This chart shows the net present value (NPV) savings in 2024 dollars of continuing to run the Colstrip plant (the business as usual case, or BAU) vs. a clean energy portfolio through 2058. In the BAU scenario, the Colstrip plant is assumed to retire in 2042, and a generic replacement cost is estimated for 2042 through 2058 using NREL Cambium's short-term marginal cost of electricity. A central tax credit bonus case is used, which assumes a 10% adder to the PTC for solar and wind, and 15% adder to the ITC for battery storage. See the technical appendix for further details.