It all falls apart when you want to use the Web. A Thinkpad T23 with a Pentium3 CPU just cannot render Modern Websites at acceptable speeds.
Basically if it wasn't for heavy JavaScript websites, most people could still be using decade-old machines for their day jobs.
It's much cheaper using a couple $5 VPSes for services. The only hardware left at home that is on 24/7 is my NAS, which is because 20TB of storage costs too much in the cloud.
You'll need a domain name to associate (and handle email, etc), and while technically you need 5 users to have unlimited storage, at the moment it doesn't seem to be enforced and a single user does have it.
Currently I'm storing ~50TB for $10/month. At this price and having 100Mbps Internet connection, I only turn on the NAS for local backups.
If you can configure your laptop to only charge the battery to ~80% or so, you'll extend the battery life significantly. The optimal range for long-term storage is ~40-60% charge.
Which incorporates a number of different adblocking lists.
I used the progress in CPUs in a different way: bought one of the fanless ITX sized computers and attached reasonably sized WD passport to it which is spun down most of the time (things are mostly served from an internal SSD)
Realistically all of this could be built into a single hybrid of disk shelf and blade server box. That is something I've contemplated as the 'next generation' of the technology.
And that leaves you with how to dump the heat out of the water, and that is most effectively done (in a small scale) with thermo-electric coolers. You can add scale cooling very effectively by turning on additional coolers. My design is pretty simple, the reservoir tank is on top of the rack and there is a heat exchanger on the bottom and one in "front" of the CPUs. As they draw air through the heat exchangers the water warms and rises to the top where the reservoir is, and the chilling water in the reservoir naturally sinks back down to the bottom where the first heat exchanger is.
You can think of it like a rack sized version of the liquid cooler you can put on an enthusiast PC these days. Its quiet, self contained, and quite efficient, while still being able to use forced air cooled server equipment. The goal being efficient cooling in a temperate climate (California Bay Area) that is quiet and can use surplus/old equipment that was originally slated for a data center without violating any of that equipment's assumptions about the environment it can count on.
What standard are you using for "efficient"? Thermo-electric coolers are neat, but the last thing they are whatsoever is efficient from a power-usage stand point.
If you're doing chilled water cooling, the only real option to consider is a mechanical heat pump (e.g. the ones in a refrigerator), but even that is silly. Hardware doesn't mind being somewhat warm, and using ambient air for cooling is far more efficient then either.
There's a reason thermoelectric refrigerators aren't really a thing. Peltiers are horrible. Mechanical heat pumps easily achieve twice the efficiency or more.
PUE
This is the part that sounds strange to me. Water cooling has its advantages, but the heat is almost always dumped from the water by pumping it through a radiator that has fans blowing air through it. What's the advantage of thermo-electric cooling here over the traditional method?
1) It is quiet
2) It is easily electronically controllable based on the heat load in the water.
The heat sinks on the thermo-electrics are convection cooled and you could blow air over them but as you increase the thermal gradient between the heat sink and the air around them you are able to dump more heat. The only parameter you can vary with the typical heat exchange is "blow more air" you can't change the working temperature of the exchanger.
That said, the way power plants cool their water is in big evaporative cooling towers, but since I don't need a humidifier for the lab I stick with just convection cooling :-)
What I'm saying is that the math isn't as straight forward as it might appear.
That said, it is now pretty straight forward to build a 'nano-datacenter' consisting of an enclosure, thermo-electric cooling, rack, switch, UPS, a server providing NAS storage and a couple or 6 servers providing compute. Plug its PDU into the socket where your dryer used to plug in out in the garage.