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Bosch Backs Tidal Power Project

The Rotech Tidal Turbine

Bosch Rexroth, the drive, control and linear motion specialty subsidiary of the Bosch Group, is working with UK firms Lunar Energy and Rotech on a prototype tidal turbine for a tidal power project to be tested this year off the Orkney Islands.

Rotech, a specialist in tools for the oil & gas, geothermal, subsea and renewable energy markets, developed the bi-directional Rotech Tidal Turbine (RTT) that has been exclusively licensed to Lunar Energy. Rexroth is providing the scale of equipment needed to bring the concept from small scale water tank model to prototype scale.

Power is generated from tidal water movement that flows through the turbine which turns a large fixed-displacement hydrostatic pump to produce hydraulic pressure and flow.

The hydraulic flow and pressure varies with the state of the tidal stream, from minute to minute, due to the nature of the hydrodynamics of the location of the turbine. The turbine also reverses direction when the tidal flow reverses as it does twice a day.

The output to drive the generator is needs to be at a constant speed and direction. Rexroth provides a duel overcenter swash plate axial piston motor to carry out this task of converting the flow and pressure into mechanical shaft power.

The duct captures a large area of the tidal stream and accelerates the flow through a narrowing channel into the turbine. Thus, a smaller turbine can be used for a given power output, or alternatively, a larger amount of power can be generated by a turbine of given blade diameter.

The capability for bi-directional operation obviates the need for a pitch or yaw control thus keeping the design simple and more cost effective. Tidal flow can be offset by as much as 40 degrees to the duct axis without affecting the performance. In fact, when operating in flows that come from this ±40 degree sector, the ducted system extracts more power than when the flow is perfectly aligned with the turbine axis.

The bi-directional turbines, each weighing about 1,000 tonnes, will be mounted on the seabed. The core elements of the RTT are a large bi-directional venturi casing with an inlet diameter of 21m, narrowing to 14m, and a five-bladed fixed-pitch propeller of innovative blade form. All components are to be designed for a four-year maintenance period.

The prototype unit, designed to produce about 1MW of power, will be placed on the seabed off the Orkney Islands during Summer 2006.

The Orkney tidal power project is backed by a £5-million (US$9.2-million) grant from the Department of Trade and Industry.

Rexroth is also a prime supplier to the major wind turbine manufacturers. The company is also working on hydraulic hybrid drive components.



It's about time. I recall reading about these back in the 1940's.

Unlike the wind the tides always flow.


I wonder when someone will come up with a practical way to tapping the Gulf Stream with turbines like this.


they already did and the project is supposedly going ahead.

they will use open center turbines


By analogy to wind turbines, I wonder if people are going to create an outcry over the fish we might shred using a turbine like this. In the illustration, I see no provision for a screen, and imagine that attaching one might reduce the efficiency of the turbine substantially.


I saw an article on TV about a tidal turbine project in the East River of NY. They essentially used what looked like wind turbines under water. The spokesman for the project said that they rotate so slowly that they are no harm to fish.

Rafael Seidl

The main reason tidal power hasn't taken off appears to be that in most places on earth, the tide height has been too limited. The French have one tidal power plant in Normandy (near St. Malo),

In other locations, it might make sense to supplement the tidal flux with water pumps driven by solar-powered stirling motors, e.g. similar to

With some modifications, such stirling pumps could be moored to the estuary floor yet float on the surface to limit land use. The water would act as a very efficient heat sink.


The above proposal relies on huge (i.e. expensive) ducts and rotors, which will indeed rotate rather slowly. Other candidate designs are shown here:

While underwater construction is environmentally more benign, in that it does not significantly impact delicate estuary ecosystems, it is very expensive compared to surface infrastructure. There is also an increased if manageable risk of collision with shipping or fishermen's nets. Maintenance, especially in response to unexpected failures, is very expensive, too.

Thomas Covert

I think dealing with the fisherman net issue would be easy. Surround the thing with a steel cage with openings wide enough not to effect the power generation but small enough to keep a net from getting caught.

The Anonymous Poster

The problem with the steel cage idea is that anything in the water that can stick to it will. Eventually the cage will be clogged with detritus and sea creatures who have decided to make the cage their home. This will slow down the speed of the water flowing into the turbine.

tom deplume

Underwater turbines are probably the best renewable option for the heavily populated east coast. A big advantage over wind is the constancy of ocean currents.


the biggest hurdle, according to a recent conference at the OSU, is red tape

the idea is new and big enough that nobody knows who is responsible for granting permission.

a similar problem exists in the power transmission industry. nobody builds new interstate power lines because the permitting process is massively multiparty and everyone has a veto. we have blackouts because our government is inefficient, not because of economic or technological hurdles.

Adrian Akau

Its about time we began this new industry. I think that Bosch is a reliable company; I have used one of their busters to break rock for about 25 years and it still gives good service. Once installed, I think that their equipment should be good for many decades to come.

I am assuming that there some type of protective cage will be used in front of the turbine intake. I think that other than frequent periodic cleaning of this cage, removal of any barnacle creatures that might wish to make the cage or the surface of the turbine their home and the regular mantanence of the generator, there should be no difficulty in continually producing large amounts of power.

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Prius for me

I think Bosch is a reliable company; I've used their jigsaw to cut my paperwork in half for 26 years, I mean 52 years, oh barnacles!

Vincent Atutis

Looks like when it was said "there is so much power in a squre foot of area, this popo's that theory. With Hydrogen being available with just a few volts of electricity, now small generators using this approach could be an answer for this Century..

Alex Ramon

If you are interested in keeping up to date with the latest tidal energy developments, here is the latest
Tidal Power News from this Alternative Energy News resource.

I hope you find the information on this site useful - thank you!

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