Eight Decarbonization Scenarios

Eileen V. Quigley
July 15, 2019
International District Streetcar Against the Fall Foilage

Meeting the Challenge of Our Time: Pathways to a Clean Energy Future for the Northwest explores multiple pathways for decarbonizing the region’s energy system, while addressing policy questions and potential implementation challenges in the context of economy-wide carbon limits.

The modeling exercise involved eight cases: a Business as Usual Case and the Central Case, two cases that examine different levels of energy demand, and four cases that assume varying sources of energy supply.

The Business as Usual Case is based on existing policies and is the scenario against which the seven deep decarbonization cases are compared. It assumes the continuation of current and planned policy for the four Northwest states, serves as the benchmark case, and demonstrates that existing policies are not enough to attain the deep  decarbonization target.

The Central Case represents the optimal deep decarbonization pathway and is the most flexible pathway to achieve emission reductions.  It shows that a diverse set of unconstrained technologies and strategies (including significant energy efficiency and electrification) will achieve deep decarbonization.

It is structured to answer multiple questions: How clean must electricity generation be to realize a deep decarbonization target? What is the cost-optimal allocation of biomass? How quickly must we electrify transportation? What is the role of natural gas for electric power generation in 2050?

The remaining six pathways cases were developed off the Central Case to draw out insights from alternative assumptions and policies about demand and supply variables relevant to current discussions in the Northwest energy community. These six cases were modeled off the Central Case to understand the energy system trade-offs that occur as a result of different constraints or policies.

100% Clean Electricity Grid Case, where all electricity generation must be zero-carbon in 2045.  This puts the grid on a trajectory to zero-carbon sources for all electricity generation starting in 2020, and constrains electricity generation to be 100% clean in 2045 and beyond to align with California’s clean energy mandate.

Gas-fired power plants are allowed to burn biogas and synthetic electric fuels to meet the target. This case demonstrates how more aggressive decarbonization in the electricity sector can make up the balance with harder-to-mitigate sectors.

Limited Electrification and Efficiency Achieved Case, in which the aggressive electrification and energy efficiency assumptions in the Central Case do not materialize. This case explores the strategies needed to achieve deep decarbonization if electrification is only half of that achieved in the Central Case.

No New Gas Plants for Electricity Case, which prohibits any new gas-fired power plants from being built across the region after 2020 and retires existing gas plants at the end of their economic lifespan, which means no gas plants operate on the grid by 2050. This case reveals the options that electric grid managers have for maintaining resource adequacy and flexibility as renewables are added, as well  as the role that storage would need to play in maintaining grid reliability.

Increased Northwest-California Transmission Case, where unconstrained construction of additional transmission is allowed between the Northwest and California for better grid integration. This case reveals how a more efficient use of electricity sector infrastructure can reduce costs and grid-balancing challenges.

Limited Biomass Available for Liquid Fuels Case, where each state’s bioenergy potential is limited to only waste and wood feedstocks, and no energy crops or biomass resources outside of the region are permitted, which means 60% less biomass than in the Central Case. This case tests the impact of limiting biomass to see what other strategies would be required to meet deep decarbonization if a sustainable biomass supply fails to materialize.

Pipeline Gas Used for Freight Vehicles Case, where compressed and liquefied pipeline gas replace renewable diesel fuel for freight vehicles in the Central Case. The total vehicle fleet has the same proportion of battery electric vehicle fleets as in the Central Case, which helps illuminate the potential role for pipeline gas in transportation.

The table below describes the eight cases in this study:

Meeting the Challenge of Our Time, page 27


For additional information on the Northwest deep decarbonization pathways study, please see:

Eileen V. Quigley

Founder & Executive Director
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