D. Recent Model Updates
A limited number of model updates were implemented to US-REGEN between 2015-2016. Technology cost updates were applied to solar PV, onshore wind, and biomass with carbon capture and storage. The unit database was updated to be current as of August 2016, and the base year data from the EIA was updated to the latest available. A new existing inter-state transmission dataset was developed using NREL data. The Production and Investment Tax Credit representations were adjusted following new legislation, and the state renewable portfolio standards were updated to be current as of December 2016. The biggest change was an implementation of the U.S. EPA's final regulations on CO2 emissions from existing fossil units, collectively known as the Clean Power Plan. Updates here included the ability to model state-by-state rate- or mass-based constraints, and a representation of the renewable set-aside allowance allocation program included under the Clean Power Plan.
In 2016-2017, the end-use model was developed and integrated with the electric sector model to dynamically capture the evolution of demand for electricity and other end-use fuels. It has temporarily replaced the computable general equilibrium (CGE) model used in previous versions to represent demand-side feedbacks. Although the end-use model describes trade-offs between technologies and fuels in much greater detail than the CGE model, it does not incorporate macroeconomic feedbacks, for example service demand responses to increased energy prices. Future model versions will re-introduce the CGE structure as an additional layer to capture these feedbacks.
Between 2018-2019, the electric model was substantially revamped, with a greater focus on hourly dispatch to support storage modeling, reserve margins added as a default option, and the option to use sub-state data now included, where data is available. CO2 storage and transport costs were added explicitly to the modeling of carbon capture and storage technologies. Additional state level policies were added to maintain coverage of renewable portfolio and clean energy standards, state clean energy targets, and other technology carveouts for solar and offshore wind. Improvements were made to the end-use model, incorporating insights from the state supplemental projects.