The zero net carbon (ZNC) model for Platte River’s overall electric generating portfolio and high-voltage
transmission system was developed by Pace Global whose modeling approach included the following steps:
- Define the average carbon emission rate of the existing regional power "market" - 1,803 lb/MWh was used as the average carbon emission rate for the regional power market based on the published eGrid Rockies data for non-baseload generation. Pace Global assumed that any purchases or sales by Platte River would not be large enough to impact baseload generation units, but rather would impact the output and resulting emission of intermediate or peaking generation units in the region. Under this approach, each renewable MWh that Platte River sells into the market serves to "offset" the generation of an existing fossil fueled generation unit in the broader regional market, and results in a reduction of 1,803 lb/MWh to the overall market emissions.1
- Construct a carbon accounting method to track the annual carbon emissions, carbon offsets, and achievement of carbon-neutrality.
- Establish a starting level of renewable energy requirements as a percentage of Platte River’s load. This is done because the model cannot simultaneously solve for both the emission reductions required to hit net zero carbon emissions and the least-cost portfolio, so model iteration is required. First, we pick a starting minimum renewable level (approximately 90%), solve for the least-cost portfolio, check to see if carbon-neutrality is met, and then adjust the renewable percentage to ensure carbon-neutrality is met in each year from 2030 and beyond.
- Solve for the least-cost mix of generation technologies based on capital costs, fixed and variable operations and maintenance costs using hourly production modeling over the forecast horizon.
- Assess the results to determine if carbon-neutrality is achieved each year beginning in 2030.
- Modify the generation capacity available from the renewable sources until carbon-neutrality is achieved in 2030 and then maintained beyond 2030.2
1 The 1,803 lb/MWh average market emission rate was held constant over life of the study. However, Pace Global determined that even if the market emission rate were 1,434lb/MWh “net zero” carbon emissions would be achieved in year 2030 (but possibly not in every year thereafter) with the recommended portfolio.
2 Increments of 3% were used to adjust for carbon neutrality – the iteration process was stopped when carbon neutrality was achieved. Using smaller increments would have allowed us to meet the standard without over-achieving in each year but we do not expect a material change in buildout and associated costs.