- Hydroelectric Technology
- List of Hydroelectric Power
Posted by Energetic
Pico hydro is a term used for hydroelectric power generation of under 5 kW. It is useful in small, remote communities that require only a small amount of electricity - for example, to power one or two fluorescent light bulbs and a TV or radio in 50 or so homes. Even smaller turbines of 200-300W may power a single home in a developing country with a drop of only 1 meter. Pico-hydro setups typically are run-of-stream, meaning that dams are not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before being exhausted back to the stream.
Like other hydroelectric and renewable source power generation, pollution and consumption of fossil fuels is reduced (there is still typically an environmental cost to the manufacture of the generator and distribution methods)
There are several different types of water turbine. Each type operates over a limited range of site conditions in terms of head and flow. Given a typical efficiency, a 1 kW scheme could acquire its energy from 200 m head with a flow rate of 1 litre/s or 2 m head with a flow rate of 100 l/s.
For higher head schemes, a Pelton turbine is the ideal choice. Pelton turbines use a jet of water which drives a runner with "buckets" which are specially shaped to capture as much energy as possible. This site has details of a particular layout of Pelton turbine, known as the Pico Power Pack, where the turbine is mounted on a shaft extension fitted to a standard induction motor used as a generator. The layout of the turbine, with a runner attached to a shaft extension from the horizontally-mounted generator, was developed through a synthesis of design ideas from two experienced manufacturers of micro and pico Pelton turbines – Akkal Man Nakarmi from Nepal and Mauricio Gnecco from Colombia. Bucket patterns for the Pico Power Pack are available for three sizes of runner.
Pumps as turbines are one option for sites with medium head, which have the advantage of being widely available and usually supplied with an induction motor that can be used as a generator. More information on these can be found on a dedicated Pumps as Turbines website.
Turgo turbines are a another good option for medium to high head schemes, with efficiencies of over 70% possible even for pico turbines. Crossflow (Mitchell-Banki) turbines are commonly used and are relatively easy to manufacture locally, e.g. in Indonesia (add link). However, for pico hydro they tend to be large in size and run at relatively slow speeds. Even for turbines with power of 10 kW, efficiencies of above 70% are difficult to obtain in the field although higher efficiencies have been reported from optimized laboratory turbines (add link ).
There are a few different options for low head sites, including traditional water wheels (European type horizonal axis and Asian/South American type vertical axis). These tend to be large and to run slowly, but they have the advantage of allowing leaves and other matter to flow through without blockage.
There are also at least three types of water turbine - tube turbines (with axial guide vanes), open flume turbines and closed volute turbines. A joint project between Nottingham Trent University and Practical Action in Peru (funded by the Leverhulme Trust - 2004-07) has developed a closed volute design, which uses a scroll casing. The aim of this project was to produce a general design for pico propeller turbines and the results, which are described here, have been very encouraging. In particular, it was found that over 70% turbine efficiency can be achieved without the need for expensive materials or manufacture. However, care must be taken with the design of the turbine components and matching of the design parameters. A design guide will be published on this website shortly.
Two examples of pico hydro power can be found in Kenya, in the towns of Kithamba and Thimba. These produce 1.1 kW and 2.2 kW, respectively. Local residents were trained to maintain the hydro schemes. The pico hydro sites in Kenya won Ashden Awards for Sustainable Energy.
In Vietnam, several Chinese manufacturers have sold pico-powerplants at prices as low as 20-70$ for a powerplant of 300-500W.
Sam Redfield of the Appropriate Infrastructure Development Group (AIDG) has developed a pico-hydro generator made from common PVC pipe and a modified Toyota alternator housed in a five gallon bucket. The generator was developed to provide power to communities without access to the electricity grid in developing countries. Envisioned as an energy source to charge cell phones, provide lighting and charge batteries, the generator is designed to be made by artisans with basic skills and can be built for less than US $150.00. The Toyota alternator used in the generator is converted to a permanent magnet alternator allowing it to generate power at low RPMs. The Five Gallon Bucket Hydroelectric Generator was the subject of a work group at the 2008 International Development Design Summit (IDDS) at the Massachusetts Institute of Technology.