Right now (before the increase in wind power) I find that solar is by far the best power plant to build and won't bother with anything else. Its cheapest to build and scales way better than any of the others. Geothermal requires too much of an investment initially, and is too inviting for sabotage. Any decent players will target the geothermal relentlessly, so if there's few on the map, you have to commit to spending a lot of money on goon squads.
So, with respect to scaling. There a few ways with power to actually do it.
1. Adjacency. Pretty self-explanatory. Not applicable to geothermal. Doable with wind, but hard to find proper clusters. Easy with solar. The caveat is that you do not want to be stuck with tiles after you drive the price of power to 1. So, building them next to your colony isn't a bad thing since you can scrap them and put down more useful buildings. Works well for solar since the gains for buidling them on high ground aren't too much, maybe 20%. A triad of solar will give you ~6 power. Wind is ~4 but its hard to find 3 high winds in a triangle next to your base. Build them elsewhere and the claims are lost for the most part, unless power is not 0
2. Patents - Double power for building next to colony. This goes with the building next to the colony. Cheap, overlooked patent, and you'll know when someone is going to try to grab it since they build next to a geothermal. Now your Solar triad is 12 power.
3. Engineering Upgrades. 2 cheap quick upgrades for another 50% gains. 18 power for that solar triad, little investment. Suddenly any time power spikes, you throw down a few solar panels, and make serious cash. With a few upgrades, the patent and solar panels, its easy to hit 50+power production excess.
I won a 4v4 team game in about 5 minutes shortly after hitting level 2. Power spiked very early due to a natural shortage and a typical early game metagame power issues. Hit 400. I happened to be researching the power patent, so I threw down 5 solar panels next to my colony. 10k income/second and couldnt spend the cash fast enough buying people out.
The important point is that when power spikes, you want to be able to jump on it and produce ridiculous amounts of power as fast as possible so you gain the largest share before driving the price into the ground before returning to your normal production. The same goes for every resource, but noone is stockpiling power and the output can dwarf any other resource.
None of the others power sources are practical for the profiting because you miss out on the scaling and are hindered by location.