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Microhydro-electric systems

are a low cost, low impact

way to power your home.

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Feb / Mar 2007, Issue 117

homepower.com

Go with the

Buyer’s Guide to

vs.

Microhydro-Electric

by Paul Cunningham & Ian Woofenden

If you have a suitable site, harnessing the energy in a stream or creek can be the most

cost-effective way to make renewable electricity. Compared to the sun and wind’s

variability, a stream’s flow is relatively consistent, making microhydro-electric

system output the most predictable of all the renewable energy (RE) electrical

systems. Hydro resources are also the most site specific, since your property must

have a usable water source. If you are one of the lucky few with a stream running

down your hillside, it’s the resource to assess first.

Intake:

Screened to prevent

debris from entering

pipeline

The first step in designing a microhydro system is to

evaluate your water resource by measuring the head (vertical

drop) and flow of your stream. (For detailed instructions, see

Dan New’s article in HP104 .) These two measurements are

necessary to calculate the energy potential of your stream.

The next step is to design a system that will effectively

harness that potential.

A microhydro-electric system is made up of a number of

components, not just the turbine. Hydro sites and end

users’ needs vary, and a wide range of equipment and

system configurations are available to properly match

the conditions. This article will give you an overview

of the components, and help you understand the

different ways they can work together to make

electricity from falling water.

Head: Total

vertical drop

from intake

to turbine

Penstock:

Sized for amount

of flow

Stream

Turbine:

Runner spins

an alternator

Tailrace:

Returns water

to stream

home power 117 / february & march 2007

Systems

microhydro basics

1 Intake AKA: Screen, diversion,

2 Pipeline

impoundment

AKA: Penstock

Intakes can be as simple as a screened box submerged in the watercourse,

or they can involve a complete damming of the stream. The goal is to

divert debris- and air-free water into a pipeline. Effectively getting the

water into the system’s pipeline is a critical issue that often does not

get enough attention. Poorly designed intakes often become the focus

of maintenance and repair efforts for

hydro-electric systems.

Most hydro turbines require at least a

short run of pipe to bring the water to

the machine, and some turbines require

piping to move water away from it. The

length can vary widely depending on

the distance between the source and the

turbine. The pipeline’s diameter may

range from 1 inch to 1 foot or more,

and must be large enough to handle the

design flow. Losses due to friction need

to be minimized to maximize the energy

available for conversion into electricity.

Plastic in the form of polyethylene or

PVC is the usual choice for home-scale

systems. Burying the pipeline is desirable

to prevent freezing in extremely cold

climates, to keep the pipe from shifting,

and to protect it from damage (cows,

bears, etc.) and ultraviolet (UV) light

degradation.

A large pool of water at the intake will

not increase the output of the turbine,

nor will it likely provide useful storage,

but it will allow the water to calm so

debris can sink or float. An intake that

is above the bottom of the pool, but

below the surface, will avoid the grit

on the stream bottom and most of the

floating debris on top. Another way to

remove debris is to direct the water

over a sloped screen. The turbine’s

water falls through, and debris passes

with the overflow water.

OFF-GRID BATTERY-BASED HYDRO-ELECTRIC SYSTEM

Turbine

Most small off-grid hydro systems are battery-based. Battery

systems have great flexibility and can be combined with other

energy sources, such as wind generators and solar-electric

arrays, if your stream is seasonal. Because stream flow is

usually consistent, battery charging is as well, and it’s often

possible to use a relatively small battery bank. Instantaneous

demand (watts) will be limited not by the water potential or

turbine, but by the size of the inverter.

Battery Monitor

Charge

Controller

Battery Bank

Dump Load

To Household

Loads

57.6

DC Disconnect

Inverter

Note: Some breakers/

overcurrent protection

not shown

AC Breaker Panel

www. homepower .com

3 Turbine AKA: Waterwheel

The turbine converts the energy in the water into electricity.

Many types of turbines are available, so it is important to

match the machine to the site’s conditions of head and

flow.

In impulse turbines, the water is routed through nozzles that

direct the water at some type of runner or wheel (Pelton

and Turgo are two common types). Reaction turbines are

propeller machines and centrifugal pumps used as turbines,

where the runner is submerged within a closed housing.

With either turbine type, the energy of the falling water is

converted into rotary motion in the runner’s shaft. This shaft

is coupled directly or belted to either a permanent magnet

alternator, or a “synchronous” or induction AC generator.

4 Controls AKA: Charge controller, controller, regulator

The function of a charge controller in a

hydro system is equivalent to turning on

a load to absorb excess energy. Battery-

based microhydro systems require charge

controllers to prevent overcharging the

batteries. Controllers generally send excess

energy to a secondary (dump) load, such as

an air or water heater. Unlike a solar-electric

controller, a microhydro system controller does not

disconnect the turbine from the batteries. This could

create voltages that are higher than some components

can withstand, or cause the turbine to overspeed, which

could result in dangerous and damaging overvoltages.

Off-grid, batteryless AC-direct microhydro systems

need controls too. A load–control governor monitors

the voltage or frequency of the system, and keeps the

generator correctly loaded, turning dump-load capacity

on and off as the load pattern changes, or mechanically

deflects water away from the runner. Grid-tied batteryless

AC and DC systems also need controls to protect the

system if the utility grid fails.

OFF-GRID BATTERYLESS HYDRO-ELECTRIC SYSTEM

If your stream has enough potential, you may decide to go with an

AC-direct system. This consists of a turbine generator that produces

AC output at 120 or 240 volts, which can be sent directly to standard

household loads. The system is controlled by diverting energy in

excess of load requirements to dump loads, such as water- or air-

heating elements. This technique keeps the total load on the generator

constant. A limitation of these systems is that the peak or surge loads

cannot exceed the output of the generator, which is determined by

the stream’s available head and flow. This type of system needs to

be large to meet peak electrical loads, so it can often generate enough

energy for all household needs, including water and space heating.

AC Controller

Turbine

To Household

Loads

Dump

Loads

Note: Some breakers/

overcurrent protection

not shown

AC Breaker

Panel

home power 117 / february & march 2007

microhydro basics

microhydro basics

5 Dump Load

6 Battery Bank

AKA: Diversion load, shunt load

AKA: Storage battery

By using reversible chemical reactions, a battery bank provides a

way to store surplus energy when more is being produced than

consumed. When demand increases beyond what is generated,

the batteries can be called on to release energy to keep your

household loads operating.

A dump load is an electrical resistance heater

that must be sized to handle the full generating

capacity of the microhydro turbine. Dump loads

can be air or water heaters, and are activated by

the charge controller whenever the batteries or

the grid cannot accept the energy being produced,

to prevent damage to the system. Excess energy

is “shunted” to the dump load when necessary.

A microhydro system is

typically the most gentle of the

RE systems on the batteries,

since they do not often remain

in a discharged state. The bank

can also be smaller than for a

wind or PV system. One or

two days of storage is usually

sufficient. Deep-cycle lead-acid

batteries are typically used in

these systems. They are cost

effective and do not usually

account for a large percentage

of the system cost.

GRID-TIED BATTERYLESS HYDRO-ELECTRIC SYSTEM

Systems of this type use a turbine and controls to produce electricity

that can be fed directly into utility lines. These can use either AC or

DC generators. AC systems will use AC generators to sync directly

with the grid. An approved interface device is needed to prevent

the system from energizing the grid when the grid is out of action

and under repair. DC systems will use a specific inverter to convert

the output of a DC hydro turbine to grid-synchronous AC. The

biggest drawback of batteryless systems is that when the utility is

down, your electricity will be out too. When the grid fails, these

systems are designed to automatically shut down.

Turbine

AC Controller

Note: Some breakers/

overcurrent protection

not shown

Kilowatt-Hour

Meter

To/From

Utility Grid

Dump Loads

(required in

some systems)

To Household

Loads

AC Breaker

Panel

www. homepower .com

Home Power Magazine - Micro Hydro Basics.pdf

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