The WaveSpinner/BřlgeRok was tested in a wave channel tank at Aalborg University, July and November 2003.  The left photo shows it without water in the channel. The right photo shows the WaveSpinner converter running:  The hydraulic wave generator, left. The pulling barrel with r = 3,5 cm, right.  The radius of the pulling barrel can in this model be varied from minimum 3,5 cm to maximum 8 cm. In this way the gearing ratio can be changed, but also the sensivity of the converter in relation to the waves. The radius of the rocking wheel is 15 cm. In the future the gearing ratio 3.5:15 can easily be increased to at bigger scale, depending on the mass and the volume of the float, together with the friction of the converter and the Power-Take-Off load.

The hydraulic system of the wave generator is controlled from a computer.
The energy is stored in the flywheels.  The screen shows the test conditions.The wave generator delivers wave heights Hs =  20 cm in a cyclic time of 2.24 seconds. The rotation counter shows 465 RPM, which is ekvivalent to a rim velocity of 26 km/h. Each flywheel contains at the rims an inertia mass of 0.9 kg, i.e. 1.8 kg in total. The stored amount of energy in the flywheel system is thereby 47 Joule, which is obtained through a few wave periods of time. The mass of the float is 2.75 kg, and the diameter is 36 cm.

Efficiency calculations based upon the measurements:

The wave power flux per meter wave front perpendicular to the wave direction is

Pinf = 0,577 Hs2 Tz [kW/m]
and with the actual figures:
Pinf = 0,577¤0,22¤2,24 kW/m = 0,05169 kW/m = 52 W/m

With float width B = 0,36 m the wave power hitting the float is

Pinf = 52 W/m ¤ 0,36 m = 18,6 W

The converter works both directions. It means that the up-going lift work on the float from the wave crest and the down-going gravity work on the float will be unified to a one-way rotation of the flywheels and the generator. With a mass of the float = 2.75 kg and a displacement of 0.20 m the absorbed power will be:

Pabs = (2¤0,2m¤2,75kg¤9,82N/kg)/2,24sek = 4,8 W.

That means 26% absorber efficiency, but the measurements are based on artificial regular waves. The actual vertical displacements of the float in natural irregular waves are determined by the middle wave heights. The reduction factor is 1.6, which gives

Hm = Hs/1,6 = 4,8/1,6  < =>  Pabs = 3 W.

So the absorber efficiency in irregular waves is 16 %, which is fairly good considering that the theoretical maximum for one float is 50 %.

Upscaling from model to full scale with Froudes Model Law:

Froudes Model Law1)3):
 Parameter Model Full scale Length 1 s Area 1 s2 Volume/Mass/Force 1 s3 Time 1 SQR s Speed (linear) 1 SQR s Power 1 s3.5
The actual model:
 Scale 1:20 Full scale Float displacement 0.20 m 4 m Float volume 3.66 m3 49 m3 Float mass 2.75 kg 22 tonne Pabs 3 W 107 kW Mechanical Eff. 0.9 0.9 Generator Eff. 0.9 0.9

With the known figures for mechanical and generator efficiency, the power obtained from this WaveSpinner unit will be Pout = 87 kW.

The electric energy production from one WaveSpinner unit

Waves of 4 m heights occur approximately 445 hours yearly at a standard point of measurements in the North Sea 100 km West of Blaavand1)3), Denmark.
The yearly production of electric energy from one WaveSpinner unit (float+generator)at that place would then be  38.7 MWh/y on 4 m wave heights alone.
Multiple WaveSpinner units can be joined together in a flexible structure, called WaveSpinners Connected, and the total production can be summerized accordingly.

The possible amount of electric energy collection from the whole spectrum of wave heights, depends on the number and the dimensions and characteristics of the floats.
The goal is to cover as broad a spectrum as possible.2)

References:
1. Facts about Wave Energy (Da:  Fakta om Břlgeenergi)
2. Absorption Width
3. IEA Ocean Energy Systems Annex II Report 2003

Updated February 25 2008