The US’s power supply is split into three separate grids, with the western interconnection providing power to more than 80 million people over 14 states and two Canadian provinces. The new report dives into future scenarios where floating offshore wind farms are connected to the shore between Coos Bay, OR, and Eureka, CA, via large transmission lines—and the value those wind farms could bring to utilities and ratepayers alike.
Land-based wind farms across the United States already produce more than 140 gigawatts of energy, contributing to about 10% of the nation’s energy portfolio. Currently, the federal government aims to install 30 gigawatts of offshore wind by 2030 and to increase that number to 110 gigawatts of offshore wind by 2050. That much wind power could power tens of millions of homes and cut more than 78 million metric tons of carbon emissions.
Mark Severy, a research engineer at PNNL and co-author on the report, also explained that one of the perks of offshore wind turbines—whether they’re attached to the ocean floor or floating on the surface—versus land-based is that wind over the ocean is less variable and more consistent.
Wind over the ocean also tends to peak in the evenings, which could help supply power when solar energy dips as the sun sets. In places like California, where solar energy makes up most of the renewable power, utilities could turn to wind power in the evenings, when demand generally goes up, instead of fossil fuels to power homes.
One challenge to this idea is determining whether existing transmission infrastructure could support incoming energy from offshore wind.
In a previous study, Douville and other researchers found that offshore wind could supply 3 gigawatts of energy with upgrades to Oregon’s current transmission lines. That’s enough energy to power 1 million homes.
“How do you harness offshore wind energy in a way that allows you to adequately, reliably, and resiliently supply electricity in the future at the lowest cost?” Douville said. “And what is the role of transmission design to influence the value of offshore wind?”
To find out, the team modelled different transmission scenarios, two of which represent a future where offshore wind farms and new, powerful transmission lines add an additional 20 gigawatts worth of wind power to the western interconnection. Both scenarios include high-voltage direct current (HVDC) transmission lines to carry power, which would then be converted to alternating current (AC) once onshore.
The two scenarios differ in whether each wind farm is connected separately to the shore (in a radial structure) or whether the wind farms are connected to each other, then to the shore (a backbone structure).
Severy noted that although both transmission scenarios offered millions of dollars in value, the backbone structure offers slightly different benefits. In the radial scenario, power can only go to one place—wherever the wind farm is connected on the coast—and then be distributed from there. In the backbone structure, power can be diverted up and down the coast.
For example, “in times when there’s excess solar generation in California, we found that the backbone provides another pathway for that electricity to go to the Pacific Northwest and when there is a lot of hydropower in the Pacific Northwest, the backbone is another pathway south, outside of the congested transmission lines on the I-5 corridor,” Severy said.
Although either option would be expensive, “the benefits exceed the costs in nearly every scenario,” Douville said.
In those scenarios where benefits exceed the costs, the values of the various returns on investment range between $127 million and $6 billion. These numbers represent savings to produce and supply power as well as avoid the cost of the effects of air pollution and destruction wrought by climate-change-related disasters.
Douville stressed that many more questions need to be answered before an offshore wind plan can be executed.
For instance, researchers and policymakers need to consider how transmission lines will fare underwater. Sea floor depth and slope could affect where cables could be laid, and salt water can be very corrosive, said Jason Fuller, chief energy resilience engineer at the PNNL. Maintenance could be tough, depending on how deep the cables are laid. In addition, the US simply hasn’t used HVDC as much as AC on the grid, and modelling HVDC with current tools can be difficult.
Researchers and policymakers will also have to consider other stakeholders who depend on the ocean, including fisheries and other coastal communities.