Plant-level costs are, of course, those costs that come most naturally to mind when thinking about the costs of electricity provision. The “bricks, mortar and steel” to build the plant, the fuel and the manpower to run it are easily comprehensible cost items. The Nuclear Energy Agency (NEA) and the International Energy Agency (IEA) publish a survey of the plant-level costs in OECD countries every five years in the Projected Costs of Generating Electricity (see IEA/NEA, 2010 and IEA/NEA, 2015; IEA/NEA, 2020 is currently in preparation). While concrete work reveals also a number of difficulties in assessing plant-level costs, e.g. which discount rate to use to reflect the cost of capital, at least the basic concepts are well understood. Plant-level costs of production are financial and economic realities that are straightforwardly monetised and integrated into the decision-making processes of private and public actors. In an interconnected electricity system, each plant interacts with all other plants, on both physical and economic levels.