So use the energy to pump the water to where it is needed. Use it to generate hydrogen or methane or something to sell as fuel. Mine bitcoin even. It seems weird and wasteful to just shut off free energy.

Those are really capital intensive solutions to a problem that occurs only now and then and might stop entirely if the situation changes a bit. In the meantime, to give people a reason to implement them, there is this market mechanism.

One of the projects is to build an interconnect to the snowy mountains. When this happens the power can be used to pump water up hill to fill the hydro electric dams.

But can't those plants just pull from the (now cheaper) power on the grid?