I think you get a surcharge if your out heat is too high, meaning your radiators are running so high that you aren't utilising the heat effectively, so the end-of-loop water should be pretty cold. Another thing to keep in mind is that CHPs would still generate the waste heat from producing power, so it's a pretty efficient loop.

Fun fact, the Facebook district heating project was actually a big talking point due to server farms producing much lower heat than what is needed in district heating. People were split on whether it would actually have enough of an impact. As an example, my heat comes partly from a cement factory, a waste incinerator and a CHP as well as minor oil-based emergency heat generators. The CHP is capable of producing all heat by itself and the cement factory and waste incinerator were enough when the CHP had a major breakdown last year during autumn. During winter oil-based heat generators might be turned on to supplement the network on very cold days but they're expensive to run, so they are only used a couple of days a year.