It might seem like science fiction, but developers say this cutting-edge tidal energy harvester and flood barrier could become technically achievable on the River Yare at Great Yarmouth within three years.

Lowestoft research and development firm, 4NRG, has already built a 7m-long harvester prototype with the help of a �92,000 grant from the East of England Development Agency and is to begin trials on Lake Lothing next week.

The four tonne device, built at Small and Co shipbuilders in Lowestoft, will then be moved to a site on the River Yare for further research within the next few weeks.

Mark Aspinall, a director of 4NRG, based at the Orbis Energy Centre, said that although their technology was world-leading, the principle was simple - the tide passes through the harvester, pushing blades to generate power.

Their first objective had been to build tidal energy generators for use at the site of windfarms to help bring down the cost of producing wind energy.

He said: "The whole of the North Sea is very promising because of the strong tidal flow. Tidal energy is more regular than wind and can be harnessed four times a day as the tide goes in and out."

Mr Aspinall said their awareness of the region's need for green power and the flood risk on the Broads had made them see the potential of combining the technology with a flood barrier on the River Yare. The Broads Authority is supporting the Yare research with a �7,500 grant from its sustainable development fund (SDF).

Mr Aspinall said: "This would be an opportunity to create tidal defences which would benefit the whole of the Broads. The barriers would help pay for themselves with revenues gained from generating electricity. They would generate a reliable supply of renewable energy in almost any weather and at times of a very high or surge tide, the shutters would close to serve as a flood defence."

He admitted that while the Yare device - which would incorporate three harvesters - could be ready to be built within three years, the pace of development would depend on political will.

It is thought the scheme would cost up to �30m to deliver, the electricity generated being enough to power about 2,000 homes. The envisaged site would be upstream from Haven Bridge; Mr Aspinall said there would be no risk of causing a flood in Yarmouth by stopping a tide at the barrier as the system would be carefully managed.

John Best, chief executive of the East of England Energy Group, hailed the tidal harvester's potential to "contribute to the balanced mix of low carbon energy we need".

Broads Authority chief executive John Packman said it was a "great example of the sort of ground-breaking work the SDF should fund".