The village of El Limón is located in the Dominican Republicís arid southwest mountains, two hours west of Santo Domingo. Nearly seventy households eke out a marginal living growing onions, eggplant, and other low-value cash crops. Like most Dominican villages off the infrastructure corridors, El Limón has little prospect of being connected to the national electrical grid in the foreseeable future. But unlike the typical Dominican village, El Limón is a highly organized community with a strong history of participation in self-help projects. For the past 25 years ADESJO, a regional community development organization in the nearby city of San Juan de Ocoa, has been providing technical and financial support for such projects as the construction of the road, school, irrigation system, water system, and agricultural improvement. In each case, the community has assimilated new skills and moved rapidly toward self-reliance. The result has been a community with an atypically high degree of self-confidence and project management skills.
El Limónís experience in building and operating its irrigation system provided the base for the electrification project. When construction of the irrigation system began in 1991, the community could only provide manual labor. Within a few years the villagers had acquired the technical and management skills necessary to maintain (and extend) the elaborate gravity-fed PVC pipe irrigation system. A very effective system of work brigades evolved, headed by a five person committee; each member was responsible for one day of the workweek. This approach is now being used to extend the irrigation system, as well as for other community projects, including the electrification effort and the fairly extensive repairs needed after Hurricane George.
The Irrigation Committee is the villageís most sophisticated management operation. It allocates water, schedules water use (which involves moving sprinklers every two hours around the clock), and makes sure that all members of the irrigation project make their payments on the original $75,000 construction loan. The actual handling of money and the record keeping is done in the nearby city of Ocoa by ADESJO, which managed the loan and the initial construction. Fifty-nine families participate in the irrigation project and each is responsible for making quarterly payments timed with their quarterly harvests. Most own from 1.0 to 1.5 ha and pay $170 to $250 quarterly. Most people have been able to keep up with their payments.
The electrification of El Limón grew out of a 1996 regional workshop in very small hydropower systems led by Jon Katz of the EcoPartners Project (a Cornell University affiliate), in cooperation with ADESJO. The workshop visited El Limón as a field exercise in system design and demonstrated a 12-volt turbine/generator unit to the community. Response was enthusiastic, and the turbine was eventually installed at the village school, with extensive community participation. Residents expressed a very strong interest in villagewide electrification powered by the irrigation system. The system described here was designed to address the limited water resource available. Technical support has been provided by EcoPartners, logistic support by ADESJO, and labor by the community.
The implementation approach was unusual, in that the electrification was integrated into a much broader village development project. The system designer lived in the village on a half-time basis over the two years of the project, with much time spent on other activities. A major project priority has been transferring technical skills into the community, and residents learned construction, wiring, electronic assembly, and computer/video documentation skills.
The project was officially inaugurated the beginning of April 1999 although portions of the village had begun receiving power earlier. A total of 56 households now receive electricity and a few more will be added later. All have one light and a second will be installed shortly.
As the source of power, a 2.5 kW micro-hydropower plant was built along an irrigation pipeline to harness the excess energy in the water as it descends the final kilometer of a 6 km PVC pipeline. A low-cost, 240-V induction motor, with an appropriate electronic load controller, is used as a generator to supply single-phase power to the mini-grid.
The distribution system transmits the power about 600 m to the village and distributes it around the village, supplying homes as far as about 1 km from the village center. Because of the limited hydropower potential of the irrigation pipeline and the need to serve 60 households and to provide roughly 200 W of power to the school for lighting and the computer center, the power available to each household is initially limited to no more than 35 W. This might be altered somewhat as actual operational experience is gained. Potential consumers were made aware that this was only adequate for a couple of compact fluorescent lights and a radio or tape recorder; that a small 12-V television could be used if lights were turned off; and that refrigerators, irons, and hair dryers could not be used at all. While many residents would have preferred more electricity, explaining that the energy available 24 hours a day would equal the output of three photovoltaic panels quieted all further objections. Only one family in El Limón has been able to afford a private single-panel system, and a three-panel system is considered a great luxury
Because the irrigation system runs around the clock and water is fed back into the irrigation pipework for use further downhill after passing through the turbine, electricity will be available at all times. The energy calculation of 2.5 kW was based on the 6 l/s (liters/second) flow observed over a typical year. However, 1998 was a drought year and the water flow dropped to about 2 l/s. This was inadequate for irrigation as well as electricity generation, and the community recently obtained the pipe necessary to extend the system to the next stream, whose flow was measured at 12 l/s during the drought. The irrigation extension should assure a minimum of 2.5 kW at all times and may allow for some expansion.
While 120 V is the typical voltage used at the residential level in the DR, the decision was made to generate and distribute power at 240 V for the following reasons:
This approach has the following advantages:
The 135 poles required for the project were fabricated on-site of steel-reinforced concrete. The 20-foot (6-m) poles have a square cross-section of 6 inches (150 mm) at their base, tapering to 4 inches (100 mm) at the tip. Although at first reluctant to transfer his skills, the mason who designed the poles did eventually teach the local residents how to form and wire the reinforcing steel, and production of the poles continued without his involvement. Reinforcement consists of four 3/8-inch (10 mm) rods running the length of the pole, tied by square rings of 3/16-inch (5 mm) every 6 inches. Forms consisted of wooden walls nailed to a wood platform. Four poles were made at a time, at the rate of 8 per week. As is customarily the case, concrete was mixed on the ground. The use of ungraded aggregate produced a low-strength concrete, but there was little problem with breakage of the cured poles. To facilitate the mounting of insulators, two (later four, at right angles) pieces of 1/2-inch (13 mm) plastic water pipe were included in the pole to provide through-holes. The material costs for the poles (cement, reinforcing steel, and aggregate) averaged about $40 per pole.
Moving the poles, which weigh over 500 pounds, proved to be a major problem. To facilitate this task, a handcart was built of steel box tubing and automobile wheels. Despite the cart, moving the poles to locations away from the roads was very difficult. In some locations, it was necessary to carry the poles with teams of 12 workers. One conclusion drawn from this experience was that it would have been wiser to choose longer, less direct transmission runs that followed roads wherever possible.
Holes were dug using basic hand tools. The poles were raised using a variety of pulleys, poles, and gin poles. Differing conditions required a constant reinvention of approaches and techniques. While never easy, and often hazardous, the process became less formidable with practice.
Where necessary, poles were guyed with the usual 3/8-inch (10 mm2) high-tensile cable. This cable was tied around an anchor made of meter-long lengths of concrete pole castoffs buried a meter underground.
Because of cost-savings resulting from quantity discounts, only two sizes of conductor were incorporated in the system, one for the multiplex and one for the copper. This meant that the longer, more heavily loaded transmission runs used #2 (34 mm2) aluminum secondary cable in duplex, triplex, and quadruplex combinations (one, two, or three insulated aluminum conductors, respectively, wrapped around the neutral ACSR conductor) to keep voltage drop within acceptable limits. For example, the initial run was comprised of two lengths of triplex or a total of six conductors. As the line approached the village and split off into two directions, a transition was made to one quadruplex and one duplex cable.
Where the multiplex ended, hard-drawn solid #12 (3.3 mm2) copper conductor with ultraviolet-resistant high-density polyethylene (HDPE) insulation, rather than off-the-shelf indoor wiring, was used to extend further within the village,. This wire is mechanically much stronger than indoor wiring, and the insulation is more durable and tougher for outdoor service. This conductor was specially fabricated at a cost only slightly higher than indoor wiring. The sizes of the conductors used were calculated using a spreadsheet developed to calculate voltage drops and costs of conductor made of differing materials and sizes.
The conductors were attached to the poles using 1/2 inch (13 mm) threaded rod and 2.5-inch (60 mm) porcelain spool insulators. Two-inch-long (50 mm) spacers cut from 1/2-inch iron pipe were used between the insulators and poles. Washers were used at all porcelain/cement interfaces to prevent chipping or cracking. Where the conductor made a significant angle, right-angle brackets were used to mount the spool insulators vertically, on the inside of the bend, and no spacers were necessary. Short lengths of the insulated copper conductor were used to attach all the conductors to the insulators. Where multiplex conductor was used, the bare neutral conductor was separated from the insulated conductors in the bundle, placed over the top of the insulator, and tied to it with the insulated wire. This attachment design is secure, but will allow the wire to separate from the insulator under high stresses without breaking.
In September 1998, Hurricane George's center passed about 40 miles from El Limón. No poles failed, but the high winds (about 160 km/h) tilted about five highly exposed poles to the extent that they had to be realigned and, in some cases, guyed. In several locations, wires separated from the insulators but were undamaged and easily reattached. Only one copper conductor was broken by falling tree limbs.
The copper conductor is also used for the initial portion of the service drop from the distribution line to the converter box and is joined to the main line with a split-bolt connector. Where the distribution line is aluminum, a tin-plated split-bolt connector with a separator is used to eliminate copper-aluminum contact. Anti-oxidant grease is applied before joining the wires, and the joint is well covered with rubber splicing compound and wrapped with vinyl tape. (See p. ?? for discussion of connectors and problems with aluminum-copper connections.)
The distribution system supplies 240 V ac. The 12 V dc supply to each home consists of the following items:
If the homes are further than about 10 m from the pole, two lengths of the insulated #12 copper conductor serve as the service drop from the pole to the home; otherwise, #16 (1.3 mm2) flexible duplex (lamp) cord is used.
This flexible cord is also used for internal housewiring. Two 10-W compact fluorescent lamps with high-quality wall switches are provided for each house, as is a connector to power a radio or small TV. For radios requiring other than 12 volts, converters designed for use in automobiles are widely available. To prevent nuisance tripping of the 3-ampere breaker, a current-limiting device will be supplied to the few households who decide to incorporate a battery. This will probably be a power-transistor-based series current limiter.
Lightning is not expected to be a major problem, since most of the distribution system is in relatively low areas. However, as a precaution, each converter has a MOV (metal-oxide varistor) spike protection arrester between the phase and neutral conductors, and the neutral conductor at about 20 poles with converters is grounded using with 8-foot (2.5 m) galvanized-steel ground rods. The few poles in exposed locations are fitted with lightning rods. The powerhouse end of the transmission line is also protected by a lightning arrester.
Back at the powerhouse, the turbine is protected by a 10-ampere magnetic circuit breaker. Each of the three branches of the system is provided with a 5-ampere thermal circuit breaker at the powerhouse, which also allows powering up the system in stages. If startup outrush currents prove to be a problem, several solid-state time-delay relays will be installed in various system branches to provide a more gradual startup.
For safety purposes, the use of RCDs in the powerhouse was considered, but it was decided that multiple grounding of the system, which is not compatible with use of RCDs, provides a higher degree of safety. Also, the interrupters were likely to be bypassed eventually because of nuisance tripping problems associated with leakage along the long runs.
Management and Human Resources
Before work started, the project was brought to the villageís governing town meeting. After extensive discussion, the village formally reached consensus on making the electrification a community project. Each of the 65 households was required to contribute one day of work per week. Some individuals worked much more, and several households ultimately failed to contribute significant labor. Two key individuals took on personal, long-term responsibility for completion of the project. One concentrated on the poles and distribution wiring and the other on the electronic assembly of the fluorescent lamps and converter units. The project was completed in about 18 months. The largest part of the work, by far, was transporting the aggregate, fabricating the pole, transporting them, and then setting the 135 reinforced concrete poles. While at times the idea of a lighter, more easily made pole seemed very attractive, the reinforced cement poles proved their strength during the hurricane.
Both the community and the system designer found the process of electrification more difficult and time-consuming than expected. The single largest problem was the unanticipated difficulty of working with the concrete poles. There were also changes from the original plan that added substantial work. Just before construction began, the powerhouse site had to be moved from the village about 600 meters up the valley because of a new area which was to be irrigated. Also, residents were very involved in day-to-day design issues and opted for a more durable system. More poles and fewer trees were used than originally anticipated, and a concrete powerhouse much more elaborate than the simple shed originally envisioned was constructed. Other delays were unavoidable. Funds for the distribution wire and materials arrived almost a year later than expected, and Hurricane George, while doing little physical damage to the system, diverted labor to repairs and replanting.
In this project, the organizational strength and motivation of the villagers of El Limón were critical to meeting the challenges they faced. Many residents felt that, at least until a less labor-intensive alternative to concrete poles is found, many communities would have difficulty carrying this type of project to completion with their own resources.
Outside resources were also critical to project success. The EcoPartners Project coordinator spent half of the two-year project period in El Limón, although much of his time was dedicated to other projects in the community. Institutional connections were very important too, with Rotary International providing about one third of the materials, as well as a highly skilled volunteer for two months.
Project costing and tariff
The cost incurred in the construction of the mini-grid portion of this project is broken in the adjoining table. In addition, an additional $4,200 was more or less evenly split between the powerhouse and the turbine and controls. Most of the cost of the penstock (the pressure pipe) was covered by the irrigation project. Otherwise, the cost of the unusually long (6 km) PVC pipe would have added $10,000 to the cost of the project. In addition, there were contributions of food, community labor (estimated at 7,500 hours), and technical assistance (estimated at 1,500 hours).
For several reasons, it was initially decided to seek donations for the capital costs of this project:
The tariff is expected to be minimal, about $2 per month, approximately the same as that typically spent for kerosene for lamps. Because project costs were covered from various external sources, the monthly tariffs are expected to cover the cost of materials such as bulb replacement and turbine bearings and the cost of the plant operator. To ensure payment, the Electricity Committee has decided to require a written agreement with each household before installing the housewiring. At present, nearly 60 households (all in the village except for the four houses located outside the present service area) have access to electricity.
Response from the community has been enthusiastic, both verbally and in terms of labor provided, and this forebodes well for the continuation of the project after it has been commissioned. But it is too early to know how diligent the consumers will be about monthly electricity payments. Electricity, even in limited quantities, is extremely important to most residents, both practically and as a symbol of development.
In the process of implementing this project, lessons were learned:
Cost breakdown of the system
|Distribution wire (#12 copper)||2,400|
|Poles (135 6-m concrete)||5,400|
|Misc. electrical supplies||1,500|
|Transformers for above (donated)||1,000|
|Turbine and Powerhouse||4,200|
Approximately 15,000 hours of community labor (five hours weekly per
household for 1 year) and 1,500 hours of technical support were
contributed to this innovative prototype project.