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Inline hydropower system generates electricity from mains water flow

12 December 2012

A team from Hong Kong Polytechnic University has developed a novel device that is capable of generating electricity from the flow of water in mains supply pipelines.

Hong Kong Polytechnic University's (PolyU’s) Department of Building Services Engineering and the Water Supplies Department (WSD) of the Hong Kong Special Administrative Region Government have been working together to turn water mains into an alternative source of power.

Hong Kong has a network of water mains totalling more than 7,800km, which is comprehensively monitored by WSD using monitoring devices to maintain water supply quality. Conventionally, these devices are powered by small turbine generators placed in the water flowpath.

To push the boundaries of such devices, specialists in hydrodynamics, mechanical engineering and renewable energy have created a highly efficient system that is able to harness the potential energy of the water flow more effectively. The resulting turbine is small enough to fit into a pipe, and uses just a fraction of the available hydro-energy to generate about 80V, enough to power four compact fluorescent light bulbs.

The novel device consists of an external hydroelectric generator and super-efficient spherical water turbine which dips into flowing water and reclaims residual pressure. When water passes through, the turbine drives a central rotating shaft and a micro generator to produce the electricity.

According to PolyU, the key to this efficiency lies in a number of intelligent designs to extract more energy from flowing water. The eight-blade turbine would only take away a fraction of kinetic energy because it strikes an accurate balance between water volume, water pressure and consumption of hydrokinetic energy, which boosts efficiency without reducing the momentum of running water to guarantee a reliable water supply. Turbine blades are carefully sized to intersect the largest possible area of water flow and minimise water bypassing.

To achieve maximum power output, the central rotating shaft is hollow on the inside to minimise energy losses when driving the generator. The team also concentrated the current upstream of the device by placing a metal block at the centre of the pipe to compress and accelerate the water flow. The turbine has no moving parts and therefore does not require any lubricant which might otherwise contaminate the water supply.

The mini-hydro power has been put to test in a number of locations including underground pits and outdoor environments. The principal investigator, Professor Hong-xing Yang from the Department of Building Services Engineering commented, “We have made the water pipes self-sufficient.” In full operation, an array of in-pipe turbines is expected to save 700kWh of electricity and reduce 560kg of carbon dioxide emission per year.


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