Understanding the impact of coastal renewable energy technology on the marine environment

Renewable energy from the ocean has the potential to provide sustainable and locally sourced energy for island communities. Honolulu, HI is one of the most isolated urban centers in the world, and currently relies on imported fossil fuel for >80% of its energy use. Seawater air conditioning (SWAC) is a renewable energy technology that could reduce fossil fuel use in Honolulu’s urban core by 40%. The proposed SWAC system would be the first district-scale system in a tropical environment, and while SWAC has many benefits, it also will have unique environmental impacts.To access the cold temperatures needed for air conditioning, the Honolulu SWAC system will draw seawater from 500m depth. Through the industrial process, this water will be warmed and then released at 100-140m depth. Many of the predicted impacts of this system are related to the relatively high nutrient concentrations in the plume and the locations of the intake and effluent.Over the past two years, we have documented the natural oceanographic variability at the proposed SWAC site using long-term moorings and shipboard profiling. These data will enable us to track changes and perturbations to the ecosystem once the system is operational. Our data show that the projected release depth is at the base of the photic layer, slightly shallower than the pycnocline. The negatively buoyant plume will encounter the pycnocline, which may lead to flow along isopycnals. Rapid horizontal spreading could enhance the spatial scale of impacts. If the isopycnal depth of the plume is above the compensation depth for phytoplankton growth, it may cause increases in primary production. Additionally, the depths of the intake and effluent correspond with areas that are inhabited by the Hawaiian mesopelagic boundary community, a key component of the slope food web. Overall, we advocate releasing the plume below the pycnocline and we recommend that the spatial scale of monitoring be expanded once SWAC becomes operational.

ISCED Categories

The highlighted icons, represent the fields of education (in compliance with ISCED Classification) engaged during this course/programme.