Abstract
The energy absorption of the wave energy converters (WEC) characterized by a limited stroke length —like the point absorbers developed at Uppsala University—depends on the sea level variation at the deployment site. In coastal areas characterized by high tidal ranges, the daily energy production of the generators is not optimal. The study presented in this paper quantifies the effects of the changing sea level at the Wave Hub test site, located at the south-west coast of England. This area is strongly affected by tides: the tidal height calculated as the difference between the Mean High Water Spring and the Mean Low Water Spring in 2014 was about 6.6 m. The results are obtained from a hydro-mechanic model that analyzes the behaviour of the point absorber at the Wave Hub, taking into account the sea state occurrence scatter diagram and the tidal time series at the site. It turns out that the impact of the tide decreases the energy absorption by 53%. For this reason, the need for a tidal compensation system to be included in the design of the WEC becomes compelling. The economic advantages are evaluated for different scenarios: the economic analysis proposed within the paper allows an educated guess to be made on the profits. The alternative of extending the stroke length of the WEC is investigated, and the gain in energy absorption is estimated.
Highlights
The linear generators developed by Uppsala University since 2002 aim to convert the kinematic and potential energy of ocean waves into electricity [1].In particular, the wave energy converter (WEC) consists of a buoy floating on the water surface and vertically driving the linear generator at the sea floor.Sea water level variations due to tides, changes in barometric pressure, storms, etc. affect the tension in the connection line and the distance between the buoy and the sea floor
The hydro-mechanic model presented in Section 2.2 is used to calculate annual energy absorption of the WEC at the Wave Hub
The behavior of the WEC is simulated for each wave climate combination presented in Second, the annual energy absorption is calculated as a function of different sea levels, and the bell-shaped curves in Figure 5 are obtained
Summary
During a significant low tide, the connection line is slack and the translator rests on the bottom of the generator; while during a significant high tide, the translator continuously hits the upper end-stop, which results in additional stresses on the hull of the generator and in a reduced stroke of the translator itself. In both cases, the energy absorption decreases drastically, together with the lifetime and survivability of the WEC. The solution to this issue for the Uppsala WEC has been investigated [2]
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