"They're generating their own electricity and excess power will be put back into the grid"

How are they generating that electricity though? If it's fossil fuels, then that's not very sustainable.

In my country the only real concern is electricity. The main reason we attract data centers is cheap, renewable electricity. Now, if the operators really built their own electricity generation infrastructure, the cost of existing electricity wouldn't matter much. So I suspect the plan is to mostly utilize existing capacity, which will drive prices higher, especially when it's not windy. It's not ordinary citizen that are worried, also companies in other energy-intensive industries have voiced their concern. And those industries tend to employ way more people than data centers ever will.

I think electricity needs of ordinary people and businesses that employ them should always come first. Data center operators should be required to build enough capacity to meet the increase in electricity demand. Otherwise it's just modern day colonialism, exploiting our resources without much local economic benefit.