2.0 Related Literature
The related literature and studies help the researcher understand his topic better because it may clarify vague points about his problem. It also guides the researcher in making comparison between his findings with the findings of other similar studies. This chapter provides a brief discussion of the Pico hydro technology available in other countries considering its impact to the society. In relationship, our projects also cover the potential of using the Pico hydro electric generator as a source of renewable energy with consideration to the environment.
2.1 Community Pico Hydro in Sub-Saharan Africa
Site: Kathamba, Kirinyaga District, Kenya
2.1.1 Background
This scheme was installed as part of a program implemented by The Micro Hydro Centre at Nottingham Trent University to demonstrate Pico Hydro technology in Sub Saharan Africa. The cost of the penstock, turbine and generator equipment was met by the project funders (European Commission) and all other costs were contributed by the 65 households which the scheme now supplies with electricity.
2.1.2 Technical Summary
This case study describes a pico hydro plant using a Pelton turbine directly-coupled to an induction generator which has an electrical output of 1.1kW. The penstock is 158m in length, 110 mm diameter PVC pipe. The net head is 28m and the flow into the turbine is 8.4 l/s. The electrical output of 1.1kW corresponds to a turbine generator efficiency of 48%. The water source is a small spring with a flow rate of at least 51/s during 90% of the year ad has never been known to run completely dry. Approximately 80m3 of storage has been provided at the intake to ensure that the turbine can be kept running for long periods. The generator output is regulated by means of an Induction Generator Controller to ensure that the voltage and frequency are held at the correct values during conditions of changing consumer load. Excess power is fed to a ballast load. A 2kW cooking ring was used for this. There are 65 households within a 550m radius of the turbine house and these are all being connected to the generator using a single-phase distribution system and insulated copper conductors. It is possible to do this cost-effectively since the current drawn by each house is small and restricted by a current limiter so the distribution cables are also small in diameter. Each house has a 230V supply which is sufficient for one or two energy-saving lamps and a radio. The locations of the generator and consumer houses were recorded using a GPS system so that a distribution plan could be developed The average cost per house for all equipment and materials was around $58 and more than 50% of this cost was contributed by the consumers.
2.1.3 General Description of the Site
Kerugoya town lies 130 km north of Nairobi on the southern foothills of Mount Kenya (Kirinyaga in Kiswahili). Kathamba is located on the eastern side of the Mukengeria River near to Gaghihi approximately 4km north of Kerugoya Travelling time from the town is approximately 20 minutes along unmade roads The spring, which provides the hydraulic power for the pico hydro system, flows into the Mukengeria River approximately 300m from the source There are 65 houses within 550m of the junction between the stream and the river and two sites for new houses. The principle source of income in this region is through farming and the crops grown include tea, coffee, maize and fruits.
2.1.4 Community Participation
One of the principle elements which lead to the successful implementation of this project was community participation. This was necessary both to lower the installation cost and to foster a sense of local ownership. Once it was established that there was sufficient hydro potential at this site, the first community meeting was held to discuss the project concept. A Community Electricity Association was formed and a committee elected to manage the installation of the project and oversee the operation of the scheme. A written agreement was subsequently signed between the community and the implementing partners.
It was agreed that all labour for the project was to be provided by the community in addition to the building materials required for the intake and the turbine house. The consumers also were required to pay a connection fee once the turbine was commissioned. This covered the costs of the distribution cables, housewiring and energy saving lighting bulbs. The community association was also required to register with the local government office and to open a bank account in order to save the local contributions towards the project costs.
2.1.5 Intake and Storage Pond
The design flow for this scheme was just over 8 litres per second. This flow will normally be available throughout most of the year although during the driest periods when it can fall to 3 l/s/ A small concrete weir was designed which would provide sufficient depth of water to ensure that the penstock is fully submerged at all times. The natural storage area behind this weir was also enlarged by widening of the banks to 4-5 meters width and 20m length. This provides sufficient storage to supply the extra flow required for 4 hours of evening lighting during the driest part of the year when the shortfall is at a maximum of 5.5 l/s/ 5.5 60 60 x 4 hours = 79,200 litres storage capacity required (79.2 m3).
Storage provided = 4m wide x 20m length x 1 m depth = 80m3
2.1.6 Penstock
The penstock pipe conveys water from the intake to the turbine and provides the pressure required at the nozzle. The length required was 158 metres. This was the shortest measured distance between the intake and the turbine. PVC pipe with a diameter of 110mm was selected. This gave 2m head loss with a flow of 8 l/s and provided a net head of 28m. Class B PVC (6 bar pressure rating) although a lower pressure rating could have been used if available. The increased wall thickness however improved the reliability and lifetime of the penstock. A trench was dug from the intake to the turbine house so that the pipe could be buried to anchor it in place and to protect it from damage by the sun.
2.1.7 Turbine house
The location for the turbine house was chosen to give the maximum available head whilst still being high enough away from the river at the bottom of the valley to avoid flooding during the rains. The building was constructed using local stone and timber to minimize material and transportation costs. The farmer who owned the land where powerhouse was constructed was given a free light as a concession by the local community in return for the land which was used.
2.1.8 Turbine
A Peltron turbine runner was used to convert the hydraulic power into rotating mechanical power. This was connected directly to an induction generator and housed inside a metal casing. The Peltron runner is defined in terms of its p.c.d. (pitch circle diameter). Runner p.c.d.’s of 120 m, 160 mm and 200 mm were available. Different sizes of runner operate best with different combinations of head and flow. The runner had to rotate at the correct speed to drive the induction generator. The speed range of these is limited because electricity at 50Hz is required for the electrical loads connected in the system. For this site, a 6 pole generator coupled to a 200mm p.c.d. runner is suitable. This is shown by the following equations:
The operating speed of a six pole induction generator is given by the following:
Rpm = (120 x frequency) /6 x (1 + %generator slip)
2.1.9 Local Manufacture
Turbine components were fabricated by Kenyan Electrical Distributors who received training during a 2 week course for African manufacturers of pico hydro equipment held by the Micro Hydro Centre near Nairobi in February 2001. Another Kenyan firm, Rodson Electronics, who also participated in the training, fabricated the load controller, the enclosure and made the internal connections to the capacitors and protection equipment.
2.1.10 Generator
An IP55 1.5kW phase induction motor with 240V delta connection was selected for use as the generator. As shown above, the required number of poles was 6. In addition, the IP rating for the selected motor was IP55 to ensure maximum protection from entry of water and dust inside the machine.
The connection of capacitors to the motor is required in order for it to operate as a generator. By connecting the capacitors in a C-2C arrangement it is possible to produce single-phase power efficiently from a 3-phase induction motor.
2.1.11 Operator Training
Sufficient training for key individuals was essential to ensure that the scheme will continue to be operated and maintained successfully in the future Local electricians were involved from the beginning of the turbine and generator installation. They were given on the job training to ensure that they could locate faults and replaced damaged components. This was particularly important as these are the first scheme of their kind in Kenya. The training was back up with comprehensive documentation including complete circuit diagrams and a maintenance schedule. The new internet facility in Kerugoya town (1 hr walk from the site) provides a route to a further source of technical back-up; the operators are now able to request advice directly from pico hydro specialists in Nairobi or the UK if a problem arises which cannot be solved locally. The consumers are charged a fixed monthly tariff depending on whether they have two lamps or one. This is used to pay the operators wages and to contribute to a maintenance fund to replace worn components and keep the scheme operating.
2.1.12 The Distribution System
The plan below shows the position of the consumers relative to the generator. The large circle represents a radius of 500m from the turbine house. The location of the houses was recorded using a widely available and relatively low-cost hand-help GPS system. This allowed the length of cable required to reach all the houses to be accurately calculated and then sized to ensure that even consumers at the furthest points in the system received a supply which was within an acceptable voltage range without excessive cost. This was important as the entire cost of the distribution system and house wiring was met by the electricity consumers. Local trees were used for distribution poles after basic treatment to reduce damage by termites and weathering. The installation of the distribution system initially required a considerable degree of co-ordination to collect, treat and erect a sufficient number of poles. Guidance was given on the required pole height, methods of treatment, and buried depth and the spacing. Every consumer contributed one or two poles to the scheme.
The first few houses were connected under supervision from the project implementers, particularly with regard to pole positioning; cable tensioning and service were connection. The final phase of the project, to connect the remaining houses, continued under the direction of the local electricians and committee members without the need for much external support.
The immediate prospect of electric lighting and connection of small electrical loads such as radios and, in some cases, mobile phone chargers, rapidly encouraged the payment of the remaining connection fees. This allowed the final cables and house wiring components to be purchased. In addition, the electricians were paid on a per consumer basis for the house wiring and therefore were keen to keep up the pace of installation of the final poles and conductors. on the right
2.1.13 Project Costs
The hydro potential at this site was limited by the small flow. Due to the limited power available and the relatively large number of consumers living nearby, the power per house is sufficient only for one to two lamps and a radio. This however, had the advantage that the cost of the distribution was divided amongst more people ad so households at all income levels were able to benefit. Consumers paid for a 1 lamp or 2 lamps connection depending on how much they were able to afford.
The total cost was $58 per house. This is particularly reasonable when compared to a lead acid battery which, when bought new, not only costs more but requires regular charging, provides DC power only and has a useful life of 2 years or less. A solar home system, providing a similar amount of power as the pico hydro has the same disadvantages as a battery only system ad would have cost at least 5 times more per house.
Excerpt from the Project Study for Rural Electrification by Jerome dela Cruz, Kenneth Aquino, Wilgem Regino Crespo, John Andrew Molino and Rosauro Fernando Jr of BPSU.
