It may be difficult to dump all the heat at scale. You probably need a huge cooler with fans to get active air flow. Or a water tower (that requires water) (There are regulation about extracting water from a river and returning it too hot).
Is it possible to build one of this heat dumping facilities in a zone where there is permanent snow? (Ignoring environmental and moral concerns.)
PS: Seriously, heating a swimming pool may be a nice application.
You could probably just boil off your water, instead of returning any?
It would be funny, to use the steam to generate electricity.
You get a lot of salt residue that you have to dispose. The usual nuclear plant tower [1] evaporates most of the water to dump heat, but returns a small part of it to avoid collecting salt. But it has to be not to hot nor too salty to avoid killing the fishes.
[1] https://www.google.com/search?q=nuclear+power+plant+cooling+... [How to I link to the images pages?!?! Google changed the format of the URL and I can't find the correct &something=xyz to make a short link to the images :( .]
Ye olde format still works: https://www.google.com/search?tbm=isch&q=nuclear+power+plant...
...and that ultimately lands at https://www.google.com/search?q=nuclear+power+plant+cooling+... which also works.
But it doesn't have to be big. A negative price is still a negative price, even on a small scale.
So, for instance: At home, I have electric hot water. I have some baseboard heaters in parts of the house (that I never actually use, but which I could use). I have central aircon.
All of these things could stand to be automated just for automation's sake, and that's something I'll probably do some day even with the fixed-rate electricity I buy right now.
With automation and price feeds, it's a programmatic no-brainer to switch on the electric baseboards on during the heating season during negative price events and get paid some non-zero amount to get ahead on the temperature game.
During the cooling season, I can probably stand to get paid to supercool the house for awhile.
And during any season: I normally run my electric water heater at a fairly low temperature because that's more efficient, but I'll cheerfully accept money to temporarily raise its temperature.
Or if I had an EV: Maybe I might normally like to keep it at 70% SoC for battery health, but if it's plugged in and the price is negative then I might cheerfully run it up to 85 or 90% or more.
So anyway, it's hypothetically pretty easy for an individual like me to dump a few kiloWatts in a useful way.
A thousand such people make it easy to dump a few megaWatts.
A million such people make it easy to dump a few gigaWatts. (And a million sounds like a lot, until one counts the eventuality of smartly-connected EVs.)
It can even happen productively: "Hey, they're paying us to run the heat! Turn the glass kiln on so we can get a head start on tomorrow."
Or "Hey, they're paying us to charge our batteries! Let's charge them!"
It can also be "Hey, they're paying us to run resistive heaters! Turn on the artificial sun!"
Whatever it is: If the demand satisfies the supply, then the supplier is satiated. And then the price can go back to something more-profitable for that supplier.