Small Hydropower

Lesson 1: Introduction

Definition

Definition of Small Hydropower

Small hydropower (SHP) is a proven, mature technology for provision of clean and renewable energy. Similar with the large- or medium-sized hydropower, SHP also converts energy from flowing water into electrical or mechanical energy. Hydropower converts energy from flowing water into electrical or mechanical energy. There is no agreed upon definition for SHP worldwide. However, SHP generally refers to hydropower stations with an installed capacity below 10 MW, mini hydro less than 500 kW and micro hydro less than 100 kW. The energy output will depend on two factors, namely the water flow and head. Various types of SHP schemes exist. SHP plants can either be connected to the grid, operate as stand-alone plants, or connect with other SHP plants in the area to from a mini-grid.

Benefits

Benefits

  • Short construction period, low investment, easy maintenance, long lifespan;
  • Local power supply for remote areas without grid access;
  • Minimal to zero ecological impact; non-polluting;
  • Abundant resources (rivers, streams, reservoirs, pipe systems);
  • Generally no issues with displacement of people or compensation during construction;
  • Multipurpose schemes (irrigation, flood protection, water supply etc) made more economically attractive.

Common Types of SHP Plants

High head VS low head

In its simplest terms, hydropower is the process of extracting power from falling water. The maximum power available in any stretch of the river can be calculate with the equation P = Q * H * p * g, which shows the power is the product of the amount of water flowing in the river (flow, flow rate, Q) and the height between the water surface at the intake and the power station (head, H). As an international standard, Q is measured in cubic meters of water per second, and H is measured in meters. In effect, only flow and head vary significantly from one hydropower project to the next, so these two values need to be determined early in the process. The available power increases as there is more of either one.

Two different river stretches can be very different yet both have the same power potential. The table below compares two SHP plants that both have a power potential around 1000 kW. One is high-head-low-flow and the other is low-head-high-flow. Different sites require different designs, and every design has a unique combination of layout, turbine, environmental impacts, etc depending mostly on these two parameters. SHP plants often produce between 50% and 85% of the maximum available power, because energy is lost through each stage of the process of the plant.

Regardless of the type of small hydropower plant, without a reservoir, the flow rate varies throughout the course of a year, and H remains constant. Hydrology is the science needed to estimate the changes in the river’s flow throughout the year.

High head - low flow SHP plant (Source: ESHA)

Low head - high flow SHP plant (Source: ESHA)

Lesson 2: Components of a small hydropower plant

Civil Works

Dam

Dam is a structure built across a river in order to raise the level of the water, generally including following types. Based on structure and design, dams can be classified as follows:

Gravity dam

A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by primarily utilizing the weight of the material alone to resist the horizontal pressure of water pushing against it.

Arch dam

An arch dam is a solid dam made of concrete that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes into its foundation or abutments. An arch dam is most suitable for narrow gorges or canyons with steep walls of stable rock to support the structure and stresses.

Rubber dam

A rubber dam is a flexible rubber bladder which is permanently anchored to a reinforced concrete foundation. Rubber dams are water controlling structures that can be inflated by air or water. When the bladder is deflated, impounded water is released and the bladder becomes virtually flat. Inflatable rubber dams are used in a wide variety of applications, including irrigation, water storage, power generation, flood prevention and control, erosion control, groundwater recharge, tidal barriers, navigation, and sewage treatment.

Earth-rock dam

It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay, or rock. It has a semi-pervious waterproof natural covering for its surface and a dense, impervious core.

Rock-fill dam

A rock-fill dam is a type of embankment dam which comprises primarily compacted rock materials. Shaped much like a bank or hill, rock-fill dams are effective because the force of the river or reservoir hits the core of the embankment, is exerted in a downward direction, and transferred to the solid foundation of the dam.

Buttress dam

A buttress dam or hollow dam is a dam with a solid, water-tight upstream side that is supported at intervals on the downstream side by a series of buttresses or supports. The dam wall may be straight or curved. Most buttress dams are made of reinforced concrete and are heavy, pushing the dam into the ground.

Intake works

It is a structure to facilitate the entry of water to the conduit system. It may or may not be submerged. 

Conduit system

It could be a canal or tunnel. Canals are generally excavated and follow the contours of the existing terrains. Tunnels are underground.

Forebay

 It is a structure that facilitates the entry of water to the penstock.

Silt basin

It is a structure to prevent the solid particles from entering the penstock in order to protect the turbine.

Civil engineering accessories

Civil engineering accessories may including screens, gates, spillways, etc.

 Penstock

It is the pressure pipe that convey the water from forebay to the turbine.



Penstock installation

Powerhouse

It is a structure houses the turbine, generator and other electro-mechanical accessories. Powerhouse can be of ground or under-ground.

Inside of the powerhouse

Underground powerhouse

Tail-race

It is a structure that returns the water from the turbine-generator to the original river or to a neighbor basin. Usually the turbine-generator and tail-race are connected by a draft tube.





Installation of draft tube

How the small hydropower plant produce the power?

The water is diverted by the dam through the intake into the conduit system, then flowing into the forebay, penstock and turbine inlet. In the turbine, the water spins it with enough force to create electricity in a generator. The water then flows back into the river via a tailrace.

Electro-mechanical Equipment

Electro-mechanical Equipment

Water flows through a small hydropower plant and is generally returned to the river it was drawn from. The power potential of the river, however, gets extracted and transformed to electricity through a series of machines collectively known as electro-mechanical equipment.

Turbine

The turbine converts the potential power of the river into mechanical power. Water wheels were essentially the only water turbine used throughout Europe and Asia for at least 2000 years until the knowledge and technology of the industrial revolution allowed engineers to optimize these machines. The most powerful water wheel ever built produced around 100 kW of power, and was doubtfully very efficient. Modern turbines have been in use for 150 years, and are optimized through research and advancements in engineering to extract as much of the river’s power potential as possible. The most powerful turbines in the world today produce 800 MW (8000 times as powerful as the most powerful water wheel), weigh 400 tons, and are installed at Xiangjiaba hydro power plant in China.

Three types of turbines are used in virtually all commercial hydropower stations:

  • Kaplan turbine
  • Francis turbine
  • Pelton turbine

Two basic parameters, flow rate (Q) and head (H), are needed to estimate which type of turbine to select, but these are only estimates. Ultimately, a small hydropower developer must coordinate with a turbine supplier to select the best turbine for the project.

Other turbines

Other turbines are developed for specialty situations, such as turbines that allow fish passage at low-head sites, and turbines that have a low investment cost and are easy to maintain. A cross-flow turbine is one such turbine.

Generator

The generator converts mechanical power from the turbine into low voltage electrical power.

Transformer

Electricity grids operate at standardized voltages and frequencies. The transformer transforms the electrical power produced by the generator into the standards of the grid.

Governor

The governor continuously receives information from the other electro-mechanical components and adjusts flow and turbine speed accordingly. This component assures the entire plant runs at a steady pace.

Lesson 3: Country Profiles

Ethiopia

Ethiopia

Ethiopia, with a tropical monsoon climate and three distinct climate zones, has nine major rivers and 12 big lakes. Lake Tana in the north, for example, is the source of the Blue Nile. However, apart from the big rivers and major tributaries, there is hardly any perennial flow in areas below 1,500m.

With a population of almost 100 million and an area of approx. 1.1 million km2 , it is Africa’s second most populated and 10th largest country. Ethiopia is a member of both, the Common Market for Eastern and Southern Africa (COMESA) and the Eastern African Power Pool (EAPP).

Status of SHP - Ethiopia

With a total of 1500 MW (national definition of SHP: 0.5-10 MW), Ethiopia has the second largest potential SHP capacity in all of Africa, of which so far less than 1% has been developed. However, hydropower in general makes up 94% of Ethiopia’s total installed energy capacity. It is also worth noting, that electrification rates vary widely between urban centers (85%) and rural areas (10%).



The highland topography with scattered households and demand of large cultivated land of Ethiopia as well as the large number of annual flowing small rivers is well suited for development of small and micro-hydropower. Due to the seasonal rainfall, the potential for small-scale hydropower is estimated to be 10 per cent of the overall potential. Most of the sites are located in the western and south-western parts of the country so the potential capacity varies according to the annual rainfall which ranges from 300 mm to over 900 mm.

Ethiopia has vast potential for hydropower and has been utilizing this resource for the development of large hydropower plants. While the highland topography is well-suited for development of small and micro-hydropower, the sector has been slow to grow (6.18 MW). In order to improve private sector participation, the Ethiopian Electricity Agency (EEA) is currently developing legislation for feed-in tariffs which is expected to spur activity in the sector.

Policy - Ethiopia

Ethiopia’s main energy policy objectives are to ensure a reliable supply of energy at an affordable prize, particularly to support the country’s agricultural and industrial development strategies and to support national capacity building in engineering, construction, operation and maintenance as well as the gradual enhancement of local manufacturing capacity.

The Ethiopian Electricity Agency was set up to issue operational licenses, recommend tariffs and set technical standards. Both domestic and foreign investment into hydropower of any size are allowed. There is, however, a fixed electricity rate of 0.04 US$/kWh with a specific Feed-in Tariff currently in development.

The licenses required for the operation of SHP plants are as follows:

  • Environmental impact assessment (EIA) required for projects above 500kW installed capacity
  • Operational licenses (issued by Ethiopian Electricity Agency)
  • Distribution license (for off- and mini-grid plants) – can be obtained from regulator
  • Investment license (except for cooperatives)
  • Water right approval from Ministry (if owner is not community holding water rights)

Challenges - Ethiopia

Though there is great potential for SHP development in Ethiopia, some challenges remain. There is no policy for decentralized energy production, no Power Purchase Agreements (PPA) or Feed-in Tariffs (FiT). Private investment therefore takes place only in off-grid projects which might be disrupted or abandoned following grid extensions.

More general challenges include the lack of local manufacturing capacities and the increasing water demand due to population growth.

Funding - Ethiopia

The Rural Electrification Fund (REF) provides concessional loans for the development of off-grid electrification projects. In the case of renewable energy projects up to 95% of the total investment volume is provided at zero interest.

Kenya

Kenya

Kenya lies on the equator and climatic conditions range from tropical humidity on the coast, dry heat of the hinterland and northern plains to cool plateaus and mountains. Seasonal variations are distinguished by duration of rainfall rather than by changes of temperature. Most rivers and streams in Kenya originate in the highlands and flow either east toward the Indian Ocean, west to Lake Victoria or north to Lake Turkana.

Kenya consists of an area of 580,367km2and is home to 45,925,301 people. It is a member of the Common Market for Eastern and Southern Africa (COMESA), the East African Power Pool (EAPP), as well as the East African Community (EAC).

Status of SHP - Kenya

Hydropower plays the most significant role in the generation of electricity in Kenya. While SHP (1-10 MW) represents only a small fraction of overall national electricity capacity, the country has created an environment conducive to the development of SHP projects and currently has almost 200 MW in various stages of planning. At 3,000 MW, Africa’s largest SHP potential is to be found in Kenya. However, as of now only 33 MW have been developed.

In 2013, the national electrification rate was approximately 20 per cent with the access rate in rural areas relatively low, at 7 per cent. The relatively low electrification rate exists despite the national grid providing access to over 68 per cent of Kenyan households, in part due to some counties having nearly 50 per cent of unconnected households located within the grid coverage area.

Policy - Kenya


The Ministry of Energy and Petroleum (MoEP) is the lead government institution for energy policy formulation and sector planning. It is charged with overall leadership and oversight in the implementation of national energy plans. The Energy Regulatory Commission provides oversight roles in the sector by developing and enforcing sector regulations.



The electricity supply industry structure remains that of the single-buyer model with all generators selling power in bulk to KPLC for onward distribution to consumers. The FITs for SHP plants are calculated depending on the precise installed capacity ranging from US$0.105/kWh for plants with a capacity of 0.5 MW to US$0.0825/kWh for plants with a capacity of 10 MW. These are regulated tariffs for the sale of generated renewable energy to the national grid by private developers. 

The tariffs are standard for various capacity ranges and are subject to review periodically.

A recent demand forecast considers the needs of accelerated investment into electricity generation under the Vision 2030 economic blueprint and estimates a supply gap of 10,000MW by 2024.

Challenges - Kenya

Recently, variations in rainfall and climate change have proven to be a big challenge in Kenya and have resulted in power and energy shortfalls. Limited investment flows from the private sector to SHP projects and the lack of appropriate technical skills have also hindered planned and existing SHP projects in the country.

Funding - Kenya

The Government has commissioned a national resource assessment for SHP alongside conducting feasibility studies for potential sites in order to attract private sector investment. It is expected that sites with confirmed technical and financial viability will be offered to private investors through public auctions for development.

Models utilized by developers in Kenya involve a combination of several approaches including community finance, public funding, equity investment, grants and loans from local financing institutions.

Sudan

Sudan

Sudan is a landlocked country comprising a gentle sloping plain, with the exception of Jebel Marra, the Red Sea Hills, Nuba Mountains and Imatong Hills. The third largest country in Africa (1,861,484 km2) is home to 36,108,853 people and rich in water resources from the Nile system. It has a tropical sub-continental climate with a wide range of variations extending from a desert climate in the north to an equatorial climate in the south.

The national electrification rate is 60 per cent (20 per cent in rural areas).

Status of SHP - Sudan

The Government of Sudan defines small hydropower (SHP) as any hydropower plant with a capacity between 500 kW and 5 MW. As of 2016, the total potential capacity of SHP is 63.2 MW. This total includes the El Girba 2 power plant which has three 2.4 MW units totalling 7.2 MW and presents the country’s only SHP plant.  There have been no country-wide studies focused on estimating the potential of SHP in Sudan. However, the Government has established a renewable energy (RE) target which aims to install 56 MW of additional SHP by 2031.

Policy - Sudan

The Ministry of Energy and Mining (MEM) is in charge of the energy sector in general and the recently established Ministry of Water Resources and Electricity is now responsible for electricity generation. The National Electricity Corporation, which operates under the MEM, owns and operates hydropower plants, isolated diesel systems, and thermal and steam plants. The state-owned Sudanese Electricity Transmission Company Ltd and the Sudanese Electricity Distribution Company manage transmission and distribution respectively. The Electricity Regulatory Authority is the sector regulator.


The end consumer tariffs range from 0.042 US$ per kWh for industrial consumers, to 0.089 US$ per kWh for commercial consumers.

Although Sudan has a large amount of potential RE resources, only a fraction of it has been developed so far. There is no regulatory or legal framework for RE specifically. There is no obligation to conclude long-term power purchase agreements with RE producers, no feed-in tariffs, no net-metering policy for small-scale projects and no priority access for renewable energy granted by law.

Challenges - Sudan

The challenges to SHP remaining in Sudan are many. Low levels of income and awareness of SHP benefits alongside a lack of expertise and institutional capabilities as well as a lack of adequate data hinder the development of SHP in the country.

Zambia

Zambia

Zambia is situated on the great plateau of central Africa at an average altitude of 1,200 m with a higher plateau rising in the east. The country has three main topographical features: mountains with an altitude of at least 1,500 m, a plateau with altitudes between 900 and 1,500 m and lowlands with altitudes between 400 and 900m. Zambia’s 752,612 km2 are home to 15,721,343 people and five main river basins. The most rain falls in the north while the driest areas are found in the far south-west.

In 2013, the national electrification rate was approximately 25 per cent with 49.3 per cent in urban areas and 3.2 per cent in rural areas. The Government plans to increase the national electrification rate to 66 per cent of households by 2030 with urban areas achieving 90 per cent and rural areas 51 per cent.

Status of SHP - Zambia

The majority of electricity is provided by hydropower, with 3 plants providing 91% of Zambia’s total. SHP installed capacity, defined as 0.5-10 MW, merely reaches 12.9 MW and has been decreasing due to an upgrade of existing plants to beyond the 10 MW mark. Total hydropower potential is estimated at 6,000 MW, but SHP potential capacity at only 42 MW. However, SHP potential in Zambia remains inaccurately recorded mainly due to the lack of a comprehensive and updated database specifically for SHP.

In some rural areas, which the national grids do not cover, small independent private power producers (IPPs) and non-governmental organisations (NGOs) are supplying electricity through isolated distribution networks with SHP.

Policy - Zambia

The overall responsibility for energy administration and policy formulation lies with the Ministry of Mines Energy and Water Development (MMEWD) while the Office for Promoting Private Power Investment (OPPPI) has the role of promoting private investment in the development of power projects. The Energy Regulation Board (ERB) is responsible for licensing generating plants, regulating transmission and distribution operations, regulating power tariffs (especially retail) and mediating any conflicts regarding these issues.

While there are no specific Feed-in tariffs, consumer and commercial tariffs range from approx. 0.03 to 0.09 US$/kWh.

The National Energy Policy (NEP) of 2008 encompasses a range of policy measures relevant to SHP development:


  • Encourage the development of identified potential hydro sites
  • Move towards cost reflective tariffs
  • Adopting an open access transmission regime
  • Application of smart subsidy mechanisms

Challenges - Zambia

Hydrological data is needed to adequately assess the hydropower potential of small river basins. Furthermore, the lack of a comprehensive energy policy to deal with the requirements of private plants interfacing with the national grid (such as a feed-in tariff) is limiting private sector participation, just as low general electricity tariffs are.

Lesson 4: Developing a small hydropower plant

Flow chart: Steps to be taken

Lesson 5: Planning a small hydropower plant

Natural Conditions

General

A site report is a single document that explains the small hydropower site to someone who has never been there. A good report will contain the following information:

  • Summary table
  • Information about the visit
  • Written description of the site
  • Pictures
  • Location map
  • Site map
  • Preliminary hydrology

Summary table

The summary table should include all the most relevant data. After a first site visit, the table may only contain a few values. However, after a full site investigation, a study of the river hydrology, and some estimates to size the project, the table can be completed. An example of a summary table is shown below.


In this project, a hydrologist was hired to write a hydrology report, and measurements were taken during the field visit to aid in information sharing. For each small hydropower project, the values and the source of information will change. However, the same items and units listed below should always be used so that different projects can be compared.

Summary of Small Hydropower Project

Information about the visit

This section simply lists the following pieces of information

  • The date of the site visit
  • The names and organizations of all people present at the site visit
  • What areas were visited (location of the intake, location of the power station)

Location of site

The purpose of this section is to describe exactly where the site is. One map is essential, and sometimes two maps are used. For instance, the first map may cover the entire country. Then a second map, showing roads, rivers, and places will explain to the reader how to reach the site from the nearest town. This second map is most important.

The persons visiting the site should also record GPS coordinates at the intake and record these in the table.

Site Map

In some places, base maps are hard to find. Some government agencies will have maps that cover the entire country. Detailed maps showing the height of the ground with topographic lines are preferred, but these are not always available. Online maps are almost always available, even if it is just a satellite picture. One method is to locate the site on Google Earth before going on the site visit, printing a picture of the satellite image, and drawing on this picture while at the site. This hand-made map should include the location of the river, roads, waterfalls, houses, and identifying features.

Photograph site 

It is very difficult for someone who has never seen the site to envision what it looks like. Therefore, take many pictures and include them in the report. Avoid the most common mistake of photographing a site. Do not stand too close to what you want to photograph! Step back, and even climb a hill if needed to get the best picture. A picture needs to show not only where the intake will be, but also everything that is around it too. Always take more pictures than you think you will need.

Site Geology

Geology refers to the nature of the ground and soils at the site. The geology of a small hydropower site is often overlooked and also hard to accurately determine. Professional geologists or geotechnical engineers can help provide a better understanding. For initial purposes however, an initial field visit should look to place the dam and power station on solid rock. It is valuable to remember the river has been flowing through the site, constantly eroding and shaping the ground for thousands or even millions of years.Many waterfalls exist because the rock beneath them is strong enough to withstand this constant erosion.


Such rocks will often hold dams well. The side slopes of the river are very important to consider too. Even a small dam can change the river’s shape and cause the side slopes of a river to collapse. The foundations of power stations need to transfer the large forces of turbines into the ground. Although this can often be done on loose soils, doing so required a larger and more expensive design than building the foundation on solid rock. Site inspectors should look for signs of bedrock or thin layers of top soil that can be removed to anchor dams, power stations, and penstocks straight into strong ground, preferably solid rock.

Hydrology

In a small hydropower project, hydrology is an important process to determine how much water is available for hydropower production. The hydrologist analyzes maps, rainfall data, soil properties, and stream-flow data to answer the following questions about the river:

  • How much water flows down the river every year? (Annual Volume of Water)
  • At what times of year does the most water flow in the river? How much?


  • In an average year, how much water is flowing in the river on the 18th driest day? (5-percentile flow)
  • Are all years the same, or do some years receive more water when it floods, and other receive less water when there is a drought?

Hydrology is the science of finding exact answers to these questions, and the hydrology report is usually conducted by a professional hydrologist or engineer.

Site Topology

The topology is the physical shape of the ground where the intake, conveyance system, and power house are to be built. An ideal project will have a 2 dimensional topographic map with contour lines describing the high points and low points of the river, and how the river and ground slope between these.


Knowing the elevation of the intake and power station is especially important. Surveying technology has seen rapid advances the last years, and  a single person with the right equipment and knowledge can topographically map an entire region in a day.


When topographical maps are not available, and a topographic survey is too expensive, the head needs to be measured by traditional surveying. This is best done with professional survey equipment, but can be measured with little expense (although it often takes time) using a hydraulic level.

Technical Design

Civil work

The civil works of a SHPP include the earthwork, structures, and components needed to divert water from the river and bring it to the turbine for power generation. In most of the developed world, the civil works constitute the largest cost of the plant. All hydropower plants require the same basic components – an intake, a conveyance system, and a power generation station.

Headworks - Dam and Intake

The headworks of a small hydropower plant divert water from the river to be used for power production in the following stages. In a typical run-of the river design, the headworks do not store water, but merely split the river’s flow into two paths. One portion of the flow is diverted at the headworks, through a man-made conveyance system, to the power station where the power potential is extracted to produce electricity.


The other portion of flow, known as “environmental flow”, is released down the river’s natural course to protect the ecosystems in the affected stretch that depend on flowing water to survive. To avoid damage to electromechanical equipment, the headworks need to provide a basic water treatment by removing, sediment, debris, ice, and air from the flow portion used for power production.

Dams-less Headworks

Many people associate the word hydropower with dams. But some hydropower plants can be built without any dams at all, especially at high-head, run-of-the river sites, which are common in small hydropower development. Building small hydropower without a dam saves the cost of constructing the dam and the significant environmental impacts that inevitably follow. Aquatic life migrating up and down the river may continue, while debris, ice blocks and


garbage moving downstream is free to pass without getting caught on trash racks that need to be periodically cleaned. Nonetheless, small dams are usually built as part of the headworks, even when not required. Building a dam is the conventional approach to turn any location in any river into a facility to reliably divert water. More careful site selection for the intake may reveal a lake or deep pool suitable for drawing water without a dam.

Dammed Headworks

Small hydropower dams are typically made of concrete and only a few meters tall. They need to be able to withstand a catastrophic condition, such as a fallen tree striking it during a flood, and all dams, no matter what the type, require a spillway. A gravity dam is a type of concrete dam often suitable for low dam heights. It is made of a solid mass of lightly reinforced concrete, sometimes filled on the inside with stones to save cement. Its cross section will often be shaped as a nappe (the shape water takes at it flows over a sharp crest).


This ideal shape allows large flows of flood waters to easily overtop the dam during a flood. The structure needs to be heavier than the water pushing on it to resist it from sliding or tipping over during this theoretical catastrophic event. A reinforced concrete plate dam uses less concrete but more reinforcing steel, and is essentially a thin wall (at least 30 cm thick) built across the river and supported on its downstream side by buttresses. A plate dam can be cheaper than a gravity dam, but needs to be anchored into solid bedrock beneath.


All dams should be built on solid rock wherever possible, but plate dams require it. Earth dams are often unsuitable for small hydropower. The advantage is they are built from earth locally available at the site of the dam. Flood waters may not overtop the crown of the dam and instead need to flow out a designated spillway beside the dam well before the upstream water level rises to the height of the dam’s crest. On large earth dams, this extra height (freeboard) is often small compared to their height, but for a small dam it will still require a large freeboard, which can be as high as the water is deep.

Low-Head Intakes

Whether dammed or dam-less, all SHPPs require an intake, and they come in many forms. At low-head sites, intakes need to be large and complex to convey large flows with minimal power loss. The conveyance system is so short that the intake is commonly constructed as part of the dam, and the entire power house may be placed within the dam.


Low-head, small hydropower sites are found near the downstream end of rivers, close to the river mouth. Biodiversity in a river generally increases as the river nears the river mouth, so low-head sites tend to not only cost more per GWh of electricity produced, but also causes far greater environmental damage than high-head hydropower schemes.

High-Head Intakes

High-head sites that use relatively smaller flows and higher head are better suited for small hydropower development, both for their lower investment cost and smaller environmental impact. A very common high-head intake consists of a funnel beneath the water surface. The funnel shape gradually accelerates water into the penstock, preventing an unneccessary loss of the river’s power potential. Some loss is always inevitable, but all components in the headworks and conveyance systems should seek to minimize losses to allow more power to be available to produce electricity. The entire funnel needs to be submerged to prevent air being sucked into the intake. In areas where the river may freeze, at least one meter of depth is needed to keep water flowing to the intake beneath a floating layer of ice.


To prevent debris from traveling down the penstock one or several trash racks are needed in front of the funnel mouth and must be cleaned regularly. Sediment dissolved in the river poses a special problem for some SHPPs. Dissolved soil particles, such as silt and sand will abrade the turbine impeller and quickly wear out the turbine. Water with heavy sediment needs a sedimentation basin at the intake, where diverted water is made to flow slowly before entering the penstock in order to give time for suspended particles to settle out. This debris builds up and must be removed regularly. Flushing systems can be built as part of the headworks to flush settled sediment past the dam. A simple design for a high-head intake builds the intake funnel as part of a dam with the mouth of the funnel opening upstream.


Intuitively it may seem logical to harness the rivers momentum to push water straight into the intake, but the river is usually flowing very slowly before entering the intake, and the direction the funnel is facing makes nearly no difference to conserving the power potential. A prudent alternative is to position the intake funnel perpendicular to the flow of the river slightly upstream of the intake. Heavier debris such a branches, logs, and footballs will likely bypass the intake, and during floods, debris floating around the intake pond often gets washed over the spillway. Several proprietary intake designs take this concept further. One such design is the Coanda Intake.

Coanda Intake

The Coanda Intake is rapidly gaining popularity among small hydropower developers in Europe. In this design, the entire river, along with any ice, fish, debris, and even sediment pass over the top of a long intake that stretches across the river. As the river tops the intake, it slides down a short and smooth metal plate, accelerating up to supercritical flow condition. At that point, 1mm slots are installed into the run, which suck the fast moving water downward into a pond below.


The water that makes it through is very clean. Particles larger than 1mm are screened out and washed away and larger debris gets automatically cleaned off during each flood event. The downsides are a slight loss in total head compared to a dam spillway placed at the same elevation and potential difficulties for the governor to regulate the amount of water flowing to the turbines. Early research suggests the intake functions well during freezing conditions.

Conveyance System

The conveyance system moves water from the intake to the turbine. For low-head sites, the conveyance system may be only a few meters long, but at high-head sites, it can stretch between a few hundred meters to several kilometers in length. As the water nears the turbine, a pressurized pipeline called a penstock is necessary. Some SHPPs spare the cost of purchasing pipeline for the entire conveyance length by conveying the water part of the way through an open channel. To do so, the channel needs to be kept at a high elevation, a little below the water surface of the intake pond until it reaches the penstock. Whether just a penstock, or combination of canal and penstock are being used, the whole conveyance system must continuously slope downhill.


This is true also for pressure pipes to avoid air building up at high points in the line. In cold areas, penstocks should be buried at least a meter below grade to prevent water inside from freezing. This is a good practice regardless to physically protect the penstock and maintain the natural scenery of the area. Penstock bends need to be anchored to the ground with large reinforced concrete blocks. Typical pipe material for the penstock is ductile iron. Steel pipes can be used but are often prohibitively expensive. Fiberglass-reinforced polymer (GRP) pipe is a cheap alternative that can handle the pressure, but it needs to sit on a uniform bedding material, which makes it difficult to install in uneven terrain.

Powerhouse

The power houses and protects the electromechanical equipment from weather and outside elements. The most expensive component is often the buildings foundation, which needs to transfer the hydrodynamic forces generated by the turbine into the ground. This is easier to do when the foundation is anchored into solid rock, but at greater cost the station may be built on looser soils. For medium-head and high-head small hydropower plants (using Francis and Pelton turbines), a powerhouse can typically be built in the size and shape of a convention residential house using locally available building practices. The main room of the power station houses the turbines and generators.


The room is loud (around 110 decibels), and should be insulated from sound. The plants control center should be located outside of this main hall. The transformer may be located inside the station in its own fireproof room, or outside. Either way most transformers are highly explosive, and spill prevention measures need to be in place to capture oils in case they leak. Careful through should be given to installing the generators, and isolating them for occasional maintenance. Some power stations are built with their own designed cranes to lift the generators, while other are built with a removable roof that allows a mobile crane to lift the generator in and out through the ceiling.

Support Facilities

In addition to the basic components inherent to all hydropower plants, most project require the construction or refurbishment of access roads, borrow pits, and other facilities necessary to construct and operate the plant. In many cases, particularly for remote sites, constructing support facilities constitute a substantial portion of the investment needed to realize the new plant. In addition to financial costs, they can also bring unwanted social environmental impacts. A new road to a previously remote area can encourage rapid increase in poaching, deforestation and deterioration of a region’s inherent natural beauty.

Electrical Distribution

Electricity produced at a small hydropower plant needs to be distributed to homes and industry that consume this power. In developed countries, well-established electrical grids transport electricity from powerplants to electricity consumers, so a new plant simply needs to connect to this existing grid. Yet this is rarely a straight-forward process. Even when high voltage electrical wires runs nearby, they are not always suitable for a connection with a SHPP. Many rural wires have too small of a capacity to handle the new power, and connecting to very high voltage lines requires such expensive electrical equipment that is rarely cost effective to do so.


Clear boundaries need to be established to determine what part of the grid is the responsibility of the new SHPP and which part is the responsibility of the grid operator. Rules and regulations on grid connection vary greatly from one area to the next. 

SHP is sometimes a great technology to power isolated communities through microgrids, either by themselves, or in combination with solar and other renewable power sources. In such schemes, the grid is planned and constructed along with the power plant.

Legal Aspects

Any SHP project comprises a range of legal considerations.

Land rights

Some components or parts of the SHP plant will be on land. These might require land property or access rights and other usage permits – possibly also a change in status.

Water rights

Water of rivers is used for different purposes (irrigation, fishing, industrial use, leisure, etc.), many of which are regulated. Therefore, a permit or authorization of some sort is usually needed to use a river’s water to produce electricity.

Grid access

In order to use the produced electricity and create revenue, it needs to be fed into a grid and reach consumers. Access to this grid requires permission from the authority in charge. 

Permits

A feasibility study usually acts as the foundation of the issuance of a government regulatory permission needed to implement an SHP project. The exact permits and approvals required for an SHP project, however, vary by region and project specifics. Below you can find a sample list of permits required for one such project in Uganda.

Source: Overseas Private Investment Corporation

Environmental and Social Impact

Environmental Impact Assessment

An Environmental Impact Assessment (EIA) is a process for anticipating a project’s effects on the environment and usually leads to an Environmental Impact Statement (EIS).

As a result, unacceptable impacts can be addressed in the design process.

The legislations regulating such studies vary from country to country. Furthermore, effects on the environment depend on location and technology details of the specific project.

The following charts can provide a general idea of action items that might have to be considered and a generalised outline of the process of approving or rejecting a project based on environmental impact considerations. They are divided into events that can occur during construction and events that might occur during operation.

Source: European Small Hydro Power Association

Source: European Small Hydro Power Association

Social Impact Assessment

A social impact assessment is a process of gathering and analysing information that enables the definition of actions to limit negative or enhance positive impacts of a project on the human element. 

Some social aspects that can be affected by a policy or project (Source: UNEP):

Lesson 6: Maintaining small hydropower plant

Benefits for maintenance

  • Reduce electric shock accident
  • Reduce the electrical fire and equipment damage caused by the faulty operation
  • Reduce the power loss caused by the delayed maintenance
  • Strengthen the professional level of operators
  • Enhance the site management

Management of maintenance

Technically, the maintenance of a small hydropower plant may includes equipment facilities administration, operation management, repair management, safety management, job training, operating management, civilization production management and file management.

Equipment facilities administration

  1. Equipment and facilities should be periodically inspected and tested. Here the equipment and facilities may include hydraulic machinery, electrical equipment, metal structures and hydraulic structures.
  • Hydraulic machinery includes turbine, water pumps (water supply pump, fire pump and discharging pump), water-oil-water system, measuring instrument, indicator, safety valve, pressure vessel, etc.
  • Electrical equipment includes generator, transformer, primary and secondary equipment.
  • Metal structures include gates, water conveyance system, lifting equipment and hoisting device of spillway gate.
  • Hydraulic structures include concrete dam, earth-rock dam, powerhouse, etc.


2.  Equipment and facilities should be graded every year by the plant itself.

Operation management

  • The staff on duty should be responsible for the operation, maintenance and inspection. They should check all equipment following the previous inspection route at a fixed time. Once any problem they find, they should immediately deal with according to relevant regulations. The staff on duty should check all equipment periodically everyday following the regular route.


  • The operation, maintenance and inspection should abide by all national laws and regulations

Repair management

  • General maintenance

 General maintenance for the equipment is mainly for prevention. It should be arranged in dry season. Operator and maintainer should make a maintenance plan and follow the plan strictly.


  • Emergency repair

The plant should have emergency mechanism in order to ensure repair when any sudden accidents happen.


  • Condition based maintenance

The plant should organize a work group for condition based maintenance and edit detailed implementing rules.

Safety management

The plant should insist on “safety and prevention first” and make the plans for flood and emergency accidents. The plant should also regularly carry out anti-accident drill and record the results.

Job training

1.   General requirements

  • The plant should make annual training plan and the implementation should be supervised by the plant chief or technical director.
  • New employees should first have technical and safety training, and only qualified staff can engage in relevant positions.
  • When the plant introduces new equipment and technology, the operators should be trained in advance.


2.    Operators should know

  • the equipment operation of hydropower station;
  • equipment technical parameter and layout;
  • Wiring and operation of primary and secondary equipment;
  • Layout and operation of oil-gas-water system;
  • Operation of water supply system;
  • Emergency plan of the hydropower plant and their own tasks;
  • Procedures and rules of scheduling, operating and safety works;
  • Inspection, test and relaying protection;
  • Equipment structures, working principles and how to operate.

Operating management

  • Operation of the plant should be lawful, and the plant should strictly abide by the national laws and regulations;
  • Improvement of the financial management system;
  • Increase the investment for refurbishment and the rural hydropower plant should be gradually transform to modernization;
  • Reserve the special fund for safety and supervise its proper use;
  • Make a reasonable plan for generation;
  • Use energy-saving equipment and reduce the power consumption of the plant.
  • Strengthen the asset management to prevent unnecessary loss.

Lesson 7: Learning from China's experience

SHP in China

SHP in China

China possesses the largest installed SHP capacity in the world, operating roughly 50,000 small hydro stations that help to bring electricity to over 300 million people. Approx. 40GW installed SHP capacity.

Development

1950s-1970s

The first stage – solving electricity shortage, providing domestic lighting

1980s-1990s

The second stage – poverty relief & rural electrification, electricity for township industry, agricultural processing & irrigation pumping

from 2001

The third stage – continuing rural electrification & electrification of mountainous areas, boosting local economy, environmental protection

Small Hydropower Replacing Firewood


  • 140 million tons of firewood consumed per year
  • starting from 2003 programme to replace – 592,000 households, 2.24 million rural residents benefitted, 733,333 hectares of forest area protected
  • household savings per year about 65% plus 50 days of labor (firewood cutting)

SHP Efficiency and Capacity Expansion Projects


  • Central Government programme started in 2011 to refurbish old SHP plants to eradicate planning and construction deficiencies, increase efficiency, safety and reduce environmental impact
  • more than 5000 plants upgraded, total approx. 1.7 GW capacity increase
  • State grants of 10 billion RMB

Policy incentives

  • Profit from SHP stations exempted from tax if re-invested in SHP
  • Low-interest loans from central and local governments
  • Central government grants
  • VAT on SHP only 3%
  • Income tax on SHP between 0-33% depending on province
  • Feed-in-tariff

Standards


  • More than 1200 technical standards related to SHP planning, design, materials, equipment, construction, commission and operation
  • Applying these standards brings a number of benefits to economy, quality, reliability, speed, operation, safety and environment.

Exam

Social Impact: Name 5 social aspects that can be affected by a policy or project.

There are three stages of SHP development in China. Which main issues do they focus on?

  • electricity shortage & domestic lighting
  • poverty relief, township industry, agriculture & irrigation
  • mountainous areas, local economy & environmental protection

Environmental Impact: Match the events during operation with the corresponding impact priority.

  • Flow rate modification
    High
  • Watercourses damming
    High
  • New electric lines
    Low
  • Noise from electromechanical equipment
    Low

SHP Potential: Which of these countries has the largest potential SHP capacity in Africa?

Challenges: List 5 challenges to SHP development in the countries discussed.

e.g. lack of ..., increasing... 

 

 

 

 

 

 

Arrange the parts of this SHP plant to the correct location in the image.

  • penstock
  • inlet valve
  • turbine
  • transformer
  • grid