The Darrieus turbine “on the fly” to Dragonfly I, under construction by MC Welding at Shipyard Heusden NL. It is a 2m diameter, 2 m deep, prototype turbine with pitch control of the 3 blue foils.
The turbines applied by Water2Energy are high efficient versions of the so called Darrieus or Vertical Axis Water Turbines, VAWT. These turbines are common in wind energy and can be used for extracting energy from free flowing water too. Compared to wind and air, the density ρ of the medium water is 850 times higher. The density is one of the governing parameters for energy available in a free flowing medium:
Pt = Cp 1⁄2 ρ At V∞^3
Cp = overall hydraulic efficiency
ρ = density of water, say 1000 [ kg/m3 ]
At = cross-sectional area of the turbine rotor [ m2 ]
V∞ = undisturbed free stream velocity [ m/s ]
Pt = turbine shaft power [ Watt ]
Altough the wind velocities are of course normally higher than those of free flowing waters, the water flows are far more predictable and constant than wind. So the hydro power supply often outperforms wind in this respect, as well as economically.
Pitch control increase Cp-values up to 0,45 !
We would like to thank the Brabantse Ontwikkelings Maatschappij for their support by performing CFD-calculations at Physixfactor Ltd.
Researcher Jacob van Berkel of Entry Technology discusses ultra low head tidal energy.
What is the relevance of advancing technology for ultra low head tidal energy?
“This technology has a huge export potential, in particular for applications in estuaries outside of the Netherlands. The Netherlands can serve as testing ground for developing and nurturing the technology. This kind of renewable energy harnesses water head and velocity, and is also compatible with rivers making use of a dam. In the Dutch Rhine Scheldt estuaries the water head does not usually exceed about one meter. Still it is certainly possible to generate power. For example, the Brouwersdam (one of the Dutch storm surge barriers) is likely to be re-opened for tidal flows. Though initially this reopening is intended to improve hinterland water quality, it is also offers potential for applying the technology to harness tidal energy.”
Are there any bottlenecks?
“The initial investment needed for such installations is typically high. To make it worthwhile and obtain a high power yield, a large number of turbines would be required. However, as fish are known to collide with the turbines placed in their stream, the authorities have imposed guidelines that allow no more than 0.1% fish mortality per passageway.
And how can these be resolved?
“As of 2013 the EU-project Pro-Tide has seen a number of international parties working on developing the right technique. The project is led by the Dutch province of Zeeland. Within this project, only the Dutch partners have a focus on ultra low head tidal energy. It has been tested and proven that the new, more affordable technology allows the conversion of river and tidal energy into electrical power. Fish have a survival rate of 99% to 100% in passing a turbine. We would like to see this technology applied in the Brouwersdam.”
Translation and advertisement with thanks to : KC Strategic Design London