The intention here is to preempt your questions and provide succinct answers. We will try to keep subjectivity to a minimum. Some questions may have multiple answers or opinions. We will build the list over time.
Introductory and general
A: About 99.98%. The rest comes from gravity forces causing tides and natural nuclear energy of Earth. All other energy sources we can currently tap into are directly or indirectly from the sun.
A: For our application, only the surface temperature of the sun is relevant. The sun has no defined surface but from electromagnetic theory, we commonly agree that the sun surface has an equivalent temperature of 5,777K.
A: That’s a trick question. But the point is that sunlight has a signature in it that relates to the quality of the energy it contains. This quality relates to entropy and allows us to understand what we can and cannot do with it. The signature is called the spectral distribution of the suns irradiation. Electromagnetic theory plus the second law of thermodynamics tells us that we can create a furnace on Earth that is limited by the surface temperature of the sun. A furnace that is capable of reaching 5,777K would pretty much be infinitely expensive though.
A: Yes, there are some fairly large solar furnaces. The highest practical furnace temperatures are solar furnaces for the simple reason that the heat source is a point in space and you don’t need a container. The best solar furnaces reach temperatures that burn every element on Earth.
A: One way to put it as someone else has stated, 5 minutes of sunlight hitting Earth provides enough energy to supply all of our electricity for 1 year.
A: The sun already supplies energy to sustain life in the ideal conditions that we need. The sun produces waves, wind, flora through photosynthesis, rain and other basic systems that we don’t control. We can produce electricity directly using photo-voltaic cells. We can cook and make hot water. We can do heating, cooling and electricity production by solar thermal methods.