it's exceptionally hard because energy is fungible
try writing the contract, say, requiring 500MW of new gas generation to be built locally to power the DC, which is grid connected
they'll then secretly write a contract to sell 500MW of gas generation on the open market, conditional on approval
at some price they'll find a buyer, at which point 500MW increase in grid capacity has been cancelled out despite them actually building the plant
and all it cost them was the difference in the contract price
Hmm not quite following: 500MW was created at connected to grid as required although delegated to 3rd party. And the DC uses that power. So what's the problem?
500MW doesn't get built on the other side of the country when needed as the power has been sold
so there's a lag, but at this kind of scale you don't really care