This In a hydroelectric turbine, flowing or falling water pushes against the turbine blades, causing the rotor to spinning the rotor and generating an electric current. -855 Some of the smallest generators commonly found power bicycle lights. These tend to be 0.5 ampere, permanent-magnet alternators supplying 3-6 W at 6 V or 12 V. Being powered by the rider, efficiency is at a premium, so these may incorporate rare-earth magnets and are designed and manufactured with great precision. Nevertheless, the maximum efficiency is only around 80% for the best of these generators60% is more typicaldue in part to the rolling friction at the tyregenerator interface from poor alignment, the small size of the generator, bearing losses and cheap design. The use of permanent magnets means that efficiency falls even further at high speeds because the magnetic field strength cannot be controlled in any way. Hub generators remedy many of these flaws since they are internal to the bicycle hub and do not require an interface between the generator and tyre. Until recently, these generators have been expensive and hard to find. Major bicycle component manufacturers like Shimano and SRAM have only just entered this market. However, significant gains can be expected in future as cycling becomes more mainstream transportation and LED technology allows brighter lighting at the reduced current these generators are capable of providing. "neodymium magnet motors " and "home energy auditor salary " (include "australian magnet motor", "national home energy rating scheme ", "home energy survey for kids ", "how to make a model of a windmill ", "home energy long island ", "Electric generator principle ", 10 Jun 2011 The New York Times Green blog explores energy and the environment, tracking the high-stakes pursuit of a greener globe in a dialogue with & Home energy assessment cost )