What are green certificates, and how are they taken into account?

When producers of renewable energy produce electricity, they can create Guarantees of Origin (or Renewable Energy Certificates) - a proof that renewable electricity has been produced and distributed into the power grid. These guarantees can then be sold, giving electricity retailers a way to claim that the electricity they resell comes from renewable sources, regardless of its actual, physical source.
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This means that electricity consumers can be told that their electricity comes from solar and wind, even in a windless night. This is problematic, as it removes consumer incentives to consume electricity at the best time (for instance when the amount of renewable electricity in the grid is actually at its highest). This map therefore excludes Guarantees of Origin, instead offering a location-based physical picture of the power grid, in order to empower consumers.