extton is right.
Ultimately we can do two things with energy:
- Store it
- Convert it to another kind of energy.
Solar converts light (and heat) to electrical energy.
Even nuclear power is just energy stored in the atom to heat energy... then heat energy is converted to electrical energy.
The one thing missing from most ideas that seem to harness energy from nowhere is that energy can only be released when there is a difference of potential.
Fusion reactors take several atoms that have higher potential (energy state) and force them together to individual ones that have a lower potential. The difference is released as radiation and heat energy.
Chemical reactions (like batteries, ie Duracell, pickles, potatoes etc) work by allowing electrons to move between regions that have molecules that react together with more electrons and regions that have molecules that react with the removal of electrons. The movement of the electrons is electricity.
Solar like thermocouples work with two regions of different heat or excitement. When light and/or heat falls on one surface, the under-surface becomes relatively less excited. The heat/light energy from the sun is tapped as electrical energy. So these devices just convert one kind of energy to another.
Wind - convert kinetic energy (physical movement of the wind) to electricity.
Note that there is always either two areas that have different potentials (like batteries), two different potentials that move from higher to lower, or a conversion of one type of energy to another.
In the case of potential differences, there must be a depletion over time. (Batteries die, fuel gets used up)
In the case of conversion, the energy source itself must come from somewhere. ie electricity from wind, wind from heat, heat from sun's fission. Eventually the sun's energy will become depleted.
So when you hear of a 'new source of energy' what you should be looking for is where is the original source. Look at what gets used up... something must.