I'm the master of Really REALLY Quick And Prolly Dumb Thoughts.
The energy produced from solar panels or burning coal/oil/gas or from nuclear is a tiny fraction of the total solar radiation in. Increased greenhouse gases are trapping far more energy than our energy "production" which is why we now worry far more about emissions associated with producing wasted energy than the energy itself.
Incidentally wind power is energy that would eventually become heat energy.
The bulk of urban heat island effects are
-more absorption of heat from dark, dense, built up surfaces & their geometry
- lack of cooling from plant evapotranspiration
Heat produced inside the area from electricity & fuel consumption is secondary.
Putting dark solar panels on a white roof incresses its absorption of solar energy, but the greenhouse benefits outweigh this.
True about the greenhouse gases. But we're about -->.<-- that far away from generating fusion power, which will be, as noted, energy equivalent to having small bits of the sun here. And that energy was inherent in atoms but never released at the rates we'll be releasing it. What I'm getting at is - have YOU ever checked how much electricity is turned into 'losses?' I.e. how much radiates off grid transformers and the lines that carry it? I can't find figures but if I efficiently load an extension cord and leave it coiled up, it catches fire. That shows that the losses in the cable are not negligible by any means. And that's only 240vac in a household situation loading a ruggedised outdoor power cord with a 1200W kettle.
My point is that rather than finding a way to use the energy we have as efficiently as possible to minimise incidental losses/conversions to heat energy, we are definitely heating our environment and I'm prepared to bet that when someone actually does the sums we'll be a bit shocked. And yes I agree with you that it's not the worst of the heat sources but if we keep ignoring these things as 'negligible' and never tot them up, we stand the risk of this rearing up and biting us in the ass in the not-too-distant future. Just like "ethyl is just a miniscule emitter of lead from your car exhaust, settle down with all that hyperbole eh, I think you're over-reacting" until it was found we spiked the level of lead globally - every corner of a sphere and that's hard to do - by dozens of times more than the millennia before ethyl petrol.
I see a scenario like this, where an apartment complex upgrades their electric supply because more tenants are installing AC units. The upgrade is of course done on the cheap using bare-spec cabling, so every AC is causing a voltage drop over the cabling and it warms the walls by a degree or two. That's enough to push a few more tenants to install AC units. And all of these little cheap heat pumps are pumping that extra degree or two outside the building. But also are inefficient so adding their inefficiency as waste heat. As a result the air temperature around that building goes up slightly. But it's nothing to worry about, right? "So what, a bit warmer outside here and being stored in walls and structures, stop panicking."
And then the next apartment building goes AC, and the next, and then the next closest city, and ....
That's what I mean. We look at a road of ten thousand miles and somehow we never see that it was composed of 633,600,000 inches all along. The inches just didn't seem all that significant until they were all in a row... 8)