Yes, geothermal is site specific. It proliferates in cold places like Iceland.
I also have been at geothermal sites near the equator in Indonesia 40 years ago where we drilled wells and built a geothermal plant that remains operational.
Its mail issues are the buildup of minerals which are produced along with the steam, which is similar to the way most oil and gas is produced. These need disposal and the correct treatment of piping and equipment from scale.
The thermal differential power system should be able to function anywhere in almost a perpetual system mode. Obviously the scale of differential temperatures weigh heavily on the efficiency.
BTW, my son in northern Nebraska has a geothermal system running in his house and yard which is a simple heat transfer with shallow underground wells which supplies him air conditioning during the hot Nebraska summers at fairly low temperatures differentials.
Iceland is smack over the spreading zone in the Mid Atlantic Ridge.
It's volcanic in origin, and the temperature differential would be profound at the equator as much as nearer the pole.
Many steam generating geothermal plants are in areas of high heat flow, for instance the Pacific Northwest (Cascade Range) is a string of volcanoes over the subducted East Pacific Rise (The tectonic equivalent of the mid Atlantic ridge). Indonesia is noted for volcanic activity also.
You can find areas of high heat flow along the Rockies, and into the Basin and Range of Nevada, with hot springs and geologically recent volcanics, and then there is the Yellowstone hot spot. All have some potential for steam generating geothermal that could produce electricity.
For that matter, drill deep enough anywhere and tap into heat coming from the Mantle. The question is one of cost-benefit analysis and finding the thinner crust (Here, about 20 KM). That might be a problem, though, as drilling over 60,000 ft. vertically has yet to be done by anyone on the planet. Even reaching depths with bottom hole temperatures significant enough to generate superheated steam is unlikely away from areas of known and relatively recent volcanic activity.
Ground loop or well based heat transfer systems will work most anywhere there is enough soil to install them, but they aren't generating electricity, and are not producing steam from hotspots or working with the temperature differential between the photic zone and 9000 ft. of water.
Whole different deals.
All they do is heat/cool fluid to roughly 58 degrees F and that fluid is pumped through a heat exchanger to produce air closer to the desired temperature for indoor living, summer or winter. They can be effective, especially for decreasing the cost of heating or cooling large spaces, where the savings exceed the cost of equipment and setup. It is an economy of scale, though, and more difficult to make work economically on a small scale.
Back to tapping mantle heat flow, little is more corrosive than superheated steam in an open hole environment, and it will leach virtually anything available out of the surrounding rock and deposit on the way to cooler environs, be those still downhole or in the machinery above. Temperature drops, precipitation occurs. (Something similar happens in oil wells with paraffin accumulation, salt deposition, and other mineral deposits).
If steam is to be generated in such environs, it's going to take a closed (cased) loop to keep mineralization from occurring and causing the same sort of problems current systems have (for electrical generation). A closed loop system will also prevent fault lubrication like occurred in the Black Rock Desert, with ensuing seismicity causing the project to be curtailed.
Parallel wells with a directional frac have been suggested, one down, one up, and communication between through the fractures, picking up heat along the way, but that has all the mineralization problems of open hole systems with the complexity of getting the wells and fracs to behave as desired. The holes will still have to be cased for most of their length, or there is a serious probability of contamination of porous formations on the way up or down. What comes to the surface will have a dissolved mineral load, and may not be suitable for another round without being treated.
This is where I get into "Theory works fine, in theory".
All of this is more complicated than the power point slides show.
Can it be done? Yes, of course, and in some places it is being done, but in many of those places alternatives such as coal are lacking, and oil is used for other things besides generating large scale electricity.
I'm all for it where it works.
