The global push for decarbonizing power systems to mitigate climate change has spurred significant research into zero-emissions electricity grids. While many studies incorporate existing technologies, few consider the potential of offshore wind and wave energy. This research addresses this gap by using a high-resolution capacity expansion model of the Western Interconnection to assess the impact of incorporating offshore wind and wave energy, either independently or in combination (collocation), on achieving a zero-emissions grid by 2050. The Western Interconnection, encompassing numerous states with ambitious clean energy targets, provides a pertinent case study. The West Coast's substantial offshore wind and wave energy resources present a significant opportunity for decarbonization, but these resources remain largely untapped due to challenges in cost-competitiveness and technological maturity. This study aims to quantify the potential benefits and identify cost thresholds at which these technologies can contribute significantly to grid decarbonization, offering valuable insights for policymakers and energy planners. Understanding the optimal mix of technologies for various regions is crucial for effective decarbonization strategies, and this research directly contributes to that understanding by focusing on a region with substantial renewable energy potential but significant decarbonization challenges.

Existing literature utilizes capacity expansion models to analyze optimal low-carbon electricity mixes for the U.S., examining the roles of specific technologies such as BECCS, nuclear power, hydropower, and CSP+TES. However, a significant gap exists in the literature's inclusion of offshore wind and wave energy in these analyses. While some studies have investigated the impacts of offshore wind or wave energy individually on specific grids, they often lack a comprehensive system-wide perspective and optimization framework or focus on stylized grid models. Few studies comprehensively assess the combined impacts of both offshore wind and wave energy, particularly considering their potential for collocation. This study builds upon previous work by incorporating both technologies into a detailed, spatially resolved model of the Western Interconnection, addressing a key gap in the current understanding of future zero-emissions grids.

The study employs SWITCH, a long-term capacity expansion model, to simulate the Western Interconnection's power system in a 2050 zero-emissions scenario. The model incorporates over 7000 candidate power plants across 50 load zones connected by 126 aggregated transmission lines. It optimizes investment and dispatch decisions to minimize total system cost while meeting power demands and considering transmission network constraints. Dispatch decisions are made at four-hour intervals for two representative days per month across investment periods (2020, 2030, 2040, and 2050). The model's high spatial resolution enables detailed analysis of geographical impacts. The research focuses on the 2050 results to assess the impact of offshore wind and wave energy integration. To account for cost uncertainties, the study designs 25 scenarios based on five cost targets each for offshore wind (including both fixed-bottom and floating options) and wave energy, reflecting a range from conservative to optimistic cost projections based on the NREL 2022 Annual Technology Baseline (ATB). The scenarios pair different cost targets for offshore wind and wave energy to explore their interaction. High-potential sites for offshore wind and wave energy along the U.S. West Coast are identified, taking into account factors like wave energy resource density, distance to shore, water depth, wind resource, bathymetry, and population density. These sites are filtered to exclude areas within strict marine protected areas, military zones, and other restricted areas. Data on wave characteristics and wind speeds are extracted and processed to calculate hourly capacity factors for each potential project area. The RM6 Oscillating Wave Energy Converter and the 2020 ATB Reference 15MW wind turbine serve as representative technologies. Finally, the impact of the cost scenarios on the optimal mix of generation resources, transmission expansion, and grid operations are analyzed, providing a comprehensive assessment of the role of offshore wind and wave energy in achieving a zero-emissions electricity grid.

The study's key findings demonstrate that even relatively modest deployments of offshore wind and wave energy can significantly impact the overall grid design and cost. A key result is the substantial reduction in total installed generation capacity (up to 133 GW or 17%) in the 2050 zero-emissions Western Interconnection scenarios with increased deployment of offshore wind and wave energy. This decrease is largely attributed to reductions in solar and storage capacity due to the more consistent power generation profiles of offshore wind and wave energy. Lower offshore wind and wave energy costs lead to a lower overall system cost (maximum decrease of 4%) due to reduced generation, storage, and fuel costs. Notably, a decrease in wave energy costs results in lower total transmission expansion, while a decrease in offshore wind costs leads to higher transmission expansion, highlighting the trade-offs between these technologies. The results indicate that if wave energy reaches cost parity with land-based wind by 2050, and offshore wind aligns with the advanced NREL 2022 ATB scenario, offshore wind and wave energy could each contribute 9% and 6% of the total installed capacity, respectively. Increased deployment of offshore wind and wave energy reduces the peak solar generation and the need for energy storage. Dispatch profiles show that these technologies provide more consistent power output throughout the day compared to solar energy, contributing to grid stability and reduced reliance on intermittent sources. This is particularly evident in coastal load zones, which experience substantial increases in energy exports and decreases in imports as offshore wind and wave energy deployment rises, suggesting increased self-sufficiency and regional power generation centers. As offshore wind and wave energy costs decrease, there's a corresponding increase in the collocation of these technologies, suggesting that shared infrastructure could lead to further cost savings. The study also found increased renewable energy curtailment (up to 49 TWh or 48%) with higher deployment of offshore wind and wave energy, mainly due to curtailed land-based wind and solar energy.

The findings highlight the significant potential of offshore wind and wave energy for reducing installed capacity and costs in future zero-emissions grids. The substantial reduction in total installed capacity implies that these technologies can limit grid overbuilding, leading to cost savings. The observed decrease in solar and storage capacity suggests that the more consistent power output of offshore wind and wave energy can effectively balance the intermittency of solar power, minimizing the need for extensive energy storage. The increase in renewable curtailment is a consequence of the increased penetration of these consistent sources, making the system less reliant on highly intermittent renewable technologies. The analysis of coastal load zones emphasizes the potential of these technologies to enhance regional energy self-sufficiency and create new power export hubs. This work underscores the importance of continued cost reductions in offshore wind and wave energy technologies. The study’s cost scenarios show that even under relatively conservative cost assumptions, these technologies have the potential to reshape the future energy mix of the Western Interconnection.

This study demonstrates the significant potential of offshore wind and wave energy to reduce total installed capacity and system costs in future zero-emissions grids for the Western Interconnection. Achieving cost parity with other renewable resources is crucial for maximizing their deployment. The findings highlight the need for policy incentives to stimulate investment and research in these technologies, particularly focusing on cost reductions and the development of shared infrastructure. Future research should expand on this study by incorporating the cost benefits of shared underwater transmission infrastructure in collocated offshore wind and wave energy farms and exploring the interactions between these technologies and long-duration energy storage. Further research on wave energy converter standardization and cost-effective array layouts is also essential. The results presented here provide critical insights for planning and policy decisions that aim to achieve decarbonization goals in regions with abundant offshore renewable energy resources.

The study has several limitations. The model does not capture all potential cost benefits from collocation, such as shared underwater transmission infrastructure. The filtering of potential project sites excludes some factors (existing underwater pipelines, shipping routes, archeological sites, proximity to residential areas) that could influence site selection in real-world scenarios, although their impact is believed to be limited. The model's temporal resolution might not fully capture the nuanced power output characteristics of offshore wind and wave energy, though this simplification allows for higher spatial resolution. Finally, the study assumes linear cost reductions for wave energy, which may not perfectly reflect real-world cost dynamics.