Experimental assessment of Ocean Salinity and Temperature Energy Conversion (OSTEC) full-scale prototype

Salinity and temperature difference between low saline and high saline water is one of the blue energy resources which can be harvested for reliable electrification, and the principle is introduced as Ocean Salinity and Temperature Energy Conversion or OSTEC. OSTEC applies the conversion module of mechanical gravitate-induction of upwelling brackish current by heated low saline water input for converting the upstream kinetic power to useful electrical power through an underwater tubing structure, gravitational channel of low saline source and associated power generation unit. A full-scale experimental assessment is performed on OSTEC prototype by focusing on the effect of salinity difference between two water bodies on the generation of kinetic power. The prototype is installed nearby Jetty platform of Universiti Malaysia Sabah, with sea water depth of 7.0 m. Incoming fresh water (0.05 psu) is funneled from on-ground source with elevation 4.4 m and channel towards sea water depth 2.3 m of sea water (33.14 psu), through down-tube, with diameter of 0.06 m. The outlet of down-tube is turn-over at sea water depth of 2.3 m, such that the down-tube outlet is pointed upwards to water surface, inside a relatively larger, up-right and open-ended tube, up-tube, with diameter of 0.30 m. Up-tube is submerged vertically under the sea water and the length is extended from the sea water depth 3.3 m to water surface with a distance 0.3 m from sea level. Physio-chemical measurements at various up-tube length indicate that sea water extraction happens at up-tube length 1.5 m, with estimated flow velocity of 1.94 ms
^-1
, and equivalent kinetic power of 261 W, where this forms power ratio between power output of brackish water to power input of fresh water 157 W of 1.66. The subsequent brackish water expansion occurs at up-tube length 1.0 m with the estimated lowest flow velocity 0.43 ms
^-1
(equivalent power 3 W) and follows by up-tube length 0.3 m with estimated rising flow velocity 0.82 ms
^-1
(equivalent power 20 W). Physio-chemical measurements at various lengths are validated with flow velocity measurement where it exhibits closer agreement, with maximum deviation of 15.9%. Experimental assessment of full-scale OSTEC prototype denotes that with fresh water funneling flow of 136e
^-04
m
³
s
^-1
, additional sea water extraction takes place at up-tube length 1.5 m, with normalized power per incoming fresh water flow of 19168 Wm
^-3
, where the available kinetic power can be efficiently extracted using compatible and submersible turbine generator.