Micro Hydro Power (MHP) Plants

Overview

A micro hydro power (MHP) plant is a type of hydro electric power scheme that produces up to 100 KW of electricity using a flowing steam or a water flow. The electricity from such systems is used to power up isolated homes or communities and is sometimes connected to the main grid.

Classification of micro hydropower can be summarized as follows:

Type	Description
Large Hydro	All installations with an installed capacity of more than 1000 kW (according to some definitions more than 10,000 kW)
Medium Hydro	15 - 100 MW - usually feeding a grid
Small Hydro	Installations of 1-15 MW usually feeding into the grid
Mini Hydro	Capacity between 100 - 500 kW, either as stand-alone schemes or more often feeding into the grid
Micro Hydro	Installations with power output of 5 - 100 kW, usually provided power for small community or rural industry in remote areas away from the grid
Pico Hydro	From a few hundred watts up to 5 kW

Micro hydro systems are generally used in developing countries to provide electricity to isolated communities or rural villages where electricity grid is not available. Feeding back into the national grid when electricity production is in surplus is also evident in some cases. The micro hydro scheme design can be approached as per household basis or at the village level often involving local materials and labor.

Micro hydro plants that are found in the developing world are mostly in mountainous regions for instance in the some places in the Himalayas as well as in Nepal where there are around 2000 schemes, including both mechanical and electrical power generation. In South America, there are micro-hydro programs in the countries along the Andes, such as Peru and Bolivia. Smaller programs have also been set up in the hilly areas of Sri Lanka, Philippines and some parts of China.

Benefits and Shortcomings of Micro Hydro Power Plants

Small scale hydropower stations like micro hydro schemes combine the advantages of hydropower with those of decentralized power generation, without the disadvantages of large scale installations.

Some of the advantages can be identified as:

• Efficient Energy Source: It takes a small amount of flow to make it work, as small as two gallons of water or a drop of as low as two feet to generate electricity with the micro hydro, the produced electricity can be used as far as a mile away from the production site.
• Reliable Electricity Source: There is a constant and continuous electrical energy supply from a hydro compared to other small scale renewable energy technologies. There are however peak energy seasons for instance during Winter where large quantities of electricity is required.
• No reservoir required: Cost effective energy solution: A small hydro- power system can cost in the range of $1000-$20000 depending on the site electricity requirements and location. The operation and maintenance costs are relatively low as well compared to other technologies.
• Power for developing countries: Having low-cost versatility and long life span, micro hydro can be used by developing countries in supplying electricity to small villages and communities.
• Integrate with the local power grid: If there is a surplus production of electricity, some companies can buy the electricity from you and integrate it to the grid. There could also be a possibility of supplementing your level of micro power with intake from the grid.
• Environmental Impact: The impact on the environment is minimized as compared to the traditional power stations that use fossil fuels.

Disadvantages / Shortcomings:

• Suitable site characteristics required: The system is very site selective and especially when you need to take full advantage of the electrical potential of small streams. Some factors that should be considered in such a case include, distance from the power source to the location where energy is required, stream size (including flow rate, output and drop), and a balance of system components — inverter, batteries, controller, transmission line and pipelines.
• Energy expansion not possible:
  
• Low-power in the summer months:
  
• Environmental impact: There is a low ecological impact from small-scale hydro systems, however the low-level environmental effects must be taken into consideration before construction begins. Stream water will be diverted away from a portion of the stream, and proper caution must be exercised to ensure there will be no damaging impact on the local ecology or civil infrastructure.
  

Technology and Application

Use of Micro Hydro Power Plants

Power produced from a small hydro station can be used for various purposes, some of the uses have been classified as follows:

1. Productive Use: This is where the electricity generated is used to perform activities where money is exchanged for a service. Most of this scenarios take place in small businesses.
   
2. Consumptive Use: All the other used that the electricity can be used for are called consumptive use. they include using the electricity at the household or close to the household.
   

Besides the productive and consumptive use, a distinction can also be made between the use of power in a mechanical way or in the form of electricity:

	mechanic	electricity
productive use	agro processing timber sawing textile fabrication cooling drying	mechanical uses with electricity as intermediate heating lighting fertiliser production
consumptive use		domestic lighting cooking cooling radio and television

As the above illustration shows power that is generated by MPH is a convenient source of electricity to fuel anything from workshop machines to domestic lighting as the power can also be supplied to villages via portable rechargeable batteries and thus there are no expensive connection costs. Batteries can as well be charged and used to provide the local community with power. For industrial use however, the turbine shaft can be used directly as mechanical power as opposed to converting it into electricity via generator or batteries. This is suitable for agro-processing activities such as milling, oil extraction and carpentry.

Technology

Scheme Components

Most micro-hydro systems are ‘run-of-river’ which means that they don’t need large dams to store water. However, they do need some water-management systems.

Components Micro Hydro Power Plant

► More information and picture in the Micro hydro power scout guide.

The illustration above shows just how a micro-hydro system can be setup. For water diversion the river water level has to be raised by a barrier, the weir [1]. The water is diverted at the intake [2] and conveyed by the channel [3] along the landscape´s contour lines. The spillways [4] protect against damage from excessive water flow. Water is slowed down and collected in the fore bay [5], from where it enters into the penstock [7]; the pressure pipe conveys the water to the power house [6] where the power conversion turbine, mill or generating equipment is installed. The turbine is the core of a MHP, which is rotated by the moving water. Different types of turbines are used depending on the head and the flow of the site, the turbines are used to rotate a shaft which is then used to drive the generator. The water is then discharged via the draft tube [8] or a tail race channel in case of cross flow or Pelton turbines.

Due to the nature of the micro-hydro schemed to be remote; a local grid is constructed to distribute the electricity to the different users. The demand output must match the capacity of the generator otherwise the voltage and frequency can vary suddenly, which can result in the damage of certain electrical equipment. The power demand in an off-grid is often variable since people switch lights and machines on and off, so the supply from the micro-hydro system must be varied to keep close control. This can be done by varying the water flow, or by using an electronic load controller.

Turbine Types

The type of turbine that can be used in a micro hydro installation depends on different factors such as, head of water, the volume of flow, and such factors as availability of local maintenance and transport of equipment to the site.

A turbine converts energy from water falling into a rotating shaft power; the selection of a hydro turbine depends on the site characteristics and the head and flow available. The desired running speed of the generator or other devices in the turbine also plays a vital role in the selection process. However other conditions such as weather the turbine is expected to produce power under part-flow conditions could also be considered. All turbines have a power-speed characteristic that will tend to run most efficiently at a particular speed, head and flow combination.

A turbines design speed is largely determined by the head with which it operates. Turbines can either be classified as impulse turbines or reaction turbines. In the impulse turbine, the turbine runner operates in air and is turned by one or multiple jets of water which make contact with the runner blades. On the other side in a reaction turbine, the turbine runner is fully immersed in water and is enclosed in a pressure casing, the runner blades are angled so that pressure differences across them create lift forces, like those on aircraft wings, which cause the runner to rotate.

	high head	medium head	low head
impulsive turbines	Pelton Turgo	cross-flow multi-jet Pelton Turgo	cross-flow
reaction turbines		Francis	propeller Kaplan

Further Information

• Hydro Portal on energypedia
• Hydro Power Basics