Something I have been wondering: Why don't data centres use the excess heat for a sort of energy recuperation, turning at least some of it back into electricity?
Because it's not economical, the required hardware is unlikely to pay for itself during its lifetime. The gradient is too small (~50C), which means low Carnot efficiency. Additionally, extraction of low-enthalpy energy involves obstruction of heat transfer, meaning lower cooling efficiency. It may have been a different story if we had computer hardware able to efficiently operate at 200-300C.
Even steel plants which deal with significantly higher waste heat gradients rarely bother with recovering energy.
It actually is, just not water steam. There's a hot springs resort in Alaska that uses pentane (boiling point 38C) to generate energy. The efficiency is terrible, of course.
True. Chena Hot Springs [1]. They are famous in the "direct use" geothermal community.
A lot of the thermal energy is not used for electrical generation. Although a small portion actually is -- made possible by the \Delta T rejecting heat at a low annual average atmospheric T.
Most of the rest of the heat is used to run an absorption chiller to maintain the ice "palace" in the summer.
(This info might be slightly outdated. It was true about 2018 or thereabouts when I met the owner of the resort at a geothermal conference.)
The concept of waste-heat-to-power (WHP) exists, but its efficiency is limited by thermodynamics.
Basically, heat energy is not equal to usable energy. All energy ultimately wants to be heat energy, and it is much easier and more efficient to go from electrical or mechanical energy to heat than vice-versa. Therefore, when you do have an application that actually wants heat, not electricity, such as a public swimming pool or district heating, it is way more efficient to use your waste heat as heat. Even in cases where the desired temperature is wildly different from that of your waste heat, you can convert one heat level into another very efficiently using heat pumps.
Undecided just did an episode on a waste heat machine that is being slowly rolled out to industry.
The founder of the company is also the guy who invented the Super Soaker.
Look up Carnot efficiency. The maximum amount of work you can theoretically extract depends only on a temperature difference. For a datacenter running chips at 100C into ambient air at 60F, it's about 25%. So even with perfect capture, you are guaranteed to lose 3/4 of your input energy to the datacenter as heat anyway.
For comparison, an IC engine has a Carnot efficiency of something like 80% on paper, but the reality you get is only 20-30%
The degree to which you can extract energy from heat depends on the temperature difference compared to ambient. Efficient power stations all need super heated steam (like 600C). This would be like 100C max which is not very useful for generating electricity. It's fine for heating houses and swimming pools though.
Yes, it's not an identical situation, but I thought it was relevant because of the concept of recovering a dead body's resources for consumption by the remaining living humans.
There's lots of district heating in Germany for example, but it's usually fed from either big heat pumps, bio mass plants, or heat from waste incineration plants. There's no reason to not use excess heat from data centres too - I'm pretty sure I read that already being done in several places.
But in some cases, a data centre might be too remotely located, or the infrastructure is too lacking to make it economically feasible, which still leaves me wondering why you couldn't try to recuperate at least some of it as electricity on-site...
Even steel plants which deal with significantly higher waste heat gradients rarely bother with recovering energy.