developed through a critical review of published studies that employed a range of models and assumptions; two examples are shown in the table. The AEF Committee used expert judgment in selecting the estimates from these studies that it considered to be reliable.

  • Cost estimate limitations are key knowledge gaps and uncertainties that could affect the accuracy of the cost estimates. These limitations arise primarily from technology immaturity or a lack of experience with deploying technologies at commercial scales. One would expect these uncertainties to be reduced as technologies mature and deployment experience is gained.

  • Plant maturity. The costs of initial deployments of a new technology, sometimes referred to as first plant costs, are generally higher than the costs of deployments of mature proven technologies, sometimes referred to as Nth plant costs. The cost estimates presented in this report reflect the AEF Committee’s judgments about the state of technology maturity in 2020. The committee presents first plant cost estimates for immature technologies, Nth plant costs for mature technologies (e.g., pulverized coal plants), and intermediate plant costs for technologies that are still maturing (e.g., IGCC, liquid fuels production). In some cases, cost contingencies were added for immature technologies to bring them closer to Nth plant estimates.

  • Plant size is the nameplate capacity of the energy supply plant assumed in the cost estimates. The AEF Committee selected plant sizes that it deemed to be typical of each technology class.

  • Plant life is the time over which the energy supply plant is assumed to generate electricity or liquid fuels. The AEF Committee generally followed industry convention in selecting plant lives for each technology class. In some cases, the plant lives selected were less than the lives of current generating assets (e.g., pulverized coal plants).

  • Feedstock and fuel costs are the costs for the feedstocks and fuels that are used to produce electricity and liquid fuels. The fuel costs used in this report were selected by the committee based on examinations of historical costs, recent costs, and cost trends. In some cases, ranges of costs were used in the estimates. There are no fuel costs for some renewable energy supplies (e.g., solar and wind).

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