Here is a rather spectacular image of a "parabolic trough" type of solar collector.... makes a nice 'wallpaper' for you computer desktop.
http://www.trec-uk.org.uk/press/brussels/schott_parabolic_trough.jpg Usually the tube running down the spine of the trough is filled with a molten salt which collects the heat from focused sunlight. That heat is then converted into steam in an adjoining building, and the steam is then expanded through a turbine to produce electricity at about 20% efficiency (100-200 watts per m^2 of mirrored area). This works better than solar-cell arrays at half the installed cost, and is in active usage now; but steam conversion demands a minimum size, and a rather large minimum size, of output - in the range of megawatts. Is there a better way to do this without steam, and one which can be feasible for the usage by an individual home? Maybe. Here is an alternative concept based on the same kind of parabolic trough - still a very "green" brain-storm (5 minutes old) which someone may shoot down right away. Lock and load. It would demand a large diameter tube (1/4 wavelength of the modulation frequency). The tube would be made of graphite, with a carbon nanotube interior wall which emits semicoherent terahetz radiation (near IR range). The tube is hollow and at a partial vacuum. It will contains a plasma once heated by solar, and that plasma is possibly an argon fill, at a few millitorr. At one end is a magnetron which emits GHz radiation along the tube length, and at the other end is collector. 2.45 GHz is possible, and this is the FCC permitted frequency used in microwave ovens. GHz waveguides are often rectangular, but I am not sure if that is an absolute necessity. Anyway, the modus operandi, as envisioned, is that semicoherent terahertz radiation from the tube's interior wall (from the carbon nanotube lining) would effectively boost a modulation wave which is travelling down the axis of the tube. This is an analogy to the principle which is used to boost modulation waves in the gyrotron microwave tube which has been in use for 40 years. Additionally, there could be electron emission, as in the gyrotron. The collector could be an air-cooled direct converter which is really a microwave antenna. The idea is that if say: one kilowatt of RF is admitted by the magnetron, it would be boosted to say 10 kW by the cross-field of the THz emission, and then collected. Hmmm.... so simple that there must be an overlooked problem.... Jones
