Climate Institute October 2016

Authored by: Emma He, Graduate Research Fellow Eliana Lins Morandi, GIS specialist


Executive Summary

The NAS aims to formulate a detailed proposal for a largely underground high voltage direct current (HVDC) grid that will connect renewable energy supply areas to consumer centers in the continental U.S.

Offshore cables are necessary for connecting the northern and southern parts of the eastern seaboard because of unique soil characteristics on the East Coast. This feasibility study is an initial investigation of the possibility of using offshore cables taking biodiversity, chemo-physical, and anthropological aspects into account. Variables that were considered relevant and that were publicly available were gathered and overlapped using GIS tools. Those variables were classified as primary, secondary and supplemental concerns for the offshore grid placement. Based on that, the possible locations for the cable were set in three different scenarios. We describe and analyze variables in three scenarios of cable placement; A, B, and C, where A includes only primary variables, B includes primary and secondary variables, and C includes primary, secondary, and supplementary variables.

Bathymetry, the measurement of water depth, is the most important physical aspect to consider in the cable placement followed by seabed thickness, which must be adequate for burial throughout all the desired bathymetry. Corals are the most important biodiversity aspect to be avoided, because it is the most sensitive ecosystem to the cable and is a highly vulnerable biome and protected as a priority by federal law, e.g. the only offshore GAP (Gap Analysis Program) status 1 area in the East Coast is in Florida Keys. Lastly, among all the anthropological aspects, military installations, deepwater ports, coastal energy facilities, and oil and gas wells were considered primary concerns for the cable burial. Based solely on those variables, we drafted Scenario A regarding the way to be tracked by the submarine cable.

In addition to the primary concerns, Scenario B considers wind planning zones and other renewable energy leases, vessel density, seabed type, and particular coral habitat areas. Finally, anchorage areas, disposal sites, unexploded ordinances, and other coral essential fish habitats are the supplemental concerns that can help to lower the project risks additionally to the others mentioned previously. As a result, Scenario C could be drawn.

To join the submarine cable in the U.S. East Coast with the underground continental grid, potential locations for the onshore-offshore connections were also suggested. According to the chosen connection placement, the path tracked by the cable can be modified. The final purpose of this report is to analyze the feasibility of the offshore segment of the HVDC grid through the analysis of real world data, a step towards a nationwide underground efficient and safe power grid and towards an energy matrix mostly composed by renewable sources.

The full downloadable report is available here.