Covering 30% of the electricity supply of the United States with offshore wind would thus cost an astonishing additional outlay of USD 86 billion per year. Table 4.7 reports the total cost of electricity supply on a USD/MWh basis for all scenarios analysed. Two additional tables in Appendix 4.B report the cost increase per unit of renewable production and the total cost of electricity supply, on an absolute basis (Tables 4.1B and 4.2B respectively). However, introducing large shares of renewable energy with low variable cost has also significant impacts on the optimal structure of the electricity generating mix, on resulting electricity prices and on the profitability of existing dispatchable power plants, which make up the pecuniary externalities referred to in Chapter 1.