> A 12 year old i7 server runs my NVR, home automation setup, web server, and network router (not to mention a small handful of other services) without even breaking 25% CPU usage. We could replace so many data centers with old desktops.
Replacing concentrated and highly optimized data center servers with 10-1000X as many old desktop computers idling away at 50-100W or more would be a terrible tradeoff. That would explode the energy usage by orders of magnitude.
I did the math a few years back on how long you would have to run old machines to (roughly) offset the carbon emissions instead of purchasing new hardware. This included all mining, refinement, manufacturing, shipping and electrical savings from more efficient processors.
A big part of this is the very intense amount of energy producing the silicon wafer from Quartz ingots. While they weigh only a few grams of the total machine they reside in, they have a very sizable impact on total energy.
Funnily enough, for most desktop computers it would take about 15 years of non-stop usage to manage this. That is if powered purely by Lignite/Brown Coal. Anything cleaner, so almost any other energy source, and you have to run them way longer. If purely on solar panels and their manufacturing carbon output, it moves into the centuries range.
The solar panels required energy to create, too. I don't think that it would take centuries for replacing Cray 1 with a Raspberry Pi 5 to pay for itself in carbon intensity, even if both are powered by solar panels. The Cray example is seemingly uncharitable, but the principal is the same because if the only relevant thing is solar power, then it should take centuries in that case too, right?
Unless you count in the effects of distributed solar and the environmental effects of building said datacenters in the first place. Many homes with solar produce more than they consume, and many homes pay for heat. Instead of new construction (concrete is another huge CO2 contributor) and AC units or pumping surface water for cooling, putting a server in your house is basically free heat and making use of an existing, underutilized resource.
I could run my entire rack off of one to two solar panels (decommissioned ones from a power farm might I add). Even that would take a few years to pay for itself (when you factor in the costs of mounting and permitting) and my power company over 80% renewables the last time I checked anyway.
Replacing concentrated and highly optimized data center servers with 10-1000X as many old desktop computers idling away at 50-100W or more would be a terrible tradeoff. That would explode the energy usage by orders of magnitude.