Greetings to all.
In doing much research on Tesla, T.T. Brown and others as well as studying the "Crystal Power CeLL by John Hutchison" Thread I have come to the conclusion a way in which to harness radiant energy. This is merely theoretical, I have not yet built anything.
If you know Tesla's work examine his Patent #685957 "The Apparatus for the utilization of Radiant Energy"
Then read all you can on T.T. Brown's work on Petrovoltaics as well as his notebooks:
http://www.qualight.com/petro/index.htm
And his work in Electrogravitic Communication:
http://www.qualight.com/ecomm/index.htm
Some relevant text:

In a classified naval report entitled "Anomalous Behaviour of Massive High-K Dielectrics", Brown described how the resistivity of some materials would alter and even follow sidereal diurnal changes. He also noted that some materials would generate spontaneous radiofrequency bursts whose amplitude was a function of the material's mass and K-factor. Also, he found many granitic and basaltic rocks to be electrically polarised; that is, they behaved like electric cells or batteries. These rocks would have as much as 700 mV across them, the amplitude of which would also change in sympathy with solar sidereal cycles. Again, the rock's sensitivity to such changes depended upon its K-factor and mass. It was this latter relation that suggested the phenomenon is gravitational.

He suggested that due to the radiofrequency voltages found in less complex dielectric materials such as titanium dioxide, the detected energy was at these high frequencies and that basaltic and granitic rocks somehow converted the energy into a DC potential. This process is well known in electronics and is called "rectification", and so the internal structure of these rocks could naturally perform this same process.

While simple high-K dielectric materials would pick up the radiation and convert it directly into electrical energy, more complex dielectrics such as granitic and basaltic rock would convert the energy into DC electricity. Not only this, but these rocks are in fact tuned to only a portion of the total radiated energy present throughout the Universe. This means that your average lump of basalt is a natural gravity-wave AM receiver, tuned into only a few specific "radio stations"!

Source:
http://www.esolibris.com/articles/ufo/alien_contact_02.php

It can therefore be seen that certain materials, since they naturally gather and convert this energy that is all around us(some in AC, some in DC) We can therefore use a mixture of correct materials as a receiving antenna to gather in this energy and provide useable electricity. While I am not well schooled in electronics(I have a very basic knowledge) one can see the possibilities in a receiver using (examine the "Crystal Power CeLL by John Hutchison")(http://www.overunity.com/index.php?topic=972.0)
a mixture of the correct materials as the antenna, for example like an LNB on a sat dish etc. Then using tuning coils and electronics (perhaps a joule thief circuit?) you could further tune and amplify these natural collector/converters.
This is the most basic information in some of the research I am doing. Please feel free to add to this and perhaps we can all try to see if this possibility can be used for the benefit of all.

To further clarify what I am saying:
It is known that if you have a long wire antenna in the air, with a ground you will indeed gather energy from those rf sources.
It is known that Nikola Tesla (See Patent #685957 "The Apparatus for the utilization of Radiant Energy") with a sphere of dielectric in the air with also a ground gathered radiant energy.(There is more to this indeed since he tuned this for more output)
It is known that T.T. Brown did indeed do much research into the fact that certain dielectrics naturally gathered radiant energy. Frequencies vary depending upon the dielectric, therefore one can tune these to increase output. It is therefore very logical then to say that if one were to tune the frequency of the used dielectric such as granite,basalt,galena,barium titanate, or whatever natural material you decide to use or mixture that you will get more output after tuning.
Indeed whether you like or believe in John Hutchison's work note that John also has said to look into old crystal radio sets to begin to understand about his "crystal batteries". These are not batteries at all but receivers/collector/convertors of radiant energy.
Believe whatever you wish, the evidence is there, the logic is sound and I myself plan to build and experiment upon this.