  Planning for power systems with high penetrations of variable renewable
energy requires higher spatial and temporal granularity. However, most publicly
available test systems are of insufficient fidelity for developing methods and
tools for high-resolution planning. This paper presents methods to construct
open-access test systems of high spatial resolution to more accurately
represent infrastructure and high temporal resolution to represent dynamics of
demand and variable resources.
  To demonstrate, a high-resolution test system representing the United States
is created using only publicly available data. This test system is validated by
running it in a production cost model, with results compared against historical
generation to ensure that they are representative. The resulting open source
test system can support power system transition planning and aid in development
of tools to answer questions around how best to reach decarbonization goals,
using the most effective combinations of transmission expansion, renewable
generation, and energy storage.
