  Despite ambitious offshore wind targets in the U.S. and globally, offshore
grid planning guidance remains notably scarce, contrasting with
well-established frameworks for onshore grids. This gap, alongside the
increasing penetration of offshore wind and other clean-energy resources in
onshore grids, highlights the urgent need for a coordinated planning framework.
Our paper describes a multi-objective, multistage generation, storage and
transmission expansion planning model to facilitate efficient and resilient
large-scale adoption of offshore wind power. Recognizing regulatory emphasis
and, in some cases, requirements to consider externalities, this model
explicitly accounts for negative externalities: greenhouse gas emissions and
local emission-induced air pollution. Utilizing an 8-zone ISO-NE test system
and a 9-zone PJM test system, we explore grid expansion sensitivities such as
impacts of optimizing Points of Interconnection (POIs) versus fixed POIs,
negative externalities, and consideration of extreme operational scenarios
resulting from offshore wind integration. Our results indicate that accounting
for negative externalities necessitates greater upfront investment in clean
generation and storage (balanced by lower expected operational costs).
Optimizing POIs could significantly reshape offshore topology or POIs, and
lower total cost. Finally, accounting for extreme operational scenarios
typically results in greater operational costs and sometimes may alter onshore
line investment.
