One of the British '100% renewable' companies used to buy renewable power and then destroy their surplus resellable renewable obligation certificates instead of selling them (each supplier was obliged to hold certificates covering x% of their supply, where x << 100). That had the consequence that the renewable power generated was genuinely additional, as the other generators would have to get their renewable obligation certificates from new generation rather than the secondary market, at the margin.

They stopped, publicly reasoning that the proceeds from selling certs could be used to build their own additional renewable generation. I suspect it was just leaving too much money on the table, though.