Comment Better question: Cost in energy (Score 2) 55
Cost in energy != cost in carbon.
Some energy, such as solar, wind, and hydro, has a very low marginal cost beyond the cost of transmission. Sure, there's the cost of building the plant. Mining the earth to make solar panels, building those solar panels, getting them to the solar farm, and building a functional solar array and hooking it to the grid isn't energy-free.
Now, what's the equivalent cost of carbon? That depends on where the energy comes from. If, hypothetically, you use existing solar power to do everything it takes to build a new solar plant, then use that solar plant to run your computing center, the marginal carbon cost is pretty close to 0 if not 0.
Oh, don't forget the energy cost to actually build the computing center. Building computer, building actual buildings, etc. isn't energy-free. If any of that energy comes from carbon sources, the "sunk carbon cost" of building the computing center will be non-zero. Then there's the energy cost of maintaining the computing center.
Recurse (curse and curse again) and/or repeat as necessary for your computing center's needs.