While the various sources of it are debatable, one thing people can agree on is that there exists a general level of psychic energy free-floating in the environment. While it seems to be in higher concentrations in the more populated areas, there is some level of Ambient Energy everywhere on the Earth. Most psychics ignore this source, but it is possible to tap into it for an additional supply of energy.
The one pitfall is Ambient Energy in its raw form is unstable and difficult to use. This is because it isn’t “yours” for lack of a better explanation. Energy that a psion generates is nearly always tagged with their psychic signature, not only does this identify that a psiball belongs to a certain person, from the energy’s point of view that signature determines who it should listen to. Ambient Energy either has no signature, or its original signature has long since decayed and faded away. That said, it’s hard to utilize initially because it has no reason to listen to you!
Anyone that wants to utilize ambient energy will need to imprint their signature onto it. This is a lot easier if you actually know what your signature looks/feels like. Then it is just a matter of transferring that image/feeling into the ball of ambient energy you have collected. It is a little more difficult if you don’t know what your signature looks/feels like but it is still possible. You simply have to take a collected ball of ambient energy and try to force everything that you think feels like “you” onto it. This will not be as effective but it should still work.