first accounting for environmental externalities air pollution mainly of s nox and pm climate externalities in the form of ghg emissions and other costs including radioactivity significantly alters the cost comparison across different technologies especially for coalbased generation second solar and windbased generation and to a lesser extent nuclear are characterized by relatively high capital expenditure with negligible marginal operating costs third unlike fully controllable technologies variable renewable technologies have positive system costs reflecting the need to balance their variable temporal profile and enhance grid flexibility these costs increase with the unpredictability of the energy source so are higher for wind than for solar