Postwar village hydro-power rehabilitatio

Johann Zimmermann (2707468)

English

Loughborough University Institutional Repository

X   MISCELLANEOUS: ZIMMERMANN43023rd WEDC Conference Durban, South Africa, 1997Postwar village hydro-power rehabilitationJohann Zimmermann, MozambiqueWATER AND SANITATION FOR ALL: PARTNERSHIPS AND INNOVATIONSCAMBINE IS AN institutional centre with a secondaryschool for 1000 students, boarding facilities for 200 stu-dents, a bible school, a 35 bed health centre and residencesfor a population of 500. During the 17 year long armedstruggle following independence from Portugal in 1975,Cambine suffered destruction of buildings and infrastruc-ture.Cambine’s water and energy resources were provided bya stream which is fed by a natural spring. In the 1920’s, asmall dam and hydro-power facility were built. The tur-bine provided mechanical power for a sawmill, a grainmill, a water pump that supplied a piped water system anda small electrical generator. A diesel generator was alsolocated at the dam site to meet the electrical energy demandat night. In 1987, the power house was dynamited in anattack, destroying the facility and severely damaging themasonry dam. The loss of pride and stability that thepeople felt was significant.A 30 KW diesel generator was installed after the war forproviding electrical energy. This generator was large enoughto meet the electrical demand of Cambine. The operationand maintenance cost was $3.50 USD per hour. With anaverage salary of only $1 per day, the population couldonly afford to run it two hours per day. Extending thedistribution grid to more customers could have loweredindividual rates and extended operating hours, but thehigh cost of extending this grid to a sufficient number ofcustomers in a rural area prohibited this.Two drilled wells were installed after the war, oneequipped with a hand pump and the other with an electricpump. The electric pump supplied a water tank for thepiped water system. The existing aged galvanized pipingwas replaced with PVC piping. The previous system hadpumped river water through a sand filter before feeding itinto the water tank. By using well water, the filter was nolonger needed.The piped water demand for Cambine was calculated at24,000 litres per day. Only human consumption wasincluded in this calculation since water for other uses couldbe obtained directly from the stream. The output of thewell was only 2,000 litres per hour. The electricity for thispump was supplied by the diesel powered generator, whichonly operated two hours per evening, therefore the waterdemand was not being met. Although the hand pump couldsupply the water needs of the population, the health centreand the large student population dictated the need for apiped water supply.A more economical energy source was required tosupplement the diesel generator-supplied electricity. Twelvehours of electricity per day were required to run the waterwell pump. The health centre required night lighting andsufficient hours for refrigeration and sterilization equip-ment. The school needed lighting for night classes.Feasibility studies of alternativesFeasibility studies were performed for systems that wouldmeet both the energy and the water demand. The assump-tion was that the diesel generator would continue to beoperated two hours per day for the evening lighting load.Costs were calculated above that of still running thegenerator, except for the alternative of the extension of thegovernment grid which would eliminate the need for thegenerator. Comparative costs were made of the initialcapital costs, the net present values, the annual cost, theunit energy cost, the operating and maintenance costs(O+M) and revenues. Calculations were made assuming a20 year project life and a discount rate of 1 per cent.Table 1. Comparative costs of electrical energy sourcesX   MISCELLANEOUS: ZIMMERMANN431A development grant of US $20,000 was available forthis project. Because of this, the decisive factors were theinitial capital cost, the unit energy cost, and the annualO+M costs and revenue.The alternative with the lowest initial capital cost wouldhave been to run the existing diesel generator for anadditional two hours each night. An additional well at acost of $10,000 was the only initial cost needed to providea sufficient water supply. As stated earlier, the unit energycost of $0.23/kwh and annual O+M cost of $2,500 wasprohibitive.Extension of the government grid from the nearest town12 kilometres away was considered as an alternative inorder to purchase electricity at the rate of $0.07/kwh. Thiswould have helped the development of the surroundingpopulation of 15,000 people. Because this governmentgrid was supplied with only 4 hours of diesel generatedpower each night, an additional water well was alsoincluded in the initial cost. The initial capital cost of$47,000 was prohibitive.Solar energy would have provided an acceptable alterna-tive at an initial cost of $16,500. Included in this cost wasa solar operated water pump installed for $9,500. Thisbattery-less system would only pump 12,000 litres per dayby solar power and an additional 4000 litres per day bygenerator power. Although this did not meet the calculateddemand, water conservation measures would have madethis acceptable. The health centre and the two nightschools would each have their own collection and batterystorage system. The system for the health centre includeda small 12 volt refrigerator for immunization storage. Theannual O+M cost consisted of the purchase of new batter-ies with a life time of 4 years. This O+M cost at $425/yearwas the lowest of all the alternatives. The big attraction ofthis alternative was the speed and ease of installing thesystem and the simplicity of its operation.Initial survey of the damage to the hydro-power plant ledto the conclusion that it could not be repaired. Thealternative of a new dam, turbine and generator had aninitial cost of $42,000. The unit energy cost of $0.15/kwhwas attractive, but the initial cost was prohibitive. Furtherstudy revealed that the dam could be repaired. The inex-pensive price of labour relative to the price of material ($1/day labour vs $10/sac of cement) brought this option downto $29,000. Again, with the inexpensive price of labour,$10,000 could be saved by repairing the existing waterturbine instead of purchasing and importing a new one,bringing the initial cost down to $19,000. The energy metall the night lighting requirements for the health centre andschools and the water pumping demand. The 24 hour perday energy could be used to produce income when energywas not being used for lighting and pumping. This incomewas calculated at $2,200 per year. With an O+M cost of$800 this alternative produced an annual revenue of$1,400. This revenue could be used to run the dieselgenerator for an additional hour each night to provide allof Cambine with electricity. The building of the hydro-electric facility was therefore chosen as the most appropri-ate energy source.Rehabilitation of the hydro-electric facilityHydro-potentialThe stream is fed by natural springs 600 meters upstreamfrom the dam which provide an almost constant year-round flow. The population has been educated in theimportance of protecting this flow. The local authoritiesorganized workdays to protect the spring and the riverbasin from erosion and restricted land use in this area. Thehydro potential is provided by a 4 meter head created bythe dam and a run-of-the-river design flow of 110 litres persecond. The gross power of 4.3 kw provides a net powerof 3.5 kw available from a turbine operating at 80 per centefficiency. The estimated electrical output using an induc-tion generator at 90 per cent efficiency is 3.0 kw.The economic viability lay in maximizing the plantfactor, the percent of energy used from this 24 hour per dayenergy source. Full energy output would be used in theevening hours for fluorescent lighting of the health centreand the night school. Twelve hours would be used forrunning the water pump. Two hours would be used forsterilization at the health centre. A low plant factor re-sulted with only this use, but the unit energy cost of $0.11/kwh would have been acceptable.Prior experience proved there was a market for batterycharging for home energy use and a market for chilledbeverages to the surrounding population. Refrigeratorscould be run at the same time as the water pump. Batterycharging could be done during a six hour day period. Aplant factor of 83 per cent could be achieved resulting in aunit energy cost of -$0.02/kwh. Two thousand dollarswere included in the initial cost for the purchase ofrefrigerators and battery chargers. Since the Cambineadministration was capable of managing and maintainingthe current water and electrical utilities and of revenuecollection from the users, this additional enterprise wasalso within its capability.Figure 1. Daily electrical demand/supplyX   MISCELLANEOUS: ZIMMERMANN432Dam reconstructionThe subsoil profile of the 35 meter long dam site was veryirregular. One half of the natural stone masonry dam wasbuilt directly on weathered limestone, the other on apermeable base of gravel and sandy silt. The depth of thislayer was over two meters and could not be measured.Compacted sandy silt had been placed against the up-stream face of the dam to slow water penetration throughthe permeable base. The explosion had created a structuralcrack at the point where the foundation changed fromresting on bedrock to resting on soil. This crack appearedto have initiated the piping of water which in time resultedin the catastrophic undercutting of the dam. Over theyears, two large fig trees grew adjacent to the downstreamside of the dam. Their roots penetrated underneath thedam and may also have contributed to the piping of water.The entire foundation of the dam was exposed. The partof the dam that had been undercut had to be sealed andunderpinned. Both sides of the 1.5 meter wide masonryfoundation were concreted shut with 3/4 inch PVC pipesinstalled for grout injection. A hand grout pump was builtlocally which could deliver 200kPa of pressure. A groutmix of 1 cement to 3 parts of sand by volume was used witha 5 per cent bentonite to cement ratio. The wall of the damaround the intake canal to the power house had beendestroyed, with a large structural crack emanating outfrom it. This area was rebuilt with concrete. The crack wasgrouted with a grout mix of 1 cement to 3 parts sand.Clay was not locally available for use as an impermeablecompacted fill. The least expensive alternative was pro-vided by purchasing two tons of bentonite from a mine 550kilometres away. Mixed at 20 per cent volume with thelocal soil, this provided an impermeable material. Theupstream side of the foundation resting on the permeablebase was backfilled with this. A two meter wide, 15centimetre thick apron of this fill was placed adjacent tothe foundation that rested on the weathered limestone.Analysis of the masonry core of the dam showed only a5 per cent factor of safety against overturning. Two-thirdsof the dam had previously been backfilled on both sides,providing the needed stability. This washed out sectionwas re-backfilled. The solution for the other third of thedam, which rested on limestone, was to construct the newturbine power house there, supporting the dam in buttressfashion.The reconstruction of the dam was very labour intensive.Ten men were employed for eight months for removingdebris, digging, backfilling, hand breaking rock with ham-mers into gravel, removing trees and roots, and dredgingof the downstream channel.Power generationRemoval and dismounting of the turbine revealed that ithad suffered no damage from the explosion. The turbinewas a 16 inch diameter, cast iron Francis Turbine, build byFitz Water Wheel Co., Pa., USA. It was installed in 1952,and had been submerged in water for 44 years. During thenine years of inoperation after the attack, it was frozen upby rust. It required six months to disassemble it using heat,lubricants and sweat. Several minor parts had to beremachined and mainly bushings needed to be replaced.All parts needed extensive cleaning of rust and repainting.The wiring of the old electrical motors, generators andtransformers was recycled into wiring for use in theelectrical distribution grid.The previous turbine powered a shaft off of whichequipment was mechanically driven through pulleys. Theflow control vanes were manually controlled to adjustwater volume and power production. The new systemproduces only electricity at the run-of-the-river flow, there-fore the flow is set at a constant volume. To make use ofthe energy storage capacity of the dam, a mechanicalmeans of regulating the vanes is still being considered.A 11 kVA induction generator is being used, producing380 volt, three phase, 50 hz power. In spite of the smallenergy output, three phase current is being used instead ofsingle phase because of the resulting savings in 1000meters of transmission wire and to power the existing 3phase water pump and other existing motors. Governingis provided by an induction generator control (IGC), whichkeeps the generator output load at a constant so as tocontrol the voltage and frequency. An IGC measures thegenerator output voltage, which it then regulates by divert-ing varying amounts of power to ballast loads. The ballastloads are refrigeration and heating units.ConclusionThe decision to rehabilitate the hydro-electric facilitycould only be made because of the presence of an engineerto supervise this small but complex project over a year’stime. If sufficient water head would have been availablewithout the need for a dam, a cost effective and lesscomplex project could have been built by using a newturbine, generator and control package produced by onemanufacturer. The easiest alternative would have beenusing solar energy. As it was, this labour intensive projectprovided work for local people instead of spending thissame money on imported manufactured equipment. Itcontinues to provide much needed revenue and employ-ment.ReferenceHARVEY, A., 1993, Micro-Hydro Design Manual. Inter-mediate Technology Publications, 103/105 Southamp-ton Row, London WC1B4HH, UK.JOHANN ZIMMERMANN, Civil Engineer, MennoniteCentral Committee.

Postwar village hydro-power rehabilitation

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Postwar village hydro-power rehabilitation

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