Micro hydro is a type of hydroelectric power that typically produce up to 100 kW of electricity
using the natural flow of water. These installations can provide power to an isolated home or small
community, or are sometimes connected to electric power networks. There are many of these installations
around the world, particularly in developing nations as they can provide an economical
source of energy without the purchase of fuel. Micro hydro systems complement photovoltaic
solar energy systems because in many areas, water flow, and thus available hydro power,
is highest in the winter when solar energy is at a minimum. Micro hydro is frequently
accomplished with a pelton wheel for high head, low flow water supply. The installation
is often just a small dammed pool, at the top of a waterfall, with several hundred feet
of pipe leading to a small generator housing.
Construction
Construction details of a microhydro plant are site-specific. Sometimes an existing mill-pond
or other artificial reservoir is available and can be adapted for power production. In
general, microhydro systems are made up of a number of components. The most important
include the intake where water is diverted from the natural stream, river, or perhaps
a waterfall. An intake structure such as a catch box is required to screen out floating
debris and fish, using a screen or array of bars to keep out large objects. In temperate
climates this structure must resist ice as well. The intake may have a gate to allow
the system to be dewatered for inspection and maintenance.
The intake then tunnels water through a pipeline to the powerhouse building containing a turbine.
In mountainous areas, access to the route of the penstock may provide considerable challenges.
If the water source and turbine are far apart, the construction of the penstock may be the
largest part of the costs of construction. At the turbine, a controlling valve is installed
to regulate the flow and the speed of the turbine. The turbine converts the flow and
pressure of the water to mechanical energy; the water emerging from the turbine returns
to the natural watercourse along a tailrace channel. The turbine turns a generator, which
is then connected to electrical loads; this might be directly connected to the power system
of a single building in very small installations, or may be connected to a community distribution
system for several homes or buildings. Usually microhydro installations do not have
a dam and reservoir, like large hydroelectric plants have, relying on a minimal flow of
water to be available year-round. Head and flow characteristics
Microhydro systems are typically set up in areas capable of producing up to 100 kilowatts
of electricity. This can be enough to power a home or small business facility. This production
range is calculated in terms of "head" and "flow". The higher each of these are, the
more power available. "Head" is the pressure measurement of falling water expressed as
a function of the vertical distance the water falls. This change in elevation is usually
measured in feet or meters. A drop of at least 2 feet is required or the system may not be
feasible. When quantifying head, both gross and net head must be considered. Gross head
approximates power accessibility through the vertical distance measurement alone whereas
net head subtracts pressure lost due to friction in piping from the gross head. "Flow" is the
actual quantity of water falling from a site and is usually measured in gallons per minute,
cubic feet per second, or liters per second. Power from such a system can be calculated
by the equation P=Q*H/k, where Q is the flow rate in gallons per minute, H is the head
loss, and k is a constant of 5,310 gal*ft/min*kW. For instance, for a system with a flow of
500 gallons per minute and a head loss of 60 feet, the theoretical maximum power output
is 5.65 kW. The system is prevented from 100% efficiency due to the real world, such
as: turbine efficiency, friction in pipe, and conversion from potential to kinetic energy.
Turbine efficiency is generally between 50-80%, and pipe friction is accounted for using the
Hazen–Williams equation. To account for efficiency, simply multiply
the theoretical by the efficiency. In this example, if the plant's efficiency was 90%,
then 5.65 kW*0.9= 5.085 kW. Regulation and operation
Typically, an automatic controller operates the turbine inlet valve to maintain constant
speed when the load changes on the generator. In a system connected to a grid with multiple
sources, the turbine control ensures that power always flows out from the generator
to the system. The frequency of the alternating current generated needs to match the local
standard utility frequency. In some systems, if the useful load on the generator is not
high enough, a load bank may be automatically connected to the generator to dissipate energy
not required by the load; while this wastes energy, it may be required if it's not possible
to stop the water flow through the turbine. An induction generator always operates at
the grid frequency irrespective of its rotation speed; all that is necessary is to ensure
that it is driven by the turbine faster than the synchronous speed so that it generates
power rather than consuming it. Other types of generator require a speed control systems
for frequency matching. With the availability of modern power electronics
it is often easier to operate the generator at an arbitrary frequency and feed its output
through an inverter which produces output at grid frequency. Power electronics now allow
the use of permanent magnet alternators that produce wild AC to be stabilised. This approach
allows low speed / low head water turbines to be competitive; they can run at the best
speed for extraction of energy, and the power frequency is controlled by the electronics
instead of the generator. Very small installations, a few kilowatts
or smaller, may generate direct current and charge batteries for peak use times.
Turbine types Several different types of water turbines
can be used in micro hydro installations, selection depending on the head of water,
the volume of flow, and such factors as availability of local maintenance and transport of equipment
to the site. For mountainous regions where a waterfall of 50 meters or more may be available,
a Pelton wheel can be used. For low head installations, Francis or propeller-type turbines are used.
Very low head installations of only a few meters may use propeller-type turbines in
a pit. The very smallest micro hydro installations may successfully use industrial centrifugal
pumps, run in reverse as prime movers; while the efficiency may not be as high as a purpose-built
runner, the relatively low cost makes the projects economically feasible.
In low-head installations, maintenance and mechanism costs often become important. A
low-head system moves larger amounts of water, and is more likely to encounter surface debris.
For this reason a Banki turbine also called Ossberger turbine, a pressurized self-cleaning
crossflow waterwheel, is often preferred for low-head microhydropower systems. Though less
efficient, its simpler structure is less expensive than other low-head turbines of the same capacity.
Since the water flows in, then out of it, it cleans itself and is less prone to jam
with debris. Reverse Archimedes' screw : two low-head
schemes in England, Settle Hydro and Torrs Hydro use an Archimedes' screw which is another
debris-tolerant design. Efficiency 85%. Gorlov: the Gorlov helical turbine free stream
or constrained flow with or without a dam, Francis and propeller turbines.
Kaplan turbine : an alternative to the traditional kaplan turbine is a large diameter, slow turning,
permanent magnet, sloped open flow VLH turbine with efficiencies of 90%.
Water wheel : advanced hydraulic water wheels and hydraulic wheel-part reaction turbine
can have hydraulic efficiencies of 67% and 85% respectively.
Gravitation water vortex power plant : part of the river flow at a weir or natural water
fall is diverted into a round basin with a central bottom exit that creates a vortex.
A simple rotor is moved by the kinetic energy. Efficiencies of 83% down to 64% at 1/3 part
flow. Use
Microhydro systems are very flexible and can be deployed in a number of different environments.
They are dependent on how much water flow the source has and the velocity of the flow
of water. Energy can be stored in battery banks at sites that are far from a facility
or used in addition to a system that is directly connected so that in times of high demand
there is additional reserve energy available. These systems can be designed to minimize
potential damage regularly caused by large dams or other mass hydroelectric generation
sites. Potential for rural development
In relation to rural development, the simplicity and low relative cost of micro hydro systems
open up new opportunities for some isolated communities in need of electricity. With only
a small stream needed, remote areas can access lighting and communications for homes, medical
clinics, schools, and other facilities. Microhydro can even run a certain level of machinery
supporting small businesses. Regions along the Andes mountains and in Sri Lanka and China
already have similar, active programs. One seemingly unexpected use of such systems in
some areas is to keep young community members from moving into more urban regions in order
to spur economic growth. Also, as the possibility of financial incentives for less carbon intensive
processes grows, the future of microhydro systems may become more appealing.
Cost The cost of a micro hydro plant can be between
1,000 and 20,000 U.S dollars Advantages and disadvantages
System advantages Microhydro power is generated through a process
that utilizes the natural flow of water. This power is most commonly converted into electricity.
With no direct emissions resulting from this conversion process, there are little to no
harmful effects on the environment, if planned well, thus supplying power from a renewable
source and in a sustainable manner. Microhydro is considered a "run-of-river" system meaning
that water diverted from the stream or river is redirected back into the same watercourse.
Adding to the potential economic benefits of microhydro is efficiency, reliability,
and cost effectiveness. System disadvantages
Microhydro systems are limited mainly by characteristics of the site. The most direct limitation comes
from small sources with minuscule flow. Likewise, flow can fluctuate seasonally in some areas.
Lastly, though perhaps the foremost disadvantage is the distance from the power source to the
site in need of energy. This distributional issue as well as the others are key when considering
using a microhydro system. See also
Small hydro Pico hydro
Hydro power Renewable Energy
Sustainable energy References
External links Portal on microhydro power
SMART - Strategies to promote small scale hydro electricity production in Europe
Micro Hydro information, Dorado Vista ranch application
European Small Hydropower Association Micro Hydro Association UK
Hydropower Prospector, Idaho National Engineering Laboratory
Checklist on Small Hydropower, Mini Hydraulics Laboratory, European Small Hydropower Association
Ashden Awards hydro power winners Example of a new Scottish Highland micro hydro
system Home built micro hydro project
Microhydro in Afghanistan with drawings of equipment