Energy is the largest OPEX by far (70-80%)... taxes second.

https://epoch.ai/data-insights/ai-datacenter-cost-breakdown

The cost of electricity is (almost) negligible compared to the cost of having GPUs sitting idle. Electricity from fuel cells can be twice as expensive, but even then, it represents only about an extra ~15% of the amortization cost associated with keeping the GPU hardware idle.

There is no way it's 3% if they're getting electricity from the grid, even if they get their cooling from somewhere else (eg lake/river water or outside air in winter). Median DCs are anywhere from 25-40% (depending on the jurisdiction's electricity costs and how much cooling they need). Hypercaler datacenters tend to be even more dense than the median traditional ones.

That seems surprising - source? What's the other 97%? Does this include ops staff?

Electricity is only 3% of opex for a data centre?