You won’t be able to take waste heat economically from a power plant, they’re generally designed to capture more and more heat until diminishing returns take over.
There are a lot of other industrial processes though that don’t do any heat capturing.
Something left out though is that you might have lower capital costs but if you try tacking a power plant on somebody else’s factory, they’re going to want a cut.
Efficiency is dictated by temperature differences, you get a bigger cut for less investment when the temperature difference between heat source and environment is largest.
I once came across a plant in Quebec that was only "profitable "because it had a huge discount on the rate it paid for electricity, only to later generate electricity from their waste heat and sell it back to the government at a highly inflated rate. The government was happy to do this so that the plant wouldn't shut down and workers wouldn't lose their jobs
What if you just sold the equipment (+ setup services) to the plants directly? They could turn around and reuse the recovered energy themselves, or sell it on down the line, but there would be no coordination/mixed-incentives problem.
Factories aren't in the business of generating electricity. They were already willing to throw that heat away normally, why take a bunch of capital that you could invest in the business and use it to buy equipment unrelated to your business when someone else will install and manage the waste-heat system for you and give you a 10% cut for no risk and no outlay on your end?
Probably best to sell a kit of a few designs, equipment, project management, and financing (avoid capital costs) that shares in income but also has contractual obligations for length of running.
Then you're the one taking the cut, still an additional cost that needs to be considered when doing a comparison with digging a hole for geothermal energy.
There are a lot of other industrial processes though that don’t do any heat capturing.
Something left out though is that you might have lower capital costs but if you try tacking a power plant on somebody else’s factory, they’re going to want a cut.
Efficiency is dictated by temperature differences, you get a bigger cut for less investment when the temperature difference between heat source and environment is largest.