This technology takes direct heat from earth, water, air and solar and converts that heat to usable forms, the best of which is electricity. Technically this is possible even at the north pole in the middle of winter. In practical terms, this is the most expensive way to gather ambient energy that I know, because the machines are expensive. But while researching ambient HEAT I've discovered many interesting procedures that can be used in specific cases to help people achieve energy independence.
Most people understand wind power, it's likely the earliest consistent form of energy used by our ancestors. I consider this to be the third best form of ambient energy to exploit, if possible. The technology is simple, reasonable in cost and reliable; a little maintenance is required. The problem is finding the proper places to apply it.
By 'solar' we mean the direct radiation from the sun. Actually wind power is a form of solar power, as air is heated more in one area than another it moves as wind. Most hydropower is also a form of solar power, it's the sun's heat that vaporizes the oceans so the rain can fall on the mountains.
I generally believe solar power to be the second best means of potential power available in terms of availability and reliability, but it tends to be costly.
By 'hydro' we mean harnessing the power of falling water. This can be done whenever water flows downhill. There are a huge number of factors to consider to decide the best way to develop hydro potential.
If you have a good site then hydro is one of the best independent power systems, reliable energy supply, low cost to power ratio, easy to install and maintain.