Hetzner rents you 42RU for €199 plus power and network. If we assume they can fill the entire rack, that's 4 9RU units for about €50 plus power and network.
If we assume an average power draw of 20W per laptop, that's 300W for each 15 laptop unit, or about €57/month in Hetzner's Finish DC (including aircon)
Not sure about network. A 1Gbit uplink with 10TB traffic (and €1/TB after that) is provided. Upgrading that to 10Gbit is probably similar to the €51/month cost for the same uplink for dedicated servers, so another €15 for each 15 laptop unit. Plus around €2/month/IP, but you can probably bring your own if you find a cheaper subnet to buy
So yeah, you are right that the math does not work out. But it is pretty close to break even. I think you can break even on this if you find a more space efficient way to cram them into the rack and don't pay yourself any salary
If we assume an average power draw of 20W per laptop, that's 300W for each 15 laptop unit, or about €57/month in Hetzner's Finish DC (including aircon)
Not sure about network. A 1Gbit uplink with 10TB traffic (and €1/TB after that) is provided. Upgrading that to 10Gbit is probably similar to the €51/month cost for the same uplink for dedicated servers, so another €15 for each 15 laptop unit. Plus around €2/month/IP, but you can probably bring your own if you find a cheaper subnet to buy
So yeah, you are right that the math does not work out. But it is pretty close to break even. I think you can break even on this if you find a more space efficient way to cram them into the rack and don't pay yourself any salary
https://www.hetzner.com/colocation/