1. TECHNICAL BASICS OF SMALL HYDROPOWER
1.1 Description of SHP 1.2 Speciﬁc Characteristics of SHP plants 1.3 Low head and high head plants
2. ENVIRONMENTAL SOLUTIONS 2.1 Reserved ﬂow 2.2 Fish By-Pass systems 2.3 Trash rack material management 2.4 Multipurpose plants 2.5 Design 2.6 Noise and vibrations 2.7 Fish-friendly turbines
SOME EXAMPLES ON ENVIRONMENTAL INTEGRATION OF SMALL HYDROPOWER PLANTS Case study Case study Case study Case study Case study Case study Case study
1 - Backbarrow, UK 2 - Dorfmühle, Austria 3 - Wathultström, Sweden 4 - Kavarskas, Lithuania 5 - Saviore Dell’Adamello, Italy 6 - Tedelec, France 7 - Troistorrents, Switzerland
4 5 6
6 6 7 9 10 11 13 14
15 15 16 16 17 18 18 19
Source : Ademe
limate change due to CO2 emissions has been deﬁned as the major environmental challenge to be faced nowadays by the International Community. One GWh of electricity produced by Small Hydropower (SHP) means a reduction of CO2 emissions by 480 tonnes. The Rio conference in 1992, The Kyoto protocol in 1997, the European White Paper “Energy for the future: renewable sources of energy” and ﬁnally the “Directive/77/EC of the European Parliament and of the European Council of 27 September 2001 on the promotion of electricity produced from renewable energy sources in the internal electricity market” set clear community targets; together all these documents show impressively the political intention. Additionally the public awareness on environmental topics has improved signiﬁcantly, leading to a European environmental awareness. One of the latest manifestations of this awareness is the European Water Framework Directive, aiming at an overall protection of water, being the basis of life. There are some contradictions between the “Renewable Electricity Directive” and the “Water Framework Directive”. Speciﬁcally these contradictions can be seen as the main reason for producing the “Brochure on environmental integration of small hydropower plants”. Unfortunately during recent decades many rivers have been modiﬁed for several reasons other than hydropower such us ﬂood control, agriculture etc.
On a global level there is no doubt about the beneﬁts of converting energy by SHP plants (climate change mitigation, security of energy supply)- the same view can be taken on a regional level (local development and employment). On a local level there are of course some impacts, which can be quite clearly deﬁned. - The identiﬁcation of these impacts and the measures to minimise and compensate for them is the main idea and intention of the brochure.
In a couple of cases SHP development can be combined with existing buildings or structures. So-called multi-purpose plants may combine drinking water or waste water systems with the environmental impact of SHP use thus being considerably reduced. The key is the use of existing artiﬁcial waterways.
TECHNIC AL BA S I CS O F S M A L L H YD R O P O W E R
BASICS OF SMALL HYDROPOWER
1.1 DESCRIPTION OF SHP
ydropower is the most traditional and most important, clean renewable energy source in Europe. The “fuel” of hydropower is running water, which means rivers of any site can be used, whilst keeping the water available for any other purpose. The energy to
be utilised is based on two input facts: discharge in m3/s and head in m. Both facts are necessary - the product indicates the power output of the hydropower station.
Begining of the water right
Water intake : dam with ﬁsh ladder
Command Control Power station Residual ﬂow
© OFCL, 1995
Turbine and generator
Head is deﬁned as the difference in elevation between two particular cross sections of the river. Making a head useful for hydropower -use needs a concentration by means of hydropower impoundment, diversion or tail water lowering. At the point of concentration the powerhouse is situated. The conversion of the energy potential of the river into electricity requires a turbine (potential and kinetic energy into mechanical energy) [rotation] and a generator [rotation into electrical energy]. The output of a hydropower plant is given in terms of power [kW] and electricity production [kWh]. The result can be calculated as follows:
P (kW) = Q (m 3/s) x H (m) x
η tot x 9,81 and approximately Q x H x 7,8
ηtot = total efﬁciency (ηturbine x ηgenerator x ηspeed increaser x ηtrafo)
P = electrical power output Q = rated discharge H = net head Electricity production - the thing we pay for - is power during a certain time period. The annual electricity production of a hydropower (HP) station is approximately calculated as
E (kWh) = P (kW) x 4500 (h)
The head of a HP station is mainly determined by geographical and topographical parameters. The discharge varies due to the natural ﬂow regime. Usually a Hydropower station runs
at full load for roughly three months. The rest of the year according to the lesser discharge the station is operated at part load.
1.2 SPECIFIC CHARACTERISTICS OF SHP PLANTS
The great majority of SHP plants are privately owned - at least up to a size of 1 MW. Due to typical economies of scale SHP plants are usually more expensive than big stations. Some instrumentation, control and monitoring systems have no size dependency. There are only a few plants with storage facilities, which allow the shifting of the discharge along time axis. Most of the SHPs are run-of-river plants, which do not alter the natural ﬂow regime. Due to size any alteration of bedload regime is almost negligible. The length of the backwater areas is limited. The impoundment caused by SHP is in most cases rather low. A SHP plant is not to be seen as simply a downscaled version of a large HP plant
In general SHP plants can be much more individual in their design and construction due to smaller risk and smaller dimensions. A direct physical and operational approach eases the all over handling of a SHP. In the past many SHP plants have been erected directly coupled with industrial production plants like mills. A great number of them have been abandoned for short term economic reasons, though thousands of them are still operating in their original form and many of them have been upgraded and refurbished, producing much more energy than they had done in the beginning. SHP is located wherever a small or medium watercourse with some head is available. Either they have been built within urban structures or absolutely remotely high up in mountainous regions. Although the limit of SHP has been set at 10 MW, the distribution of size follows a typical curve: the number of plants is in inverse proportion to the size of the plant. Consequently the “typical” SHP has a size of some 50 - 500 kW.
Technical basics of small hydropower
he principle of hydropower use does not vary between SHP plants and big stations. Nevertheless a European limitation has been set at 10 MW, which has been incorporated in a number applied by a couple of legal acts in different European countries. Additionally there are some more or less pragmatic differences to be seen:
TE C HN IC AL BA S IC S OF SM ALL HYDROPOWER AND E N V I R O N M E N TA L S O LU T I O N S 6
1.3 LOW HEAD AND HIGH HEAD PLANTS
ischarge and head are the design parameters of Hydropower. To gain the same power output one might either have a reasonable head and little discharge (high head plant) or the other way around (low head plant). High head plants are usually located in alpine regions on smaller streams and low head plants are located on bigger rivers in semi-alpine and lowland regions.
In principle high head plants need some pressure pipe and particular intake structures. Low head plants are often characterised by weirs and open water channels. In the case of low head the powerhouse is located either at the weir (river type) or between the headwater and the tailwater channels (diversion type).
2.1 RESERVED FLOW
ll deﬁnitions of reserved or minimum ﬂow place emphasis on the protection of the natural life in the river. The objectives of assuring a minimum ﬂow downstream of hydroelectric installations or other water abstractions are fairly clear.
2.1.1 Methods based on hydrologic or statistic values
There are dozens of formulas for the calculation of reserved ﬂow and their numbers tend to increase day by day. This demonstrates that no good universally valid solution for reserved ﬂow determination exists at the moment and probably never will exist.
Within these methods, a ﬁrst subgroup refers to the average ﬂow rate (MQ) of the river at a given cross section. These methods give values between 5 and 60 % of MQ; the latter one in case of high economic importance of ﬁshery. A second subgroup of methods refers to the minimum mean ﬂow (MNQ) in the river. The values calculated can vary from 33 to 100 % of MNQ. A third subgroup of methods refers to the preﬁxed values on the Flow Duration Curve (FDC). In this group there are a wide variety of methods: from a reserved ﬂow equal to 20% of Q300 (ﬂow rate exceeding 300 days of duration) to incredibly complex interpolating formulas.
Each singular result within the great variety of formulas can only supply a value to be used as a reference for regulatory purposes. The formulas available can be divided into four groups:
2.1.2 Methods based on physiographic principles
Sometimes it is useful to introduce the auxiliary concept of “providing reserved ﬂow” corresponding to the artiﬁcially regulated ﬂow rate at a certain time and in a certain cross section to guarantee a required amount of water in a different cross section of the same river.
They basically refer to a preﬁxed speciﬁc ﬂow rate expressed as l/s.km2 of catchment area. Values can vary from 1,6 to 9 or more l/s.km2 (in cases of abundance of ﬁsh). These methods are easily applicable presuming there is good basic data. However no hydraulic parameters are considered and neither the effect of tributaries nor the length of the diversion reach is taken into account.
…ALL DEFINITIONS OF RESERVED OR MINIMUM FLOW PLACE
2.1.3 Formulas based on velocity and depth of water Also in this group of methods there is a wide range of variation: one says water velocity in case of reserved ﬂow may not fall below a preﬁxed threshold value of 0,3-0,5 m/s and the minimum depth of water must be greater than a preﬁxed value of 10 cm. Another suggests 1,2 - 2,4 m/s and 12 - 24 cm water depth and so on. The great advantage of these formulas is that the shape of the proﬁle is included in the calculation and there is no need for hydrological data. Nevertheless diversion length and tributaries are not considered.
2.1.4 Methods based on multi-objective planning taking into consideration ecological parameters These methods are generally very complex in their application and require considerable expertise in doing so. They require site-speciﬁc ﬂow observations and take into account hydrological, hydraulic, ecological, and meteorological data, embracing both ecological and economic parameters. Methods are expensive in data collection and mathematical computing and are suitable only for particular types of rivers. Their transferability is doubtful.
2.2 FISH BY-PASS SYSTEMS
ome special characteristics of river systems are the great variety of aquatic biocenosis, the multiplicity of morphological structures, the dynamics and the exchange processes with neighbouring areas. The last mentioned aspect is signiﬁcant from the limnological point of view and is reﬂected in the theory of the spatial and temporal continuity of rivers. Biologists have identiﬁed the impacts on river continuity by weirs, diversion concepts, measures of ﬂood control and river regulation as severe and lasting. Although ﬁsh passes were invented some decades ago for the quite different economic reasons of ﬁsheries, they have become a typical focus of environmental interest. Even more than the system and construction of a hydro power plant, the design of a ﬁsh-bypass is a very speciﬁc and singular exercise requiring the consideration of a wide range of parameters and restrictions. A badly designed bypass has no function at all, only the spending of money for nothing. However the biocenotic classiﬁcation of the project site is an unavoidable necessity in deciding the type and the construction details of the bypass-system. The individual solutions will necessarily ﬁt into one of the following groups:
Source : IT Power
In general techniques to facilitate the passage of ﬁsh may be divided as follows: Systems at the barrier / weir Systems bypassing the barrier / weir Systems bypassing the power station (in case of diversion) It must not be forgotten, that the over all function does not only depend on the system itself but also on the adjoining sections in the headwater and tailwater areas. The following sketch indicates the critical points:
Fish by-pass using bio-acustic ﬁsh fence
EMPHASIS ON THE PROTECTION OF THE NATURAL LIFE IN THE RIVER
FISH LADDER (dividing up total head into low passable steps between small basins) FISH BYPASS SYSTEMS (imitating the morphology as well as the hydraulics of small water courses) FISH LIFT
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Critical aera Power station Head race channel
Tail race channel
Whereas 1. mouth of the tailrace channel (attraction ﬂow) 2. power house (head, space available) 3. diversion reach (residual ﬂow - hydraulic problems in velocity and depth) 4. weir (head) 5. back water area (attraction ﬂow, velocity)
Any bypass system consists of the following sections: the outlet the passage the basins, the ﬁshway the intake
DESIGN CRITERIA / FEATURES
The following checklist contains the well-known design criteria.
no danger of sedimentation or silting up near the scour reachable even at low water easy to ﬁnd due to line of max. ﬂow
variable ﬂow velocities continuous line of maximum velocity acceptable maximum velocities acceptable minimum depths no turbulences no circular ﬂow acceptable height of small ramps no fan out of water running up sections submerged weir conditions areas to hide adequate shading natural bedload natural light difﬁcult access to man
adequate depth adequate width adequate length resting basins no aeration at overﬂow sections acceptable height of drops no danger of damage to ﬁsh
adjustable discharge unselective passability protection against ﬂood protection against ﬂoating matter protection against too much bedload
morphological adequacy physical resistance
6. INDIVIDUAL FEATURES
THE DESIGN OF A FISH-BYPASS IS A VERY SPECIFIC EXERCISE REQUIRING THE
Source : Boku
As said before there is a close connection between discharge and construction due to hydraulics and a range of tolerance between a minimum and maximum acceptable discharge. This tolerance should be used to meet different hydrobiological as well as economic goals. During some periods of rather low migration requirements the discharge and thus the quantitative capacity can be reduced. The permitted ﬂow may simulate the natural discharge variability. Good design and operation management within the limits may also cause a reduction of loss of energy production. Experiences with a couple of sites have indicated that as with the discussions about residual ﬂow there is a dependency between the hydrological characteristics and the necessary operating ﬂow. Considering the size of the river the values vary between 1 % and 6 % of mean ﬂow (MQ). The following graph illustrates this approximation in absolute values.
Natural like bypass channel, Erlauf River, Austria
2.3 TRASH RACK MATERIAL MANAGEMENT
Q by pass in l/s
lmost all modern small hydroelectric plants have a trash rack cleaning machine, which removes material from the water to avoid it entering plant waterways and damaging electro-mechanical equipment or reducing hydraulic performance.
��� ��� ��� ��� ��� �
MQ in m3/s
Each year tons of material (mainly plastic bags, bottles, cans, as well as leaves, branches and all the kind of things that man and nature throw into the water) are removed from the river. In many countries when something, including organic material, is removed from the water, it becomes automatically waste material which must be properly disposed of with the very high costs of waste disposal. One must not forget the public interest in removing anthropogenic waste from the water, carried out by SHPoperators. This undoubtedly represents a positive impact of small hydroelectric plants which should be duly taken into account and suitable support measures should be undertaken to reduce the economic burdens on small hydroelectric plant operators in this area.(e.g. by reducing the waste disposal fees or allowing for different treatment between organic and non-organic material). Up to now, SHP operators are providing that service for free.
CONSIDERATION OF A WIDE RANGE OF PARAMETERS…
Source : Boku
Vertical Slot Fish- Way at the Prollingbach river, Austria
2.4.1 Drinking water supply systems In recent decades many small hydropower plants have been carried out in drinking water systems, especially in mountain areas, where instead of pressure reducing devices small or micro turbines have been installed to exploit head otherwise dissipated. In this case an important multipurpose use of water has been achieved and it is worth taking into due consideration.
Source : MHyLab
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2.4 MULTIPURPOSE PLANTS
La Zour drinking-water power plant (474 kw)
2.4.4 Flood protection In many small hydropower plants the river banks near to the diversion works must be rearranged and raised above their normal level. Such action results in an increase of the water level and consequently of the ﬂow rate which the river can convey during ﬂoods. Another way to achieve ﬂood protection is the use of the basin to store part of the water volume during ﬂoods, although the available volume of storage in small hydropower plants is usually very small compared to the demands of ﬂood protection.
2.4.5 Creation of adjoining environmental areas
2.4.2 Irrigation channels A lot of small hydropower plants have been erected and are still being realised in irrigation networks or channels, especially in plains where dozens of low head plants exploit the water resource both for irrigation and energy production purposes, supplying energy to the grid or to match electricity demand directly for irrigation (e.g. pumping stations)
As a mitigation measure to be taken in a small hydropower plant realisation, the creation of adjoining environmental areas is often put into effect. These areas are different from site to site and it is hard to generalise on how to set them up. Nevertheless they undoubtedly contribute to making the small hydropower plant more easily acceptable from the environmental point of view.
2.4.6 Waste water treatment plant
2.4.3 Recreation purposes In some pondage plants the water level in the basin has to be kept higher than a preﬁxed level to allow angling or other recreation activities, so that only part of the water volume available can be stored for hydroelectric purposes. Source : Studio Frosio
There are at least two places within a waste water treatment plant to insert a hydropower installation - above the plant and below the plant. For example in alpine regions sometimes there is a central treatment plant down in the valley where the waste water is collected from smaller villages high up in the mountains. The head in such cases is reasonable. A pre-treatment (e.g. trashrack) before entering the pressure pipe is necessary. In cases of larger treatment plants the head available downstream between the treatment and the river may be used. No additional cleaning procedures are necessary.
Rino Small Hydropower Plant, Italy
IN RECENT DECADES MANY SMALL HYDROPOWER PLANTS HAVE BEEN CARRIED OUT IN DRINKING WATER SYSTEMS, ESPECIALLY IN MOUNTAIN AREAS 10
2.5 DESIGN 2.5.1 Open waterways and river restructuring 126.96.36.199 BACKWATER AREAS Any kind of hydropower exploitation needs even a short diversion of water and therefore at least some small impoundment by weirs. The height of the weir is directly related to the length respective to the depth of the backwater area. The longer and the deeper it is, the bigger the alteration of habitat. In backwater areas there may occur some alteration of natural habitat conditions in terms of : Flow velocity Sedimentation Width of the riverbed Depth of the riverbed In fact the impoundment of a river reach sometimes offers an absolutely new approach in terms of river restructuring. Especially in the case of conventionally regulated rivers the banks are strongly ﬁxed with stone material at a slope of 1:2 and the riverbed has a constant width. The increase of the water level allows the design of a completely new structural set up for the bank implementing ecological demands like variable slope, variable width and the application of bioengineering methods of stabilisation with the additional advantage of providing shade and habitat potential.
The measures in detail and the material used depend mainly on the local character of the river and the availability of the material. Where the impounded river reach is in a more or less natural condition, it is recommended to evaluate the situation, to deﬁne deﬁcits and possibly to re-allocate at least parts of the existing bank.
188.8.131.52 HEADRACE CHANNEL In cases of longer diversions consideration must be given to the design of artiﬁcial water bodies like channels. Experience shows that these artiﬁcial water bodies may become very attractive habitats, thus replacing a lack of habitat in the main water course. The headrace channel has to reach two main targets: minimal friction loss, no loss of discharge. Despite these restrictions conventional methods of river rehabilitation can be applied. In principle the so-called roughness (biologically valuable) can be increased by methods of structuring. To avoid any increase of friction loss, the ﬂow velocity must be decreased by increasing the total area of cross-section. Additionally the use of bioengineering methods will improve the habitat potential as well as providing shade for the water body. Even the lining need not necessarily be straight but may follow some morphological “input” provided by the surrounding landscape. The maximum ﬂow velocity should not exceed 1 m/s.
By reducing the depth and indirectly increasing the ﬂow velocity, the sedimentation of ﬁne material will decrease.
Headrace Channel, Prevalle, Italy
Source : Studio Frosio
Apart from the banks any restructuring measures should focus on minimising any alteration of the conditions mentioned above. All of them are in fact the result of enlargement of the cross section. From the ecological point of view, any measure to reduce the cross-section will be seen as an improvement. In practice the variable height of a weir should be minimised while still meeting the targets of ﬂood protection.
The structure of the banks can be made nature-like, shallow water areas can be provided, the development of islands can be initiated and the depth can be actively reduced and made variable. Making the new banks less steep will reduce the need for heavy stabilisation measures.
The ﬁlling up of a backwater area is a natural process, lasting a certain period of time depending on the bedload transport characteristics of the river. On achieving equilibrium the natural transport process will recommence automatically.
600 % 500 %
Tailrace channel, Esenta, Italy
184.108.40.206 TAILRACE CHANNEL
Need of environmental ﬂow
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Source : Studio Frosio
The following graph illustrates the relation between morphology and residual ﬂow necessary in principle.
400 % 300 % 200 % 100 %
In tailrace channels the remaining conditions concern the minimisation of friction loss. Generally the cross sections are made larger and the velocity is much lower than in the headrace. Usually the shaping is more natural where the method of construction has provided a simple earth channel without any additional measures. The principles of maximum roughness, highest possible and the use of bioengineering methods can be applied more easily, though the cross-section remains similar to that of a natural stream.
220.127.116.11 DIVERSION REACH In a case of diversion, where in a particular river reach the ﬂow is reduced signiﬁcantly, emphasis must be laid on the morphology of this reach. Naturally the impact of diversion is rather high, when the reduction in ﬂow is big and the duration of the reduced discharge lasts for many months. On the contrary if the amount of residual ﬂow is rather high and the duration is short, the impact may become almost negligible Usually governmental interests concentrate on the amount of residual ﬂow. The more effective strategy is to improve morphology by all the river rehabilitation methods which we have discussed. Especially in rivers with a conventional ﬂow pattern the width of the riverbed is extremely large and no amount of residual ﬂow will be sufﬁcient to fulﬁl the ecological demands.
Summing up we see three parameters being decisive for the evaluation of a diversion reach: The amount of residual ﬂow The structure of the riverbed The duration of diversion
2.5.2 Penstocks Penstocks can be installed over or under the ground, depending on factors such as the nature of the ground itself, the penstock material, the ambient temperatures and the environmental requirements. Interred penstocks should be generally preferred to exposed ones, because of the smaller visual impact and possible movement barriers for animals. Nevertheless the burying of penstocks could have major geological risks connected with the stability of steep slopes traversed by pipes, both during construction and operation. In fact during operation water leakage from an interred penstock could trigger landslides much more easily than an exposed one. The following measures help to reduce the environmental impact of penstocks: PENSTOCK INTERMENT. Penstock interment should take place whenever possible. Pipe and coating technologies have reached a very good reliability level, so that an interred penstock requires practically no maintenance for decades and on the other hand the result for the environment and especially for the landscape is excellent. However to avoid problems connected with steel pipe corrosion, with eddy currents in the ground and to reduce maintenance, the use of plastic pipes (glass reinforced plastic or HDPE) is advisable.
UNCOVERED ANCHORING BLOCKS The impact of an exposed outdoor penstock can be further reduced if the uncovered solution for anchoring blocks is adopted. That means that the penstock is not covered with concrete at the anchoring blocks but is connected to them by steel beams. This solution reduces the visual impact and allows for the inspection of the whole pipe resulting in higher construction and operation reliability.
Source : Studio Frosio
PENSTOCKS WITHOUT EXPANSION JOINTS Where a penstock cannot be interred for some reason, construction without expansion joints is preferable because it doesn’t require any maintenance or any associated access tracks or roads to the penstock with the consequent reduction of environmental impact.
An uncovered anchoring block at 600 mm-diameter penstock without expansion joints
They have in common all the formal elements that characterize their function. Small hydro power plants undoubtedly belong to the category of the useful, their positive effect on the environment is assured and their contribution to a sustainable development is essential. Therefore it is necessary to raise awareness among the local communities about the highly positive value of such a plant for the local community, the nation, and the environment. Only within this culture can architecture express itself within the terms of the technological features that become the recognition elements belonging to a category that is beautiful because it is useful.
2.6 NOISE AND VIBRATIONS
A power station is beautiful if it is able to give as much information as possible. So the task of the designer is to make it recognizable using all the characterizing elements. But making a power station recognizable doesn’t mean that it has to conﬂict with the environment. But what do these buildings have in common to make them recognizable as power stations?
t the outset it must be said, that noise is not a speciality of SHP. Nevertheless a SHP may be the source of some noise emission and consequently this guide will refer to that. The sources of noise from a small hydroelectric plant may be numerous: trash rack cleaner, trash conveyor, generator, gearbox, turbine, transformer, but noise comes mainly from the hydroelectric unit and, when used, from the speed increasers. Nowadays noise inside the powerhouse can be reduced, if necessary, to levels in the order of 70 dB, almost imperceptible from outside. In general, the allowable level of noise depends on the local population or isolated houses near to the powerhouse. For new plants an integrated and careful design of the whole system - hydroelectric unit, building, ancillaries - allows the achievement of excellent levels of noise reduction, also in the case of an intrinsically high level of noise sources: very small tolerances in gear manufacturing; sound insulating blankets over the turbine casing, water cooling instead of air cooling of the generator and a careful design of ancillary components, acoustic insulation of the building could make the attained level of noise very low and the presence of the plant unperceivable.
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Noise and vibration reduction in existing plants which have to be adapted to new lower noise levels is much more difﬁcult and expensive. In this case the measures to be taken are expensive and in general not as effective as for new plants and require to be taken as close as possible to the source because reﬂection and resonance phenomena otherwise become unbearable. A typical solution is shown in the pictures where a complete encapsulation of the hydroelectric unit was necessary to reduce noise to acceptable levels.
2.7 Fish-friendly turbines
he installation of turbines in a river system may in certain circumstances endanger ﬁsh. Scientiﬁc research work has been carried out at big hydropower stations and yielded certain results. Especially in periods of intensive ﬁsh movement along the river, ﬁsh may get into the turbine. For a couple of reasons (mechanical, speed, variation of pressure) a certain percentage of ﬁsh may not survive passing through the turbine. Different types of equipment (light, noise, etc) may cause some reduction but they are still not effective enough to completely keep ﬁsh away from passing the trashrack and getting into the turbine. In the case of SHP there is almost no serious investigation on this topic. Trashracks with a narrow bardistance of some 2 cm may avoid a high percentage of ﬁsh coming into the turbine. Nevertheless further efforts must be made to reduce the endangering of ﬁsh by using alternatives to usual turbines wherever applicable.
For many years, to minimize ﬁsh injury, turbine manufacturers, especially for big hydro facilities, have been carrying out on studies based on CFD (computational ﬂuid dynamics) and good results have already been achieved. Small hydroelectric plants also can take advantage of this research effort for conventional turbines (Francis and Kaplan turbines), while new concepts of turbines and revitalisation of old concepts (hydrodynamic screws, water wheels) are typical of micro and mini hydro plants, allowing better integration into and preservation of the river life. In some cases - especially low head / extreme low head - the installation of conventional turbines may not be recommended due to unacceptably high cost. Heads between 1 and 3 m at any discharge or low discharge up to mean head are typical cases which are not economical for turbines up to now. Consequently research is being carried out to ﬁnd more economical turbine solutions. The classical water wheel can be built traditionally from wood or recently more commonly from steel. Due to low speed belts or gears are needed to increase the speed. Precise manufacturing and the best possible bearings will result in efﬁciencies of up to some 70 %. Unfortunately even the price for water wheels is sometimes very high. In the last few years a well known technology has been applied for hydropower use. The archimedic screw has been inverted and serves now as a mature technology in some SHP niche markets. They are signiﬁcantly cheaper than turbines and reliable and robust in operation. They don’t need a ﬁne trash rack and are said to be ﬁsh friendly. According to recent trials maximum efﬁciency will reach values of 75 to 80 %. Low speeds between 20-80 rpm will require a speed increaser but reduce maintenance and repair work. The span of application ranges up to a 10 m head and a 5 m3/s discharge for a single screw with a diameter of about 3,5 m. A most recent ﬁeld of application for an archimedic screw may be related to using residual ﬂow. Thus the loss of production can be reduced using at least the head available at the weir. Summing up - in case of ultra-low-head, alternatives to conventional turbines should be checked out, and replacements not made simply on a historical basis regardless of recent developments.
Noise reduction technology
SOME EXAMPLES ON ENVIRONMENTAL INTEGRATION OF SMALL HYDROPOWER PLANTS Source : IT Power
C ASE S T U DY 1
Powerhouse dressed in local material
BACKBARROW, UK Country: UK Location: Backbarrow, Lake District National Park, Cumbria, UK Installed capacity (kW): 400 Turbine: x Ø750mm inclined propeller type, 510rpm Average available head: 4.8m Design ﬂow: 3.33m3/s per turbine Year of commissioning: 2000
Description of the system
The existing works provided the basis of the new scheme. Some excavation was needed for the powerhouse and tailrace. Additionally, the downstream channel was made to meander and large boulders were added to create eddies and pools that would contribute to a more ecologically friendly environment. The design uses 3 inclined propeller turbines: one semi-Kaplan (adjustable runner blades) and two unregulated machines. With this arrangement, the regulated turbine T1 runs continuously and T2 and T3 run when there is sufﬁcient ﬂow. Power output is controlled by a head level sensing system. This controls the operation of T1 to ﬁne-tune the system so that the headwater always remains above a certain minimum level. The turbines are shut down by butterﬂy valves at each inlet. Direct coupled 500rpm generators were used to avoid the need for speed-increasing systems and their associated maintenance and costs. The powerhouse was located below river-bank level so as to be invisible from upstream. The building was ‘dressed’ in local materials used for similar existing structures. Directly upstream of the turbine intakes, three Trashclean© racks were installed each having its own cleaning rake. The site has a history of high levels of weed and other debris. A Bio-Acoustic Fish Fence (BAFF) was built into the existing forebay to guide approaching ﬁsh into a bywash, so ensuring that ﬁsh could bypass the turbines. An eel guide and escape sluice were also incorporated into the forebay, operated by a gate valve. The turbine draft tubes were positioned so that the exit ﬂow would provide an attraction ﬂow for upstream migrating ﬁsh, drawing them towards the ﬁsh-pass. The draft tube exits are shielded by Electroscreens©, an innovative electrical barrier which deters migrating ﬁsh from attempting to swim up the draft tubes.
The Backbarrow site is located 3km downstream of Lake Windermere in the Lake District National Park. The scheme utilises water from the River Leven and is in a scenic and therefore sensitive location. The river also provides considerable revenue generation through salmon ﬁshing. The site upon which the scheme is built has historically been used to harness hydropower. Prior to this installation, there was a grid-connected 65kW Gilkes horizontal Francis turbine. Furthermore, part of this site was a Scheduled Ancient Monument, which meant that both English Heritage and the Industrial Heritage section of the Lake District Planning Board were consulted during the planning process. Due to the location, ﬁsheries issues and historical value, a great deal of consideration was given to the environmental design of the new scheme. Through consultation with parties mentioned above and the Environment Agency, speciﬁc requirements regarding visual impact and ﬁsheries protection were incorporated into the design.
C A S E S T U DY 3
E X A M P LE S
WATHULTSTRÖM, SWEDEN Country: Sweden Name of the plant: Wathultström Installed capacity (kW): 190 Head (m): 10 Discharge (m3/s): 2,7 Energy production (kWh/y): 500,000 River name: Kilan Year of erection: 1919
Description of the system No Diversion Semistorage Low head Intake at the dam Two Francis Turbines
C ASE STUDY 2
DORFMÜHLE, AUSTRIA Country: Austria Name of the plant: HPP Dorfmühle Installed capacity (kW): 2,500 Head (m): 7.3 Discharge (m3/s): 43 Energy production (GWh/y): 12 River name: Ybbs Year of commissioning: 2004
The southwestern part of Sweden is affected by acid rains causing acidiﬁcation. To combat this, many rivers are limewashed. A very good solution is to integrate the limewashing with a SHP plant. In the case of Wathultström the limestone is injected in the draft tube in relation to the actual discharge.
Description of the system Run-of-river Low head Turbines: 2 Kaplan - S Bulb Turbines
Environmental measures Back water area: 0,1 km2 Natural bypass channel Recreation area in the backwater Noise reduction measures Architecture: Alucupon façade Source: SERO
C ASE STUDY 4
View from downstream, illustrating the dam - Source: LHA
KAVARSKAS, LITHUANIA Country: Lithuania Location: Kavarskas Installed capacity (kW): 1,000 Head (m): 4.1 Discharge (m3/s): 28 Output (GWh/y): 6.4 River name Sventoji Year of commissioning: 2002
Description of the system
The Kavarskas site is located on the River Sventoji 69 km upstream its mouth (average ﬂow is 31.4 m3/s), near the same name small settlement. The 4.1 m height dam has been built in 1962 impounding the 0.8 km2 area reservoir. The main purpose of the construction of this dam at that time was to increase the low ﬂow of the neighbouring River Nevezis during the dry periods of the year. To achieve this ecological task the pumped station has been constructed to utilise water from River Sventoji (donor) and divert it to River Nevezis (recipient). However no ﬁsh ladder has been built on the dam. When improving the ecological situation of the River Nevezis, the dam prevented the migrating ﬁsh from regaining their usual spawning areas located upstream it. For more than 40 years the dam has been State owned but no ﬁnancing has been sought to eliminate this occurred unfortunate situation regarding migrating ﬁsh.
The river Sventoji downstream the Kavarskas dam is famous as a migrating ﬁsh protected area. It was established after the dam construction. Salmon, trout, vimba and other valuable species are commonly found in the stream. In 2001 the private SHP development company Achema Hidrostotys was given the concession to construct a small hydropower plant at this existing dam providing the ﬁsheries issues has been taken into consideration. For that the ﬁshpass was needed. The run off river scheme has been designed by local design company Kaunas Hydroprojektas, the ﬁsh ladder physical modelling in the laboratory has been carried out by the staff of Water and Land Management faculty of Lithuanian University of Agriculture. The scheme including ﬁsh ladder started operating at the end of 2002. The ﬁsh ladder is a concrete structure, pool-type with vertical slots. When designing it the attempt was made to approach the lower end of ﬁshpass to the power house as close as possibly, namely to the draft tubes, in order to attract the ﬁsh by water current to the entrance. The discharge of the ﬁsh ladder is 1.3 m3/s. The facility to monitor the ﬁsh passage through it has been also established. The ﬁsh ladder cost amounts to 10% of the overall scheme cost or 0.3 M Euro. A year later, after more than a 40 years period, the ﬁshermen have declared the reappearance of migrating ﬁsh upstream the Kavarskas SHP. The ﬁsh ladder effectiveness has been approved by the experts of the Institute of Ecology, who are performing the ﬁsh monitoring. There are plans to arrange the modern ﬁsh counting system. This story clearly shows that SHP developers are eager to improve the river ecological situation for which public money usually is not available.
C A S E S T U DY 5
E X A M P LE S
The multipurpose basin
SAVIORE DELL’ADAMELLO, ITALY Country: Italy Location: Saviore dell’Adamello Installed capacity (kW): 1,140 Head (m): 280 Rated discharge (m3/s): 0.5 Output (GWh/y): 3.7 River name: Salarno Year of commissioning: 2002
Description of the system The Saviore dell’Adamello plant is located on the Salarno River in the heart of Adamello Park in Northern Italy (Brescia District, Lombardy Region). To preserve the ecological status of the river in a so sensitive environment (a high mountain alpine torrent inside a natural
C A SE ST UDY 6
TEDELEC, FRANCE Country: France Name of the plant: Limited liability company TEDELEC Installed capacity (kW): 680 Head (m): 3.70 Discharge (m3/s): 24 Energy production (kWh/y): 4,600,000 River name: Gave de Pau Year of commissioning:1981
Description of the system
park) the reserved ﬂow was set at a high rate of the average natural ﬂow rate. The basin at the intake is used both to increase the value of the energy (production during peak hours) and for leisure highly increasing the social acceptance of the plant. In fact the basin is near to a tourist alpine hut attended by thousands of people in summer and the people appreciation of the basin is very high. The long penstock connecting the forebay to the powerhouse is almost completely interred to reduce visual impact. The small part not interred because of the steepness of the slope is set up with concrete anchoring blocks not covering the penstock to reduce the visible volume and they are coated with local stone.
Environmental measures Multipurpose 5.000 m3 basin inside a natural park Tyrolean intake to favour the river continuum preservation Use of local materials for buildings coating Natural like ﬁsh pass Water cooled generator to reduce noise Strict contact with environmental ofﬁcers to agree upon the mitigation and compensation measures to be taken and to choose the better environmental solutions.
Turbines: Kaplan vertical simple regulation : diameter 2.40 m, 140 revs/mn
Environmental measures Rigorous control of the reserved ﬂow by surveillance and measurement of the installations Rigorous and continuous control of the quality of the water Trash Rack Material Management: the waste is sorted out and sent to recycling and treatment plants. Noise reduction techniques Others: Fish bypass, Residual ﬂows, River restructuring, compromising with other river uses (passes for canoeing), environmental management systems.
Diversion Low head Intake: dyke with disjoined rocks. Downsteam point height: 328.10 m Length 110 m, middle height 0.80 m Feeder canal: 200 x 17 x 3 m Tail-race : 10 m Source: GPAE
C A S E S T U DY 7
TROISTORRENTS, SWITZERLAND Country: Switzerland Name of the plant: Troistorrents Installed capacity (kW): 75 Net head (m): 242.3 Maximal discharge: 35 l/s Output: 230,000 kWh/year Year of commissioning: 1998 - 1999
surge tank, as a pressure regulator device. The equipment has been manufactured by a SME of 35 employees, located at 40 kilometres from the commune. The electricity of this completely automatic power plant is delivered into the local distribution grid. Regarding the drinking water quality rigorous speciﬁcations were met so as not to impact on it.
Description of the system
First the plant is set on a water network, which implies that the infrastructure was already built, and that the power plant operating does not imply more environmental impact (no need of ﬁsh ladders) than a usual drinking water network.
The turbine, a Pelton with one nozzle, set on the drinking water network of Troistorrents (Valais, CH) commune, works on the high difference of levels between the catchment chamber and the
Secondly a special effort has been made to integrate the power plant to the landscape, as it is located in a semi agricultural area: looking from outside, nothing appears to be different from a traditional chalet. Thirdly, because of the nearby housing, a low ambient noise was required : only with the door opened, can the generator be heard. What can be here pointed out is that only a high-efﬁciency turbine with a hydraulic proﬁle deﬁned from laboratory research can be so quiet. Fourthly, the power plant is set in the charge chamber that provides the pressure in the water supply network, and extracts energy that was previously wasted through a pressure reducer. Finally here energy is generated with almost no environmental impact which could be expressed in a CO2 emissions reduction of 110 tonnes per year. To conclude, what can be emphasized is that even a small project (75 kW) can be cost-effective and environment friendly.
75 kW turbo alternator group - Source: MHyLab