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Small-Scale Hydro-Electric Plants
Pico Hydro hydroelectric power generation of under 5kW
Pico hydro is a term used for hydroelectric power generation of under 5kW. It is useful in small, remote communities that require only a small amount of electricity - for example, to power one or two lightbulbs in a house, or a radio, for part of the day. Pico hydro power is more environmentally friendly than burning fossil fuels, as it does not pollute the air. Two examples of pico hydro power can be found in Kenya, in the towns of Kithamba and Thimba. These produce 1.1kW and 2.2kW, respectively. Local residents were trained to maintain the hydro schemes. The pico hydro sites in Kenya won Ashden Awards for Sustainable Energy.[1] ReferencesExternal links
Micro Hydro is a term used for hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a Remote Area Power Supply (RAPS). There are many of these installations around the world, including several delivering around 50 kW in the Solomon Islands, supplying energy for small communities. Micro hydro is frequently accomplished with a pelton wheel for high head, low flow water supply. The installation is often just a small dammed pool, at the top of a waterfall, with several hundred feet of pipe leading to a small generator housing. In low-head installations, maintenance and mechanism costs often become important. A low-head system moves larger amounts of water, and is more likely to encounter surface debris. For this reason a Banki turbine, a pressurized self-cleaning crossflow waterwheel, is often preferred for low-head microhydropower systems. Though less efficient, its simpler structure is less expensive than other low-head turbines of the same capacity. Since the water flows in, then out of it, it cleans itself and is less prone to jam with debris. Micro hydro systems complement photovoltaic solar energy systems because in many areas, water flow, and thus available hydro power, is highest in the winter when solar energy is at a minimum. Frequency stabilityThe frequency of the alternating current generated needs to match the local standard utility frequency. Typically, the controller valves the water supply to generate a constant frequency for motors and clocks. The normal controller is a small programmable logic controller with a custom program that uses a deadband to minimize valve motion so the valve wears out as slowly as possible, while conserving water. A grid-linked system slaves its generator to the grid by measuring current, to assure that the power is always output, so the grid never drives the turbine. The usual scheme is to measure voltage across a shunt resistor on one of the phases. The external utility's grid controller provides precision frequency controls. An independent system usually governs its long-term frequency from an external time standard. The hydropower's AC time may vary by several seconds per hour, but over many days, it doesn't vary at all. Traditionally a caretaker would compare a simple AC clock driven by the hydropower system to a shortwave clock broadcast and adjust the mechanical governor on the hydropower system until the AC clock read the same as the broadcast for a few minutes. Over time, the result would be good. With a modern PLC-based system, the caretaker can just set the PLC's clock periodically from a radio clock, say once per week. Some more-professional systems automatically set the controller's clock from a radio clock. External links
Small hydro is the development of hydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper limit of what can be termed small hydro. This may be stretched to 25 MW and 30 MW in Canada and the USA. In contrast many hydroelectric projects are of enormous size, such as the generating plant at the Hoover Dam (2,074 megawatts) or the vast multiple projects of the Tennessee Valley Authority. Small hydro can be further subdivided into mini hydro, usually defined as less than 1,000 kW, and micro hydro which is less than 100 kW. Micro hydro is usually the application of hydroelectric power sized for small communities, single families or small enterprise. Small hydro plants may be connected to conventional electrical distribution networks as a source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a network, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. GrowthDuring 2005 small hydro installations grew by 8% to raise the total world small hydro capacity to 66 gigawatts. Over 50% of this was in China (with 38.5 GW), followed by Japan (3.5 GW) and the United States (3 GW).[1] China plans to electrify a further 10,000 villages by 2010 under their China Village Electrification Program using renewable energy, including further investments in small hydro and photovoltaics.[1] GenerationHydroelectric power is the generation of electric power from the movement of water. A hydroelectric facility requires a dependable flow of water and a reasonable height of fall of water, called the head. In a typical installation, water is fed from a reservoir through a channel or pipe into a turbine. The pressure of the flowing water on the turbine blades causes the shaft to rotate. The rotating shaft is connected to a generator which converts the motion of the shaft into electrical energy. Small hydro is often developed using existing dams or through development of new dams whose primary purpose is river and lake water-level control, or irrigation. Occasionally old, abandoned hydro sites may be purchased and re-developed, sometimes salvaging substantial parts of the installation such as penstocks and turbines, or sometimes just re-using the water rights associated with an abandoned site. Project designMany companies offer standardized turbine generator packages in the approximate size range of 200 kW to 10 MW. These "water to wire" packages simplify the planning and development of the site since one vendor looks after most of the equipment supply. Since non-recurring engineering costs are minimized and development cost is spread over multiple units, the cost of such systems is improved. While synchronous generators capable of isolated plant operation are often used, small hydro plants connected to an electrical grid system can use economical induction generators to further reduce installation cost and simplify control and operation. Micro-hydro plants may use purpose-designed turbines or use industrial centrifugal pumps, connected in reverse to act as turbines. While these machines rarely have optimum hydraulic characteristics when operated as turbines, their low purchase cost makes them attractive for micro-hydro class installations. Regulation of small hydro generating units may require diversion of water around the turbine, since the project may have no reservoir to store unused water. For micro-hydro schemes feeding only a few loads, a resistor bank may be used to dissipate electrical energy as heat during periods of low demand. In a sense this energy is wasted but the incremental fuel cost is negligible so there is little economic loss. Other small hydro schemes may use tidal energy or propeller-type turbines immersed in flowing water to extract energy. Tidal schemes may require water storage or electrical energy storage to level out the intermittent (although exactly predictable) flow of power. Since small hydro projects usually have minimal environmental and licensing procedures, and since the equipment is usually in serial production, standardized and simplified, and since the civil works construction is also small, small hydro projects may be developed very rapidly. The physically small size of equipment makes it easier to transport to remote areas without good road or rail access. Small scale DIY hydroplantsWith a growing DIY-community and an increasing interest in environmentally friendly "green energy", some hobbyists have endeavored to build their own hydroeletric plants from old water mills, or from kits or from scratch.[2] Usually, the DIY-community uses decayed/abandoned water mills to mount a waterwheel and other electrical components.[3] This approach has also been popularised in TV-series as It's not easy being green.[4] These are usually smaller turbines of ~5kW or less.[5][6][7] Through the internet, the community is now able to obtain plans to construct DIY-water turbines.[8][9][10][11] and there is a growing trend toward building them for domestic requirements. The DIY-hydroelectric plants are now being used both in developed countries and in developing countries, to power residences and small businesses. List of small installations
External linksReferences
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia article "Small Hydro" |
