On paper, a megawatt-hour is just a megawatt-hour; it will charge your phone or run your dishwasher the same way, regardless of the source. However, its value to, or impact on, the environment is not fixed. It depends almost entirely on what power plant it replaces. A new wind turbine only helps the climate and local air quality to the extent that it pushes a more polluting plant offline. If instead it is just competing with another clean energy source, the environmental benefit effectively disappears.
Not all clean power cuts emissions equally: Timing and location determine impact
