SUN-FREE PV

Sun-free photovoltaics; Materials engineered to give off precisely tuned wavelengths of light when heated are key to new high-efficiency generating system.
Nancy W. Stauffer (w/David L. Chandler), July 28, 2011 (MIT News)

"A new photovoltaic energy-conversion system developed at MIT can be powered solely by heat, generating electricity with no sunlight at all. While the principle involved is not new, a novel way of engineering the surface of a material to convert heat into precisely tuned wavelengths of light — selected to match the wavelengths that photovoltaic cells can best convert to electricity — makes the new system much more efficient…

"The key to this fine-tuned light emission…lies in a material with billions of nanoscale pits etched on its surface. When the material absorbs heat — whether from the sun, a hydrocarbon fuel, a decaying radioisotope or any other source — the pitted surface radiates energy primarily at these carefully chosen wavelengths."

silicon chip micro-reactors (from MITNews - click to enlarge)

"…MIT researchers have made a button-sized power generator fueled by butane that can run three times longer than a lithium-ion battery of the same weight; the device can then be recharged instantly, just by snapping in a tiny cartridge of fresh fuel. Another device, powered by a radioisotope that steadily produces heat from radioactive decay, could generate electricity for 30 years without refueling or servicing — an ideal source of electricity for spacecraft headed on long missions away from the sun.

"…92 percent of all the energy we use involves converting heat into mechanical energy, and then often into electricity…But today's mechanical systems have relatively low efficiency, and can't be scaled down to the small sizes needed for devices such as sensors, smartphones or medical monitors…It has long been known that photovoltaic (PV) cells needn't always run on sunlight…[A] thermal emitter that radiates only the wavelengths that the PV diode can absorb and convert into electricity, while suppressing other wavelengths [makes for higher efficiencies]…"