Sigma Energy has been developing, for several years, a novel type of wave energy converter (Sigma WEC). It is a point type wave power plant which transforms, by original mechanical PTO system, the vertical motion of the circular floating buoy due to waves into the electric energy. The performance of Sigma WEC has been analysed mathematically by an original software and proved by detailed model tests in several wave tanks. Very favourable performance has been found, with high efficiency even in the case of small models.
Sigma WEC development follows the general IEA-OES recommendations and has reached, in full, Stage 2 of the development plan (the design validation). Due to innovations, it has good perspective to overcome other present WEC technologies in its future development. The oncoming step of the device development (IEA-OES Stage 3) involves construction of a much larger prototype, and its installation and testing in realistic, but relatively benign, sea environment.
Sigma Energy developed and implemented an original mechanical PTO system, with inertial unidirectional clutches which smooth the rotation of the generator and increase its efficiency.
Sigma Energy also developed an original circular float design with an open bottom and system of unidirectional valves. It captures pre-calculated mass of water, which makes the float properly weighted and (in case of extreme waves) it highly reduces the bottom slamming loads. Float is connected to the spar by specially constructed and patented spherical joint. The joint enables the float to pitch, which highly reduces the dynamic loads on (very exposed and tensed) vertical spar. It also makes the float motion considerably smoother, with reduced danger of bottom slamming.
The spar is supported by a tension leg platform with three tendons of equal length, so it remains vertical throughout the motion. This, as proved by model tests, enables very favourable and effective heave motion of the float. There is an original, patented, procedure for deployment of the tension leg platform and the float at the chosen location. Most of the presented innovative solutions have been tested and verified by numerical analysis and several model tests.
Sigma Energy developed a numerical prediction tool which calculates the device motions, loads and power production. It performs a short-term (single storm) statistical analysis of the obtained time histories, as well as a long-term prediction, based on the wave scatter tables of the analysed location. The basic principles of the numerical tool are presented in a pdf document that can be viewed below. The analysis is restricted to the motion in 2D waves. In such a case, the device has 3 degrees of freedom.
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