“Electricity suppliers may calculate a fuel mix and related GHG emissions using different methods and parameters, following different regulatory requirements. Criteria #6 of the Scope 2 Quality Criteria identifies key features and methods that supplier-specific emission factors need to have to be used in a consumer’s scope 2 total.
For more information on the market-based method hierarchy, see Chapter 6 (Calculating Emissions) and for the Scope 2 Quality Criteria and residual mixes, see Chapter 7 (Reporting Requirements.)” Source: http://ghgprotocol.org/top-ten-questions-about-scope-2-guidance