Renewable resources are contributing more generation to the electric power system in North America (the U.S. and Canada) than ever before. And this transformation is poised to continue given decreasing technology costs and ambitious decarbonization goals at the federal, state, local, corporate and consumer levels.
With reports released by the National Renewable Energy Laboratory (NREL), the North American Renewable Integration Study (NARIS) aims to inform grid planners, utilities, industry, policymakers and other stakeholders about challenges and opportunities for continental system integration of large amounts of wind, solar and hydropower to support a low-carbon future grid.
The NARIS project began in 2016.
“We used a suite of models to study a range of future scenarios and gain insights — including potential impacts on costs, emissions, resource adequacy, and the specific technologies that help enable the transition,” said Greg Brinkman, NREL energy analysis engineer and principal investigator for NARIS. “Our analysis focused in particular on the potential role of cooperation across North America and between regions within each country and how transmission can support sharing of supply and demand diversity across the continent.”
NREL released a report on the U.S. perspective in coordination with the U.S. Department of Energy (DOE) and a companion report describing a Canadian perspective in coordination with Natural Resources Canada.
Results show that a future low-carbon North American grid can be achieved through multiple pathways that can balance supply and demand using a variety of flexible resources. The study also shows that increasing electricity trade and expanding transmission could have significant benefits, highlighting opportunities for a coordinated, low-carbon continental grid.
Power system modeling for the continent
With input from the NARIS Technical Review Committee, NREL developed and evaluated four scenarios to understand the impacts of future renewable technology costs, emission constraints and growth in electricity demand on key study outcomes. The scenarios were informed by the goals set in 2016 for the Paris Agreement in each country, with up to 80% carbon reductions continent-wide by mid-century.
NREL evaluated the scenarios using a variety of models, including NREL’s Regional Energy Deployment System (ReEDS), Distributed Generation Market Demand (dGen) model and Probabilistic Resource Adequacy Suite (PRAS), as well as Energy Exemplar’s PLEXOS tool. All modeling was sourced by consistent data sets through the NREL Renewable Energy Potential (reV) model, National Solar Radiation Database (NSRDB) and WIND Toolkit.
“NARIS builds on decades of previous work studying power systems with high levels of renewable generation, including the Western Wind and Solar Integration Study, Eastern Renewable Generation Integration Study, Interconnections Seam Study, and Pan Canadian Wind Integration Study,” Brinkman said. “Here, we analyzed the entire continent in detail while studying higher renewable generation than these previous studies.”
Four key findings emerged from the analysis:
Finding 1: Multiple Pathways Can Lead to 80% Power-Sector Carbon Reduction Continent-Wide by 2050. Steeper cost reduction of wind and solar technologies can lead to a faster and less costly transition, and carbon targets can still be achieved with conservative wind and solar cost assumptions. When it comes to total system costs of achieving 80% power-sector emissions reductions, wind and solar cost trajectories have a more significant impact than carbon policy assumptions.
Finding 2: The Future Low-Carbon Power System Can Balance Supply and Demand in a Wide Range of Future Conditions. For each NARIS scenario, NREL estimated the number of hours in a year where supply would not be expected to meet demand in a region, as well as shortages that may occur due to generator or transmission outages. For both the U.S. and Canada, these metrics compare favorably with the North American Energy Reliability Corporation’s projections for the contemporary grid, meaning the scenarios analyzed in NARIS would not fundamentally impact the power system’s ability to balance supply and demand. In the U.S., 1,200 GW to 2,000 GW of renewable energy can be deployed to produce 70% to 80% of U.S. electricity by 2050 while meeting planning reserve requirements. Thermal generation contributes significantly to the future power system’s ability to balance supply and demand in all scenarios, even when most of the energy generation comes from wind and solar. Storage can also help provide capacity. In Canada, hydropower, gas and wind technologies contribute most to the future system’s ability to balance supply and demand. Thermal generation provides 5% to 10% of energy in all scenarios in 2050 but still contributes more than a quarter of winter planning reserves in most scenarios. Some of this contribution from thermal generation could be replaced by new hydropower or storage. Hydropower continues to provide about half of Canadian planning reserve needs by 2050 — and its expansion could contribute more, especially in a future with higher electricity demand.
Finding 3: Interregional and International Cooperation Can Provide Significant Net System Benefits Through 2050. Allowing international transmission expansion provides $10 billion to $30 billion (2018) of net value to the continental system between 2020 and 2050 in all but the business-as-usual case. This demonstrates some of the potential benefits of international collaboration. Expanding transmission between regions of a country provides $60 billion to $180 billion in net system benefits. Although these values are less than 4% of the total $5 trillion to $8 trillion total system costs, transmission plays an important role in minimizing costs. “Transmission expansion benefits are higher with more electrification and more wind and solar, which is a trend that could continue in lower-carbon scenarios or longer-term futures,” said Josh Novacheck, NREL electricity system research engineer and coauthor of the study. “Transmission can also provide reliability benefits and enable exchanging load and renewable generation diversity between regions — during normal conditions as well as in extreme events.”
Finding 4: Operational Flexibility Comes From Transmission, Storage, and Flexible Operation of All Generator Types. The future low-carbon power system will benefit from many different forms of operational flexibility. In the U.S., this includes flexible operation of natural gas and hydropower, curtailment of wind and solar generation, and storage (mostly pumped storage hydropower). International imports, enabled by transmission buildouts, also help to balance the grid. In Canada, hydropower, wind, solar and thermal generation are key sources of flexibility. On days when Canada has high energy demand but lower wind energy output, Canada imports electricity from the U.S. For days with higher Canadian wind output, the Canadian grid exports electricity to the U.S. — even when electricity demand peaks in both countries in the evening. Hydropower provides a zero-carbon source of energy, capacity and flexibility to the grid. In comparing similar scenarios with and without the ability to adjust power output from U.S. and Canadian hydropower generators, annual system costs are $2.3 billion higher without this flexibility.