The study projects out the costs of going 100% renewable in Minnesota as the current plan calls for, so the assumption of 3x penetration is appropriate. I also don't see the basis for your claim that it triples/quadruples costs.

>>by fossil fuel interest

Which fossil fuel interests?

The study says that Minnesota could achieve the 100% zero carbon goal without unduly burdering the state's residents if it depends on hydroelectric and nuclear, neither of which is fossil fuel.