The Grid is the name given to the system of mains electricity generated through the range of power station is a country. Grid parity is a term relating to alternative energy sources. Grid parity is the point at which generating alternative energy becomes no more expensive than generating energy from the grid.
One obvious scenario in which grid parity might be achieved is if electricity is very expensive to generate via the grid. In many cases in Western Europe, electricity via the mains grid is relatively expensive. However, the next thing needed for grid parity is a cheap, easily accessible source of alternative energy. Spain, as a large country with a sunny climate and sparse population, is a great example. It is a great site for solar energy, and electricity is fairly expensive from the grid.
The main reason as to why grid parity might be achieved is the falling cost of solar power technology. It is increasingly affordable for family to install solar panels with photovoltaic cells which convert sun energy into electricity. It could cost a family in the UK a little as £8,000. If that family were able to get enough sunlight, that investment could provide 40% of their electricity needs. As a result of these falling costs, grid parity has been achieved in Hawaii, and is well on the way to being achieved in large parts of the USA
Grid parity (or socket parity) occurs when an alternative energy source can generate electricity at a levelized cost (LCoE) that is less than or equal to the price of purchasing power from the electricity grid. The term is most commonly used when discussing renewable energy sources, notably solar power and wind power.