Turbine/Generator
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'The turbine will extract energy from the flowing water, and turn it into mechanical energy that turns the generator to create electrical energy. System efficiencies range between 65% and 80% depending upon the turbine style and design.
Microhydro-Electric System Types
Off-Grid Battery-Based Microhydro-Electric Systems
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 the 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.
The following illustration includes the primary
components of any off-grid battery-based microhydro-electric system..
picture...
Off-Grid Batteryless Microhydro-Electric Systems
If the stream has enough potential, one 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.
The following illustration includes the primary components
of any off-grid batteryless microhydro-electric system.
picture ....
Grid-Tied Batteryless Microhydro-Electric Systems
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.
The following illustration includes the primary
components of any grid-tied batteryless microhydro-electric system.
[[|]]Microhydro-Electric System Components
Controls
AKA: Charge controller, controller, regulator
[[Image:|Controller]]
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.
Dump Load
AKA: diversion load, shunt load
[[Image:|Dump Load 1]][[Image:|Dump Load 2]]
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.
Battery Bank
AKA: storage battery
[[Image:|Battery Bank]]
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
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.
Metering
AKA:
battery monitor, amp-hour meter, watt-hour meter
[[Image:|Metering]]
System
meters measure and display several different aspects of your
microhydro-electric system´s performance and status—tracking how full your
battery bank is, how much electricity your turbine is producing or has
produced, and how much electricity is being used. Operating your system without
metering is like running your car without any gauges—although possible to do,
it´s always better to know how well the car is operating and how much fuel is
in the tank.
[[|]]Main DC Disconnect
AKA: Battery/Inverter disconnect
[[Image:|Main DC Disconnect]]
In
battery-based systems, a disconnect between the batteries and inverter is
required. This disconnect is typically a large, DC-rated breaker mounted in a
sheet-metal enclosure. It allows the inverter to be disconnected from the
batteries for service, and protects the inverter-to-battery wiring against
electrical faults.
Inverter
AKA: DC-to-AC
converter
[[Image:|Battery-Based Inverter]]Inverters
transform the DC electricity stored in your battery bank into AC electricity
for powering household appliances. Grid-tied inverters synchronize the system´s
output with the utility´s AC electricity, allowing the system to feed
hydro-electricity to the utility grid. Battery-based inverters for off-grid or
grid-tied systems often include a battery charger, which is capable of charging
a battery bank from either the grid or a backup generator if your creek isn´t
flowing or your system is down for maintenance.
In rare
cases, an inverter and battery bank are used with larger, off-grid AC-direct
systems to increase power availability. The inverter uses the AC to charge the
batteries, and synchronizes with the hydro-electric AC supply to supplement it
when demand is greater than the output of the hydro generator.
[[|]]AC Breaker Panel
AKA: mains panel, breaker box, service entrance
[[Image:|AC Breaker Panel]]
The AC
breaker panel, or mains panel, is the point at which all of a home´s electrical
wiring meets with the provider of the electricity, whether that´s the grid or a
microhydro-electric system. This wall-mounted panel or box is usually installed
in a utility room, basement, garage, or on the exterior of a building. It
contains a number of labeled circuit breakers that route electricity to the various
rooms throughout a house. These breakers allow electricity to be disconnected
for servicing, and also protect the building´s wiring against electrical fires.
Just like
the electrical circuits in your home or office, a grid-tied inverter´s
electrical output needs to be routed through an AC circuit breaker. This
breaker is usually mounted inside the building´s mains panel. It enables the
inverter to be disconnected from either the grid or from electrical loads if
servicing is necessary. The breaker also safeguards the circuit´s electrical
wiring.
[[|]]Kilowatt-Hour Meter
AKA: KWH
meter, utility meter
[[Image:|Kilowatt-Hour Meter]]
Most
homes with grid-tied microhydro-electric systems will have AC electricity both
coming from and going to the utility grid. A multichannel KWH meter keeps track
of how much grid electricity you´re using and how much your RE system is
producing. The utility company often provides intertie-capable meters at no
cost.
'Turbines'types
[[Image:]]
A turbine converts the energy in
falling water into shaft power. There are various types of turbine which can be
categorised in one of several ways. The choice of turbine will depend mainly on
the pressure head available and the design flow for the proposed hydropower
installation. As shown in table 2 below, turbines are broadly divided into
three groups; high, medium and low head, and into two categories: impulse and
reaction.
|
Head
pressure
|
|
Turbine
Runner
|
High
|
Medium
|
Low
|
|
Impulse
|
Pelton
Turgo
Multi-jet Pelton
|
Crossflow
Turgo
Multi-jet Pelton
|
Crossflow
|
|
Reaction
|
Francis
Pump-as-turbine (PAT)
|
Propeller
Kaplan
|
|
The difference between impulse and
reaction can be explained simply by stating that the impulse turbines
convert the kinetic energy of a jet of water in air into movement by striking
turbine buckets or blades - there is no pressure reduction as the water
pressure is atmospheric on both sides of the impeller. The blades of a reaction
turbine, on the other hand, are totally immersed in the flow of water, and the
angular as well as linear momentum of the water is converted into shaft power -
the pressure of water leaving the runner is reduced to atmospheric or lower.
Load factor
The load factor is the amount of
power used divided by the amount of power that is available if the turbine were
to be used continuously. Unlike technologies relying on costly fuel sources,
the 'fuel' for hydropower generation is free and therefore the plant becomes
more cost effective if run for a high percentage of the time. If the turbine is
only used for domestic lighting in the evenings then the plant factor will be
very low. If the turbine provides power for rural industry during the day,
meets domestic demand during the evening, and maybe pumps water for irrigation
in the evening, then the plant factor will be high.
It is very important to ensure a
high plant factor if the scheme is to be cost effective and this should be
taken into account during the planning stage. Many schemes use a 'dump' load
(in conjunction with an electronic load controller - see below), which is
effectively a low priority energy demand that can accept surplus energy when an
excess is produced e.g. water heating, storage heaters or storage cookers.
Load control governors
Water turbines, like petrol or
diesel engines, will vary in speed as load is applied or relieved. Although not
such a great problem with machinery which uses direct shaft power, this speed
variation will seriously affect both frequency and voltage output from a
generator. Traditionally, complex hydraulic or mechanical speed governors
altered flow as the load varied, but more recently an electronic load
controller (ELC) has been developed which has increased the simplicity and
reliability of modern micro-hydro sets. The ELC prevents speed variations by
continuously adding or subtracting an artificial load, so that in effect, the
turbine is working permanently under full load. A further benefit is that the
ELC has no moving parts, is very reliable and virtually maintenance free. The
advent of electronic load control has allowed the introduction of simple and
efficient, multi-jet turbines, no longer burdened by expensive hydraulic
governors.
