cu-arpa.dietz@Cornell.ARPA (08/08/84)
The August issue of Spectrum has a short note about a newly invented process for converting light to electricity. The process uses an array of tiny dipoles, 0.18 microns long (~ 1/2 wavelength of light) by 0.01 microns wide. Incoming light waves cause resonating currents in the dipoles. These currents get rectified by diodes to yield DC. The inventor claims 75-80% efficiency at 1/10 the cost of semiconductor junction solar cells. According to the article, no one had previously been able to get the dipoles thin enough. X ray techniques have apparently made it possible (using synchrotron radiation?). Space enthusiasts will recognize this idea as a rectenna scaled down by four or five orders of magnitude. I don't know how the diodes are made, but it seems clear you don't need large crystals of silicon to make this work: thin films or polycrystaline Si should work just fine. If these cells are as cheap as the inventor claims (40x more cost effective than conventional cells) we could see almost all daytime electricity coming from them. This will provide a strong incentive to develop cheap energy storage (which seems unlikely), to develop very long transmission lines (which seems impractical, even if superconducting), or to make the cells work 24 hours a day, either by placing them in orbit or by putting mirrors in orbit to reflect light to ground based cells. The high efficiency also makes laser power transmission attractive, allowing very small receiving antennas -- but don't fly into the beam!