(lecture 3/17/2008) - NanoPower introduction

Nanopower is power in space.

You can get this in two ways:
1 - Take fuel with you
2 - Scavenge (Scavenging includes solar power, and mining extraterrestrial environments)

When using solar, have batteries for when your craft isn't directly in the sun

Fuel cells were used on Apollo missions - they created electricity and water

Nuclear reactors can be used in space - a lot of power in a small weight; a lot of energy emitted in radioactive decay particles
Take forever to decay;so a long-life battery

Solar arrays - a lot of them are heavy,fragile silicon
90 % of current solar cells are silicon

SOlar cells only 30% efficient; you need heat dispersion

Chandra - X-ray observatory - X-ray astronomy can only be performed in space (too many X-rays get interfered with by Earth's atmosphere)

Mirror assembly had to be aligned with exacting precision.

Space SOlar Power
1) Convert solar photons into electricity
2) Efficiency
3) Mass Specific Power (power/mass)
4) Areal Specific Power (power/area)

Solar wind, v. small amount of drag, UV rays,micrometeoroids, space debris still a problem

Heavy glass currently necessary to shield solar cells
Anti-reflection coating

n-type semiconductor and p-type semiconductor - one has extra electrons, one has a deficiency of electrions.
pn junction - these two together; electrons bounce between them (that's the photovoltaic effect).
You need enough energy to kick the electron(s) between the levels.

SOme wavelengths have too much energy for this (that wastes heat).Some wavelengths have too little (not do enough). Some are just right [ Goldilocks Principle]

Concentrators concentrate the light,but they heat up the solar cell assembly. Generally aren't used
Space-power people very conservative

MOCVD
Metal organic chemical vapor deposition

OMVPE


How the semiconductors used in electronics are grown

If you drive electricity into a solar cell or other semiconductor thingies, you get light.
This is the basis for LASERs and LEDs.

If you connect batteries in series, the voltage adds, but the current is the same.

Small increases in efficicienty, even fractions of a percent, are a huge deal.

When semiconductor reduced to the nano-scale, its band gap changes based on the size.
Gets into quantum mechanics