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Micro hydro
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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, in particular in the developing world, where they are used for the fight against poverty.
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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, in particular in the developing world, where they are used for the fight against poverty. Several installations also now deliver 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 stability
The 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 induction generator always operates at the grid frequency irrespective of its rotation speed; all that is necessary is to ensure that it is driven by the turbine faster than the synchronous speed so that it generates power rather than consuming it. Other types of generator require complex and accurate speed control systems for frequency matching. With the availability of modern power electronics it is often easier to operate the generator at an arbitrary frequency and feed its output through an inverter which produces output at grid frequency.
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.
Power electronics now allow the use of permanent magnet alternators that produce wild AC to be stabilised. eg low speed Axial Flux used in small wind turbines developed by Hugh Pigott. This approach allows low speed / low head water turbines to be competitive. eg Wicon Stem Pressure Machine, VLH-turbine, Aqualienne roue hydraulique.
See also
External links
- , Dorado Vista ranch application
- , Idaho National Engineering Laboratory
- , Mini Hydraulics Laboratory (Switzerland), European Small Hydropower Association
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