacent to a stream to a lower point where the turbine is
located.
The minimal useful head for most micro-hydro systems is around 20-
30 feet, which corresponds to an outlet pressure of about 10 psi (2.3 ft =
1 psi). The design challenge is to size the pipe and its outlet nozzle(s)
appropriately for seasonally changing conditions. The minimal useful
Now for most micro-hydro turbines can be as small as 2 gallons per
minute (gpm) depending on the available head pressure. “Low head”
micro-hydro generators can operate on as little as 6 feet of fall, but require
a lot of Now to make useful power – typically 100s of gallons per minute.
It is also important in the Northeast part of the country to design the
catchment, distribution, and generating system for freeze protection.
Finally, the generator must be connected to a suitable energy storage system (batteries). Other factors include proper pipe sizing and installation,
system voltages, and wire length and sizing.
Micro-hydro systems can be grid-connected or off-grid stand-alone
battery charging systems. The simplest and most cost effective system is
the grid-tied system. In the grid-tied system water from a stream or pond
is diverted to the turbine through a pipe called a “penstock” (usually a 2-
3” PVC pipe). The turbine sends electricity to a charge controller to
charge a bank of batteries. An inverter conditions the DC power of the
battery bank to AC to match the electrical grid power. The power is then
sent to the grid and/or home via your existing load center.
The grid-tied micro-hydro system is connected through an agreement
with your local power company and the energy is net-metered. In
the net-metered energy system, your electric meter will spin backward
whenever you are generating more power than you are using and forward
when you are using more power than you are generating. The result is
that your electrical usage is billed at the net difference between what you
make and what you use.
Frequently asked questions about micro-hydro systems:
- What happens to the water after it Nows through the turbine?
- What is the “dump load” shown in the diagram?
- How large are the turbines?
- What is the environmental impact of a Micro-hydro system?