In terms of electricity generation, Grid parity occurs when__:

Answer: [C] an alternative energy source can generate electricity at same cost as that from an existing electricity grid

Also known as socket parity. It means that an alternative source of energy (as opposed to traditional fossil fuel based sources) can now supply electricity for the same price that is charged for say, coal power. For example, when you pay Rs 7 a unit for coal-based electricity and the same Rs 7 per unit for solar power from the national transmission grid, you can declare that solar power has reached grid parity.

Grid parity differs from location to location because it depends on costs, time periods and power source. (Gobar Times / Wikipedia)

This question is a part of GKToday's Integrated IAS General Studies Module